Hybrid capacitors, especially sodium-ion capacitors (SICs), which combine the complementary merits of high-energy batteries and high-power capacitors, have received increasing research interest and have been expected to bridge the gap between the rechargeable batteries and EDLCs. The biggest challenge for SICs is to overcome the kinetics discrepancy between the sluggish faradaic anode and the rapid nonfaradaic capacitive cathode. To boost the Na+ reaction kinetics, robust and conductive Na2Ti2O5–x nanowire arrays have been constructed as an accessible and affordable SIC anode. It is found that the utilization of oxygen vacancies (OVs) can endow Na2Ti2O5–x high electrical conductivity, introduce intercalation pseudocapacitance, and maintain the crystal structure integrity. It exhibits high reversible discharge capacity (225 mAh g–1 at 0.5C), superior rate capability, and ultralong lifespan when utilized as self-supported and additive-free anode for SIB, remaining almost 100% capacity retention after 20 000 cycles at 25 C. When assembled as flexible hybrid SIC (4.5 cm3) with rGO/AC film cathode, a high-level energy density of 70 Wh kg–1 at power density of 240 W kg–1 based on active materials can be achieved, and high volumetric energy density (15.6 Wh L–1) and power density (120 W L–1) based on the whole packge volume can be delivered with superior cycle stability (5000 cycles, 82.5%).

The three-dimensional (3D) hybrid aerogels built from graphene and polypyrrole-derived nitrogen-doped carbon nanotubes (G-NCNTs) are synthesized by facile hydrothermal and heat treatment process using graphite oxide (GO) and polypyrrole nanotubes (PNTs) as precursors. The 3D G-NCNTs hybrid aerogels, in which the NCNTs are dispersed homogeneously in the graphene sheets, are designed to efficiently support Pt nanoparticles. Comparing with 3D graphene (GA), the 3D G-NCNTs supported Pt-based catalyst possesses improved electrocatalysis activity and stability toward methanol oxidation reaction (MOR). The mass activity of Pt/G-NCNTs-1/2 catalyst is 0.74 A mg−1Pt, which is 1.4 times that of the Pt/GA catalyst (0.54 A mg−1Pt). In addition, the retention rate after 1000 cycles for Pt/G-NCNTs-1/2 catalyst is as high as 82.4%, obviously superior to 68.5% of Pt/GA catalyst. The enhanced electrochemical performance is ascribed to the synergistic effect of GA and NCNTs. The introduction of NCNTs can uniformly disperse and strongly anchor Pt nanoparticles due to the increase in nitrogen active sites. Moreover, the NCNTs introduced into GA may prevent the restacking of graphene sheets, and provide a large accessible surface area for better dispersing Pt nanoparticles and transporting reactants and products.The three-dimensional (3D) hybrid aerogels built from graphene and polypyrrole-derived nitrogen-doped carbon nanotubes (G-NCNTs) are synthesized by facile hydrothermal and heat treatment process using graphite oxide (GO) and polypyrrole nanotubes (PNTs) as precursors. The 3D G-NCNTs hybrid aerogels, in which the NCNTs are dispersed homogeneously in the graphene sheets, are designed to efficiently support Pt nanoparticles. Comparing with 3D graphene (GA), the 3D G-NCNTs supported Pt-based catalyst possesses improved electrocatalysis activity and stability toward methanol oxidation reaction (MOR). The enhanced electrochemical performance is ascribed to the synergistic effect of GA and NCNTs.Download high-res image (513KB)Download full-size image

Li–S battery is one of the most promising candidates for next-generation energy storage technology. However, the rapid capacity fading and low-energy-density limit its large-scale applications. Scholars invest a lot of effort to introduce new materials. A neglected problem is that reasonable structure is as important as new material. In this review, four kinds of cathode structures were analyzed through morphology and electrochemical properties. The relationship between structures and properties was elaborated through reaction mechanism. The advantages and disadvantages of each structure were discussed. We hope the summary and discussion provide inspiration for structure design in Li–S battery cathode materials.

Development of novel electrode materials with high energy and power densities for lithium-ion batteries (LIBs) is the key to meet the demands of electric vehicles. Transition metal oxides that can react with large amounts of Li+ for electrochemical energy storage are considered promising anode materials for LIBs. In this work, NiCo2O4 nanosheets and nanocones on Ni foam have been synthesized via general hydrothermal growth and low-temperature annealing treatment. They exhibit high rate capacities and good cyclic performance as LIB anodes owing to their architecture design, which reduces ion and electron transport distance, expands the electrode–electrolyte contact, increases the structural stability, and buffers volume change during cycles. Notably, NiCo2O4 nanosheets deliver an initial capacity of 2239 mAh g−1 and a rate capacity of 964 mAh g−1 at current densities of 100 and 5000 mA g−1, respectively. The corresponding values of nanocones are 1912 and 714 mAh g−1. Hence, the as-synthesized NiCo2O4 nanosheets and nanocones, which are carbon-free and binder-free with higher energy densities and stronger connections between active materials and current collectors for better stability, are promising for use in advanced anodes for high-performance LIBs.

Molybdenum dioxide (MoO2) has been adopted as an advanced auxiliary support material for its outstanding electrical properties to anchor metal nanoparticles (NPs). To overcome the drawback of MoO2 electronic conductivity, a novel hierarchical carbon coated molybdenum dioxide (MoO2@C) nanotube built from ultra-thin nanosheets was utilized as a nanostructured support. Pt NPs were uniformly deposited onto the MoO2@C support and a hierarchical Pt-based anode catalyst was successfully synthesized. Benefitting from several favourable features, including high exposed surface area, short diffusion distance, fast charge transfer and homogeneous Pt NPs dispersion, the Pt/MoO2@C catalyst exhibited an improved activity along with enhanced stability for methanol electrooxidation when compared with that of the Pt/C catalyst. This novel hierarchical structure is helpful for the further applications in hydrogen evolution reaction, supercapacitors and batteries.

•The nitrogen doping in graphene and etching graphene layers at the same time.•The nanoholes on the graphene sheet have high density about 1.4 × 1010 holes per cm2.•The graphene still stable due to the nanoholes on graphene layers with not excessive damage of graphene lattice.•The nanoholes on graphene layers help the electrolyte infiltrate into the electrode.The 3D N-doped graphene nanomesh foam (3DNGF) has been synthesized as the Lithium-sulfur battery cathode material for the first time. A method of in situ doping nitrogen and meanwhile etching graphene layer is introduced. The BET result shows the 3DNGF has a large specific surface area more than traditional three-dimensional graphene. Transmission electron microscopy (TEM) observation and Raman spectra confirm the nanoholes on the graphene. The 3DNGF/S composite exhibits an initial discharge capacity of 1134 mAh g−1 at 0.2C in the first cycle with the sulfur utilization of 67%. The electrode reserves a specific capacity of 578 mAh g−1 after 500 cycles at 0.5C, with a capacity decay of 0.06% per cycle. Its specific capacity at 2C can still reach to 729 mAh g−1, indicating the good rate performance.The 3D N-doped graphene nanomesh foam (3DNGF) was synthesized by an in suit etching method. The nanoholes on the graphene sheets with diameter range approximately from 30 to 70 nm with high density about 1.4 × 1010 holes per cm2. The specific surface area of 3DNGF is 384 m2 g−1, much higher than the common 3D graphene. After 0.5C for 500 cycles, the 3DNGF/S exhibits a specific capacity of 578 mAh g−1 with a capacity decay only 0.06% per cycle. Even at 2C rate, the reversible specific capacity still was 729 mAh g−1.Download high-res image (105KB)Download full-size image

•A novel low-cost high-performance aqueous asymmetric device was designed.•The device presents a maximum energy/power densities of 60.4 Wh kg−1 and a 2400 W kg−1.•The capacitance of the device can still maintains 88.2% after 10,000 cycles.A high energy/power density aqueous asymmetric supercapacitor device is assembled by self-assembled NiCo2O4/MnO2 composite as a positive electrode and MoO3@PPy composite as a negative electrode in Na2SO4 electrolyte. Due to the synergistic effect of electronic conductivity of PPy and high-rate metal oxides, the heterostructure electrodes reveal better charge transport and cycling stability. The overall areal capacitance retentions for the NiCo2O4/MnO2 and MoO3@PPy electrode materials are 97.5% and 86.2% after 6000 cycles, respectively. Such unique nanoarchitecture in the hybrid device further presents remarkable electrochemical performance with high capacitance and ideal cycle life at high rates. The novel device with an expanded operating voltage window of 1.6 V, presents a high energy density of 60.4 Wh kg−1 and a maximum power density of 2400 W kg−1. The device demonstrates a good cycle life with 88.2% capacitance retention after 10,000 cycles. This strategy for the choice provides a promising route for the next-generation device of energy storage and conversion with high energy, high power density, and long life.Download high-res image (60KB)Download full-size image

•Mo-modified NCM is synthesized by the solvent evaporated-calcination method.•The bifunctional improvement for both doping and coating are developed.•Long life cycle performance is improved by Mo modifying.•The method is promising for the applications for industrialized production.Long-life property is one of the key factors for wide applications of lithium-ion batteries. Here, Mo-modified Ni-rich cathode material LiNi0.5Co0.2Mn0.3O2 (NCM) is synthesized successfully via a solvent evaporating way followed with a calcination method. This strategy delivers two kinds of effects including Mo-doping and Mo-coating. Mo not only intercalates into the crystal lattice of NCM, but also forms a film-like coating layer on the surface to impede side reactions between electrode and electrolyte. Thus, its specific capacity, rate capability and cycle performance are improved simultaneously, especially in terms of long cycling life property. A series of physical and electrochemical characterizations are used to study the modified performance, and the sample with 1.0 wt% Mo modifying presents the best property with an approximate 3.5 nm coating layer surrounding the surface. Besides, the capacity retention ratio reaches to 89.7% even after 500 cycles between 3.0 and 4.3 V. However, Mo-modified samples have an obvious attenuation in the later period after charging to a higher voltage of 4.6 V although they have preferable cycle performance at the preliminary stage. The results indicate that the reaction mechanisms are diverse at different voltage ranges, which may guide subsequent researches.Download high-res image (373KB)Download full-size image

Layered Li-rich oxide (LLRO) is an attractive candidate for high-energy-density and high-voltage cathode material for next generation lithium ion batteries because of its high specific capacity and low cost. There still remain challenges in simultaneously achieving a multi-functional structure and composition in a LLRO, to achieve better electrochemical performance. Here we report a controllable co-precipitation and calcination method to synthesize LLRO by tuning the crystal nucleation, growth and heterogeneous contraction processes. The resultant LLRO adopts a hierarchical ball-in-ball hollow structure consisting of uniform multi-elemental (Mn–Ni–Co) primary nanocrystals, and exhibits high reversible capacity, remarkable cycle stability and superior rate performance. As a result, the resultant LLRO presents a high capacity of 193 mA h g−1 at 3C (a current density of 750 mA g−1) with a capacity retention of 87.6% after 400 cycles, and exhibits a capacity of 132 mA h g−1 at a high rate of 10C; moreover, it displays a quite slow voltage decay of ∼240 mV and a high energy density of 668 W h kg−1 after 200 cycles at 1C. The excellent electrochemical performance can be attributed to the combined merits of the multi-functional structure and composition, wherein the hierarchical hollow architecture facilitates efficient electron/ion transport and high structural stability, while multi-elemental components offer high reversible capacity.

Despite the promising high energy density at low cost, lithium sulfur batteries suffer from the fatal shuttle effect caused by intermediate dissolution during cycling, significantly shortening their cycle life. Herein, we report a facile synthesis of sulfur/carbon composites. Through a one-step calcination, nano-sized ZnS particles coated with nitrogenous carbon are directly prepared from cheap industrial rubber vulcanization accelerators (a kind of organic sulfide), and then in situ oxidized to obtain nitrogenous carbon coated sulfur composites, with a three dimensional cell-stacked structure. This particular frame with a high level of in situ introduced polar functional groups provides abundant obstacles and chemical traps to effectively immobilize the intermediates, allowing for excellent storage performance and long-term cycle life. Outstandingly, the composite exhibits a remarkably low decay rate of 0.028% per cycle after 120 cycles at 0.1C-rate, under the sulfur loading of 3.6 mg cm−2.

High-performance supercapacitors, as highly promising candidates for bridging the gap between conventional lithium-ion batteries and traditional electrostatic capacitors, are the key to progress in the field of energy storage. To improve the performance of supercapacitors, the exploration of novel functional electrode materials is always at the forefront of technology. Herein, the rational design of a novel deformable soft supercapacitor, which is based on a compressible capacitive polyvinyl alcohol/polypyrrole (PVA/PPy) composite hydrogel and a flexible carbon nanotubes (CNTs) film, is reported. Due to the unique layered wrinkle structure of the PVA/PPy composite hydrogel, whose internal structure contains a large amount of water, the fabricated supercapacitor exhibits fascinating mechanical properties, including elasticity, compressibility and softness. In addition, the CNTs self-supported film without any binder shows an excellent flexibility as well as a stable capacitance in long-term cycles, which results in an enhanced cycle performance of the (PVA/PPy)(−)//CNTs(+) supercapacitor. Furthermore, the (PVA/PPy)(−)//CNTs(+) supercapacitor exhibits a high working voltage (0–2 V) accompanied with an energy density of 33.3 W h kg−1 (a power density of 1600 W kg−1). The high-performance compressible soft supercapacitor with deformability heralds a new territory of hydrogel-based supercapacitor for energy storage applications.

Good progress has been made in improving lithium sulfur batteries through trapping sulfur in porous carbon materials by controlling the pore size. However, microporous carbon/sulfur composites suffer from lower sulfur contents through the traditional sulfur loading methods. In this paper, we present an effective and facile approach to prepare a double-hollow-sphere structured microporous carbon coated sulfur composite by in situ oxidizing the microporous carbon coated metal sulfide precursor. The composite efficiently traps sulfur inside the microporous-walled hollow carbon sphere. With the appropriate sulfur content ranging from 55 wt% to 75 wt%, the composites demonstrate promising cycling performance. The composites deliver a capacity retention of 96.11% at 0.2C after 100 cycles, and a relatively low decay rate of 0.05% per cycle after 1000 cycles at 1C.

The high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) with submicron particle size (LNMO-8505P70010) has been synthesized based on nickel-manganese compound, which is obtained from pre-sintering the nickel-manganese hydroxide precipitation at 850 °C. The LNMO materials based on nickel-manganese hydroxide (LNMO-70010, LNMO-850570010, and LNMO-8501070010) have also been synthesized for comparison to study the pre-sintering impact on the properties of LiNi0.5Mn1.5O4 material. The morphologies and structures of the obtained samples have been analyzed by X-ray powder diffraction and scanning electron microscopy. The nickel-manganese compound has a spinel structure with high crystallinity, making it a good precursor to form high-performance LNMO with lower content of Mn3+ and impurity. The obtained LNMO-8505P70010 delivers discharge capacities of 125.4 mA h g−1 at 0.2 C, and the capacity retention of 15 C reaches 73.8 % of the capacity retention of 0.2​ C. Furthermore, it shows a superior cyclability with the capacity retention of 96.4 % after 150 cycles at 5 ​C. Compared with the synthesis method without pre-sintering, the synthesis method with pre-sintering can save energy while reaching the same discharge specific capacity.

For the next-generation energy-storage devices, high power density supercapacitors can be used as complementary power supplies. However, the shortcomings such as low energy density, complicated synthesis process, and high cost have limited their wide applications. Moreover, their rigid bulk structures hinder their applications in wearable electronics. Herein, we developed a fiber-shaped supercapacitor (FSC) with a volumetric energy density of up to 7.9 mW h cm−3 and volumetric capacitance of 28.8 F cm−3. This new FSC consists of a self-supported hybrid film electrode and free-standing polyester fiber electrode that are prepared using simple hydrothermal and vacuum filtration methods, respectively. The FSC also has high flexibility under different bending degree tests and long cycle life (capacitance retention efficiency is 98.6% after 10 000 cycles). Based on the abovementioned discussion, it can be concluded that this new type of FSC with the advantages of low-cost, high flexibility, ultrahigh energy density, and ultralong cycle life will play an important role in many fields and is expected to act as a new star in the energy storage devices.

Well-ordered, self-supported ultralong nanowire arrays (NWAs) with a 3D structure and tailored hydrogen titanate (HTO) phase have been synthesized via a facile template-free hydrothermal method and subsequent calcination and utilized as anodes in Li-ion capacitors (LICs) directly without any ancillary materials. The 3D structure constructed from ultralong nanowires and a rooftop network is beneficial to structural stability, electrolyte penetration, rich electro-active sites and short Li-ion transport paths. Moreover, the tailored HTO phase can introduce stronger and more effective Li-ion diffusion channels for the fast Li-ion insertion/extraction reaction. These merits from morphological and crystal structural design yield superior electrochemical performance in terms of high capacity, excellent rate capability and ultralong lifespan. The LIC assembled with a HTO NWA anode and activated carbon (AC) cathode achieves an attractive energy storage of 93.8 W h kg−1 and a capacitance retention of 78.8% after 3000 cycles at a high current density of 5.0 A g−1 within 0.0–3.0 V. Even at a rapid charging rate within 8.0 s, an excellent energy density of 33.3 W h kg−1 and a high power density of 15 kW kg−1 can be retained. Therefore, the HTO NWAs//AC LIC is a promising candidate as an energy storage system for high-energy and high-power applications.

Metal oxides have attracted renewed interest in applications as energy storage and conversion devices. Here, a new design is reported to acquire an asymmetric supercapacitor assembled by all free-standing metal oxides. The positive electrode is made of 3D NiO open porous nanoribbons network on nickel foam and the negative electrode is composed of SnO2/MnO2 nanoflakes grown on carbon cloth (CC) substrate. The combination of two metal oxide electrodes which replaced the traditional group of carbon materials together with metal oxide has achieved a higher energy density. The self-supported 3D NiO nanoribbons network demonstrates a high specific capacitance and better cycle performance without obvious mechanical deformation despite of undergoing harsh bulk redox reactions. The SnO2/MnO2 nanoflakes as the pseudocapacitive electrode exhibit a wide range of voltage window (−1 to 1 V), which is conducive to electrochemical energy storage. The (CC/SnO2/MnO2)(−)//(NiO/Ni foam)(+) asymmetric supercapacitor device delivers an energy density of 64.4 Wh kg–1 (at a power density of 250 W kg–1) and two devices in series are applied to light up 24 red LEDs for about 60 s. The outstanding electrochemical properties of the device hold great promise for long-life, high-energy, and high-power energy storage/conversion applications.Keywords: asymmetric supercapacitor device; hydrothermal method; metal oxides; NiO nanoribbons; SnO2/MnO2 nanoflakes

Three-dimensional hierarchical nitrogen-doped graphene (3D-NG) frameworks were successfully fabricated through a feasible solution dip-coating method with commercially available sponges as the initial backbone. A spongy template can help hinder the graphene plates restacking in the period of the annealing process. The Pt/3D-NG catalyst was synthesized employing a polyol reduction process. The resultant Pt/3D-NG exhibits 2.3 times higher activity for methanol electro-oxidation along with the improvement in stability as compared with Pt/G owing to their favorable features including large specific surface area, high pore volume, high N doping level, and the homogeneous dispersion of Pt nanoparticles. Besides, Pt/3D-NG also presents high oxygen reduction reaction (ORR) performance in acid media when compared with Pt/3D-G and Pt/G. This work raises a valid solution for the fabrication of 3D functional freestanding graphene-based composites for a variety of applications in fuel cell catalysis, energy storage, and conversion.

Nitrogen-doped carbon nanotubes (CNx-NTs), platinum (Pt)-based catalysts supports, were prepared by pyrolysis of polypyrrole nanotubes (PPy-NTs), which were synthesized using a self-degraded template method. The morphology, structure and physicochemical properties of CNx-NTs supports and Pt/CNx-NTs catalysts were investigated by scanning electron microscope, Brunauer-Emmett-Teller surface area, transmission electron microscopy, X-ray diffraction, and X-Ray photoelectron spectroscopy. Fine Pt nanoparticles are uniformly deposited onto the CNx-NTs supports, which possess well-defined nanotube morphology. The Pt/CNx-NTs catalysts, especially Pt/CNx-NTs-800 catalyst (CNx-NTs prepared at pyrolysis temperature of 800 °C), exhibit outstanding electrochemical performance toward methanol oxidation reaction (MOR), compared with commercial Pt/C catalyst, which is attributed to high nitrogen content and nanotube morphology of the support. High nitrogen content can better disperse and anchor Pt nanoparticles, and nanotube structure may provide an open network around the active catalysts for facilitating the mass transfer. Under the same electrocatalytic activity, the Pt loading of the Pt/CNx-NTs-800 catalyst is reduced by 56.3% comparing with commercial Pt/C catalyst. The results indicate that the CNx-NTs-800 as support greatly reduces the loading of noble metal platinum, further promoting the commercialization process of proton exchange membrane fuel cells (PEMFCs).

•Pt/C/graphene aerogel (GA) hybrid catalyst synthesized via a facile hydrothermal process.•Pt/C/GA possesses a well-defined 3D graphene framework with encapsulating of Pt/C catalyst.•Pt/C/GA catalyst exhibits remarkably higher stability than standard Pt/C catalyst.•This simple method can be widely applied in fabrication of high durable supported catalysts.Three-dimensional (3D) structured Pt/C/graphene aerogel (Pt/C/GA) hybrid as a remarkable high stability electrocatalyst is synthesized through a facile and green hydrothermal process. Thanks to the unique 3D graphene framework structure, Pt/C/GA hybrid catalyst demonstrated enhanced stability towards methanol electrooxidation with no decrease of electrocatalytic activity. Besides, Pt/C/GA hybrid catalyst also exhibits a significantly enhanced stability to scavenge crossover methanol under the high potential in acid solution compared with the standard Pt/C catalyst: Pt/C catalyst lost nearly 40% of its initial activity after 1000 cyclic voltammetry cycles, by contrast, only 16% for Pt/C/GA. Moreover, it is noteworthy that after 200 cycles, the mass activity of Pt/C/GA is always much higher than that of Pt/C. A significant stability enhancement is achieved due to the unique 3D macroporous graphene structure as well as the efficient assembly between the Pt/C catalyst and graphene aerogel. Importantly, our synthetic strategy can be easily applied to the commercial PtRu/C catalyst to improve its durability. This simple, convenient and green synthetic method highlights the potential in fabrication of high durable electrocatalyst for fuel cell applications.Three-dimensional structured Pt/C/graphene aerogel hybrids demonstrate high stability towards methanol electrooxidation due to the unique 3D graphene structure as well as the efficient assembly between the Pt/C and graphene aerogel.

At present, low platinum catalysts have attracted much attention in the whole world. It is an effective strategy for reducing platinum loading to use an efficient support to enhance the catalytic activity. In this paper, a uniform structure of carbon and TiO2 nanowires is synthesized through a two-step hydrothermal reaction and used as an efficient Pt-based anode catalyst support. Physical characterization confirms the special core/shell structure. The carbonization temperature greatly affects the graphitization degree, porosity and surface chemical properties of the carbon shell. Electrochemical measurements indicate that the catalyst obtained at 800 °C has excellent electrochemical activity and durability. Its electrochemically active specific surface area is much higher than that of Pt/C. Its activity for methanol oxidation is about 1.4 times higher than that of Pt/C. The enhanced performance is attributed to the design of the special core/shell structure. The uniform dispersion of carbon and titania nanowires produces a strong synergistic effect and generates highly active Pt loading sites. The carbon shells can greatly improve the electronic conductivity and suppress the crystal growth of TiO2 during calcination. Meanwhile, a large number of defects within the carbon shells are also conducive to the dispersion of Pt nanoparticles. In addition, the core of TiO2 nanowires can enhance the hydrophilicity of the carbon shell and produce a strong metal–support interaction with Pt nanoparticles, which improve the activity and durability of catalysts.

N-Doped carbon quantum dots (NCQDs)/multiwall-carbon nanotube (MWCNT) supports are synthesized by a one pot hydrothermal treatment process at different contents of precursor. NCQDs–MWCNT as support can be widely used in the process of electrocatalysis. In this paper, the Pt/NCQDs–MWCNT catalysts are prepared by a microwave-assisted polyol process (MAPP) method and the effects of NCQDs with different contents on the performance of Pt-based anode catalysts for methanol oxidation reaction (MOR) are systematically demonstrated. The electrochemical tests reveal that the Pt/NCQDs–MWCNT catalyst exhibits the best performance for MOR when precursor content is 3 g. In terms of the electrochemical and characterization results, the moderate content of precursor for NCQDs plays multiple roles in the electrocatalytic performance: promoting the dispersion of untreated MWCNT significantly in solution; providing the plentiful oxygen-containing groups to deposit Pt nanoparticles; and facilitating the formation of homogeneous Pt nanoparticles.

Mesoporous nitrogen-doped carbon (MNC) with a high surface area has been synthesized via carbonizing polyaniline using silica nanoparticles as template. The more silica nanoparticles, the smaller the micropore surface area is and the larger the mesoporous surface area is. Moreover, with an increase in the amount of silica nanoparticles, the electrocatalytic activity of Pt/MNC catalysts shows a downward trend after an intimal increase, and the Pt/MNC-1/6 (with the weight ratio of aniline monomer to silica nanoparticles of 1/6) catalyst has the highest activity, ascribed to the optimal Pt nanoparticles size, which is closely related to the pore structure of the support. In addition, the electrocatalytic activity and stability of Pt/MNC-1/6 catalyst are significantly superior to that of Pt/nitrogen-doped carbon (Pt/CNx) catalyst. For the same electrocatalytic activity, the Pt loading of Pt/MNC-1/6 catalyst is reduced by 33.3% compared to the Pt/CNx catalyst. The high electrocatalytic activity originates from the introduction of mesoporous structures that can facilitate mass transfer and improve the dispersion of Pt nanoparticles. Furthermore, the Ostwald ripening behavior of Pt nanoparticles is limited in the mesoporous structure of MNC-1/6, which weakens the aggregation effect of Pt nanoparticles during the electrocatalytic processes, thus enhancing the electrocatalytic stability of the catalyst.

•Effect of different structures of cathode carbon supports on DMFC performance is studied.•Compression ratio of catalyst layer is critical for MEA on DMFC.•2D structured rGO sheets exhibit a strong tendency to horizontal stacking, during the MEA fabrication.•MWNTs is optimal for cathode catalyst support in DMFC among CB, MWNTs and rGO.Carbon black (CB), multiwalled carbon nanotubes (MWNTs), reduced graphene oxide (rGO) are used as the cathode catalyst supports to investigate the effect on direct methanol fuel cell (DMFC) performance by using rotating disk electrode and fuel cell testing. The results of linear sweep voltammetry (LSV) and cyclic voltammetry (CV) show that the electrocatalytic activity sequence for oxygen reduction reaction (ORR) is Pt/rGO > Pt/MWNTs > Pt/C catalysts. The single cell tests results show that the maximum power densities of DMFC with Pt/C, Pt/MWNTs and Pt/rGO cathode catalysts are 74.0, 74.2 and 3.3 mW cm−2, respectively. The experimental results indicate that the performance of DMFC is substantially influenced by the structures of cathode catalyst supports. The significant differences in DMFCs performance are due to the compression ratios and hydrophilic/hydrophobic properties of catalyst layers with different structures of carbon supports, which strongly affect electrochemical active sites and mass transport in cathode catalyst layers. Long-term testing of DMFCs indicates that Pt/MWNTs exhibits superior stability. Considering the factors of the power and lifetime comprehensively, MWNTs is optimal candidate among the three investigated carbon supports.The significant differences in DMFCs performance are due to the compression ratios and hydrophilic/hydrophobic properties of catalyst layers with different structures of carbon supports, which affect electrochemical active sites and mass transport in cathode catalyst layers.Download high-res image (167KB)Download full-size image

Electrode materials with high tap densities and high specific volumetric energies are the key to large-scale industrial applications for the lithium ion battery industry, which faces huge challenges. LiNi0.5Co0.2Mn0.3O2 cathode materials with different particle sizes are used as the raw materials to study the effect of the mass ratio of mixed materials on the tap density and electrochemical performance of mixed materials in this work. Physical and electrochemical characterizations demonstrate that the tap density of mixed powders with different particle sizes is higher than those of materials with a single particle size. The tap density of as-prepared material has a decreasing trend with the increase of the ratio of 9 μm sized particle in the materials. The highest tap density among all of the kinds of materials reaches up to 2.66 g cm−3. Besides, the mixed material with a mass ratio of 7:2:1 has a bigger specific surface area and it presents better cycle behaviors and rate capability than other materials. The specific volumetric capacity of this mixed sample reaches up to 394.3 mA h cm−3 with 1C rate charge/discharge, and it has improvements of 8.5%, 22.2% and 40.6% over any single particle size of 9 μm, 6 μm and 3 μm, respectively, which contributes to the industrial production of Li–Ni–Co–Mn–O cathode materials for lithium ion batteries.

Sodium titanate/titania composite nanotubes/nanorods (STNS) are synthesized from anatase titania by the hydrothermal method and subsequent annealing in the range of 300–700 °C. The changes in the composition and morphology of STNS are investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results reveal that the composition of STNS changes from “Na2−xHxTi2O5” to “Na2Ti6O13” and their morphology changes from nanotubes to nanorods. The products obtained at 400 °C and 600 °C correspond to the intermediate state of reactions. Pt-based catalysts are prepared by a microwave-assisted ethylene glycol process, and are also characterized by physical analysis and electrochemical measurements. The variations of the catalytic activity and stability of Pt/C-STNS catalysts show the interesting “M” shape with the increase of the annealing temperature of STNS. The Pt nanoparticles supported on STNS-400 nanotubes and STNS-600 nanorods exhibit more uniform dispersion and superior electrocatalytic performance for methanol electrooxidation. The main reason seems to be that both of them are multiphase composites with a large number of phase interfaces and crystal defects, which is conducive to the deposition of Pt nanoparticles. The uniform dispersion of Pt nanoparticles plays an essential role in the electrochemical performance of catalysts. In addition, the presence of the “anatase TiO2” phase in both of them can further enhance the electrochemical performance due to the metal–support interaction. Moreover, compared to commercial Pt/C, the Pt/C-STNS-600 catalyst exhibits higher electrochemical activity and stability, suggesting that superior catalysts can be developed by designing the structure and composition of the supports.

A novel sandwich-structured graphene–Pt–graphene (G–P–G) catalyst has been synthesized by a convenient approach. The obtained G–P–G catalyst has been characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, and electrochemical measurements. Structural characterization shows that the G–P–G catalyst has a well-defined sandwich-like morphology. The results of electrochemical measurements indicate that the G–P–G exhibits 1.27 times higher activity for methanol electrooxidation than that of the Pt/graphene catalyst. Importantly, the results of the accelerated potential cycling test demonstrate that the G–P–G catalyst possesses 1.7 times higher stability than that of Pt/graphene. The significantly enhanced electrochemical performance is ascribed to its unique sandwich-like structure. Pt nanoparticles are anchored between the two adjacent graphene sheets, substantially enhancing the metal–support interaction, and graphene could act as a “mesh bag” to prevent the Pt species from leaking into the electrolyte, so its stability has considerably been enhanced. The effect of composited graphene amount on the stability of the hybrid has also been systematically studied. The stability of the catalyst increases with the increase of the introduced GO amount and the G–P–G50 shows optimized electrocatalytic performance. These findings suggest that the sandwich-structured G–P–G catalyst holds tremendous promise for fuel cells.

•The modification of NCQDs is an innovative approach to change the properties of MWCNT.•NCQDs-MWCNT support has been successfully synthesized by a facile hydrothermal treatment.•NCQDs can improve the dispersion of MWCNT and Pt nanoparticles.•The electrochemical performance of Pt/NCQDs-MWCNT catalyst is superior to that of Pt/MWCNT.The modification of N-doped carbon quantum dots (NCQDs) is an innovative approach to change the properties of multiwall-carbon nanotube (MWCNT). Here we report a facile hydrothermal treatment to synthesize NCQDs-MWCNT support, which acts as an improved catalyst support of Pt-based anode catalyst for direct methanol fuel cells. The structural properties of homemade catalysts are characterized by X-ray diffraction, Energy dispersive analysis of X-ray, transmission electron microscopy and X-ray photoelectron spectroscopy. The results indicate that Pt nanoparticles are well dispersed onto NCQDs-MWCNT and have a synergetic interaction with NCQDs. The results of electrochemical measurements reveal that Pt/NCQDs-MWCNT catalyst exhibits 1.3 times higher activity for methanol electrooxidation than that of Pt/MWCNT. The enhanced performance of Pt/NCQDs-MWCNT is attributed to the fact that NCQDs improve the dispersion of MWCNT and more uniform Pt nanoparticles are stabilized on NCQDs-MWCNT. NCQDs play a critical role in electrocatalytic performance for methanol electrooxidation.The electrochemical performance of Pt/NCQDs-MWCNT catalyst is higher than that of Pt/MWCNT.

Graphitic carbon nitride (g-C3N4) has been demonstrated as an advanced support material for Pt nanoparticles (NPs) due to its excellent stability and abundant Lewis acid for anchoring metal NPs. However, its non-conductive nature and low surface areas still impede its application in electrochemical fields. Herein, a π–π stacking method is presented to prepare graphene/ultrathin g-C3N4 nanosheets composite support for PtRu catalyst. The weaknesses of g-C3N4 are greatly overcome by establishing a 2D layered structure. The significantly enhanced performance for this novel PtRu catalyst is ascribed to reasons as follows: the homogeneous dispersion of PtRu NPs on g-C3N4 nanosheets due to its abundant Lewis acid sites for anchoring PtRu NPs; the excellent mechanical resistance and stability of g-C3N4 nanosheets in acidic and oxidative environments; the increased electron conductivity of support by forming a layered structure and the strong metal-support interaction (SMSI) between metal NPs and g-C3N4 NS.

A three-dimensional (3D) structured Pt/graphene aerogel has been synthesized by a facile one-pot solvothermal process. The as-synthesized catalyst is characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and electrochemical tests. It has been found that the Pt/graphene aerogel catalyst exhibits a well-developed 3D interconnected porous graphene framework with Pt nanoparticles (NPs) decorated on the surface of the graphene aerogel. More importantly, the as-made Pt/graphene aerogel catalyst exhibits a much higher electrocatalytic activity and stability than the Pt/graphene for methanol electrooxidation. The enhancement may result from the unique 3D graphene architecture, and the efficient assembly between the Pt NPs and graphene aerogel. These outstanding properties suggest that the Pt/graphene aerogel catalyst holds tremendous potential for fuel cell applications.

Layered structure LiNi0.6Co0.2Mn0.2O2 cathode material was synthesized via a two-step solid state reaction with industrial Ni0.6Co0.2Mn0.2(OH)2 and Li2CO3 in this paper. The samples prepared at different sintering temperatures (750–850 °C) and sintering times (10–18 h) were analyzed by physical and electrochemical methods to gain the optimal sintering condition, and an additional XRD Rietveld refinement was taken to get more reliable structural parameters. The results demonstrated that the higher temperature leads to larger primary particle size and severer agglomeration, while duration factor may affect the electrochemical performance rather than the structure and morphology of the materials. The optimized NCM622 material has an initial discharge capacity of 156.3 mA h g−1 at 1 C, whose capacity retention even reached 102.9% after 100 cycles. In addition, the three dispersed peaks (P1, P2, P3) in particle distribution analysis and RSEI, Re, Rct in electrochemical impedance spectroscopy have been separated and discussed in detail.

The effects of Cr3+ doping and citric acid combustion on the electrochemical properties of Li4Ti5O12 were systematically investigated. The solid-state reaction process was used to synthesize four samples marked as LTO, C-LTO, LT-Cr-O, and C-LT-Cr-O, respectively. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) techniques were employed to study their structures and morphologies. The cyclic voltammetry (CV) tests, electrochemical impedance spectroscopy (EIS) analysis, and charge–discharge cycling were performed to study their electrochemical performance. The experimental results showed that the C-LT-Cr-O sample exhibited the advantages both of the Cr3+ doping and the citric acid combustion, presented high ordered morphology and high phase purity, and displayed a discharge capacity of 101.3 mAh g−1 with about 91.8 % capacity retention after 1000 cycles at 10C discharge rate. Therefore, the C-LT-Cr-O material is a promising anode material to be used in lithium ion batteries.

PtRu supported on a C@g-C3N4 NS (g-C3N4 nanosheet coated Vulcan XC-72 carbon black) catalyst has been prepared by a microwave-assisted polyol process (MAPP). The results of electrochemical measurements show that the PtRu/C@g-C3N4 NS catalyst has excellent activity due to more uniform dispersion and smaller size of PtRu nanoparticles (PtRu NPs), and higher stability ascribed to the stronger metal–support interaction (SMSI) between PtRu NPs and the composite support. Physical characterisation using techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) has indicated that the bulk g-C3N4 shell outside of the as-prepared C@bulk g-C3N4 (bulk g-C3N4 coated Vulcan XC-72 carbon black, C@bulk g-C3N4) indeed exfoliated to layered g-C3N4 nanosheets and formed a composite material of Vulcan XC-72 coated with g-C3N4 nanosheets. Furthermore, the results indicate that the mass catalytic activity of the PtRu/C@g-C3N4 NS catalyst substantially enhanced, which is a factor of 2.1 times higher than that of the PtRu/C catalyst prepared by the same procedure and the accelerated potential cycling tests (APCTs) show that the PtRu/C@g-C3N4 NS catalyst possesses 14% higher stability and much greater poison tolerance than as-prepared PtRu/C. The significantly enhanced performance of the PtRu/C@g-C3N4 NS catalyst is ascribed to the following reasons: the inherently excellent mechanical resistance and stability of g-C3N4 nanosheets in acidic and oxidative environments; the increased electron conductivity of the support by forming a core–shell structure of C@g-C3N4 NS; SMSI between metal NPs and the composite support. Based on this novel approach to fabricate a C@g-C3N4 NS hybrid nanostructure, many other interesting applications might also be discovered.

High voltage spinel LiNi0.5Mn1.5O4 has been synthesized by an ethanol-assisted hydrothermal method. LiNi0.5Mn1.5O4 has also been synthesized by a precipitation method and hydrothermal method for comparison. The materials were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical tests. The ethanol-assisted hydrothermal process improves the dispersity and decreases the size of particles in the presence of ethanol. With small size particles, LiNi0.5Mn1.5O4 has an excellent rate capability. Its discharge capacity is 81.7 mA h g−1 at a high rate of 20 C. On the other hand, the ethanol-assisted hydrothermal process mixes the reagents homogeneously and improves the crystallinity. It leads to low impurities and low Mn3+ ion content, which are beneficial for electrochemical performance. The LiNi0.5Mn1.5O4 exhibits remarkable long-term cyclability. After 1000 cycles at a 5 C discharge rate, its discharge capacity is 102.1 mA h g−1 with a capacity retention ratio of 88.1%. It also has good high temperature performance with a capacity retention of 82.0% after 200 cycles at 55 °C.

•Li, Al co-doped LiMn2O4 was synthesized using industrial raw materials in bulk scale (>20 kg).•Li, Al co-doping significantly changed the unit cell parameter and atomic arrangement.•The expansion of LiO4 tetrahedron and contraction of MO6 octahedron were identified by Rietveld refinement of XRD.•The optimized composition is Li1.06Mn1.86Al0.08O4 with high-rate performance and good structure-stabilization.•Li1.06Mn1.86Al0.08O4 has capacities of 91 mAh g−1 at 0.5 C and of 88 mAh g−1 at 10 C at 55 °C after 200 cycles.Li, Al co-doped LiMn2O4 (Li1+xMn2−x−yAlyO4, 0 ≤ x ≤ 0.12, 0 ≤ y ≤ 0.1) cathode has been synthesized via a solid-state reaction designedly using industrial raw materials in bulk scale (>20 kg). The multicomponent substitution effects on the crystal structures are examined systematically by Rietveld refinement of X-ray diffraction, and the resultant electrochemical properties for Li-ion batteries are also evaluated by galvanostatic charge–discharge and electrochemical impedance spectroscopy measurements. As a result, Li, Al co-doping significantly changes the unit cell parameter and atomic arrangement. With the increasing of doping levels, a cell dimension contracts with concomitant changes in bond length, whereby the MO6 octahedron (M = Mn/Li/Al) shrinks to provide structural integrity and the LiO4 tetrahedron expands to facilitate a fast electrochemical process. The strong spinel-framework contributes to a better structure-stabilization, resulting in a superior capacity retention ratio of 90% after 200 cycles at 0.5 C at 55 °C for the optimized composition (Li1.06Mn1.86Al0.08O4), which possesses an initial value of 102 mAh g−1. Meanwhile, the expansion of LiO4 tetrahedron leads to better high-rate performance, bringing about a capacity of 88 mAh g−1 upon cycling at 10 C at 55 °C. Further, Li1.06Mn1.86Al0.08O4 displays lower impedance than that of the pristine LiMn2O4.The strong spinel-framework contributes to a better structure-stabilization, resulting in a superior capacity retention ratio of 90% after 200 cycles at 0.5 C at 55 °C for the optimized composition (Li1.06Mn1.86Al0.08O4), which possesses an initial value of 102 mAh g−1.

•A convenient approach to prepared Pt/C–TiO2 nanotubes (TNTs) via a microwave-assisted polyol process.•Carbon-coated TNTs possess three-phase position which is conducive to deposit Pt nanoparticles.•The higher electronic conductivity of TNTs is more beneficial to exhibit performance of platinum.•The enhanced activity and stability of Pt/C–TNTs is attributed to the combination of carbon and TNTs.In this paper, Pt nanoparticles have been successfully deposited on the mixture of carbon black and one-dimensional self-ordered TiO2 nanotubes (TNTs) array by a microwave-assisted polyol process to synthesize Pt/C–TNTs catalyst. TiO2 nanoparticles (TNPs) are used instead of TNTs to prepare catalyst as a reference. The obtained samples are characterized by physical characterization and electrochemical measurements. The results show that Pt nanoparticles are uniformly deposited on the three-phase interfaces between carbon and TNTs. The Pt/C–TNTs possesses substantially enhanced activity and stability in electrochemical performance. Such remarkable properties are due to the excellent composite carrier of C–TNTs: (1) TNTs has strong corrosion resistance in acidic and oxidative environment and a metal support interaction between Pt and TNTs; (2) Compared to TNPs, TNTs is more suitable for electro-catalytic field on account of its better electronic conductivity; (3) Compared to TNPs, TNTs can improve the anti-poisoning ability of catalyst for methanol oxidation. (4) Amorphous carbon can improve the dispersion of platinum particles; (5) The distribution of carbon improves the poor conductivity of TNTs. These studies indicate that Pt/C–TNTs compound is a promising catalyst for methanol electrooxidation.Pt nanoparticles have been successfully deposited on the mixture of carbon black and one-dimensional self-ordered TiO2 nanotubes (TNTs) array by a microwave-assisted polyol process to synthesize Pt/C–TNTs catalyst. The Pt nanoparticles deposited on the three-phase positions between carbon and TNTs exhibit the improved activity and stability, which is attributed to the combination of the advantage of carbon and TNTs.

•Pd catalyst with ITO and CNTs as a mixture support for DFAFC was first prepared by microwave-assisted polyol process.•The activity and stability of Pd/ITO-CNTs catalyst is significantly higher than those of Pd/CNTs.•When ITO content is 50% of ITO/CNTs support mass, Pd/ITO-CNTs exhibits the best performance.Indium tin oxide (ITO) and carbon nanotube hybrid has been explored as a support for Pd catalyst. Pd/ITO-CNTs catalysts with different ITO contents were prepared by the microwave-assisted polyol process. The as-prepared Pd/ITO-CNTs catalysts were characterized by X-ray diffraction (XRD), energy dispersive analysis of X-ray (EDAX), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and electrochemical measurements in this work. The TEM results show that Pd particle size distribution in the Pd/ITO-CNTs catalyst is more uniform than that in Pd/CNTs, indicating that the ITO can promote the dispersion of Pd nanoparticles. It is found that there is metal-support interaction between Pd nanoparticles and ITO in the Pd/ITO-CNTs catalyst through XPS test. The results of electrochemical tests prove that the Pd/ITO-CNTs catalysts exhibit higher electro-catalytic activity and stability than Pd/CNTs toward formic acid electrooxidation. When the ITO content is 50% of ITO-CNTs support mass, the Pd/ITO-CNTs catalyst has the best catalytic performance for formic acid electrooxidation. The peak current density of formic acid electrooxidation on the Pd/ITO-CNTs50% electrode is 1.53 times as high as that on Pd/CNTs, 2.31 times higher than that on Pd/ITO. The results of aging test show that the peak current density on the Pd/ITO-CNTs decreases by only 14.0%, while 56.1% on the Pd/CNTs after 500 cycles. It is due to the promoting effect of In2O3 and SnO2 in ITO, and metal-support interaction between Pd nanoparticles and ITO.The addition of ITO in Pd/CNTs catalyst significantly improves the activity and stability of catalyst for formic acid electrooxidation due to excellent stability and high electrical conductivity of ITO, and metal-support interaction between Pd nanoparticles and ITO.

•Pd catalyst with ATO and CNTs as a mixture support was first prepared by microwave-assisted polyol process.•The activity and stability of Pd/ATO-CNTs catalyst is obviously higher than that of Pd/CNTs.•When CNTs content is 10% of ATO/CNTs support mass, Pd/ATO-CNTs catalyst exhibits the best performance.We report on a mixture of antimony doped tin oxide (ATO) and carbon nanotubes as a novel support of Pd catalyst (Pd/ATO-CNTs) with the aims to enhance electron and proton conductivity of hybrid support, and catalytic activity and stability for formic acid electrooxidation. The surface content, morphology and structure of the as-prepared Pd/ATO-CNTs catalysts with different CNTs contents have been characterized by X-ray diffraction (XRD), energy dispersive analysis of X-ray (EDAX), inductively coupled plasma-optical emission spectroscopy (ICP-OES), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and high angle annular dark field STEM (HAADF-STEM), respectively. The electrocatalytic properties of the samples for formic acid electrooxidation reaction are investigated by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The results show that the activity and stability of Pd/ATO-CNTs catalyst is obviously higher than that of Pd/CNTs catalyst for formic acid electrooxidation due to unique physical and chemical properties of ATO and metal-support interaction between Pd nanoparticles and ATO. Moreover, the Pd/ATO-CNTs10 (CNTs content is 10 wt.% of ATO-CNTs support mass) with smaller Pd particle size and narrower size distribution on surface of the hybrid support exhibits the best performance for formic acid electrooxidation among all the samples.The activity and stability of Pd/ATO-CNTs catalyst is obviously higher than that of Pd/CNTs catalyst for formic acid electrooxidation due to excellent stability and high electrical conductivity of ATO, and metal-support interaction between Pd nanoparticles and ATO.

The effects of Ti substitution for Ni, carbon coating on the structure and electrochemical properties of LiMn1.5Ni0.5O4 are studied. LiMn1.5Ni0.5O4, LiNi0.4Ti0.1Mn1.5O4 and carbon-coated LiNi0.4Ti0.1Mn1.5O4 cathode materials have been synthesized by a solid-state reaction using industrial raw materials in bulk scale. X-ray diffraction clearly shows that LiMn1.5Ni0.5O4 has higher crystallinity after Ti doping. Scanning electron microscopy clearly exhibits that Ti doping does not change the basic spinel structure, as well as coated carbon layer covers the surfaces of the LiNi0.4Ti0.1Mn1.5O4 particles. In addition, charge–discharge tests indicate that LiNi0.4Ti0.1Mn1.5O4 sample has higher discharge capacities at the rates of 0.5, 1 and 3 C at 25 °C. It should be noted that carbon-coated LiNi0.4Ti0.1Mn1.5O4 shows higher discharge capacities at the rates of 5, 7 and 10 C at 25 °C as well as various rates for 55 °C. Cyclic performances developed at 25 and 55 °C demonstrate that the capacity retention is remarkably improved compared to the two uncoated samples. The influence of the Ti-doping and carbon-coating on the coulombic efficiency at high temperature (55 °C) has also been investigated. Among the various samples investigated, surface modification with carbon gives an improved coulombic efficiency. The remarkably enhanced electrochemical properties of the carbon-coated sample may be because of the suppression of the solid electrolyte interfacial (SEI) layer development and faster kinetics of both the Li+ diffusion, as well as the charge transfer reaction.

•3D-NGA is prepared via a combined hydrothermal, thermal treatment and template-removing process.•Pt/3D-NGA exhibits a 3D porous structure, high N-doped level and uniform dispersion of Pt NPs.•Pt/3D-NGA presents exceptional catalytic activity and stability for methanol electrooxidation.•This method can be suitable for synthesis of 3D metal or metal oxide/graphene-based composites.Three dimensional porous nitrogen-doped graphene aerogel (3D-NGA) was successfully fabricated via a combined hydrothermal self-assembly, thermal treatment and template-removing process. The as-synthesized Pt/3D-NGA catalysts exhibit an interconnected 3D porous structure, high N-doped level and uniform dispersion of Pt NPs. In studying the electrocatalytic performance of samples towards methanol electrooxidation, we found that Pt/3D-NGA hold a high electrochemical active surface area (ECSA) of 90.7 m2 g− 1 and better catalytic activity as well as stability compared to Pt/G and Pt/3D-GA catalysts. Our studies provide a simple approach to synthesize 3D metal or metal oxide/graphene-based composites, holding great potential for fuel cell applications.Download high-res image (306KB)Download full-size image

•MoO3-C nanocomposite is used as a novel anode catalyst support.•The composition of MoO3-C is an innovative material to enhance the property of catalyst.•Pt/MoO3-C shows 1.95 times higher activity for methanol oxidation than commercial Pt/C.•Pt/MoO3-C possesses 2.36 times higher stability than commercial Pt/C.Molybdenum trioxide (MoO3) has been considered an advanced auxiliary support for Pt nanoparticle anchorage due to its excellent activity and stability. Nevertheless, its non-conductivity property still impedes its applications in electrocatalytic fields. Thus, the MoO3 and carbon composite of a nanostructure is synthesized through sintering process and served as an efficient co-support for Pt-based anode catalyst in this paper. The electrochemical measurements demonstrate that Pt/MoO3-C catalyst shows higher catalytic activity and stability than the as-prepared Pt/C. Significantly, it exhibits 1.95 times higher activity and 2.36 times better durability for methanol oxidation when compared with commercial Pt/C. The remarkably enhanced performance of this novel Pt/MoO3-C catalyst for methanol electrooxidation can be ascribed to the abundant Pt nucleation active sites, uniformly dispersed Pt nanoparticles and the strong metal-support interaction between Pt and MoO3-C. These outstanding properties suggest Pt/MoO3-C a promising catalyst for practical application of fuel cell.The electrochemical performance of Pt/MoO3-C catalyst is higher than those of commercial Pt/C and as-prepared Pt/C catalysts.

Based on its abundance and low cost, sodium based batteries have aroused extensive attention for large scale energy-storage systems. In the current work, Na3V2(PO4)3 prepared by a facile solution evaporation method (denoted as NVP-SE) is used as cathode materials for sodium ion battery, with a control sample by solid state method. Raman spectrum and TEM are used to study the carbon layer coated on NVP-SE. The results show a highly graphitization and well-coated carbon layer, which is predominant by sp2 carbon. Graphitized carbon leads to high electrical conductivity, which can improve the rate performance of Na3V2(PO4)3 materials. Besides, GITT tests show high Na-ion diffusion coefficient. Even at 30 C, the NVP-SE cathode still delivers a capacity of 70 mAh g−1. Moreover, the material also shows great long term cycling performance. After 500 cycles at 1 C rate and 1000 cycles at 5 C, its discharge capacities are still 103.3 mAh g−1 and 85.4 mAh g−1, which maintain 92.6% and 85.0% of its initial capacity. Thus, simple preparation process and excellent electrochemical performance for Na3V2(PO4)3/C extend it as a potential material for high power applications.

A novel sandwich-structured graphene–Pt–graphene (G–P–G) catalyst has been synthesized by a convenient approach. The obtained G–P–G catalyst has been characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, and electrochemical measurements. Structural characterization shows that the G–P–G catalyst has a well-defined sandwich-like morphology. The results of electrochemical measurements indicate that the G–P–G exhibits 1.27 times higher activity for methanol electrooxidation than that of the Pt/graphene catalyst. Importantly, the results of the accelerated potential cycling test demonstrate that the G–P–G catalyst possesses 1.7 times higher stability than that of Pt/graphene. The significantly enhanced electrochemical performance is ascribed to its unique sandwich-like structure. Pt nanoparticles are anchored between the two adjacent graphene sheets, substantially enhancing the metal–support interaction, and graphene could act as a “mesh bag” to prevent the Pt species from leaking into the electrolyte, so its stability has considerably been enhanced. The effect of composited graphene amount on the stability of the hybrid has also been systematically studied. The stability of the catalyst increases with the increase of the introduced GO amount and the G–P–G50 shows optimized electrocatalytic performance. These findings suggest that the sandwich-structured G–P–G catalyst holds tremendous promise for fuel cells.

At present, low platinum catalysts have attracted much attention in the whole world. It is an effective strategy for reducing platinum loading to use an efficient support to enhance the catalytic activity. In this paper, a uniform structure of carbon and TiO2 nanowires is synthesized through a two-step hydrothermal reaction and used as an efficient Pt-based anode catalyst support. Physical characterization confirms the special core/shell structure. The carbonization temperature greatly affects the graphitization degree, porosity and surface chemical properties of the carbon shell. Electrochemical measurements indicate that the catalyst obtained at 800 °C has excellent electrochemical activity and durability. Its electrochemically active specific surface area is much higher than that of Pt/C. Its activity for methanol oxidation is about 1.4 times higher than that of Pt/C. The enhanced performance is attributed to the design of the special core/shell structure. The uniform dispersion of carbon and titania nanowires produces a strong synergistic effect and generates highly active Pt loading sites. The carbon shells can greatly improve the electronic conductivity and suppress the crystal growth of TiO2 during calcination. Meanwhile, a large number of defects within the carbon shells are also conducive to the dispersion of Pt nanoparticles. In addition, the core of TiO2 nanowires can enhance the hydrophilicity of the carbon shell and produce a strong metal–support interaction with Pt nanoparticles, which improve the activity and durability of catalysts.

While Li-rich Mn-based layered oxide is an appealing candidate for high energy density and high-voltage cathode materials for Li-ion batteries (LIBs), its applications are severely restricted by its low coulombic efficiency and poor rate capability. Herein, we report an effective approach to fabricate layered-spinel capped nanotube assembled 3D Li-rich hierarchitectures, by using a hydrothermal and ionic interfusion method. The unique 3D hollow hierarchical structure of the resulting material greatly shortens the pathways of electron and ion transfer, while maintaining reliable structural stability. Moreover, layered-spinel multicomponents introduce more effective 3D Li-ion diffusion channels (an excellent Li-ion diffusion coefficient of 1.55 × 10−10 cm2 s−1) and offer high coulombic efficiency. The structure–composition–property relationship is investigated by hierarchical structure controllable synthesis, Rietveld refinement crystallographic analysis and Li-ion transport kinetics measurement. As a result, when utilised as a cathode material for LIBs, this 3D Li-rich hierarchitecture delivers a high capacity of 293 (±3) mA h g−1 at 0.1C, shows a superior capacity retention of 89.5% after 200 cycles at 1C and exhibits a high capacity of 202 (±3) mA h g−1 even at 5C.

PtRu supported on a C@g-C3N4 NS (g-C3N4 nanosheet coated Vulcan XC-72 carbon black) catalyst has been prepared by a microwave-assisted polyol process (MAPP). The results of electrochemical measurements show that the PtRu/C@g-C3N4 NS catalyst has excellent activity due to more uniform dispersion and smaller size of PtRu nanoparticles (PtRu NPs), and higher stability ascribed to the stronger metal–support interaction (SMSI) between PtRu NPs and the composite support. Physical characterisation using techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) has indicated that the bulk g-C3N4 shell outside of the as-prepared C@bulk g-C3N4 (bulk g-C3N4 coated Vulcan XC-72 carbon black, C@bulk g-C3N4) indeed exfoliated to layered g-C3N4 nanosheets and formed a composite material of Vulcan XC-72 coated with g-C3N4 nanosheets. Furthermore, the results indicate that the mass catalytic activity of the PtRu/C@g-C3N4 NS catalyst substantially enhanced, which is a factor of 2.1 times higher than that of the PtRu/C catalyst prepared by the same procedure and the accelerated potential cycling tests (APCTs) show that the PtRu/C@g-C3N4 NS catalyst possesses 14% higher stability and much greater poison tolerance than as-prepared PtRu/C. The significantly enhanced performance of the PtRu/C@g-C3N4 NS catalyst is ascribed to the following reasons: the inherently excellent mechanical resistance and stability of g-C3N4 nanosheets in acidic and oxidative environments; the increased electron conductivity of the support by forming a core–shell structure of C@g-C3N4 NS; SMSI between metal NPs and the composite support. Based on this novel approach to fabricate a C@g-C3N4 NS hybrid nanostructure, many other interesting applications might also be discovered.

Molybdenum dioxide (MoO2) has been adopted as an advanced auxiliary support material for its outstanding electrical properties to anchor metal nanoparticles (NPs). To overcome the drawback of MoO2 electronic conductivity, a novel hierarchical carbon coated molybdenum dioxide (MoO2@C) nanotube built from ultra-thin nanosheets was utilized as a nanostructured support. Pt NPs were uniformly deposited onto the MoO2@C support and a hierarchical Pt-based anode catalyst was successfully synthesized. Benefitting from several favourable features, including high exposed surface area, short diffusion distance, fast charge transfer and homogeneous Pt NPs dispersion, the Pt/MoO2@C catalyst exhibited an improved activity along with enhanced stability for methanol electrooxidation when compared with that of the Pt/C catalyst. This novel hierarchical structure is helpful for the further applications in hydrogen evolution reaction, supercapacitors and batteries.

Layered Li-rich oxide (LLRO) is an attractive candidate for high-energy-density and high-voltage cathode material for next generation lithium ion batteries because of its high specific capacity and low cost. There still remain challenges in simultaneously achieving a multi-functional structure and composition in a LLRO, to achieve better electrochemical performance. Here we report a controllable co-precipitation and calcination method to synthesize LLRO by tuning the crystal nucleation, growth and heterogeneous contraction processes. The resultant LLRO adopts a hierarchical ball-in-ball hollow structure consisting of uniform multi-elemental (Mn–Ni–Co) primary nanocrystals, and exhibits high reversible capacity, remarkable cycle stability and superior rate performance. As a result, the resultant LLRO presents a high capacity of 193 mA h g−1 at 3C (a current density of 750 mA g−1) with a capacity retention of 87.6% after 400 cycles, and exhibits a capacity of 132 mA h g−1 at a high rate of 10C; moreover, it displays a quite slow voltage decay of ∼240 mV and a high energy density of 668 W h kg−1 after 200 cycles at 1C. The excellent electrochemical performance can be attributed to the combined merits of the multi-functional structure and composition, wherein the hierarchical hollow architecture facilitates efficient electron/ion transport and high structural stability, while multi-elemental components offer high reversible capacity.

High voltage spinel LiNi0.5Mn1.5O4 has been synthesized by an ethanol-assisted hydrothermal method. LiNi0.5Mn1.5O4 has also been synthesized by a precipitation method and hydrothermal method for comparison. The materials were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical tests. The ethanol-assisted hydrothermal process improves the dispersity and decreases the size of particles in the presence of ethanol. With small size particles, LiNi0.5Mn1.5O4 has an excellent rate capability. Its discharge capacity is 81.7 mA h g−1 at a high rate of 20 C. On the other hand, the ethanol-assisted hydrothermal process mixes the reagents homogeneously and improves the crystallinity. It leads to low impurities and low Mn3+ ion content, which are beneficial for electrochemical performance. The LiNi0.5Mn1.5O4 exhibits remarkable long-term cyclability. After 1000 cycles at a 5 C discharge rate, its discharge capacity is 102.1 mA h g−1 with a capacity retention ratio of 88.1%. It also has good high temperature performance with a capacity retention of 82.0% after 200 cycles at 55 °C.

Well-ordered, self-supported ultralong nanowire arrays (NWAs) with a 3D structure and tailored hydrogen titanate (HTO) phase have been synthesized via a facile template-free hydrothermal method and subsequent calcination and utilized as anodes in Li-ion capacitors (LICs) directly without any ancillary materials. The 3D structure constructed from ultralong nanowires and a rooftop network is beneficial to structural stability, electrolyte penetration, rich electro-active sites and short Li-ion transport paths. Moreover, the tailored HTO phase can introduce stronger and more effective Li-ion diffusion channels for the fast Li-ion insertion/extraction reaction. These merits from morphological and crystal structural design yield superior electrochemical performance in terms of high capacity, excellent rate capability and ultralong lifespan. The LIC assembled with a HTO NWA anode and activated carbon (AC) cathode achieves an attractive energy storage of 93.8 W h kg−1 and a capacitance retention of 78.8% after 3000 cycles at a high current density of 5.0 A g−1 within 0.0–3.0 V. Even at a rapid charging rate within 8.0 s, an excellent energy density of 33.3 W h kg−1 and a high power density of 15 kW kg−1 can be retained. Therefore, the HTO NWAs//AC LIC is a promising candidate as an energy storage system for high-energy and high-power applications.

For the next-generation energy-storage devices, high power density supercapacitors can be used as complementary power supplies. However, the shortcomings such as low energy density, complicated synthesis process, and high cost have limited their wide applications. Moreover, their rigid bulk structures hinder their applications in wearable electronics. Herein, we developed a fiber-shaped supercapacitor (FSC) with a volumetric energy density of up to 7.9 mW h cm−3 and volumetric capacitance of 28.8 F cm−3. This new FSC consists of a self-supported hybrid film electrode and free-standing polyester fiber electrode that are prepared using simple hydrothermal and vacuum filtration methods, respectively. The FSC also has high flexibility under different bending degree tests and long cycle life (capacitance retention efficiency is 98.6% after 10000 cycles). Based on the abovementioned discussion, it can be concluded that this new type of FSC with the advantages of low-cost, high flexibility, ultrahigh energy density, and ultralong cycle life will play an important role in many fields and is expected to act as a new star in the energy storage devices.

Good progress has been made in improving lithium sulfur batteries through trapping sulfur in porous carbon materials by controlling the pore size. However, microporous carbon/sulfur composites suffer from lower sulfur contents through the traditional sulfur loading methods. In this paper, we present an effective and facile approach to prepare a double-hollow-sphere structured microporous carbon coated sulfur composite by in situ oxidizing the microporous carbon coated metal sulfide precursor. The composite efficiently traps sulfur inside the microporous-walled hollow carbon sphere. With the appropriate sulfur content ranging from 55 wt% to 75 wt%, the composites demonstrate promising cycling performance. The composites deliver a capacity retention of 96.11% at 0.2C after 100 cycles, and a relatively low decay rate of 0.05% per cycle after 1000 cycles at 1C.

Sodium titanate/titania composite nanotubes/nanorods (STNS) are synthesized from anatase titania by the hydrothermal method and subsequent annealing in the range of 300–700 °C. The changes in the composition and morphology of STNS are investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results reveal that the composition of STNS changes from “Na2−xHxTi2O5” to “Na2Ti6O13” and their morphology changes from nanotubes to nanorods. The products obtained at 400 °C and 600 °C correspond to the intermediate state of reactions. Pt-based catalysts are prepared by a microwave-assisted ethylene glycol process, and are also characterized by physical analysis and electrochemical measurements. The variations of the catalytic activity and stability of Pt/C-STNS catalysts show the interesting “M” shape with the increase of the annealing temperature of STNS. The Pt nanoparticles supported on STNS-400 nanotubes and STNS-600 nanorods exhibit more uniform dispersion and superior electrocatalytic performance for methanol electrooxidation. The main reason seems to be that both of them are multiphase composites with a large number of phase interfaces and crystal defects, which is conducive to the deposition of Pt nanoparticles. The uniform dispersion of Pt nanoparticles plays an essential role in the electrochemical performance of catalysts. In addition, the presence of the “anatase TiO2” phase in both of them can further enhance the electrochemical performance due to the metal–support interaction. Moreover, compared to commercial Pt/C, the Pt/C-STNS-600 catalyst exhibits higher electrochemical activity and stability, suggesting that superior catalysts can be developed by designing the structure and composition of the supports.