Developing bifunctional efficient and durable non-noble electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly desirable and challenging for overall water splitting. Herein, Co–Mn carbonate hydroxide (CoMnCH) nanosheet arrays with controllable morphology and composition were developed on nickel foam (NF) as such a bifunctional electrocatalyst. It is discovered that Mn doping in CoCH can simultaneously modulate the nanosheet morphology to significantly increase the electrochemical active surface area for exposing more accessible active sites and tune the electronic structure of Co center to effectively boost its intrinsic activity. As a result, the optimized Co1Mn1CH/NF electrode exhibits unprecedented OER activity with an ultralow overpotential of 294 mV at 30 mA cm–2, compared with all reported metal carbonate hydroxides. Benefited from 3D open nanosheet array topographic structure with tight contact between nanosheets and NF, it is able to deliver a high and stable current density of 1000 mA cm–2 at only an overpotential of 462 mV with no interference from high-flux oxygen evolution. Despite no reports about effective HER on metal carbonate hydroxides yet, the small overpotential of 180 mV at 10 mA cm–2 for HER can be also achieved on Co1Mn1CH/NF by the dual modulation of Mn doping. This offers a two-electrode electrolyzer using bifunctional Co1Mn1CH/NF as both anode and cathode to perform stable overall water splitting with a cell voltage of only 1.68 V at 10 mA cm–2. These findings may open up opportunities to explore other multimetal carbonate hydroxides as practical bifunctional electrocatalysts for scale-up water electrolysis.

Developing highly efficient and stable non-Pt electrocatalysts for the oxygen reduction reaction (ORR) to replace the state-of-the-art noble metal is essential for commercialization of fuel cells. Fe–N–C-based electrocatalysts are considered as a promising alternative to commercial Pt/C. An efficient electrocatalyst commonly requires large density of active site, high surface area, and desirable porosity, especially multimodal porosity with both large pores for efficient mass transfer and small pores for exposing as many active sites as possible. Herein, a lamellar metal organic framework (MOF) was developed as a precursor to directly achieve such a highly active Fe–N–C electrocatalyst with high surface area and desirable bimodal porosity. The mesopores arising from the special lamellar morphology of MOF benefits efficient mass transfer, and the nanopores resulting from pyrolysis of the MOF makes the majority of active sites accessible to electrolyte and thus effective for ORR. Uniform distribution of active elements N, C, and Fe at the molecular level in MOF precursor ensures abundant well-dispersed highly active sites in the catalyst. As a result, the catalyst exhibited superior ORR electrocatalytic activity and stability to commercial Pt/C. This strategy, using rarely reported lamellar MOF to prepare ORR catalysts with the merits mentioned, could inspire the exploration of a wide range of electrocatalysts from lamellar MOF precursors for various applications.Keywords: electrocatalysis; fuel cells; metal organic frameworks; nanostructures; oxygen reduction reaction;

I–III–VI2 group “green” quantum dots (QDs) are attracting increasing attention in photoelectronic conversion applications. Herein, on the basis of the “simultaneous nucleation and growth” approach, Cu–In–Ga–Se (CIGSe) QDs with light harvesting range of about 1000 nm were synthesized and used as sensitizer to construct quantum dot sensitized solar cells (QDSCs). Inductively coupled plasma atomic emission spectrometry (ICP-AES), wild-angle X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses demonstrate that the Ga element was alloyed in the Cu–In–Se (CISe) host. Ultraviolet photoelectron spectroscopy (UPS) and femtosecond (fs) resolution transient absorption (TA) measurement results indicate that the alloying strategy could optimize the electronic structure in the obtained CIGSe QD material, thus matching well with TiO2 substrate and favoring the photogenerated electron extraction. Open circuit voltage decay (OCVD) and impedance spectroscopy (IS) tests indicate that the intrinsic recombination in CIGSe QDSCs was well suppressed relative to that in CISe QDSCs. As a result, CIGSe based QDSCs with use of titanium mesh supported mesoporous carbon counter electrode exhibited a champion efficiency of 11.49% (Jsc = 25.01 mA/cm2, Voc = 0.740 V, FF = 0.621) under the irradiation of full one sun in comparison with 9.46% for CISe QDSCs.Keywords: alloying strategy; Cu−In−Ga−Se (CIGSe) QDs; high efficiency; photovoltaic cells; quantum dot sensitized solar cells;

Metal–nitrogen coordination sites, M–Nx (M = Fe, Co, Ni, etc.), have shown great potential to replace platinum group materials as electrocatalysts for oxygen reduction reaction (ORR). However, the real active site in M–Nx is still vague to date due to their complicated structure and composition. It is therefore highly desirable but challenging to develop ORR catalysts with novel and clear active sites, which could meet the needs of comprehensive understanding of structure–function relationships and explore new cost-effective and efficient ORR electrocatalysts. Herein, well-defined M–O6 coordination in metal–catecholates (M–CATs, M = Ni or Co) is discovered to be catalytically active for ORR via a four-electron-dominated pathway. In view of no pyrolysis involved and unambiguous crystalline structure of M–CATs, the M–O6 octahedral coordination site with distinct structure is determined as a new type of active site for ORR. These findings extend the scope of metal–nonmetal coordination as an active site for ORR and pave a way for bottom-up design of novel electrocatalysts containing M–O6 coordination.Keywords: electrocatalysis; metal−organic frameworks; MOFs; ORR; oxygen reduction reaction;

Transition-metal phosphides have recently been identified as low-cost and efficient electrocatalysts that are highly active for the hydrogen evolution reaction. Unfortunately, to achieve a controlled phosphidation of nonprecious metals toward a desired nanostructure of metal phosphides, the synthetic processes usually turned complicated, high-cost, and even dangerous due to the reaction chemistry related to different phosphorus sources. It becomes even more challenging when considering the integration of those active metal phosphides with the structural engineering of their conductive matrix toward a favorable architecture for optimized catalytic performance. Herein, we identified that the biomass itself could act as an effective synthetic platform for the construction of supported metal phosphides by recovering its inner phosphorus upon reacting with transition-metals ions, forming well-dispersed, highly active nanoparticles of metal phosphides incorporated in the nanoporous carbon matrix, which promised high catalytic activity in the hydrogen evolution reaction. Our synthetic protocol not only provides a simple and effective strategy for the construction of a large variety of highly active nanoparticles of metal phosphides but also envisions new perspectives on an integrated utilization of the essential ingredients, particularly phosphorus, together with the innate architecture of the existing biomass for the creation of functional nanomaterials toward sustainable energy development.

AbstractThe exploration of new efficient OER electrocatalysts based on nonprecious metals and the understanding of the relationship between activity and structure of electrocatalysts are important to advance electrochemical water oxidation. Herein, we developed an efficient OER electrocatalyst with nickel boride (Ni3B) nanoparticles as cores and nickel(II) borate (Ni-Bi) as shells (Ni-Bi@NB) via a very simple and facile aqueous reaction. This electrocatalyst exhibited a small overpotential of 302 mV at 10 mA cm−2 and Tafel slope of 52 mV dec−1. More interestingly, it was found that the OER activity of Ni-Bi@NB was closely dependent on the crystallinity of the Ni-Bi shells. The partially crystalline Ni-Bi catalyst exhibited much higher activity than the amorphous or crystalline analogues; this higher activity originated from the enhanced intrinsic activity of the catalytic sites. These findings open up opportunities to explore nickel(II) borates as a new class of efficient nonprecious metal OER electrocatalysts, and to improve the electrocatalyst performance by modulating their crystallinity.

AbstractThe exploration of new efficient OER electrocatalysts based on nonprecious metals and the understanding of the relationship between activity and structure of electrocatalysts are important to advance electrochemical water oxidation. Herein, we developed an efficient OER electrocatalyst with nickel boride (Ni3B) nanoparticles as cores and nickel(II) borate (Ni-Bi) as shells (Ni-Bi@NB) via a very simple and facile aqueous reaction. This electrocatalyst exhibited a small overpotential of 302 mV at 10 mA cm−2 and Tafel slope of 52 mV dec−1. More interestingly, it was found that the OER activity of Ni-Bi@NB was closely dependent on the crystallinity of the Ni-Bi shells. The partially crystalline Ni-Bi catalyst exhibited much higher activity than the amorphous or crystalline analogues; this higher activity originated from the enhanced intrinsic activity of the catalytic sites. These findings open up opportunities to explore nickel(II) borates as a new class of efficient nonprecious metal OER electrocatalysts, and to improve the electrocatalyst performance by modulating their crystallinity.

Due to their wide tunable bandgaps, high absorption coefficients, easy solution processabilities, and high stabilities in air, lead sulfide (PbS) quantum dots (QDs) are increasingly regarded as promising material candidates for next-generation light, low-cost, and flexible photodetectors. Current single-layer PbS-QD photodetectors suffer from shortcomings of large dark currents, low on–off ratios, and slow light responses. Integration with metal nanoparticles, organics, and high-conducting graphene/nanotube to form hybrid PbS-QD devices are proved capable of enhancing photoresponsivity; but these approaches always bring in other problems that can severely hamper the improvement of the overall device performance. To overcome the hurdles current single-layer and hybrid PbS-QD photodetectors face, here a bilayer QD-only device is designed, which can be integrated on flexible polyimide substrate and significantly outperforms the conventional single-layer devices in response speed, detectivity, linear dynamic range, and signal-to-noise ratio, along with comparable responsivity. The results which are obtained here should be of great values in studying and designing advanced QD-based photodetectors for applications in future flexible optoelectronics.

AbstractA binder-free efficient MoNi4/MoO3-x nanorod array electrode with 3D open structure is developed by using Ni foam as both scaffold and Ni source to form NiMoO4 precursor, followed by subsequent annealing in a reduction atmosphere. It is discovered that the self-templated conversion of NiMoO4 into MoNi4 nanocrystals and MoO3-x as dual active components dramatically boosts the hydrogen evolution reaction (HER) performance. Benefiting from high intrinsic activity, high electrochemical surface area, 3D open network, and improved electron transport, the resulting MoNi4/MoO3-x electrode exhibits a remarkable HER activity with extremely low overpotentials of 17 mV at 10 mA cm−2 and 114 mV at 500 mA cm−2, as well as a superior durability in alkaline medium. The water–alkali electrolyzer using MoNi4/MoO3-x as cathode achieves stable overall water splitting with a small cell voltage of 1.6 V at 30 mA cm−2. These findings may inspire the exploration of cost-effective and efficient electrodes by in situ integrating multiple highly active components on 3D platform with open conductive network for practical hydrogen production.

AbstractGeSe is a promising absorber material for photovoltaic applications due to its attractive material, optical, and electrical properties as well as its low toxicity and earth abundance. The first GeSe-based solar cell with 1.48% efficiency has been recently reported through self-regulated rapid thermal sublimation. However, most of the fundamental physical and electronic properties of GeSe such as refractive index, dielectric constant, carrier mobility, lifetime, and diffusion length remain unclear, despite the necessity of this for the design of high-performance GeSe solar cells. In this work, the above basic properties of GeSe are systematically studied by using spectroscopic ellipsometry, space charge limited current measurements, and transient absorption spectroscopy. These comprehensive results provide a solid foundation for the further development of GeSe solar cells.

AbstractExploring facile and easily-scalable methods for synthesizing earth-abundant, cost-effective and efficient hydrogen evolution reaction (HER) electrocatalysts is essential for the mass production of hydrogen as a clean and sustainable energy carrier. We report here a simple strategy to produce Mo2C nanocrystals embedded in carbon network (Mo2C@C) by the direct pyrolysis of ammonium molybdate and polyvinylpyrrolidone (PVP). It is found that PVP can be effectively used as a single source to form carbides and carbon network. The long polymer chain and coordinating capability with transition metal of PVP make it possible to form connected porous carbon network and well-dispersed Mo2C nanocrystals in several nanometers. The carbonization of PVP not only effectively in-situ prevents the aggregation of Mo2C nanocrystals during their formation, but also provides conductive porous matrix. As a result, the Mo2C@C composite exhibits the superior electrocatalytic performance for HER, which can be ascribed to the large number of active sites from plenty of small Mo2C nanocrystals and the efficient mass and electron transport network from carbon matrix. This strategy may inspire the exploration of cost-effective functional polymer as single source for both carbon precursor and nanostructure-directed reagent to mass-produce well-defined metal carbides nanostructures embedded in porous carbon network for energy applications.

Controlled synthesis of Pt-based bimetallic nanocrystals with a tunable size and structure has demonstrated great potential to advance their electrocatalytic performances. We present herein a facile but effective strategy for the rapid aqueous synthesis of PtCu nanodendrites (NDs) with advanced electrocatalytic performance. The systematical investigation on the influence of reaction conditions on the formation of PtCu NDs reveals that the underpotential deposition of Cu not only accelerates the growth of NDs but also significantly modulates their size and branch structure as well as their composition. Electrochemical tests demonstrate that Pt55Cu45 NDs with a smaller size and fewer branches but a higher content of Cu exhibit the highest electrocatalytic activity for both the oxygen reduction reaction and the methanol oxidation reaction, compared with Pt92Cu8 NDs, Pt NDs and commercial Pt/C. These results may inspire the engineering of a wide range of metallic alloyed nanocrystals to advance their electrocatalytic performances for diverse applications.

Developing highly efficient low-cost electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline electrolyte is essential to advance water electrolysis technology. Herein, Ni(OH)2 nanoplates aligned on NiAl foil (Ni(OH)2/NiAl) are developed by simply dealloying NiAl foil in KOH, which exhibits high electrocatalytic activity for OER with a small overpotential of 289 mV to achieve 10 mA cm−2 and outstanding durability with no detectable degradation during long-term operation. Furthermore, such Ni(OH)2/NiAl can effectively act as an active and robust hierarchical scaffold to simply electrodeposit other catalysts with intrinsically higher activity such as NiMo and NiFe nanoparticles for highly efficient HER and OER, respectively. The prepared NiFe/Ni(OH)2/NiAl displays superior OER catalytic activity with overpotentials of 246, 315, and 374 mV at 10, 100, and 500 mA cm−2, respectively. While NiMo/Ni(OH)2/NiAl catalyst exhibits remarkable HER performance with a small overpotential of 78 mV to deliver 10 mA cm−2. Consequently, the electrolysis device composed of the above two electrocatalysts demonstrates superb water splitting performance with a cell voltage of 1.59 V at 10 mA cm−2. These results open up opportunities to explore and optimize low-cost advanced catalysts for energy applications.

A hierarchical assembled ITO nanowire array with both horizontal and vertical nanowire branches was fabricated as a new three-dimensional fractal nanobiointerface for efficient cancer cell capture. Comparing with ITO nanowire array without branches, this fractal nanobiointerface exhibited much higher efficiency (89% vs 67%) and specificity in capturing cancer cells and took shorter time (35 vs 45 min) to reach the maximal capture efficiency. As indicated by the immunofluorescent and ESEM images, this enhancement can be attributed to the improvement of topographical interaction between cells and the substrate. The introduction of horizontal and vertical nanowire branches makes the substrate topographically match better with cell filopodia and provides more binding sites for cell capture. The live/dead cell staining and proliferation experiments confirm that this fractal nanobiointerface displays excellent cyto-compatibility with an over 96% cell viability after capture. These results provide new insights and may open up opportunities in designing and engineering new cell-material interfaces for advanced biomedical applications.

GeSe has recently emerged as a promising photovoltaic absorber material due to its attractive optical and electrical properties as well as earth-abundant and low-toxic constituent elements. However, no photovoltaic device has been reported based on this material so far, which could be attributed to the inevitable coexistence of phase impurities Ge and GeSe2, leading to detrimental recombination-center defects and seriously degrading the device performance. Here we overcome this issue by introducing a simple and fast (4.8 μm min–1) rapid thermal sublimation (RTS) process designed according to the sublimation feature of the layered structured GeSe. This new method offers a compelling combination of assisting raw material purification to suppress deleterious phase impurities and preventing the formation of detrimental point defects through congruent sublimation of GeSe, thus providing an in situ self-regulated process to fabricate high quality polycrystalline GeSe films. Solar cells fabricated following this process show a power conversion efficiency of 1.48% with good stability. This preliminary efficiency and high stability, combined with the self-regulated RTS process (also extended to the fabrication of other binary IV-VI chalcogenide films, i.e., GeS), demonstrates the great potential of GeSe for thin-film photovoltaic applications.

Organic–inorganic hybrid perovskite single-crystalline thin films (SCTFs) are promising for enhancing photoelectric device performance due to high carrier mobility, long diffusion length, and carrier lifetime. However, bulk perovskite single crystals available today are not suitable for practical device application due to the unfavorable thickness. Herein, we report a facile space-confined solution-processed strategy to on-substrate grow various hybrid perovskite SCTFs in a size of submillimeter with adjustable thicknesses from nano- to micrometers. These SCTFs exhibit photoelectric properties comparable to bulk single crystals with low defect density and good air stability. The clear thickness-dependent colors allow fast visual selection of SCTFs with a suitable thickness for specific device application. The present substrate-independent growth of perovskite SCTFs opens up opportunities for on-chip fabrication of diverse high-performance devices.

Understanding the origin of high activity of Fe–N–C electrocatalysts in oxygen reduction reaction (ORR) is critical but still challenging for developing efficient sustainable nonprecious metal catalysts in fuel cells and metal–air batteries. Herein, we developed a new highly active Fe–N–C ORR catalyst containing Fe–Nx coordination sites and Fe/Fe3C nanocrystals (Fe@C-FeNC), and revealed the origin of its activity by intensively investigating the composition and the structure of the catalyst and their correlations with the electrochemical performance. The detailed analyses unambiguously confirmed the coexistence of Fe/Fe3C nanocrystals and Fe–Nx in the best catalyst. A series of designed experiments disclosed that (1) N-doped carbon substrate, Fe/Fe3C nanocrystals or Fe–Nx themselves did not deliver the high activity; (2) the catalysts with both Fe/Fe3C nanocrystals and Fe–Nx exhibited the high activity; (3) the higher content of Fe–Nx gave the higher activity; (4) the removal of Fe/Fe3C nanocrystals severely degraded the activity; (5) the blocking of Fe–Nx downgraded the activity and the recovery of the blocked Fe–Nx recovered the activity. These facts supported that the high ORR activity of the Fe@C-FeNC electrocatalysts should be ascribed to that Fe/Fe3C nanocrystals boost the activity of Fe–Nx. The coexistence of high content of Fe–Nx and sufficient metallic iron nanoparticles is essential for the high ORR activity. DFT calculation corroborated this conclusion by indicating that the interaction between metallic iron and Fe–N4 coordination structure favored the adsorption of oxygen molecule. These new findings open an avenue for the rational design and bottom-up synthesis of low-cost highly active ORR electrocatalysts.

To promote the oxygen reduction reaction (ORR) on a non-precious-metal catalyst, integrating two-dimensional (2D) nanosheets and one-dimensional (1D) nanotubes in one catalyst is considered as one of the desirable approaches since this hybrid architecture can host more useful active sites and enhance mass/electron transfer. Herein, we demonstrated a sodium chloride-assisted strategy for the in situ synthesis of a three-dimensional (3D) hybrid of carbon nanosheets and nanotubes. The micrometer-scale sodium chloride (NaCl) crystal acted as a recyclable skeleton to adsorb the precursors on its surfaces, which assisted the formation of micrometer-sized graphitic carbon nanosheets with nanometer thickness by the template effect during the pyrolysis, and iron-based nanocrystals with a size of tens of nanometers by helping the distribution of iron sources and preventing their aggregation. The small iron-based nanocrystals favored the growth of long CNTs connected to carbon nanosheets and the outmigration of carbon atoms during the cooling process, which led to the formation of carbon-layer encapsulated metallic iron nanoparticles between the carbon nanosheets or inside the carbon nanotubes. Benefiting from these features, the developed hybrid exhibited a significantly enhanced electrocatalytic activity and durability for the ORR. The results may open up opportunities for exploring cost-effective high-performance electrocatalysts for energy applications.

Semiconductor-based photocatalytic H2 generation as a direct approach of converting solar energy to fuel is attractive for tackling the global energy and environmental issues but still suffers from low efficiency. Here, we report a MoS2/CdS nanohybrid as a noble-metal-free efficient visible-light driven photocatalyst, which has the unique nanosheets-on-nanorod heterostructure with partially crystalline MoS2 nanosheets intimately but discretely growing on single-crystalline CdS nanorod. This heterostructure not only facilitates the charge separation and transfer owing to the formed heterojunction, shorter radial transfer path, and fewer defects in single-crystalline nanorod, thus effectively reducing the charge recombination, but also provides plenty of active sites for hydrogen evolution reaction due to partially crystalline structure of MoS2 as well as enough room for hole extraction. As a result, the MoS2/CdS nanosheets-on-nanorod exhibits a state-of-the-art H2 evolution rate of 49.80 mmol g–1 h–1 and an apparent quantum yield of 41.37% at 420 nm, which is the advanced performance among all MoS2/CdS composites and CdS/noble metal photocatalysts. These findings will open opportunities for developing low-cost efficient photocatalysts for water splitting.

Co nanoparticle-encapsulated N-doped carbon nanotubes (Co@N-CNTs) are prepared as a Pt-free electrocatalyst for oxygen reduction reaction (ORR) via direct pyrolysis of a CoAl-layered double hydroxide (CoAl-LDH)/melamine mixture. The approach could bundle the following distinct features: (i) commercially available melamine as both carbon and nitrogen bi-functional sources; (ii) scalably prepared CoAl-LDH precursor chosen to play a triple role in catalyzing the formation of N-CNTs and serving the electroactive Co nanoparticles, as well as in facilitating the growth of long N-CNTs owing to the confinement effect of the non-active Al2O3 matrix formed; (iii) an alternative to prepare one-dimensional length-and-performance-tunable N-CNTs, which are obtained typically by using catalytic chemical vapor deposition (CCVD) of two gaseous carbon and nitrogen resources on the surface of an LDH layer. The long Co@N-CNTs exhibits the highly enhanced electrocatalytic activity and stability for ORR (onset potential at 929 mV, half-wave potential at 849 mV vs. RHE, and limited current density at 6.0 mA cm−2). The CoAl-LDH precursor-based approach may open up a simple and feasible alternative to design and produce low-cost electrocatalysts for fuel cells.

Well-defined pomegranate-like N,P-doped Mo2C@C nanospheres were prepared by simply using phosphomolybdic acid (PMo12) to initiate the polymerization of polypyrrole (PPy) and as a single source for Mo and P to produce N,P-doped Mo2C nanocrystals. The existence of PMo12 at the molecular scale in the polymer network allows the formation of pomegranate-like Mo2C@C nanospheres with a porous carbon shell as peel and Mo2C nanocrystals well-dispersed in the N-doped carbon matrix as seeds. This nanostructure provides several favorable features for hydrogen evolution application: (1) the conductive carbon shell and matrix effectively prevent the aggregation of Mo2C nanocrystals and facilitate electron transportation; (2) the uniform N,P-doping in the carbon shell/matrix and plenty of Mo2C nanocrystals provide abundant catalytically highly active sites; and (3) nanoporous structure allows the effective exposure of active sites and mass transfer. Moreover, the uniform distribution of P and Mo from the single source of PMo12 and N from PPy in the polymeric PPy–PMo12 precursor guarantees the uniform N- and P-co-doping in both the graphitic carbon matrix and Mo2C nanocrystals, which contributes to the enhancement of electrocatalytic performance. As a result, the pomegranate-like Mo2C@C nanospheres exhibit extraordinary electrocatalytic activity for the hydrogen evolution reaction (HER) in terms of an extremely low overpotential of 47 mV at 10 mA cm–2 in 1 M KOH, which is one of the best Mo-based HER catalysts. The strategy for preparing such nanostructures may open up opportunities for exploring low-cost high-performance electrocatalysts for various applications.Keywords: electrocatalysis; HER; molybdenum carbide; nanostructures; nanostructures

•Novel MoS2/CdS nanodots-on-nanorods heterostructures were prepared by a facile one-pot solvothermal method.•MoS2 nanodots allow for more active sites, effective electron transfer and hole extraction for efficient HER.•The electron transfer kinetics of MoS2/CdS was firstly investigated by femtosecond transient absorption spectroscopy.The efficiency of CdS-based photocatalysts for H2 evolution is limited by the ultrafast charge recombination. Here, we demonstrated the one-pot synthesis of a novel MoS2/CdS photocatalyst with the structure of partially crystalline MoS2 nanodots growing on single-crystalline CdS nanorods. This heterostructure not only effectively reduces the bulk and surface charge recombination owing to single-crystalline CdS nanorod matrix and efficient electron transfer, also provides plenty of active sites for hydrogen evolution reaction (HER) and accessible room for prompt hole extraction. The femtosecond transient absorption (TA) analysis reveals the effective electron transfer from CdS to MoS2 in ~20 ps. As a result, MoS2/CdS exhibits extraordinary photocatalytic activity with a H2 evolution rate of 60.28 mmol/g/h under visible light irradiation, far exceeding all previous HER photocatalysts with MoS2 as cocatalysts.MoS2/CdS nanodots-on-nanorods was rationally designed and prepared by a facile one-pot solvothermal method. Benefited from the unique nanostructure, this MoS2/CdS heterostructure exhibits a superior photocatalytic performance for hydrogen evolution.

The key challenges in enhancing the power conversion efficiency (PCE) of a quantum dot-sensitized solar cell (QDSSC) are efficiently achieving charge separation at the photoanode and improving the charge transfer, which is limited by the interface between the electrolyte and the counter electrode (CE). Here, hierarchically assembled ITO@Cu2S nanowire arrays with conductive single-crystalline ITO cores and Cu2S nanocrystal shells were designed as efficient QDSSCs CEs. These arrays not only provided an efficient three-dimensional charge transport network but also allowed for the effective deposition of more Cu2S nanocrystals as active sites to catalyze the electrolyte reaction. This design considerably reduced the sheet and charge transfer resistance of the CE, thus decreasing the series resistance and increasing the shunt resistance of the QDSSC. As a result, QDSSCs with this CE exhibited an unprecedentedly high Voc of 0.688 V, a fill factor of 58.39%, and a PCE of 6.12%, which is 21.2% higher than that of the conventional brass/Cu2S CE.

We report here the selective synthesis of air-stable phase-pure pyrite FeS2 nanocubes, spheroidal nanocrystals, and microspheres by solvent-induced oriented attachment (OA). It was found that the solvents could control the OA process and thus the morphologies of the products. Solvent exchange experiments and detailed Raman analysis revealed that 1-octanol contributed to the long-term stability of these pyrite nanomaterials.

The development of highly stable and efficient catalysts for sluggish cathode oxygen reduction reaction (ORR) is extremely important for the long-term operation and the commercialization of proton exchange membrane fuel cells (PEMFCs) but still challenging. We present herein a facile strategy to efficiently embed Pt nanocrystals into N-doped porous carbon/carbon nanotubes (Pt@CNx/CNT). The N-doped porous carbon shells not only effectively prevented Pt nanocrystals from detachment, dissolution, migration, and aggregation during accelerated durability tests or heat-treatment at 900 °C, but also allowed the access of electrolyte to the Pt surface and preserved the good electron transfer of CNT by avoiding the structural damage of carbon nanotubes (CNTs). The interaction between the embedded Pt nanocrystals and the encapsulating CNx layer was found in Pt@CNx/CNT, which markedly affected the electronic structure of Pt nanocrystals and contributed to the improvement on the catalytic activity and stability of Pt@CNx/CNT. As a result, the Pt@CNx/CNT catalyst exhibited an excellent thermal stability, durability, and sufficient catalytic activity for ORR. The demonstrated strategy could be easily extended to produce a wide range of other electrocatalysts with even better activity and extraordinary stability.Keywords: high durability nanostructures; N-doped carbon; PEMFCs; platinum

Molybdenum sulfide materials have been shown to be promising non-precious metal catalysts for the hydrogen evolution reaction (HER). This work reports a facile and scalable preparation method for amorphous MoS2 nanosheet arrays directly deposited on carbon cloth (a-MoS2 NA/CC) using a highly reproducible physical vapor deposition (PVD) approach. As a result of the three-dimensional nanostructure of the catalyst, the amorphous nature and the abundant exposed edge sites of MoS2, the a-MoS2 NA/CC composite exhibited superior catalytic activity and stability for the HER in acidic solutions.

The development of low-cost electrocatalysts with comparable activity for oxygen reduction reaction (ORR) to substitute platinum-based catalysts is imperative but still challenging for the commercialization of fuel cells. Herein, we reported a strategy to effectively confine iron carbide nanocrystals in N-doped carbon coated on carbon nanotubes (CNx@CNT), which prevented the agglomeration of iron carbide during pyrolysis and thus provided the sufficient highly active catalytic sites. Together with the benefit from three-dimensional conductive network of CNT-based core–shell structure for fast electron transfer and rapid mass transfer, the developed nanocatalyst exhibited the significantly enhanced electrocatalytic activity for ORR, as well as high durability and methanol tolerance. Moreover, it was interestingly found that the types of the confined iron compounds appreciably affected the performance of the catalysts, and Fe3C might be most effective on improving ORR activity in this case.Keywords: carbon nanotubes; iron carbides; nitrogen-doped carbon; non-noble-metal catalysts; oxygen reduction reaction;

Urchin-like micro/nano heterostructure Au@CdS/WO3 was synthesized by using a facile photodeposition method with no need for an additional stabilizer, which can be used as an efficient all-solid Z-scheme visible-light photocatalyst for H2 generation with a high H2 evolution rate.

Quantum-dot-sensitized solar cell (QDSSC) has been considered as an alternative to new generation photovoltaics, but it still presents very low power conversion efficiency. Besides the continuous effort on improving photoanodes and electrolytes, the focused investigation on charge transfer at interfaces and the rational design for counter electrodes (CEs) are recently receiving much attention. Herein, core–shell nanowire arrays with tin-doped indium oxide (ITO) nanowire core and Cu2S nanocrystal shell (ITO@Cu2S) were dedicatedly designed and fabricated as new efficient CEs for QDSSCs in order to improve charge collection and transport and to avoid the intrinsic issue of copper dissolution in popular and most efficient Cu/Cu2S CEs. The high-quality tunnel junctions formed between n-type ITO nanowires and p-type Cu2S nanocrystals led to the considerable decrease in sheet resistance and charge transfer resistance and thus facilitated the electron transport during the operation of QDSSCs. The three-dimensional structure of nanowire arrays provided high surface area for more active catalytic sites and easy accessibility for an electrolyte. As a result, the power conversion efficiency of QDSSCs with the designed ITO@Cu2S CEs increased by 84.5 and 33.5% compared to that with planar Au and Cu2S CEs, respectively.

A new N-doped carbon nanomaterial with nanoporous coaxial nanocable structure was designed for achieving the requirements of high nitrogen content, proper nitrogen bonding state, and sufficient electron and mass transportation for an oxygen reduction reaction (ORR) catalyst. The nanoporous sheaths provided more catalytic sites and allowed oxygen and reactants to easily access them for fast mass transfer, whereas carbon nanotube cores provided a three-dimensional conductive network and guaranteed fast electron transfer. As a result, the designed low-cost catalyst exhibited excellent electrocatalytic performance and is one of the most active metal-free ORR catalyst.

Among the issues that restrict the power conversion efficiency (PCE) of quantum-dot-sensitized solar cells (QDSSCs), insufficient catalytic activity and stability of counter electrodes (CEs) are critical but challenging ones. The state-of-the-art Cu/Cu2S CEs still suffer from mechanical instability and uncertainty due to the reaction of copper and electrolyte. Herein, ITO@Cu2S core–shell nanowire arrays were developed to fabricate CEs for QDSSCs, which have no such issues in Cu/Cu2S CEs. These nanowire arrays exhibited small charge transfer resistance and sheet resistance, and provided more active catalytic sites and easy accessibility for electrolyte due to the three-dimensional structure upon use as CEs. More interestingly, it was found that the interface of ITO/Cu2S significantly affected the performance of ITO@Cu2S nanowire array CEs. By varying synthetic methods, a series of ITO@Cu2S nanowire arrays were prepared to investigate the influence of ITO/Cu2S interface on their performance. The results showed that ITO@Cu2S nanowire array CEs with a continuous Cu2S nanocrystal shell fabricated via an improved cation exchange route exhibited excellent and thickness-dependent performance. The PCE of corresponding QDSSCs increased by 11.6 and 16.5% compared to that with the discrete Cu2S nanocrystal and the classic Cu/Cu2S CE, respectively, indicating its promising potential as a new type of CE for QDSSCs.Keywords: counter electrodes; interface; nanowires; quantum dots; solar cells

The importance of the oxygen reduction reaction (ORR) in fuel cells and high energy density metal–air batteries has attracted intense research interests in looking for low-cost ORR catalysts as substitutes for expensive and scarce Pt-based catalysts. N-doped graphene and carbon nanotubes prepared in a low-cost and scalable way have demonstrated their potential although the performance still needs to be improved. In view of the requirements for a high-performance ORR electrocatalyst, this work focused on developing the nanocomposites of N-doped reduced graphene oxide (N-rGO) and N-doped carbon nanotubes (N-CNT) as low-cost efficient ORR catalysts by integrating the advantages of abundant highly-active sites from N-rGO and a three-dimensional conductive network for efficient mass and electron transport from N-CNT. By optimizing the preparation method and dedicatedly tuning the composition, the much enhanced ORR activity and superior durability and tolerance to methanol were achieved for the self-assembled N-doped composite (N-rGO–CNT) at a mass ratio of 1:5 rGO/CNT. Further improvement of the ORR electrocatalytic activity of the composite was also demonstrated by introducing iron into the composite.

The kesterite Cu2ZnSn(S,Se)4 (CZTSSe) is an ideal candidate for light harvesting materials in earth-abundant low-cost thin-film solar cells (TFSC). Although the solution-based processing is a most promising approach to achieve low-cost solar cells with high power conversion efficiency, the issues of poor crystallinity and carbon residue in CZTSSe thin films are still challenging. Herein, a non-hydrazine solution-based method was reported to fabricate highly crystallized and carbon-free kesterite CZTSSe thin films. Interestingly, it was found that the synthetic atmosphere of metal organic precursors have a dramatic impact on the morphology and crystallinity of CZTSSe films. By optimizing the processing parameters, we were able to obtain a kesterite CZTSSe film composed of compact large crystal grains with trace carbon residues. Also, a viable reactive ion etching (RIE) processing with optimized etching conditions was then developed to successfully eliminate trace carbon residues on the surface of the CZTSSe film.

Developing catalysts with high electrocatalytic activity for oxygen reduction reaction (ORR) has recently attracted much attention because the sluggish ORR limits the performance and commercialization of current PEMFCs and metal–air batteries as well. Herein, a facile approach was reported to synthesize Mn3O4 nanoparticle coated carbon nanotubes (Mn3O4/CNTs) and self-deposit well-dispersed Pt nanocrystals on Mn3O4/CNTs to obtain Pt/Mn3O4/CNTs hybrid catalysts via in situ reduction of support matrix with no need of any capping agent and additional reducing agent. As a result of good dispersion of uncapped Pt nanocrystals, interconnected carbon nanotube conductive network, and possible synergetic co-catalytic effect from heterojunction interfaces of Pt nanocrystals and Mn3O4, the as-prepared Pt/Mn3O4/CNTs hybrid catalysts demonstrated much enhanced electrocatalytic activity for ORR. The reported strategy may inspire the development of new high efficient hybrid electrocatalysts in a cost-effective way with the potential to harness the metal/oxide interaction to improve the performance of catalysts.

Pt hollow nanostructures assembled by nanocrystals were in situ grown and hung onto graphene layers to combine the merits from favorable catalyst morphology control and synergetic improvement effect of the graphene support, resulting in a composite with enhanced electrocatalytic performance.

Urchin-like micro/nano heterostructure Au@CdS/WO3 was synthesized by using a facile photodeposition method with no need for an additional stabilizer, which can be used as an efficient all-solid Z-scheme visible-light photocatalyst for H2 generation with a high H2 evolution rate.

Pt hollow nanostructures assembled by nanocrystals were in situ grown and hung onto graphene layers to combine the merits from favorable catalyst morphology control and synergetic improvement effect of the graphene support, resulting in a composite with enhanced electrocatalytic performance.

Controlled synthesis of Pt-based bimetallic nanocrystals with a tunable size and structure has demonstrated great potential to advance their electrocatalytic performances. We present herein a facile but effective strategy for the rapid aqueous synthesis of PtCu nanodendrites (NDs) with advanced electrocatalytic performance. The systematical investigation on the influence of reaction conditions on the formation of PtCu NDs reveals that the underpotential deposition of Cu not only accelerates the growth of NDs but also significantly modulates their size and branch structure as well as their composition. Electrochemical tests demonstrate that Pt55Cu45 NDs with a smaller size and fewer branches but a higher content of Cu exhibit the highest electrocatalytic activity for both the oxygen reduction reaction and the methanol oxidation reaction, compared with Pt92Cu8 NDs, Pt NDs and commercial Pt/C. These results may inspire the engineering of a wide range of metallic alloyed nanocrystals to advance their electrocatalytic performances for diverse applications.

The importance of the oxygen reduction reaction (ORR) in fuel cells and high energy density metal–air batteries has attracted intense research interests in looking for low-cost ORR catalysts as substitutes for expensive and scarce Pt-based catalysts. N-doped graphene and carbon nanotubes prepared in a low-cost and scalable way have demonstrated their potential although the performance still needs to be improved. In view of the requirements for a high-performance ORR electrocatalyst, this work focused on developing the nanocomposites of N-doped reduced graphene oxide (N-rGO) and N-doped carbon nanotubes (N-CNT) as low-cost efficient ORR catalysts by integrating the advantages of abundant highly-active sites from N-rGO and a three-dimensional conductive network for efficient mass and electron transport from N-CNT. By optimizing the preparation method and dedicatedly tuning the composition, the much enhanced ORR activity and superior durability and tolerance to methanol were achieved for the self-assembled N-doped composite (N-rGO–CNT) at a mass ratio of 1:5 rGO/CNT. Further improvement of the ORR electrocatalytic activity of the composite was also demonstrated by introducing iron into the composite.

Developing catalysts with high electrocatalytic activity for oxygen reduction reaction (ORR) has recently attracted much attention because the sluggish ORR limits the performance and commercialization of current PEMFCs and metal–air batteries as well. Herein, a facile approach was reported to synthesize Mn3O4 nanoparticle coated carbon nanotubes (Mn3O4/CNTs) and self-deposit well-dispersed Pt nanocrystals on Mn3O4/CNTs to obtain Pt/Mn3O4/CNTs hybrid catalysts via in situ reduction of support matrix with no need of any capping agent and additional reducing agent. As a result of good dispersion of uncapped Pt nanocrystals, interconnected carbon nanotube conductive network, and possible synergetic co-catalytic effect from heterojunction interfaces of Pt nanocrystals and Mn3O4, the as-prepared Pt/Mn3O4/CNTs hybrid catalysts demonstrated much enhanced electrocatalytic activity for ORR. The reported strategy may inspire the development of new high efficient hybrid electrocatalysts in a cost-effective way with the potential to harness the metal/oxide interaction to improve the performance of catalysts.

A new N-doped carbon nanomaterial with nanoporous coaxial nanocable structure was designed for achieving the requirements of high nitrogen content, proper nitrogen bonding state, and sufficient electron and mass transportation for an oxygen reduction reaction (ORR) catalyst. The nanoporous sheaths provided more catalytic sites and allowed oxygen and reactants to easily access them for fast mass transfer, whereas carbon nanotube cores provided a three-dimensional conductive network and guaranteed fast electron transfer. As a result, the designed low-cost catalyst exhibited excellent electrocatalytic performance and is one of the most active metal-free ORR catalyst.

Molybdenum sulfide materials have been shown to be promising non-precious metal catalysts for the hydrogen evolution reaction (HER). This work reports a facile and scalable preparation method for amorphous MoS2 nanosheet arrays directly deposited on carbon cloth (a-MoS2 NA/CC) using a highly reproducible physical vapor deposition (PVD) approach. As a result of the three-dimensional nanostructure of the catalyst, the amorphous nature and the abundant exposed edge sites of MoS2, the a-MoS2 NA/CC composite exhibited superior catalytic activity and stability for the HER in acidic solutions.

To promote the oxygen reduction reaction (ORR) on a non-precious-metal catalyst, integrating two-dimensional (2D) nanosheets and one-dimensional (1D) nanotubes in one catalyst is considered as one of the desirable approaches since this hybrid architecture can host more useful active sites and enhance mass/electron transfer. Herein, we demonstrated a sodium chloride-assisted strategy for the in situ synthesis of a three-dimensional (3D) hybrid of carbon nanosheets and nanotubes. The micrometer-scale sodium chloride (NaCl) crystal acted as a recyclable skeleton to adsorb the precursors on its surfaces, which assisted the formation of micrometer-sized graphitic carbon nanosheets with nanometer thickness by the template effect during the pyrolysis, and iron-based nanocrystals with a size of tens of nanometers by helping the distribution of iron sources and preventing their aggregation. The small iron-based nanocrystals favored the growth of long CNTs connected to carbon nanosheets and the outmigration of carbon atoms during the cooling process, which led to the formation of carbon-layer encapsulated metallic iron nanoparticles between the carbon nanosheets or inside the carbon nanotubes. Benefiting from these features, the developed hybrid exhibited a significantly enhanced electrocatalytic activity and durability for the ORR. The results may open up opportunities for exploring cost-effective high-performance electrocatalysts for energy applications.

Mixed organic–inorganic halide perovskite materials have been successfully used as light harvesters in efficient solar cells. Developing reproducible and manageable processes to prepare large-scale highly-crystalline perovskite films with large grains for reducing charge recombination at grain boundaries and thus enhancing the efficiency of large-area perovskite solar cells will advance their practical application. Here we report a reproducible and easily-scalable method using solvent-extraction and water vapor modulated post-annealing to promote the grain growth and simultaneously heal the pinholes in perovskite thin films. Significant enhancement in crystalline grain size and elimination of pinholes are achieved by introducing water vapor in the post-annealing atmosphere. The grain size and morphology are closely related to the amount of water vapor. 2 vol% water in the DMF modulated annealing atmosphere can effectively facilitate the integration of small primary perovskite grains and the merging of grain boundaries as well as the healing of the pinholes during post-annealing, leading to high-quality pinhole-free perovskite films with large-aspect-ratio crystalline grains. As a result, PSCs with a device efficiency of over 17%, corresponding to 14.4% improvement of average efficiency over the devices post-annealed in DMF only atmosphere with the absence of water vapor, and better stability and reduced hysteresis can be readily achieved. Compared with the prevailing anti-solvent dripping method which need precise control of the dripping timing, the present method combining solvent-extraction and water vapor modulated post-annealing is more compatible and reproducible for preparing large-area high-quality perovskite thin films, opening up opportunities for the development of large-area high-performance perovskite solar cells and other optoelectronic devices.