Engineered graphene materials (EGMs) with unique structures and properties have been incorporated into various components of polymer electrolyte membrane fuel cells (PEMFCs) such as electrode, membrane, and bipolar plates to achieve enhanced performances in terms of electrical conductivity, mechanical durability, corrosion resistance, and electrochemical surface area. This research news article provides an overview of the recent development in EGMs and EGM-based PEMFCs with a focus on the effects of EGMs on PEMFC performance when they are incorporated into different components of PEMFCs. The challenges of EGMs for practical PEMFC applications in terms of production scale, stability, conductivity, and coupling capability with other materials are also discussed and the corresponding measures and future research trends to overcome such challenges are proposed.

•3D Fe-embedded N doped carbon framework catalyst for microbial fuel cells.•Outstanding oxygen reduction reaction performance in a neutral pH solution.•Operation time more than 250 h in a feed period.A kind of 3D Fe-embedded N doped carbon framework catalyst is successfully developed and tested in the present work as a robust cathode catalyst for microbial fuel cells (MFCs). Due to the well-arranged mesopores, the high surface area, the interconnected conductive networks as well as the finely dispersed Fe-N active species, the as-prepared 3D Fe-N-C catalyst exhibits significantly enhanced ORR activity compared to commercial Pt/C. More precisely, the 3D Fe-N-C yields a more-positive half-wave potential of −0.08 V (vs. SCE) and remarkably stable limiting current of ∼6.2 mA cm−2. The 3D Fe-N-C shows also an excellent tolerance to methanol as well as remarkably long-term stability with more than 82.4% retention of its initial activity after 55.5 h operation. Based on the as-prepared 3D Fe-N-C as the air cathode catalyst, a stable microbial fuel cell (MFC) device is fabricated and tested, performing a maximum power density of 3118.9 mW m−2 at a high current density of 9980.8 mA m−2. More importantly, it is found that the Fe-N-C MAFC device could steadily operate for more than 250 h in a feed period, which is substantially longer than the Pt/C-MFC device.A microbial fuel cell with high power density output is fabricated, using for air cathode a 3D Fe-embedded N doped carbon framework as Pt-free catalyst.Download high-res image (365KB)Download full-size image

•Straightforward synthesis of new Co-N-doped carbon-based (Co-N@HCS) hollow nanospherical structures.•Co-N@HCS exhibits high OER and ORR electrocatalytic performance methanol tolerance and stability.•Excellent properties of Co-N@HCS are attributed to high surface area and 3D hollow architecture.Non-precious materials have been considered as promising bifunctional catalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In the present work, a three dimensional (3D) Co-N co-doped hollow carbon sphere (HCS) electrocatalyst is synthesized at room temperature by the aid of a facile preparation method.The as obtained Co-N co-doped catalyst exhibits excellent catalytic activity towards both ORR and OER due to its high surface area and to 3D hollow architecture. For the ORR, the catalyst shows more positive onset-potential (of ∼0.962 V vs. RHE) and larger diffusion limiting current density (5.55 mA cm−2) compared with benchmark Pt/C catalyst in alkaline medium. Moreover, the as synthesized catalyst exhibits low potential (1.720 V vs. RHE) at the current density of 10 mA cm−2 and small Tafel slope (81 mV dec−1) for OER. In addition, the catalyst exhibits remarkable methanol tolerance and good long-term stability under working conditions. This strategy provides a facile and effective method for the preparation of non-noble metal catalysts with 3D hollow structure for energy conversion and storage applications.Straightforward synthesized Co-N-doped carbon-based hollow nanospheres exhibit high performance for both OER and ORR due to their high surface area and 3D hollow architecture.Download high-res image (252KB)Download full-size image

•Hydrophobic protic ionic liquids (PILs) were applied to catalyst layer.•PILs modified Pt/C catalysts exhibit high activity toward OER.•PILs can reduce carbon corrosion kinetics under cell reversal.Pt/C has been commercially used as anode electrocatalyst for fuel cells but generally exhibits limited durability under conditions of fuel starvation and subsequent cell reversal. Herein we report an improved scaffold concept to simultaneously stabilize the catalyst against particle growth and reduce the adverse effects of cell reversal by modifying Pt/C with suitable protic ionic liquids (PILs). The modified Pt/C catalysts show enhanced cell reversal tolerance because of their high activity towards oxygen evolution reaction (OER), up to 300 mV lower overpotential compared to the unmodified Pt/C. Moreover, the PIL modified catalysts show better resistance to the loss of electrochemical surface area (ECSA) under simulated cell reversal conditions. The results indicate that modification of Pt/C catalysts with PILs is a promising strategy to enhance the stability and durability of electrocatalysts in fuel cell applications with the risk of frequent fuel starvation events, such as automotive fuel cells.

Novel thin layer graphite encapsulated α-Fe2O3 nanoparticles were fabricated via a facile molecular self-assembly approach. This α-Fe2O3@graphite composite, used as anode in LIBs, exhibited a stable specific capacity of 518.5 mAhg−1 at the current density of 1000 mAg−1 with 88.2% of retention up to 1000 cycles and delivered a reversible capacity of 374 mAhg−1 even at 5C rate. The high cyclic stability and superior rate performance may be addressed to the formed graphite coating layer, which can buffer the volume expansion, enhance the structural stability and increase the electrical conductivity of the Fe2O3. Moreover, the thin layer graphite coating structure can provide high specific surface area, sufficient void space to shorten the pathway of Li ions, improve the electrolyte penetration and accelerate the electrochemical Li ion storage.

LiNi1/3Co1/3Mn1/3O2 cathode coated with a thin layer of graphene (~8 nm) is successfully synthesized by self-assembly and pyrolysis of polyelectrolyte layers on the surface of NMC particles. The graphene coated NMCs still possess a layered structure with good crystallinity and demonstrate a superior electrochemical performance (e.g., rate capability and cycling stability). The best graphene coated NMC cathode is prepared at a calcination temperature of 800 °C, exhibiting a capacity retention of ~90% vs. 78% for pristine NMC @ cycle 100 and 1 C rate. The improvement in cycling performance is further enlarged after 500 cycles (74% vs. 51%). This can be attributed to the dual functions of graphene coating in enhancing electronic conductivity and protecting NMC surface from the contact with electrolyte during the electrochemical reaction.

Electrode architecture design is of critical importance to the development of advanced hybrid electrode materials for supercapacitors. Here, we report a novel electrode architecture that is composed of Fe2O3 nanocubes and carbon nanotube functionalized carbon. This functionalized electrode demonstrates superior electrochemical performance, characterized by a high capacitance of 1687 mF cm−2 at a current density of 2 mA cm−2, excellent cycling stability, and 95.8% retention after 20 000 cycles. This work presents a new approach for fabricating advanced hybrid electrode materials for supercapacitor applications.

•Facile synthesis of 2D-Co-Ni mixed MOFs by electrodeposition.•In-situ growth of metal oxide anchored carbon matrix on Ni foam.•The achieved 2D-CMO electrode exhibits excellent rate performance with high mass loading.•This approach is expected to be a universal strategy for in-situ growth of metal oxide anchored carbon matrix electrodes.Despite the significant advances in preparing carbon-metal oxide composite electrodes, strategies for seamless interconnecting of these two materials without using binders are still scarce. Herein we design a novel method for in situ synthesis of porous 2D-layered carbon–metal oxide composite electrode. Firstly, 2D-layered Ni-Co mixed metal-organic frameworks (MOFs) are deposited directly on nickel foam by anodic electrodeposition. Subsequent pyrolysis and activation procedure lead to the formation of carbon–metal oxides composite electrodes. Even with an ultrahigh mass loading of 13.4 mg cm−2, the as-prepared electrodes exhibit a superior rate performance of 93% (from 1 to 20 mA cm−2), high capacitance (2098 mF cm−2 at a current density of 1 mA cm−2), low resistance and excellent cycling stability, making them promising candidates for practical supercapacitor application. As a proof of concept, several MOF derived electrodes with different metal sources have also been prepared successfully via the same route, demonstrating the versatility of the proposed method for the preparation of binder-free carbon–metal oxide composite electrodes for electrochemical devices.A novel 2D carbon−metal oxide composite electrode was prepared by four steps and demonstrated as promising binder-free electrode materials for supercapacitors with ultrahigh rate performance of 93% (from 1 to 20 mA cm−2) and high mass loading (13.4 mg cm−2). Moreover, this new general strategy is also expected to facilitate the synthesis of carbon–metal oxide composite electrodes for other electrochemical devices.

•Amine-functionalized imidazolium-based poly(ionic liquid) brushes were synthesized.•The total CO2 adsorption capacity reaches 2.46 mmol g−1 under CO2 partial pressure of 0.2 bar at 25 °C.•Different types of CO2 adsorption were divided using temperature programmed desorption process.•The adsorption capacity decreases in the first two TPD cycles and remains stable in the later cycles.Amine-functionalized imidazolium-based poly(ionic liquid) brushes on titanate nanotubes are synthesized using a convenient “grafting through” technique. The carbon dioxide adsorption performance of the synthesized polymer brushes is evaluated using temperature programmed desorption (TPD) process. TPD profiles of the synthesized polymer brushes after carbon dioxide adsorption reveal that carbon dioxide molecules can adsorb on the synthesized polymer brushes through physical adsorption, reaction with 2-position carbon of imidazole rings, and chemical reaction with amine groups. The total carbon dioxide adsorption capacity of the synthesized poly(ionic liquid) brushes with polymer content of 46 wt.% achieves 2.43 mmol g−1 at 25 °C under carbon dioxide partial pressure of 0.2 bar, higher than that of the corresponding free polymer powders (1.28 mmol g−1) under the same conditions. The total adsorption capacity decreases to 1.46 mmol g−1 after two TPD adsorption/desorption cycles and it however remains almost constant in the later cycles.

•Graphene oxide-TiO2 nanotube and nanowire for dye-sensitized solar cell.•Graphene oxide-TiO2 nanotubes show optimal performance.•Facilitated electron transport at the graphene oxide -TiO2/dye|electrolyte interface.An effective photoanode is essential for an efficient dye-sensitized solar cell (DSSC). In this paper, composites of TiO2 nanotubes (or nanowires) and reduced graphene oxide (RGO) with different RGO contents are prepared through a hydrothermal method and applied as the photoanode for DSSCs. The composition, morphology, and photovoltaic performance of the composites were evaluated in detail. We show that the RGO content in the composite is a critical factor for the photovoltaic properties of devices constructed from these composites. The DSSC performance initially increases and then decreases with increasing RGO content of the composites. The morphology of the TiO2 nanostructure also has a profound impact on the DSSC performance. TiO2 nanotubes are more favorable than TiO2 nanowires for the construction of the composites in terms of DSSC performance. The DSSC based on the RGO- TiO2 nanotubes with 2% of RGO exhibits optimal performance with an overall energy conversion efficiency of 5.33%. The enhanced DSSC performance of the RGO- TiO2 nanotubes results from the facilitated electron transport at the RGO- TiO2/dye|electrolyte interface and improved dye adsorption on the photoanode.

Protic organic ionic plastic crystals (POIPCs) are a type of novel solid-state proton conductors. In this work, guanidinium nonaflate ([Gdm-H][NfO]) is reported to be a model POIPC. Its structure–property relationship has been investigated comprehensively. Infrared analysis of [Gdm-H][NfO] and its deuterated analogue [Gdm-D][NfO] confirms the complete formation of the protic salts. The cations in as-prepared [Gdm-D][NfO] are estimated to consist of [C(ND2)2(NHD)]+ and [C(ND2)3]+ with a molar ratio of around 1:1. The deuteration also proves that each guanidinium cation has six displaceable protons. Thermogravimetric analysis demonstrates that [Gdm-H][NfO] exhibits superior thermal stability in both nitrogen and air atmospheres. Isothermogravimetric analysis reveals its negligible vapor pressure with an estimated high enthalpy of vaporization (120.9 kJ mol−1). Differential scanning calorimetry measurements of [Gdm-H][NfO] show four evident endothermic peaks prior to its melting transition at 186.2 °C with a low entropy of melting (17.70 J K−1 mol−1). Shortly before the onset temperature of melting transition (186.2 °C), partial melting (partial liquefaction) was observed via polarized optical microscopy in the temperature region of 176–186 °C while the reason for partial melting of ionic plastic crystals is not clear yet. Variable-temperature powder X-ray diffraction tests confirm the related solid-solid phase transitions and demonstrate that [Gdm-H][NfO] exhibits short-range disorder and long-range positional order in the plastic crystalline phases. Dielectric spectroscopy measurements show that its ionic conductivity reaches 2.1 × 10−3 S cm−1 at 185 °C. The proton conduction in the plastic crystalline phases of [Gdm-H][NfO] is assumed to happen via the vehicle mechanism. In the molten state, the proton conduction follows a combination of the vehicle mechanism and the Grotthuss mechanism (structural diffusion). In summary, due to their exceptional physicochemical properties, POIPCs like [Gdm-H][NfO] are promising electrolyte materials for high temperature (100–200 °C) proton exchange membrane fuel cells. In addition, POIPC-based solid-state proton conductors are also expected to find applications in sensors and other electrochemical devices.

•N and S co-doped ORR catalysts are synthesized from a novel ionic liquid.•The obtained catalysts show superior ORR performance and excellent durability.•The 3DOM structure of the catalyst contributes to its catalytic activity.The development of efficient and durable catalyst for oxygen reduction reaction (ORR) is critical for the practical application of proton exchange membrane fuel cell (PEMFC). A novel imidazole based ionic liquid is synthesized in this study and used subsequently for the preparation of a N and S co-doped metal-free catalyst with three dimensional ordered microstructure. The catalyst prepared at 1100 °C showed improved ORR catalytic performance and stability compared to commercial Pt/C catalyst. We demonstrate that the high graphitic N content and high degree of graphitization of the synthesized catalyst is responsible for its superb ORR activity. Our results suggest that the N and S co-doped metal-free catalyst reported here is a promising alternative to traditional ORR catalyst based on noble metal. Furthermore, the current study also demonstrate that importance of morphology engineering in the development of high performance ORR catalyst.

•Successful synthesis of OAPS derived N-doped nanoporous carbon materials, NNC.•NNC shows high surface of 1942 m2 g−1 and well-defined nanopores of ∼1 nm.•NNC exhibits high capacitance of 230 F g−1 at 1 A g−1 and delivers a high energy density of 5 Wh kg−1.•NNC cells show high stability with performance loss of less than 5% over 10,000 cycles at 50 mV s−1.Development of nitrogen-doped carbon materials with well-defined nanoporous structure is critical due to their versatile applications for the electrochemical energy conversion and storage devices. In this work, we report a new and facile strategy for the synthesis of N-doped nanoporous carbon materials (NNC) with adjustable nitrogen content (3.63–5.37%), large surface area (1942 m2 g−1), uniform and well-defined nanopores (∼0.85–1 nm) and high nanopore volume (0.53–0.88 cm3g−1) derived from octa(aminophenyl)silsesquioxane (OAPS). OAPS is miscible with phenolic resol, forming an uniformly distributed and self-templated and cross-linked copolymer of OAPS and resol and NNC materials after carbonization and removal of monodispersed silica domains. The symmetric supercapacitor assembled by the electrodes with OAPS to resol ratio of 95:5 in 1 M H2SO4 electrolyte exhibits the high specific capacitance of 230 F g−1 at 1 A g−1 due to the pseudocapacitive contribution of the N-groups, and delivers a high energy density of 5 Wh kg−1 with a power density of 1445 W kg−1 and high stability with performance loss of less than 5% over 10,000 cycles at 50 mV s−1.

An oxygen electrode finds many applications in various electrochemical energy conversion devices such as fuel cells and metal–air batteries. Highly efficient gas–proton transportation at the electrode is very important to enhance the power density of these devices. Herein, we report the construction of a highly efficient oxygen electrode with substantially improved proton conductivity and gas transportation properties using three dimensionally ordered macroporous Nafion/Cs2.5H0.5PW12O40, 3DOM Nafion/CsHPW, scaffold supported Pt/C nanocomposites. The best results were obtained for cells with 3DOM Nafion/CsHPW with 10% CsHPW, achieving a maximum power density of 955 mW cm−2, 31% higher than 730 mW cm−2 for the cell with the conventional Nafion-binder based oxygen electrode. The proton conductivity of the 10% 3DOM Nafion/CsHPW catalyst layer is 1.56 × 10−2 S cm−1, 112% higher than 7.35 × 10−3 S cm−1 measured for the conventional catalyst layer with the Nafion binder. The results demonstrate the significant advantages of the oxygen electrodes with the Pt/C-3DOM Nafion/CsHPW architecture over the conventional Nafion-binder based ones, with the significantly enhanced proton conductivity of uniformly distributed CsHPW nanoparticles (NPs) and much better gas diffusion properties of the 3DOM architecture.

Pt nano-particles are loaded onto the surface of an active carbon material through in-situ electrochemical reduction. With 0.66 % mole percentage of Pt, the kinetics of electrochemical hydrogen insertion into porous carbon material is significant improved. The enhancement resulted from the H underpotential deposition on Pt surface and subsequent H spillover from Pt surface to carbon interlayers.Pt nano-particles were homogeneously formed on the surface of porous carbon material. The metallic Pt catalyst was found to enhance the electrochemical hydrogen insertion into porous carbon materials through the spillover effect on Pt. With 0.66 % mole percentage of Pt loaded onto carbon, the rate as well as the columbic efficiency of H insertion process for Pt loaded AC is much higher than those for AC without Pt loading.

•A coaxial core–shell structured TiO2@carbon nano-rod arrays was fabricated and its pseudocapacitive performance was investigated.•Polydopamine self-assembled from dopamine was deposited into the TiO2 nano-tubes and used as a precursor for the carbon nano-rod generation.•The formed TiO2@carbon nano-rod arrays shows high areal capacitance and fast charge/discharge capability with the enhanced electrical conductivity and increased surface area of the coaxial nano-rod structure.A coaxial core–shell structured TiO2@carbon nano-rod arrays (TiO2@C NRAs) was constructed and tested as a supercapacitor electrode in this study. Dopamine was self-assembled into a polydopamine nano-rod arrays within the TiO2 nano-tube arrays (TiO2 NTAs) and was used as a precursor for the carbon nano-rod generation. Electrochemical measurements showed that the electrodes made with coaxial TiO2@C NRAs exhibited substantially higher electrochemical performances such as larger areal capacitance and faster charge/discharge capability than those of the pristine TiO2 NTA electrode and porous active carbon materials. Benefiting from the enhanced electrical conductivity and increased surface area of the coaxial nano-rod structure, the prepared coaxial TiO2@C NRAs electrode achieved a remarkable areal capacitance of 40.75 mF cm−2 at a current density of 0.2 mA cm−2, which was significantly higher than that of the pristine TiO2 NTAs (0.31 mF cm−2).

A comprehensive strategy has been developed to synthesize highly ordered mesoporous Nafion membranes with different structure symmetries including 2D hexagonal (2D-H), 3D face-centered (3D-FC), 3D cubic-bicontinuous (3D-CB) and 3D body-centered (3D-BC), using a soft template method with the assistance of a silica colloidal mediator. The Nafion membrane derived from the self-assembled mesoporous Nafion–silica composites maintained the microstructures of the silica framework, which was confirmed by small angle X-ray scattering (SAXS) and TEM. The in situ time-resolved synchrotron SAXS clearly indicates that the presence of silica colloids is critical for the formation of the highly ordered mesoporous structured phase in the precursor solution. The best results are observed on Nafion membranes with 2D-H structure in terms of proton conductivity and cell performance under reduced relative humidity (RH) conditions, achieving proton conductivities of 0.08, 0.062 and 0.038 S cm−1 at 100, 40 and 0%RH, respectively. Moreover, the power output of the mesoporous Nafion membrane cells show a S-shaped dependence on RH and are stable under anhydrous conditions (i.e., 0% RH), demonstrating the outstanding high water retention capability of the mesoporous structure of the membranes.

Development of new types of proton conducting materials with efficient transport of protons is one of the most important remaining challenges for elevated-temperature proton exchange membrane fuel cells. Herein, we report the design and synthesis of a new type of proton conducting material based on three dimensional ordered macroporous silica (3DOM silica) incorporated with inorganic Cs2.5H0.5PW electrolytes. The highly ordered structure of 3DOM silica provides well inter-connected pathways for efficient proton transport, especially at high operating temperatures. At a doping amount of 90 wt% of Cs2.5H0.5PW, the proton conductivity of the formed composite electrolyte reaches 0.248 S cm−1 at 170 °C and the activation energy is about 5.775 kJ mol−1. The novel electrolytes also showed good stability as well as excellent single cell performance at 170 °C. The results described here demonstrate that the 3DOM silica/Cs2.5H0.5PW electrode has great potential for high temperature proton exchange membrane fuel cell applications.

Recently, we have developed a semidirect breath figure (sDBF) method for direct fabrication of large-area and ordered honeycomb structures on commercial polystyrene (PS) Petri dishes without the use of an external polymer solution. In this work, we showed that both the pore size and the pore uniformity of the breath figure patterns were controllable by solvent amount. The cross-sectional image shows that only one layer of pores was formed on the BF figure patterns. By combing the sDBF method and Pickering emulsion and using the modular building blocks, we endowed the honeycomb-structured Petri dish with molecular recognition capability via the decoration of molecularly imprinted polymer (MIP) nanoparticles into the honeycomb pores. The radioligand binding experiments show that the MIP nanoparticles on the resultant honeycomb structures maintained high molecular binding selectivity. The reusability study indicates that MIP-BF patterns had excellent mechanical stability during the radioligand binding process. We believe that the modular approach demonstrated in this work will open up further opportunities for honeycomb structure-based chemical sensors for drug analysis, substrates for catalysts, and scaffold for cell growth.Keywords: honeycomb structures; molecular imprinting; molecular recognition; Petri dish; Pickering emulsion; semidirect breath figure

A new configuration of hydrogen ion supercapacitors was reported. A positive electrode composed of pseudocapacitive MnO2, highly dispersed into active porous carbon through an impregnation method, was combined with a nitrogen-doped highly ordered mesoporous carbon with enhanced electrochemical hydrogen insertion capacity as a negative electrode. During the operation, hydrogen ion shuttled between MnO2 and carbon electrodes. The MnO2 was formed on the surface of nanostructured carbon through a spontaneous redox reaction. Operating in an aqueous neutral solution, the hybrid device demonstrated an extended working voltage to ∼2.1 V with good cycle life.Keywords: electrochemical hydrogen insertion; highly ordered mesoporous carbon; hydrogen ion supercapacitor; pseudocapacitive MnO2 electrode

The great demand for high-temperature operation of polymer electrolyte membrane fuel cells (PEMFCs) has been well answered by short-side-chain perfluorinated sulfonic acid (SSC-PFSA) membranes through a good balance between transport properties and stability. It has been evidenced that fuel cells assembled with SSC-PFSA possess higher and more stable performance at elevated temperature up to 130 °C compared to that of fuel cells based on conventional long-side-chain (LSC) PFSA (Nafion®) membranes. Moreover, the shorter side-pendent chains and the absence of the ether group and of the tertiary carbon also endow SSC-PFSAs with better durability, making them more suitable for working at harsh conditions in fuel cell systems. This critical review is dedicated to summarizing the properties of SSC-PFSA and providing insight into an understanding of their micro-morphologies, mass diffusion, enhanced proton transportation and their mutual correlation. Diversified measurement techniques applied to investigate the evolution of micro-morphologies, unique diffusion and transportation properties of SSC-PFSAs are reviewed. Despite the higher crystalline and higher water absorption of SSC-PFSAs than those of LSC-PFSAs, the notably less developed and less interconnected ionic clusters in SSC-PFSAs lead to lower mass permeability, and hence the high water uptake is not as well translated into transportation performance as expected. The factors and reasons for the enhanced electrochemical performance of SSC-PFSAs such as higher proton conductivity at elevated temperatures and low humidity conditions are also discussed and understood. Highlights of recent advances in SSC-PFSA-based membranes for fuel cell applications at wider temperature ranges are summarized as general references for researchers to further prompt the development of SSC-PFSAs. The SSC-PFSAs based membranes give a bright future for the next generation of high-temperature PEMFCs.

•Short side chain membranes are investigated in wide humidity and temperature range.•Reinforced composite membrane presents excellent electrochemical performances.•water uptake of the membrane is important for the performance.The short-side-chain (SSC) perfluorosulfonic acid (PFSA) membranes are important candidates as membrane electrolytes applied for high temperature or low relative humidity (RH) proton exchange membrane fuel cells. In this paper, the fuel cell performance, proton conductivity, proton mobility, and water vapor absorption of SSC PFSA electrolytes and the reinforced SSC PFSA/PTFE composite membrane are investigated with respect to temperature. The pristine SSC PFSA membrane and reinforced SSC composite membrane show better fuel cell performance and proton conductivity, especially at high temperature and low relative humidity conditions, compared to the long-side-chain (LSC) Nafion membrane. Under the same condition, the proton mobility of SSC PFSA membranes is lower than that of the LSC PFSA membrane. The water vapor uptake values for Nafion 211 membrane, pristine SSC PFSA membrane and SSC PFSA/PTFE composite membrane are 9.62, 11.13, and 11.53 respectively at 40 °C and they increase to 9.89, 12.55 and 13.09 respectively at 120 °C. The high water content of SSC PFSA membrane makes it maintain high performance even at elevated temperatures.

•Hydrogen crossover of membranes with variable side chain was investigated.•Short side chain perfluorosulfonic acid membrane has slower decay.•Membrane decay is related to the hydrogen crossover.In this study, hydrogen crossover in long side chain Nafion 211 membrane and short side chain Aquivion membrane is studied under different conditions. It is found that both temperature and relative humidity significantly influence the hydrogen crossover in the polymer electrode membranes (PEMs). The difference in hydrogen crossover behavior between Nafion 211 membrane and Aquivion membrane is revealed. The influence of hydrogen crossover on the fuel cell lifetime is also investigated under open circuit voltage (OCV). It is proved hydrogen crossover in the PEM would lead to possible degradation of the PEM and the decrease of electro-chemical surface area in the catalyst of the single cell. Single cell assembled with Aquivion membrane shows slower OCV and ECSA decay compared to the Nafion 211 single cell. Our results suggest that the PEM fuel cell lifetime is closely related to the hydrogen crossover in the PEM. The current study also highlights the possibility of improving the fuel cell durability by rational design of the PEM morphology.

Highly ordered and periodic mesoporous Nafion membranes with controlled structural symmetries including 2D hexagonal, 3D face-centered, 3D cubic-bicontinuous and 3D body-centered have been successfully synthesized by a novel colloidal silica mediated self-assembly method with high proton conductivity particularly under conditions of low humidity.

•Porous polytetrafluoroethylene stabled separator for Li-ion battery.•Highly thermal stability and low thermal shrinkage.•Excellent capacities at high rate discharge.PVDF–HFP/ePTFE composite separator with high thermal stability and low thermal shrinkage characteristic has been developed. The PVDF–HFP acts to absorb the electrolyte and shutdown at elevated temperature. The thermally stable ePTFE matrix is adopted to improve the mechanical strength and sustain the insulation after the shutdown. This novel separator presents good ion conductivity (up to 1.29 mS cm−1) and has a low thermal shrinkage of 8.8% at 162 °C. The composite separator shutdown at 162 °C and keep its integrity before 329 °C. Cells based on the composite separator show excellent capacities at high rate discharge and stable cycling performance.

In this work, we developed a novel composite membrane by anchoring perfluorosulfonic acid into the hydrophilic poly(lactic-co-glycolic acid) (PLGA) nanofibrous network which was synthesized by electrospinning method. It was clear that the PLGA/Nafion composite membranes possessed high Nafion loading, excellent dimensional stability and proton transport capacity. When the humidity of the membrane changed from soaking in water to 25 RH% at 90 °C, the PLGA fiber network effectively controlled the swelling of Nafion resin and reduced the humidity-generated shrinkage stress from 2.2 MPa (Nafion211 membranes) to 0.5 MPa (PLGA/Nafion composite membranes). The proportion of humidity-induced stress to the yield strength was also reduced to 4.4%, in comparison to 21.2% of that of Nafion211 membrane. The area proton conductivity of the PLGA/Nafion composite membrane achieved 48.2 S cm−2, compared with 36.0 S cm−2 of Nafion211 membranes in the same condition. The excellent proton transport capacity greatly improved the performance of fuel cell assembled with PLGA/Nafion composite membranes and effectively reduced the dynamic response time from 22 s (Nafion211 membranes) to 7 s (PLGA/Nafion composite membranes).Graphical abstractProton exchange membrane with high dimensional stability, good proton conductivity and fast dynamic response was developed by anchoring perfluorosulfonic acid into the hydrophilic poly(lactic-co-glycolic acid) (PLGA) nanofibrous network.Highlights► Stable proton exchange membrane. ► hydrophilic poly(lactic-co-glycolic acid) nanofibers as membrane supports. ► Low humidity-induced stress to the yield strength. ► High physical stability.

A comprehensive strategy has been developed to synthesize highly ordered mesoporous Nafion membranes with different structure symmetries including 2D hexagonal (2D-H), 3D face-centered (3D-FC), 3D cubic-bicontinuous (3D-CB) and 3D body-centered (3D-BC), using a soft template method with the assistance of a silica colloidal mediator. The Nafion membrane derived from the self-assembled mesoporous Nafion–silica composites maintained the microstructures of the silica framework, which was confirmed by small angle X-ray scattering (SAXS) and TEM. The in situ time-resolved synchrotron SAXS clearly indicates that the presence of silica colloids is critical for the formation of the highly ordered mesoporous structured phase in the precursor solution. The best results are observed on Nafion membranes with 2D-H structure in terms of proton conductivity and cell performance under reduced relative humidity (RH) conditions, achieving proton conductivities of 0.08, 0.062 and 0.038 S cm−1 at 100, 40 and 0%RH, respectively. Moreover, the power output of the mesoporous Nafion membrane cells show a S-shaped dependence on RH and are stable under anhydrous conditions (i.e., 0% RH), demonstrating the outstanding high water retention capability of the mesoporous structure of the membranes.

Development of new types of proton conducting materials with efficient transport of protons is one of the most important remaining challenges for elevated-temperature proton exchange membrane fuel cells. Herein, we report the design and synthesis of a new type of proton conducting material based on three dimensional ordered macroporous silica (3DOM silica) incorporated with inorganic Cs2.5H0.5PW electrolytes. The highly ordered structure of 3DOM silica provides well inter-connected pathways for efficient proton transport, especially at high operating temperatures. At a doping amount of 90 wt% of Cs2.5H0.5PW, the proton conductivity of the formed composite electrolyte reaches 0.248 S cm−1 at 170 °C and the activation energy is about 5.775 kJ mol−1. The novel electrolytes also showed good stability as well as excellent single cell performance at 170 °C. The results described here demonstrate that the 3DOM silica/Cs2.5H0.5PW electrode has great potential for high temperature proton exchange membrane fuel cell applications.

An oxygen electrode finds many applications in various electrochemical energy conversion devices such as fuel cells and metal–air batteries. Highly efficient gas–proton transportation at the electrode is very important to enhance the power density of these devices. Herein, we report the construction of a highly efficient oxygen electrode with substantially improved proton conductivity and gas transportation properties using three dimensionally ordered macroporous Nafion/Cs2.5H0.5PW12O40, 3DOM Nafion/CsHPW, scaffold supported Pt/C nanocomposites. The best results were obtained for cells with 3DOM Nafion/CsHPW with 10% CsHPW, achieving a maximum power density of 955 mW cm−2, 31% higher than 730 mW cm−2 for the cell with the conventional Nafion-binder based oxygen electrode. The proton conductivity of the 10% 3DOM Nafion/CsHPW catalyst layer is 1.56 × 10−2 S cm−1, 112% higher than 7.35 × 10−3 S cm−1 measured for the conventional catalyst layer with the Nafion binder. The results demonstrate the significant advantages of the oxygen electrodes with the Pt/C-3DOM Nafion/CsHPW architecture over the conventional Nafion-binder based ones, with the significantly enhanced proton conductivity of uniformly distributed CsHPW nanoparticles (NPs) and much better gas diffusion properties of the 3DOM architecture.

Protic organic ionic plastic crystals (POIPCs) are a type of novel solid-state proton conductors. In this work, guanidinium nonaflate ([Gdm-H][NfO]) is reported to be a model POIPC. Its structure–property relationship has been investigated comprehensively. Infrared analysis of [Gdm-H][NfO] and its deuterated analogue [Gdm-D][NfO] confirms the complete formation of the protic salts. The cations in as-prepared [Gdm-D][NfO] are estimated to consist of [C(ND2)2(NHD)]+ and [C(ND2)3]+ with a molar ratio of around 1:1. The deuteration also proves that each guanidinium cation has six displaceable protons. Thermogravimetric analysis demonstrates that [Gdm-H][NfO] exhibits superior thermal stability in both nitrogen and air atmospheres. Isothermogravimetric analysis reveals its negligible vapor pressure with an estimated high enthalpy of vaporization (120.9 kJ mol−1). Differential scanning calorimetry measurements of [Gdm-H][NfO] show four evident endothermic peaks prior to its melting transition at 186.2 °C with a low entropy of melting (17.70 J K−1 mol−1). Shortly before the onset temperature of melting transition (186.2 °C), partial melting (partial liquefaction) was observed via polarized optical microscopy in the temperature region of 176–186 °C while the reason for partial melting of ionic plastic crystals is not clear yet. Variable-temperature powder X-ray diffraction tests confirm the related solid-solid phase transitions and demonstrate that [Gdm-H][NfO] exhibits short-range disorder and long-range positional order in the plastic crystalline phases. Dielectric spectroscopy measurements show that its ionic conductivity reaches 2.1 × 10−3 S cm−1 at 185 °C. The proton conduction in the plastic crystalline phases of [Gdm-H][NfO] is assumed to happen via the vehicle mechanism. In the molten state, the proton conduction follows a combination of the vehicle mechanism and the Grotthuss mechanism (structural diffusion). In summary, due to their exceptional physicochemical properties, POIPCs like [Gdm-H][NfO] are promising electrolyte materials for high temperature (100–200 °C) proton exchange membrane fuel cells. In addition, POIPC-based solid-state proton conductors are also expected to find applications in sensors and other electrochemical devices.

Highly ordered and periodic mesoporous Nafion membranes with controlled structural symmetries including 2D hexagonal, 3D face-centered, 3D cubic-bicontinuous and 3D body-centered have been successfully synthesized by a novel colloidal silica mediated self-assembly method with high proton conductivity particularly under conditions of low humidity.