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Acid loss and plasticization of phosphoric acid (PA)‐doped polymer electrolyte membranes are critical hampers for its actual application especially during startup/shutdown stages due to the produced water and thermal stress. To conquer these barriers, a proton conductor confinement strategy is introduced, which may trap PA molecules in the side‐chain acidophilic microphase and weaken plasticizing effect caused by PA toward the polymer backbone to remain membrane tensile stress. The grafted polyphenylene oxide (PPO) is synthesized as model polymers, both molecular electrostatic potential and molecular dynamics reveal the retention mechanism between PA and side‐chain of PPO as well as the aggregation state of PA. Through precisely regulating polymer side‐chain structure and defined plasticization quantitative indicator, significant refinements in membrane's conductivity, durability, and single‐cell performance are achieved successfully. The designed PPO membranes exhibit ultra‐fast and stable proton conducting even at low proton carrier concentrations and under wide‐range working temperature between 80 oC–180 °C as well as satisfied resistance to harsh accelerated aging test. These insights will shed light on holistic understanding of PA interactions and retention from molecular level, and provide radical approaches toward high‐performance PA/PEMs design. [ABSTRACT FROM AUTHOR]

Development of high temperature polymer electrolyte membrane fuel cells (HT‐PEMFCs) at elevated temperatures is important for the enhancement of tolerance toward CO impurities and for the development of non‐precious metal catalysts. The key challenge in such HT‐PEMFCs is the high temperature polymer electrolyte membranes. Herein, the development of in situ formed metal pyrophosphates (MP2O7, where M = Sn, Ti, and Zr) in phosphoric acid doped polybenzimidazole (PA/PBI) composite membranes for HT‐PEMFCs is reported. The formation mechanism of MP2O7, and characteristics of MP2O7/PA/PBI composite membranes are studied in detail. In contrast to the rapid decay in performance of pristine PA/PBI membrane cells, the in situ formed MP2O7/PA/PBI composite membranes show significantly higher proton conductivity, improved performance, and stability at elevated temperatures of 200–250 °C. The best results are obtained on the in situ formed SnP2O7/PA/PBI composite membrane cells, exhibiting a high peak power density of 476 mW cm−2 and proton conductivity of 51.3 mS cm−1 at 250 °C. The excellent durability of SnP2O7/PA/PBI composite membrane is due to the uniform distribution of in situ formed SnP2O7 nanoparticles in PBI membranes and the formation of a gel‐like region, thin and irregular amorphous layer on the SnP2O7 with the high acid retention ability. This effectively alleviates the PA leaching at elevated temperatures of the new HT‐PEMFCs. [ABSTRACT FROM AUTHOR]

Porous proton exchange membranes (PEMs) with abundant porous structures show enhanced phosphoric acid (PA) doping levels and proton transport capability. However, the high PA loss rate and serious hydrogen cross‐over lead to poor membrane stability. Enhancing the stability of PA‐doped porous PEMs is therefore crucial for obtaining high‐performance proton exchange membrane fuel cells. Herein, a porous polybenzimidazole membrane with dense double skin layers is reported using amino tris (methylene phosphonic acid) (ATMP) constructed. This membrane effectively alleviates hydrogen permeation and PA loss in a water/anhydrous environment and exhibits enhanced stability. Surprisingly, as an organic proton conductor, ATMP has strong hydrogen bonding with PA, leading to the formation of more continuous proton transport channels. Due to the dense double skin layers protection and the synergistic mass transfer of ATMP and PA, the porous membrane shows excellent proton conductivity (0.112 S cm−1) and a H2‐O2 fuel cell peak power density of 0.98 W cm−2 at 160 °C. Moreover, it presents excellent fuel cell stability, with a voltage decay rate of only 5.46 µV h−1. In addition, the porous membrane surpasses the traditional working temperature range, operating in the range of 80–220 °C. This study provides new insight into developing high‐performance porous PEMs. [ABSTRACT FROM AUTHOR]

The durability degradation during stack‐operating conditions seriously deteriorates the lifetime and performance of the fuel cell. To alleviate the rapid potential rise and performance degradation, an anode design is proposed to match the working temperature of high‐temperature proton exchange membrane fuel cells (HT‐PEMFCs) with the release temperature of hydrogen from palladium. The result is significantly enhanced hydrogen oxidation reaction (HOR) activity of Pd and superior performance of the Pd anode. Furthermore, Pd as hydrogen buffer and oxygen absorbent layer in the anode can provide additional in situ hydrogen and absorb infiltrated oxygen during local fuel starvation to maintain HOR and suppress reverse‐current degradation. Compared with the traditional Pt/C anode, the Pd/C also greatly improved HT‐PEMFCs durability during start‐up/shut‐down and current mutation. The storage/release of hydrogen provides innovative guidance for improving the durability of PEMFCs. [ABSTRACT FROM AUTHOR]

Polymer electrolyte membranes (PEMs) play vital roles in electrochemical energy conversion and storage devices, such as polymer electrolyte membrane fuel cell (PEMFC), redox flow battery, and water electrolysis. As the crucial component of these devices, PEMs need to possess high ion conductivity and electronic insulation, remarkable mechanical and chemical stability, and outstanding isolation function for the materials on both sides of the cathode and anode. Polyvinylpyrrolidone has received widespread attention in the research of PEMs owing to its tertiary amine basic groups and exceptional hydrophilic properties. This review focuses on the application status of polyvinylpyrrolidone‐based PEMs in PEMFC, vanadium redox flow battery, and alkaline water electrolysis, and describes in detail the key scientific problems in these fields, providing constructive suggestions and guidance for the application of polyvinylpyrrolidone‐based PEMs in electrochemical energy conversion and storage devices. [ABSTRACT FROM AUTHOR]

High‐temperature polymer electrolyte membrane fuel cells (HT‐PEMFCs) play an important role in the future hydrogen application system. However, there are still many issues of HT‐PEMFCs, especially on performance and durability, to be solved. Massive platinum usage is one of the most intractable issues. Herein, iron phosphide to platinum‐based catalyst is introduced for the better activity of hydrogen oxidation reaction (HOR). This catalyst shows a similar HOR performance with commercial catalyst while only one‐eighth noble metal is used in the anode of HT‐PEMFCs. The HT‐PEMFCs with Pt/FeP/C anode reach 465 mW cm−2 with a loading mass of 0.125 mgPt cm−2, and maintain long‐term stability. The excellent HOR activity and better fuel cell performance are attributed to the weakened absorption of hydrogen intermediate and concentrated phosphate species by that iron phosphide, leading to enhanced HOR activity and better fuel cell performance. This study provides new strategies for designing advanced HOR catalysts for HT‐PEMFCs. [ABSTRACT FROM AUTHOR]

Direct liquid fuel cells (DLFCs) are proposed to address the problems of high cost and complex storage and transportation of hydrogen in traditional hydrogen–oxygen proton exchange membrane fuel cells. However, present fuels of organic small molecules used in DLFCs are restricted to problems of sluggish electrochemical kinetics and easily poisoning of precious metal catalysts. Herein, we demonstrate reduced phosphotungstic acid as a liquid fuel for DLFCs based on its advantages of high chemical and electrochemical stability, high electrochemical activity on common carbon material electrodes, and low permeability through proton exchange membranes. The application of phosphotungstic acid fuel effectively solves the problems of high cost of anode catalysts and serious fuel permeation loss in traditional DLFCs. A phosphotungstic acid fuel cell achieves a peak power density of 466 mW cm−2 at a cell voltage of 0.42 V and good stability at current densities in the range from 20 to 200 mA cm−2. [ABSTRACT FROM AUTHOR]

Development of direct formic acid fuel cell (DFAFC) is significantly constrained by low output performance and poor durability because of the sluggish formic acid oxidation reaction (FAOR) and the poisoning by COads intermediate on the Pt‐based electrocatalyst at low operating temperatures. By operating DFAFCs at elevated temperatures, the peak power density (PPD) of the cell based on the Pt/C catalyst increases significantly. For example, the PPD of DFAFC reaches 198 mW cm−2 at 240 °C, eight times higher than that of the DFAFC at 70 °C. The study shows the surprising transition in power performance of DFAFCs at elevated temperatures. The increase of PPD for DFAFC against temperature is 121 mW cm−2/100 °C at temperatures above 115 °C, almost three times higher than the 45 mW cm−2/100 °C obtained at lower temperatures. The fundamental reason for the substantially enhanced power output and durability is the gradual transformation of the reaction kinetics from sluggish direct FAOR at low temperatures to fast H2 oxidation reaction at elevated temperatures due to the increased in situ decomposition of formic acid on Pt/C catalysts at temperatures above 100 °C. This study demonstrates that operation at temperatures above 160 °C is most effective to promote performance and durability of DFAFCs. [ABSTRACT FROM AUTHOR]

Electrocatalyst supports, in particular carbonaceous materials, play critical roles in the electrocatalytic activity and stability of precious metal group (PMG)‐based catalysts such as Pt, Pd, and Au for the electrochemical alcohol oxidation reaction (AOR) of fuels such as methanol and ethanol in polymer electrolyte membrane fuel cells (PEMFCs). Carbonaceous supports such as high surface area carbon provide electronic contact throughout the catalyst layer, isolate PMG nanoparticles (NPs) to maintain high electrochemical surface area, and provide hydrophobic properties to avoid flooding of the catalyst layer by liquid water produced. Compared to high surface area carbon, PMG catalysts supported on 1D and 2D carbon materials such as graphene and carbon nanotubes show enhanced activity and durability due to the intrinsic effect of the underlying carbonaceous supports on the electronic states of PMG NPs. The modification of the electronic environment, in particular the d‐band centers of PMG NPs, weakens the adsorption of AOR intermediates, facilitates breaking of the C−C bonds, and thus enhances the electrocatalytic activity of PMG catalysts. The doping of heteroatoms further facilitates the electrocatalytic activity for the AOR through the structural, bifunctional, and electronic effects, in addition to the enhanced dispersion of PMG NPs in the carbon support. The prospects for the development of effective PMG‐based catalysts for high‐performance alcohol‐fuel‐based PEMFCs is discussed. [ABSTRACT FROM AUTHOR]

One of the effective strategies to pursue the highly durable high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) is to introduce inorganic fillers to the phosphoric acid-doped polybenzimidazole (PA/PBI) membranes. Among the inorganic fillers, phosphates such as phosphosilicate are effective in mitigating acid loss at elevated temperatures (200–300 °C). In this paper, the effect of in situ formed phosphosilicate on the performance and stability of SiO 2 /PA/PBI composite membranes is studied in detail. The mechanical properties and electrochemical performances of the in situ formed SiO 2 /PA/PBI membranes depend strongly on the content of in situ formed Si 5 P 6 O 25 fillers and its distribution and microstructure in the membrane. Such in situ formed SiO 2 /PA/PBI composite membranes show a high conductivity of 53.5 mS cm−1 at 220 °C. The assembled single cell shows a maximum peak power density (PPD) of 530.6 mW cm−2 and excellent stability at elevated temperature of 220 °C for over 130 h. The exceptional stability at 220 °C is most likely due to the existence of predominant amorphous phosphosilicate phases in the in situ formed SiO 2 /PA/PBI composite membranes, which inhibits the evaporation and leaching of PA at elevated temperatures. The results indicate the practical application of in situ formed SiO 2 /PA/PBI composite membranes for HT-PEMFCs. • In situ formation of predominantly amorphous phosphosilicate phases in SiO 2 /PA/PBI composite membranes. • The as-synthesized SiO 2 /PA/PBI membrane based PEMFCs can operate at elevated high temperatures of 200–250 °C. • The composite membranes based PEMFCs show high performance and excellent stability at 220 °C. • The in situ formed predominantly amorphous phosphosilicate phases can effectively contain PA at high temperatures. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) are well known electrocatalyst supports due to their high electrical conductivity, structural stability, and high surface area. Here, we demonstrate that the number of inner tubes or walls of CNTs also have a significant promotion effect on the activity of supported Pd nanoparticles (NPs) for alcohol oxidation reactions of direct alcohol fuel cells (DAFCs). Pd NPs with similar particle size (2.1-2.8 nm) were uniformly assembled on CNTs with different number of walls. The results indicate that Pd NPs supported on triple-walled CNTs (TWNTs) have the highest mass activity and stability for methanol, ethanol, and ethylene glycol oxidation reactions, as compared to Pd NPs supported on single-walled and multi-walled CNTs. Such a specific promotion effect of TWNTs on the electrocatalytic activity of Pd NPs is not related to the contribution of metal impurities in CNTs, oxygen-functional groups of CNTs or surface area of CNTs and Pd NPs. A facile charge transfer mechanism via electron tunneling between the outer wall and inner tubes of CNTs under electrochemical driving force is proposed for the significant promotion effect of TWNTs for the alcohol oxidation reactions in alkaline solutions. [ABSTRACT FROM AUTHOR]

An excellent hybrid proton exchange membrane (PEM) is prepared using a one‐step synthesis to anchor phosphotungstic acid (HPW) into a polyvinylpyrrolidone (PVP) matrix. The hybrid membrane exhibits high proton conductivity and excellent stability. The impressive performance of a single cell based on the hybrid membrane, with a power density of 618 mW cm–2 at 50 °C, demonstrates promising potential for application in fuel cells. [ABSTRACT FROM AUTHOR]

To reconcile the tradeoff between conductivity and dimensional stability in AEMs, a novel Gemini quaternary ammonium poly (ether ether ketone) (GQ-PEEK) membrane was designed and successfully synthesized by a green three-step procedure that included polycondensation, bromination, and quaternization. Gemini quaternary ammonium cation groups attached to the anti-swelling PEEK backbone improved the ionic conductivity of the membranes while undergoing only moderate swelling. The grafting degree (GD) of the GQ-PEEK significantly affected the properties of the membranes, including their ion-exchange capacity, water uptake, swelling, and ionic conductivity. Our GQ-PEEK membranes exhibited less swelling (≤40 % at 25-70 °C, GD 67 %) and greater ionic conductivity (44.8 mS cm−1 at 75 °C, GD 67 %) compared with single quaternary ammonium poly (ether ether ketone). Enhanced fuel cell performance was achieved when the GQ-PEEK membranes were incorporated into H2/O2 single cells. [ABSTRACT FROM AUTHOR]

In situ synthesis is a powerful approach to control nanoparticle formation and consequently confers extraordinary properties upon composite membranes relative to conventional doping methods. Herein, uniform nanoparticles of cesium hydrogen salts of phosphotungstic acid (CsPW) are controllably synthesized in situ in Nafion to form CsPW-Nafion nanocomposite membranes with both improved proton conductivity and methanol-crossover suppression. A 101.3 % increase of maximum power density has been achieved relative to pristine Nafion in a direct methanol fuel cell (DMFC), indicating a potential pathway for large-scale fabrication of DMFC alternative membranes. [ABSTRACT FROM AUTHOR]

Abstract: We report here a novel method to immobilize water soluble tungstophosphoric acid (H3PW12O40, HPW) on Pt/C nanoparticles via the electrostatic interaction between the negatively charged HPW and the positively charged functional groups of chitosan which has been attached to Pt/C nanoparticles to provide positively charged sites for the self-assembly of HPW. The HPW assembled Pt/C catalysts (donated as Pt/C-chitosan-HPW) were characterized by XRD, FTIR, TGA, zeta potential, and X-ray photoelectron spectroscopy (XPS). The results indicate that HPW assembled on chitosan-functionalized Pt/C is very stable and Pt/C-chitosan-HPW catalyst has a higher utilization efficiency as compared to that of pristine Pt/C catalyst. Electrochemical activity of Pt/C-chitosan-HPW catalysts for methanol oxidation and oxygen reduction reaction (ORR) is significantly higher than that of Pt/C catalysts without assembled HPW. The enhanced electrocatalytic activities of HPW assembled Pt/C catalysts are most likely due to the synergistic effect between assembled HPW and Pt/C nanoparticles and the presence of HPW leads to a downward shift in the d-band center of Pt catalyst and facilitates the oxidative removal of COads poisoning species for methanol oxidation and desorption of Oads species for ORR on Pt catalysts. [Copyright &y& Elsevier]

Abstract: A novel and simple method to functionalize multi-walled carbon nanotubes (MWCNTs) is developed using tetrahydrofuran (THF) solvent as the functionalization and anchoring agent. The effectiveness of the method is demonstrated by the synthesis of uniformly distributed Pt and PtSn nanoparticles on THF-functionalized MWCNTs. Transmission electron microscopy and X-ray diffraction results indicate that Pt and PtSn nanoparticles with a narrow particle size distribution and an average particle size of ∼4nm are synthesized on THF-functionalized MWCNTs. The lattice parameter of PtSn/MWCNTs increases with the Sn content, indicating the successful formation of PtSn binary nanoparticles. The results demonstrate the applicability and effectiveness of the THF-functionalized MWCNTs as effective catalyst supports in the development of highly dispersed and active Pt and Pt-based electrocatalysts for low temperature fuel cells. The successful functionalization of MWCNTs by THF also indicates that there could be a strong σ–π interaction between the MWCNTs and the THF. [Copyright &y& Elsevier]

A highly ordered mesoporous Nafion membrane with a remarkable water retention ability was synthesized viaa micelle templating method with self-assembled Pluronic F108 surfactants and its capability to operate under completely dry gas streams is demonstrated. [ABSTRACT FROM AUTHOR]

Tin pyrophosphate is a feasible solid-state proton conductor as electrolyte and ionomers for applications in fuel cells and sensors, etc. Nevertheless, the morphology and proton conductivity of the SnP 2 O 7 varies vigorously due to different fabrication methods, molar ratios of phosphorous to tin and sintering temperature. In this work, a core-shell SnP 2 O 7 (c-SnP 2 O 7) has been fabricated via a conventional acid method between SnO 2 nanoparticles and various phosphoric acids including H 3 PO 4 , H 4 P 2 O 7 , (HPO 3) x and P 2 O 5 under temperature as low as 200 °C. The transformation of SnO 2 to c-SnP 2 O 7 in these phosphoric acids follows dissolving and reprecipitation mechanism where Sn(HPO 4) 2 is the intermediate species. In addition, the dominated factor for the transformation is the presence of P 2 O 7 4− due to the condensation or hydration of various phosphoric acids. The as-synthesized c-SnP 2 O 7 contains crystalline SnP 2 O 7 inner core, an amorphous phosphate intermediate layer and an outer-layer with gel-like phosphorous-rich species. Furthermore, the phosphorous-rich gel layer contributes to outstanding proton conductivity of c-SnP 2 O 7 up to 8.0 × 10−2 S cm−1 at 260 °C and excellent durability of 115 h at 240 °C and anhydrous conditions. Overall, the core-shell SnP 2 O 7 is a promising proton conductor to be used in elevated temperature fuel cells. [ABSTRACT FROM AUTHOR]

To maintain membrane hydration and operate effectively, polymer electrolyte membrane fuel cells (PEMFCs) require elaborate water management, which significantly increases the complexity and cost of the fuel cell system. Here we propose a novel and entirely different approach to membrane hydration by exploiting the concept of bipolar membranes. Bipolar membrane (BPM) fuel cells utilize a composite membrane consisting of an acidic polymer electrolyte membrane on the anode side and an alkaline electrolyte membrane on the cathode side. We present a novel membrane electrode assembly (MEA) fabrication method and demonstrate experimentally and theoretically that BPM fuel cells can (a) self-humidify to ensure high ionic conductivity; and (b) allow use of non-platinum catalysts due to inherently faster oxygen reduction kinetics on an alkaline cathode. Our Pt-based BPM fuel cell achieves a two orders of magnitude gain in power density of 327 mW cm −2 at 323 K under dry gas feed, the highest power output achieved under anhydrous operation conditions. A theoretical analysis and in situ measurements are presented to characterize the unique interfacial water generation and transport behavior that make self-humidification possible during operation. Further optimization of these features and advances in fabricating bipolar MEAs would open the way for a new generation of self-humidifying and water-management-free PEMFCs. [ABSTRACT FROM AUTHOR]

In high-temperature formic acid fuel cell (HT-FAFC), the dehydrogenation behavior of formic acid plays a significant role in boosting cell output performance by leading to a favorable and powerful hydrogen oxidation reaction (HOR) on the anode side instead of the direct formic acid oxidation reaction (dFAOR). The formic acid dehydrogenation mechanism of HT-FAFC at 200 °C is investigated by regulating concentration and flow rate. As a competitive path of dehydrogenation, unfavorable dehydration occurs simultaneously accompany by carbon monoxide (CO) release. It is found that high formic acid concentration is conducive to the dehydrogenation to produce more hydrogen, however, the reduction of water vapor content may promote the dehydration reaction and result in the inhibition of dehydrogenation. As the non-preferable alternative, the dehydration-caused total CO release remains under CO maximum tolerance (3%) of Pt catalyst at 200 °C which is unlikely to affect the power output of HT-FAFC. The permeation of formic acid can be considered as a barrier when the high concentration exceeds 12 mol L−1 or the flow rate exceeds 1 mL min−1. These findings may deepen understanding of formic acid consuming behavior of HT-FAFC anode, which helps to formulate strategies to improve cell performance in general. • Dehydrogenation behaviors of formic acid under HT-DFAFC at 200 °C have been studied. • The dehydrogenation pathways are determined by the ratio of formic acid to water. • Performance of DFAFC at 200 °C is controlled by hydrogen consumption for HOR. • The optimal performance of the HT-FAFC we may achieve is 203 mW cm−2 under 200 °C. [ABSTRACT FROM AUTHOR]

Highlights: [•] Sub-monolayer Sn(Ru or RuSn) decorated Pt/C nanoparticles was synthesized. [•] All decorated Pt/C showed enhanced electrocatalytic activities for CO, formaldehyde. [•] The Sn decorated Pt/C showed the highest electrocatalytic activity for formadehyde. [ABSTRACT FROM AUTHOR]

Abstract: The intrinsic relationship between proton conductivity, thermal stability and structural symmetries of phosphotungstic acid (HPW)-functionalized mesoporous silica (HPW-meso-silica) membrane was investigated with mesoporous silica from 2D hexagonal p6mm, 3D face-centered cubic (), body-centered , to cubic bicontinuous symmetries. HPW-meso-silica nanocomposites with 3D mesostructures display a significantly higher proton conductivity and higher stability as a function of relative humidity in comparison to 2D mesostructures. The best result was obtained with body-centered cubic ()-HPW-meso-silica, showing proton conductivities of 0.061Scm−1 at 25°C and 0.14Scm−1 at 150°C, respectively, and an activation energy of 10.0kJmol−1. At 150°C, the cell employing a HPW-meso-silica membrane produced a maximum power output of 237mWcm−2 in a methanol fuel without external humidification. The high proton conductivity and excellent performance of the new methanol fuel cells demonstrate the promise of HPW-meso-silica nanocomposites with 3D mesostructures as a new class of inorganic proton exchange membranes for use in direct methanol fuel cells (DMFCs). [Copyright &y& Elsevier]

• Atomically dispersed bimetallic FeCu coordinated with N-CNTs, FeCu/N-CNTs, are developed. • FeCu/N-CNTs show PA enhance activity and stability for ORR at elevated temperatures. • PA/PBI cells based on FeCu/N-CNTs cathode show a high and stable power performance at 230 degrees. • DFT calculation verifies the promotion mechanism of phosphate on bimetallic FeCu for ORR. Phosphate poisoning of Pt electrocatalysts is one of the major barriers that constrains the performance of phosphoric acid-doped polybenzimidazole (PA/PBI) membrane fuel cells. Herein, we developed new atomically dispersed bimetallic FeCu coordinated with nitrogen-doped carbon nanotubes (FeCu/N-CNTs) as Pt-free oxygen reduction reaction (ORR) electrocatalysts. The cell with FeCu/N-CNTs cathodes delivers a peak power density of 302 mWcm−2 at 230℃, similar to that using Pt/C electrocatalysts (1 mg Pt cm−2) but with a much better stability. In contrast to phosphate poisoning of Pt/C, FeCu/N-CNTs show PA enhanced activities. DFT calcualtions indicate that phosphate promotion effect results from the stronger binding of phosphate on Cu sites, which decreases the activation energy barrier for the cleavage of the O 2 double bond and provides local protons to facilitate the proton-coupled electron transfer ORR. The results also show that FeCu/N-CNTs have a much better activity for ORR as comapre to Fe single atom catalysts coordinated with nitrogen-doped carbon nanotubes, Fe/N-CNTs. This study demonstrates the promising potential of bimetallic FeCu/N-CNTs as true Pt-free, highly active and durable cathodes for PA/PBI based high temperature polymer electrolyte fuel cells. [ABSTRACT FROM AUTHOR]

Heteropoly acids have been employed to increase the proton conductivity of phosphoric acid (PA) doped polymer membranes for high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). In this work, we develop a new composite membrane based on phosphotungstic acid (PWA) doped polyethersulfone-polyvinylpyrrolidone (PES-PVP) matrix, forming PWA/PES-PVP composite membrane for HT-PEMFCs. The homogeneous distribution of PWA on the PES-PVP membrane enhances its mechanical strength. In addition, there is a strong interaction between PWA and PA that is confirmed experimentally by the attenuated total reflectance Fourier Transform Infrared spectroscopy and semi-empirical quantum mechanics calculation. This enhances not only the PA uptake but also the proton conductivity of the PWA/PES-PVP composite membrane. 1H nuclear magnetic resonance spectroscopy results elucidate that the high proton conductivity of the PA doped PWA/PES-PVP membranes is due to their higher proton content and mobility compared to the pristine PA doped PES-PVP membrane. The best results are observed on the PES-PVP composite membrane with addition of 5 wt% PWA, reaching proton conductivity of 1.44 × 10−1 S cm−1 and a peak power density of 416 mW cm−2 at 160 °C and anhydrous conditions. PWA additives increase the proton conductivity and cell performance, demonstrating significantly positive effects on the acid-base composite membranes for high temperature polymer electrolyte membrane fuel cell applications. Image 1 • Homogeneous PWA/PES-PVP composite membranes are prepared. • Both experiments and simulation indicate a strong interaction between PWA and PA. • PWA addition increases the proton content and mobility of the PA/PES-PVP membrane. • Optimum content of PWA on PES-PVP composite membrane is 5 wt%. [ABSTRACT FROM AUTHOR]

Tin pyrophosphate has been employed as a proton conductor in polymer electrolyte membranes (PEMs) at temperatures over 200 °C. However, neither the aggregation of the SnP 2 O 7 nanoparticles nor the proton conduction mechanism of the material has been clearly clarified in PEM. The present work reports a polybenzimidazole (PBI)/SnP 2 O 7 composite membrane with homogeneous distribution of the inorganic phase. The membrane is successfully fabricated by in-situ transformation of SnO 2 nanoparticles to core-shell SnP 2 O 7 nanoparticles in the PBI matrix during fuel cell operation. Further in-depth analysis shows that the core-shell SnP 2 O 7 contains a crystalline SnP 2 O 7 core, an amorphous SnP 2 O 7 intermediate layer and a gel-like outer layer mainly containing H 4 P 2 O 7. In addition, the crystal growth of the SnP 2 O 7 nucleus consumes ions from the amorphous SnP 2 O 7 layer, where the reacted ions are compensated by the diffusion of Sn4+ and P 2 O 7 4− ions from the gel-like outer layer. Also, the fuel cell with the composite membrane shows superior proton conductivity and durability compared to the pristine phosphoric acid-doped PBI membrane at 240 °C for over 50 h. That is due to the presence of H 4 P 2 O 7 in the outer layer, which contributes to high and stable proton conductivity of the core-shell SnP 2 O 7 at 220–260 °C. [ABSTRACT FROM AUTHOR]

Abstract One critical issue for the application of high-temperature polymer electrolyte membranes (HT-PEMs) is to obtain good balance between their proton conductivities and mechanical strength. In this work, a novel strategy has been developed to achieve the balance by increasing the number of functional groups in the grafting site of the side chain of polysulfone (PSU). 2,4,6-tri(dimethylaminomethyl)-phenol (TDAP) with three tertiary amine groups was grafted on PSU (TDAP-PSU) to achieve higher phosphoric acid (PA) uptake at a lower grafting degree. Moreover, the bundle of amine groups in one grafting site reduces the volume swelling compared to the single tertiary amine group grafted PSU membrane (DMA-PSU). Thereby, the TDAP-PSU membrane with 75% grafting degree achieves comparable PA uptake with the DMA-PSU membrane with 99% grafting degree, whereas the mechanical strength of former membrane after PA doping is 2.2 times higher than that of the later one after PA doping. Moreover, single cells based on the TDAP-PSU membrane reach the peak power density of 453 mW cm−2 and excellent stability without external humidification. Overall, increasing the number of active groups in the grafting site of the polymer side chain is a promising strategy to deal with the trade-off between the proton conductivity and membrane dimensional stability of HT-PEMs. Graphical abstract fx1 Highlights • 2,4,6-tri(dimethylaminomethyl)-phenol grafted polysulfone (TDAP-PSU) was synthesized. • Phosphoric acid doped TDAP-PSU membrane shows high conductivity and tensile stress. • The fuel cell with the membrane shows a power density of 498 mW cm−2 at 180 °C. [ABSTRACT FROM AUTHOR]

The bipolar membrane fuel cells (BPMFCs), which have a unique acid-alkaline jointed membrane electrode assembly (MEA) structure, have demonstrated their great potential for self-humidification during operation. Although the self-humidification ability of such bipolar membranes (BPMs) has recently been validated by a one-dimensional BPM model, the transport mechanism and the formation of self-humidification in the MEAs are not well understood. In the present study, a two-dimensional cross-channel MEA model is developed to elucidate the mechanisms and enhancement of water transport on self-humidification with comprehensive consideration of the three electrochemical reaction zones. The water–formation interface model has been successfully investigated by theoretical and experimental interface reaction kinetics, streamlines of water flux present the formation process and mechanism of self-humidification. A critical current (voltage) value, beyond which self-humidification is initiated, is identified. It is also found that such critical current (voltage) can be adjusted by changing the membrane thickness and the water uptake property of the ionomer. It is concluded that fabricating BPMs with proper membrane thickness and water uptake property are effective strategies to enhance the water management and cell performance in BPMFCs. [ABSTRACT FROM AUTHOR]

The acidic-alkaline interface of a bipolar membrane fuel cell (BPMFC) is the place to generate water, which significantly affect the output performance of BPMFC by regulating the water distribution due to the ion conductivity and oxygen reduction reaction (ORR) kinetics in cathode. To investigate the influence of water diffusivity (D w) on the water distribution, four alkaline polymer electrolytes with different D w is selected as anion exchange membrane or alkaline electrolyte ionomer to assemble BPMFCs. A combined experimental and simulated study reveals the positive correlation relationship of D w to the water distribution and performance of BPMFC. By increasing the D w of the alkaline polymer electrolytes, the interfacial-generated water amount can be increased and promptly transport to the cathode, thereby satisfying the ion conductivity and increasing the ORR kinetics, and breakthrough the peak power density of the BPMFC with 1.06 W cm−2 without humidification. •Positive correlation relationship between D w , water distribution and performance of BPMFC. •More water distributed to cathode improve the ORR dynamics. •Breakthrough the performance of the BPMFC with 1.06 W cm−2. •Water distribution reduced influence of R s of BPMFC. [ABSTRACT FROM AUTHOR]

Poly(vinyl pyrrolidone) (PVP)-based high-temperature polymer electrolyte membranes (HT-PEMs) doped with phosphoric acid (PA) present an attractive prospect for high-temperature fuel cell. However, its proton conductivities and mechanical properties are inversely dependent on PVP content in membranes. Herein, chloromethyl-polysulfone is used as a polymeric crosslinker to fabricate cross-linked PVP. The effects of chloromethylation degree of polysulfone on PVP cross-linking degree, free volume and other parameters are studied. The quaternary amine groups introduced by cross-linking reaction enhances PA adsorption and retention capacity of membrane. The increased molar free volume created by polymeric crosslinker can accommodate more PA storage and reduce the polymer main chain plasticization. Thus, the mechanical properties of membranes are maintained. When compared to uncross-linked C-PVP-0/PA, the cross-linked C-PVP-13.7%/PA exhibits improved mechanical strength with increasement of 140% (4.5 MPa) and enhanced proton conductivity with increasement of 119% (120.0 mS cm−1@160 °C). Also, these superior characteristics allow a significantly enhanced H 2 –O 2 fuel cell performance with the membrane of 724.9 mW cm−2 @160 °C, which has increasement of 50% in comparison with that of the C-PVP-0%/PA membrane, and excellent durability. These praiseworthy results suggest that the cross-linked membrane within moderately molar free volume is potential to act as HT-PEMs materials for real-world applications. [Display omitted] • Highly conductive cross-linked poly(vinyl pyrrolidone) membranes were synthesized. • Conductivities and tensile strength were enhanced with increasing molar free volume. • Trade-off between proton conductivity and tensile strength is highlighted. • The single cell with membrane shows a peak power density of 724.9 mW cm−2 at 160 °C. [ABSTRACT FROM AUTHOR]

Abstract: Novel methanol-blocking polymer electrolyte composite membranes were prepared by inserting purple membrane (PM) to the bulk phase of Nafion® resin. Results of scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) analyses show that PM was well-dispersed in Nafion® membrane. Compared with recast Nafion®, blending PM changed the microstructure of Nafion® membrane and significantly improved the methanol-blocking efficiency by 31.6% in maximum. With PM content of 0.3wt% in the composite, the highest membrane selectivity factor and single cell power density of 62.1mWcm−2 were achieved. This satisfactory cell performance has given a promising prospect of Nafion®/PM composite membranes in the application in DMFC. [Copyright &y& Elsevier]

Abstract: In the present study, a novel composite methanol-blocking polymer electrolyte membrane was prepared by anchoring water-soluble phosphotungstic acid (HPW) in bulk phase of Nafion through interactions between HPW and Cs+ ions. Results of morphology and elemental mapping analysis indicated that this composite membrane had a dense structure with uniformly distributed Cs–HPW clusters. The composite membrane exhibited a rather low methanol diffusion coefficient (P, 0.97×10−6 cm2 s−1) and also the comparable conductivity (σ, 3.6×10−2 Scm−1) contrast with pristine Nafion (σ, 5.1×10−2 Scm−1). The selective factor (σ/P) of the composite membrane was six times higher than that of pristine Nafion. Single cell performance results showed that the maximum power density increased by 26% over the cell performance of pristine Nafion under the same conditions. [ABSTRACT FROM AUTHOR]

Abstract: In this study, purple membrane (PM) was applied as a methanol-blocking agent on Nafion® membranes. A series of well-organized poly(diallyldimethylammonium chloride)/PM multilayer films were obtained on a Nafion® 212 surface (PDDA/PM/Nafion®) to form composite membranes by the electrostatic layer-by-layer (LbL) self-assembly method. The effect of the PDDA/PM/Nafion® heterogenic interface on proton conductivity and methanol permeability was studied by alternating the deposited surface. With five PDDA/PM bilayers, double-sided modification (PDDA/PM)DF-5 and single-side modification (PDDA/PM)SF-5 resulted in excellent methanol blocking with a 73.4% and 64.7% reduction in methanol permeability in comparison with unmodified Nafion® 212, respectively. Indeed, the involvement of PM suppressed the methanol crossover. With regard to the selectivity factor (PDDA/PM)DF-1 composite membranes showed approximately 2-fold improvement as compared with unmodified Nafion® membranes. The cell performance of (PDDA/PM)SF-1 composite membranes achieved a power density of 27.0mWcm−2 which is 48.4% increase compared to cells using unmodified Nafion® 212 membranes. Moreover, with (PDDA/PM)DF-1, we achieved a power density of 34.4mWcm−2. This study highlights the potential application of PM as multifunctional protein membrane in direct methanol fuel cells. [ABSTRACT FROM AUTHOR]

The properties of high temperature polymer electrolyte membranes (HT-PEMs) are determined directly by the polymer matrix with phosphoric acid (PA) doping. Here, new polymer materials based on poly (arylene piperidine)s (PAPs) are prepared by one-step polymerization as PA absorbing matrix for HT-PEM fuel cells (HT-PEMFCs) application. The PAPs show excellent thermal stability and high glass transition temperature. Among PAPs, PA doped poly (N-methyl-piperidine- co - p -terphenyl) (PPT/PA) shows a high proton conductivity of 96.0 mS cm−1 at 180 °C without humidification and an excellent tensile strength of 12 MPa, which is much better than that of PA doped commercial poly [2,2'-(p -oxydiphenylene)-5,5′-benzimidazole] (OPBI/PA). The enhancement on conductivity of PPT/PA is attributed to the formation of micro-phase separation. A single cell based on PPT/PA membrane presents outstanding performance with a maximum power density of 1220.2 mW cm−2 with H 2 /O 2 feeding under 0.15 MPa backpressure in cathode at 180 °C, which is 1.85 times of that with OPBI/PA membrane (660.8 mW cm−2). Furthermore, a H 2 /air single cell with PPT/PA shows excellent stability at a constant current density of 120 mAcm−2 and 150 °C for 1600 h. This work indicates PAPs (especially, PPT) are a promising PA doping polymer matrix for high temperature polymer electrolyte membrane fuel cells application. Image 1 • Poly (arylene piperidine)s (PAPs) were synthesized by one-step polymerization. • Micro-phase separation is found in phosphoric acid doped PAPs membranes. • The optimized PAPs membrane has high tensile strength and proton conductivity. • The single cell with PPT/PA shows a peak power density of 1.22 W cm−2 at 180 °C. • The single cell shows an excellent stability of 1600 h at 150 °C. [ABSTRACT FROM AUTHOR]

Phosphoric acid (PA)-doped high temperature polymer electrolyte membranes (HT-PEMs) are crucial materials for HT-PEM fuel cells (HT-PEMFCs). However, the development of HT-PEMs suffers from the trade-off between proton conductivity and mechanical strength. High proton conductivity requires a high doping level of PA, and PA acts as a plasticizer that reduces the mechanical properties. Here, a new strategy is employed to address the unresolved challenges; the strategy is to graft poly(1-vinylimidazole) as PA doping sites on the polysulfone backbone. This is achieved via atom transfer radical polymerization. High proton conductivity is achieved because of the formation of micro-phase separated structures, and the mechanical properties are retained because of the reduced plasticizing effect, which is caused by the separation of PA adsorption sites and the polymer backbone. The prepared PA-doped membranes have excellent proton conductivity of 127 mS cm−1 at 160 °C and outstanding tensile strength of 7.94 MPa. Meanwhile, single H 2 -O 2 cell performance with the optimized membrane is impressive, reaching a peak power density of 559 mW cm−2 at 160 °C. More importantly, this work provides new insight into solving the trade-off between proton transport and mechanical strength for PA-doped HT-PEMs. • Poly(1-vinylimidazole) grafted on polysulfone membranes were synthesized. • Phosphoric acid doped membranes possess micro-phase separation structure. • The membranes display enhanced conductivity with increasing length of side chains. • The tensile strength of phosphoric acid doped membranes still remains 7.94 MPa. • The single cell with membranes shows a peak power density of 559 mW cm−2 at 160 °C. [ABSTRACT FROM AUTHOR]