High Temperature Polymer Electrolyte Research Articles

High-performance imidazole-containing polymers for applications in high temperature polymer electrolyte membrane fuel cells

This work focuses on the development of high temperature polymer electrolyte membranes (HT-PEMs) as key materials for HT-PEM fuel cells (HT-PEMFCs). Recognizing the challenges associated with the phosphoric acid (PA) doped polybenzimidazole (PBI) membranes, including the use of carcinogenic monomers and complex synthesis procedures, this study aims to develop more cost-effective, readily synthesized, and high-performance alternatives. A series of superacid-catalyzed polyhydroxyalkylation reactions have been carefully designed between p-terphenyl and aldehydes bearing imidazole moieties, resulting in a new class of HT-PEMs. It is found that the chemical structure of aldehyde-substituted N-heterocycles significantly impacts the polymerization reaction. Specifically, the use of 1-methyl-2-imidazole-formaldehyde and 1H-imidazole-4-formaldehyde monomers leads to the formation of high-viscosity, rigid, and ether-free polymers, denoted as PTIm-a and PTIm-b. Membranes fabricated from these polymers, due to their pendent imidazole groups, exhibit an exceptional capacity for PA absorption. Notably, PTIm-a, carrying methylimidazole moieties, demonstrates a superior chemical stability by maintaining morphology and structural stability during 350 h of Fenton testing. After being immersed in 75 wt% PA at 40 °C, the PTIm-a membrane reaches a PA content of 152%, maintains a good tensile strength of 13.6 MPa, and exhibits a moderate conductivity of 50.2 mS cm−1 at 180 °C. Under H2/O2 operational conditions, a single cell based on the PTIm-a membrane attains a peak power density of 732 mW cm−2 at 180 °C without backpressure. Furthermore, the membrane demonstrates stable cycle stability over 173 h within 18 days at a current density of 200 mA cm−2, indicating its potential for practical application in HT-PEMFCs. This work highlights innovative strategies for the synthesis of advanced HT-PEMs, offering significant improvements in membrane properties and fuel cell performance, thus expanding the horizons of HT-PEMFC technology.

Ethylenediamine tetramethylenephosphonic acid boosting the electrocatalytic interface construct and proton transfer for high-temperature polymer electrolyte membrane fuel cells

High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) show excellent application prospects due to its enhanced tolerance of hydrogen impurity. However, the sluggish electrode kinetics caused by its inefficient electrocatalytic interface and proton transfer severely restricts its performance. To overcome the sluggish electrode kinetics, the ethylenediamine tetramethylenephosphonic acid (EDTMPA) was successfully incorporated into the catalysts layer to regulate the phosphoric acid (PA) distribution to boost the electrocatalytic reaction interface and proton transfer, thus increasing the output power and stability of HT-PEMFCs. The hydrophilic H2PO4− and electron donor N atom of EDTMPA could efficiently decrease the absorption of PA on the catalyst surface and facilitate proton transportation in the membrane electrode, as demonstrated by our experiments. The fuel cell assembled with the prepared membrane electrode shows a high reactivity of 1175 mW cm−2 and excellent stability, which is much better than the past reference report. The results of this work provide new insights into the utilization of small molecules with phosphate groups to enhance phosphate tolerance and proton conduction, and there is also a further improvement in the reactivity, durability, and utilization of the electrocatalysts in HT-PEMFCs.

Theoretical Studies on the Chemical Degradation and Proton Dissociation Property of PBI used in High-Temperature Polymer Electrolyte Membrane Fuel Cells.

High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are gaining more and more attention due to their higher efficiency than low-temperature ones. Polybenzimidazole (PBI) membranes are the most popular membranes used in HT-PEMFCs. However, their chemical stability and chemical degradation mechanisms, which directly affect the lifetime of fuel cells, have been hardly reported. We applied the density functional theory and used ABPBI as an example membrane to investigate the chemical degradation mechanisms of PBI membranes. The possible degradation mechanisms that occurred on eight sites have been proposed, where sites 2 and 3 located on the phenyl ring are determined as two weak sites toward OH radical and oxygen molecule attack. When the terminal is the H atom at site 7, it is also weak under OH radical attack. Regarding these, the substituent effect on the chemical stability of polymers has been studied. By introducing four -C2F5 or -CN groups, the barrier heights of the corresponding degradation reactions are increased; thus, the chemical stabilities of related membranes are improved. The selection of terminal atoms was also explored for alleviating the chemical degradation of the membrane. The investigated proton transfer properties of nine model compounds revealed that introducing four -C2F5 or -CN groups improves the proton dissociation properties occurring at the cathode. The increase of phosphoric acid concentration is helpful for the proton transfer at both the membrane and the cathode. This work may hopefully help the design and synthesis of HT-PEMFCs with good stability and high efficiency.

Constructing immobilized H3PO4 network in nanosized ZSM-5 zeolitic framework achieves high proton conductivity after acceleration acid leaching test

In the midst of demand for the high and stable anhydrous proton conducting membrane for the high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), phosphoric acid (PA)-doped polybenzimidazole (PBI) is positioned as one of the most promising candidates. The key to develop the PA-PBI is to address the issue of phosphoric acid leaching, which causes significant performance deterioration. Here we introduced the nanosized ZSM-5 zeolite which plays the role of the rigid cage for confining H3PO4 to the PBI, and then evaluated by utilizing the acceleration acid leaching test (ALT) to put long-term operation in perspective. The ZSM-5 not only retain the high degree of PA after ALT, but also constructs the efficient proton conducting channel derived by the chemically-immobilized H3PO4 in pore channel. After ALT, PBI electrolyte membrane with 5 wt% of ZSM-5 exhibited 2.8 × 10−5 S cm−1 of proton conductivity at 150 °C anhydrous condition, which is three orders higher magnitude than pure PBI (1.1 × 10−8 S cm−1). Furthermore, H2/O2 HT-PEMFC single-cell constructed with PBI/5%ZSM-5 displayed an excellent maximum power density of 387 mW cm−2 at 150 °C anhydrous conditions, even after the ALT. The results indicate the possible improvement of the long-term stability of the fuel cell by utilizing readily available ZSM-5.

Ultra-Low-Potential Methanol Oxidation on Single-Ir-Atom Catalyst.

Methanol oxidation plays a central role to implement sustainable energy economy, which is restricted by the sluggish reaction kinetics due to the multi-electron transfer process accompanied by numerous sequential intermediate. In this study, an efficient cascade methanol oxidation reaction is catalyzed by single-Ir-atom catalyst at ultra-low potential (<0.1 V) with the promotion of the thermal and electrochemical integration in a high temperature polymer electrolyte membrane electrolyzer. At the elevated temperature, the electron deficient Ir site with higher methanol affinity could spontaneous catalyze the CH3OH dehydrogenation to CO under the voltage, then the generated CO and H2 was electrochemically oxidized to CO2 and proton. However, the methanol cannot thermally decompose with the voltage absence, which confirm the indispensable of the coupling of thermal and electrochemical integration for the methanol oxidation. By assembling the methanol oxidation reaction with hydrogen evolution reaction with single-Ir-atom catalysts in the anode chamber, a max hydrogen production rate reaches 18 mol gIr -1 h-1, which is much greater than that of Ir nanoparticles and commercial Pt/C. This study also demonstrated the electrochemical methanol oxidation activity of the single atom catalysts, which broadens the renewable energy devices and the catalyst design by an integration concept.

Ultra‐Low‐Potential Methanol Oxidation on Single‐Ir‐Atom Catalyst

AbstractMethanol oxidation plays a central role to implement sustainable energy economy, which is restricted by the sluggish reaction kinetics due to the multi‐electron transfer process accompanied by numerous sequential intermediate. In this study, an efficient cascade methanol oxidation reaction is catalyzed by single‐Ir‐atom catalyst at ultra‐low potential (&lt;0.1 V) with the promotion of the thermal and electrochemical integration in a high temperature polymer electrolyte membrane electrolyzer. At the elevated temperature, the electron deficient Ir site with higher methanol affinity could spontaneous catalyze the CH3OH dehydrogenation to CO under the voltage, then the generated CO and H2 was electrochemically oxidized to CO2 and proton. However, the methanol cannot thermally decompose with the voltage absence, which confirm the indispensable of the coupling of thermal and electrochemical integration for the methanol oxidation. By assembling the methanol oxidation reaction with hydrogen evolution reaction with single‐Ir‐atom catalysts in the anode chamber, a max hydrogen production rate reaches 18 mol gIr−1 h−1, which is much greater than that of Ir nanoparticles and commercial Pt/C. This study also demonstrated the electrochemical methanol oxidation activity of the single atom catalysts, which broadens the renewable energy devices and the catalyst design by an integration concept.

Investigation of phosphoric acid influence on the oxygen reduction reaction on carbon-supported platinum electrocatalyst via rotating disk electrodes

Phosphoric acid (PA), utilized as an electrolyte in high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), has been observed to exert a detrimental effect on oxygen reduction reaction (ORR) electrocatalyst, consequently compromising cell performance. To comprehensively elucidate the impact of phosphoric acid on ORR, this study employs a range of electrochemical techniques, including electrochemical impedance spectroscopy and voltammetry method. The negative influence of PA on commercial Pt/C electrocatalyst manifests differently under various potentials and PA concentrations. Upon the introduction of PA, the decay rate and amplitude of ECSA, as calculated by Hupd adatoms, are notably smaller compared to the kinetic current density generated by the oxygen reduction reaction. Particularly, in the kinetic-controlled potential range, the negative impact of PA becomes more pronounced at higher electrode potentials, accompanied by a significantly steeper Tafel slope. Additionally, the EIS results suggest that phosphoric acid may gradually transform into polyphosphoric acid at a high concentration, accentuating the poisoning effect of PA under steady-state conditions. However, a high PA concentration can substantially alter the electrolyte properties, potentially leading to an inaccurate assessment of PA tolerance in electrocatalysts. Hence, it is imperative to consider the appropriate PA concentration when evaluating PA tolerance and to discern the poisoning mechanism under different electrode potentials.

A pore scale model study of mass transfer and electrochemical reaction in cathode catalytic layer of high-temperature polymer electrolyte membrane fuel cells

The mass transfer and related electrochemical reactions in the catalytic layer (CL) are crucial for the performance of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), but there is a lack of understanding of the optimal phosphoric acid content and Pt/C catalyst loading in the CL. In this work, we investigate the influences of Pt/C catalyst numbers (NPt/C) and phosphoric acid film thickness (δPA) on mass transfer and electrochemical reactions of the cathode CL using a pore-scale model (300 × 300 × 300 nm3). The results reveal that larger NPt/C and δPA can impede oxygen diffusion, while lower NPt/C and δPA lead to fewer reaction active sites and lower conductivity, both of which result in lower current density. Therefore, the balance of three-phase transport is extremely important for CL. There is a 3D volcanic relationship between current density, Pt/C catalysts, and phosphoric acid film. At NPt/C = 200 (7407 per μm3) and δPA = 4 nm (the volume fractions of 37.22 % and 17.87 %), the highest current density can be achieved at a potential of 0.5 V (vs. RHE), which increased with the decrease of potential. This work is valuable for understanding the optimizing the microstructure and three-phase transport pathway of the CL to improve the performance of HT-PEMFCs.

The characteristics of high temperature polymer electrolyte membranes for fuel cell based on 2-pyridene based polybenzimidazole blended with poly(vinyl-phosphonic acid)

The present study has focused on exploring new 2-pyridine-bridge-based polybenzimidazole (2-Py-PBIs) based materials for various energy-related uses in proton exchange membrane fuel cells (PEMFC). An electrochemical device, which transforms chemical energy into electrical energy, is known as fuel cell. Using solution polymerization with polyphosphoric acid as a solvent, a series of 2-Py-PBIs were synthesised from the 4,4'-([2,4′-bipyridine]-2′,6′-diyl)bis (benzene-1,2-diamine). 2-Pyridine bridge Polybenzimidazoles are cross-linked with poly (vinylphosphonic acid), which helps us to improve membrane properties like mechanical properties and proton conductivities. FT-IR was used to characterize chemical structure, Ubbelohde viscometer was employed to determine the inherent viscosity. Additionally investigated were the oxidative stability, swelling ratio, ion exchange capability, and water uptake for 2-Py-PBIs. Thermogravimetric analysis is used to evaluate thermal stability. The obtained 2-Py-PBIs membranes were thermally stable and mechanically strong when compared with conventional polybenzimidazole-based membranes. The 2-Py-PBIs:PVPA membranes showed proton conductivity between 0.10 µS/m to 4.65 µS/m.

Conquering Heavy-Loading Decay of High-Temperature Polymer Electrolyte Membrane Fuel Cells with a Conductive Polymer-Based Phosphoric Acid Reservoir

Conquering Heavy-Loading Decay of High-Temperature Polymer Electrolyte Membrane Fuel Cells with a Conductive Polymer-Based Phosphoric Acid Reservoir

Sulfonated poly(ether ether ketone)-Protic ionic Liquid-Based anhydrous Proton-Conducting composite polymer electrolyte membranes for High-Temperature fuel cell applications

A high-temperature polymer electrolyte membrane fuel cell (PEMFC) has enormous potential to produce clean energy with minimal environmental pollution along with high energy density and conversion efficiency. In the present work, anhydrous proton-conducting polymer electrolyte membranes for prospective high-temperature fuel cell application were successfully prepared using different protic ionic liquids (PILs) and sulfonated poly(ether ether ketone) (SPEEK). The protic ionic liquids (PILs), 2-hydroxyethylammonium formate, diethylmethyl ammonium triflate, 1-ethylimidazolium bis(trifluoromethylsulfonyl)imide, 1,2-dimethyl imidazolium bis(trifluoro methylsulfonyl)imide, and diethylmethylammonium methanesulfonate were selected based on their favorable physicochemical properties. The effect of the incorporation of the PIL on the structural, thermal, and electrical transport properties of the composite SPEEK polymer electrolyte membranes was studied. The prepared polymer electrolyte membranes (PEMs) were characterized using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffractometry (XRD), and electrochemical impedance spectroscopy (EIS) techniques. FTIR results indicated an interaction between the PIL and the SPEEK, which resulted in homogeneous and flexible membranes. The DSC results confirmed good miscibility and elucidated plasticizing effect of the incorporated PIL on the SPEEK polymer matrix. All the PEMs showed good thermal stability and high-temperature anhydrous proton conductivity, achieving best proton conductivity, ≈8 × 10–3 S cm−1 at 120 °C and low activation energy ≈0.26 eV, making it suitable for prospective high-temperature PEMFC applications.

TiO2 nanolayer coated carbon support for highly durable high-temperature polymer electrolyte membrane fuel cell cathode

Carbon corrosion of Pt/C electrocatalyst in the cathode is a critical issue for the practical application of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). Herein, we introduce a nanolayer composed of TiO2 nanoparticles between Pt and carbon support, which not only protects the carbon from corrosion but also forms a strong metal-support interaction between Pt and TiO2. The Pt nanoparticles are uniformly dispersed on the prepared C@TiO2 support (mean size: 2.27 nm). After potential sweeping for 5000 cycles in the acid solution, the electrochemical surface area loss of the homemade Pt/C@TiO2 is 10.9%, which is approximately half of that of commercial Pt/C (19.1%). In the practical HT-PEMFC single cell, Pt/C@TiO2 exhibits superior durability than Pt/C as well. After the accelerated durability test, the maximum power density of Pt/C@TiO2-MEA decreases by 8.6%, which is significantly lower than that of Pt/C-MEA (23.9%), suggesting a great potential application of Pt/C@TiO2 in HT-PEMFCs.

Comparative analysis of degradation mechanisms in HT-PEM fuel cells under start–stop and load cycling with hydrogen and nitrogen-diluted feeds

The integration of reformers into high-temperature polymer electrolyte membrane (HT-PEM) fuel cells presents a significant opportunity to improve fuel flexibility and cost-effectiveness. To understand their degradation, we applied two start–stop cycling procedures: one with pure H2 and another with an 80 vol % H2 and 20 vol % N2 mix to simulate reformate gas. We also performed a load cycling test with H2 as anode gas. The results indicated that degradation rate of pure H2 start–stop cycling showed 306 μV h−1, while load cycling demonstrated a degradation rate of 19.7 μV h−1 for the current density of 0.2 A cm−2, and 88.2 μV h−1 for the current density of 0.4 A cm−2. Start–stop cycling with diluted gas resulted in a constant voltage drop with a degradation rate of 3.129 mV h−1. Electrochemical impedance spectroscopy (EIS) indicated an increased ohmic resistance during start–stop cycling and higher charge transfer (high-frequency) and mass transport (low-frequency) resistance with nitrogen introduction. Scanning electron microscope results confirmed MEA degradation. In conclusion, start–stop cycling and anode gas dilution are stressors that accelerate HT-PEM fuel cell degradation, reducing its lifetime.

Using distribution of relaxation times to separate the impedances in the membrane electrode assembly for high-temperature polymer electrolyte membrane fuel cells

In the membrane electrode assembly (MEA) of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), many types of resistance existed, but they have not been distinctly characterized in previous research. In this study, the distribution of relaxation times (DRT) methodology is employed, in conjunction with a home-built electrochemical electrode analysis system (EEAS), to figure out the specific resistance components in the cathode gas diffusion electrode (GDE). The impedance analysis by the DRT method was conducted using the electrochemical impedance spectrum obtained at different temperatures and current densities of the cathode only, isolated from the MEA environment. The four peaks (designated as Peak 0 to 3) were depicted at DRT plots of cathode GDE below 103 Hz. By comparing the DRT plots for different conditions and considering the EEAS structure, the four peaks were explained to be caused by distinct resistances occurring at the electrode and interface. The regions of each peak were distinguished according to their position changes with temperature and current density. Furthermore, by contrasting the DRT plots of the cathode GDE with those of MEA containing the same cathode, an additional peak (referred to as Peak 4) is identified between 103 Hz and 104 Hz, which was attributed to resistance originating from the anode. This study could provide a new approach for future research of new catalysts and electrodes utilizing the resistance analysis of MEA for HT-PEMFC.

Elucidating the Complex Oxidation Behavior of Aqueous H3PO3 on Pt Electrodes via In Situ Tender X-ray Absorption Near-Edge Structure Spectroscopy at the P K-Edge.

In situ tender X-ray absorption near-edge structure (XANES) spectroscopy at the P K-edge was utilized to investigate the oxidation mechanism of aqueous H3PO3 on Pt electrodes under various conditions relevant to high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) applications. XANES and electrochemical analysis were conducted under different tender X-ray irradiation doses, revealing that intense radiation induces the oxidation of aqueous H3PO3 via H2O yielding H3PO4 and H2. A broadly applicable experimental procedure was successfully developed to suppress these undesirable radiation-induced effects, enabling a more accurate determination of the aqueous H3PO3 oxidation mechanism. In situ XANES studies of aqueous 5 mol dm-3 H3PO3 on electrodes with varying Pt availability and surface roughness reveal that Pt catalyzes the oxidation of aqueous H3PO3 to H3PO4. This oxidation is enhanced upon applying a positive potential to the Pt electrode or raising the electrolyte temperature, the latter being corroborated by complementary ion-exchange chromatography measurements. Notably, all of these oxidation processes involve reactions with H2O, as further supported by XANES measurements of aqueous H3PO3 of different concentrations, showing a more pronounced oxidation in electrolytes with a higher H2O content. The significant role of water in the oxidation of H3PO3 to H3PO4 supports the reaction mechanisms proposed for various chemical processes observed in this work and provides valuable insights into potential strategies to mitigate Pt catalyst poisoning by H3PO3 during HT-PEMFC operation.

Investigating the Impact of Catalyst Penetration into Gas Diffusion Layer on the Performance of High-Temperature Polymer Electrolyte Membrane Fuel Cells

The catalyst fabrication method, cell assembly, and operating conditions in polymer electrolyte membrane fuel cells (PEMFC) impact the catalyst penetration into the gas diffusion layer (GDL), alter its porous structure, and, consequently, the overall cell performance. This study investigates the effect of the catalyst layer (CL) penetration thickness, catalyst loading amount, and cell compression during assembly on species and current distributions, and overall cell performance. GDLs with large penetration thickness show a substantial resistance to reactant and proton transport, particularly at high current densities resulting in a drop in the cell performance. For zero, 50%, and 100% penetrations, the average current densities at an operating voltage of 0.4 V are 0.8329, 0.7920, and 0.71112 A cm−2, respectively. This indicates a performance loss of 5% and 15% for 50% and 100% penetrations in comparison to zero penetration. Higher catalyst loading results in greater penetration, negating the benefit of enhanced kinetics. Performance typically decreases by 3%–5% for 50% penetration and 12%–15% for 100% penetration when penetration levels increase for a certain Pt loading. An attempt is made to investigate the interplay between the effect of reactant and proton transport limitations on their distributions and cell performance. The combined effect of catalyst penetration and cell compression during the assembly has a crucial impact on cell performance with the starvation of reactants at high-density regions. The study highlights the necessity of optimizing the penetration thickness, catalyst loading, and cell assembly to achieve maximum cell performance.

Assessment of polybenzimidazole/MOF composite membranes for the improvement of high-temperature PEM fuel cell performance

This study aims to determine the most effective utilization of ZIF-8 type metal-organic framework (MOF) doped polybenzimidazole (PBI) composite membrane in high-temperature polymer electrolyte membrane fuel cells (HT-PEMFC) and investigate how ZIF-8 filler affects performance. ZIF-8 particles were prepared by solvothermal method and added to the PBI polymer using a weight percentage varying from 1 to 5 %. XRD, BET, and TEM examined the prepared ZIF-8. Composite membrane properties were investigated by XRD, SEM analysis, proton conductivity measurements, acid doping, and acid stripping tests. The HT-PEMFC performances of the membranes were carried out using Hydrogen and dry air at 150–180. The highest performance was acquired with the composite ZIF8/PBI-2 membrane as 0.432 W/cm2 at 170 °C. The obtained result is explained by easier proton transfer over ZIF-8's enlarged tunnel network. This study proposes a promising strategy to use ZIF-8 to prepare a PBI composite membrane with excellent proton conductivity, acid doping, and low acid leaching for HT-PEMFC application. The current study's findings can support future research on PBI/MOF-based composite membranes for HT-PEMFC applications.

High-performance and robust high-temperature polymer electrolyte membranes with moderate microphase separation by implementation of terphenyl-based polymers

Acid loss and plasticization of phosphoric acid (PA)-doped high-temperature polymer electrolyte membranes (HT-PEMs) are critical limitations to their practical application in fuel cells. To overcome these barriers, poly(terphenyl piperidinium)s constructed from the m- and p-isomers of terphenyl were synthesized to regulate the microstructure of the membrane. Highly rigid p-terphenyl units prompt the formation of moderate PA aggregates, where the ion-pair interaction between piperidinium and biphosphate is reinforced, leading to a reduction in the plasticizing effect. As a result, there are trade-offs between the proton conductivity, mechanical strength, and PA retention of the membranes with varied m/p-isomer ratios. The designed PA-doped PTP-20m membrane exhibits superior ionic conductivity, good mechanical strength, and excellent PA retention over a wide range of temperature (80–160 °C) as well as satisfactory resistance to harsh accelerated aging tests. As a result, the membrane presents a desirable combination of performance (1.462 W cm−2 under the H2/O2 condition, which is 1.5 times higher than that of PBI-based membrane) and durability (300 h at 160 °C and 0.2 A cm−2) in the fuel cell. The results of this study provide new insights that will guide molecular design from the perspective of microstructure to improve the performance and robustness of HT-PEMs.

Stability and performance of in-situ formed phosphosilicate nanoparticles in phosphoric acid-doped polybenzimidazole composite membrane fuel cells at elevated temperatures

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 SiO2/PA/PBI composite membranes is studied in detail. The mechanical properties and electrochemical performances of the in situ formed SiO2/PA/PBI membranes depend strongly on the content of in situ formed Si5P6O25 fillers and its distribution and microstructure in the membrane. Such in situ formed SiO2/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 SiO2/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 SiO2/PA/PBI composite membranes for HT-PEMFCs.

Effect of Polytetrafluorethylene Content in Fe‐N‐C‐Based Catalyst Layers of Gas Diffusion Electrodes for HT‐PEM Fuel Cell Applications

AbstractFe‐N‐C catalysts are a promising alternative to replace cost‐intensive Pt‐based catalysts in high temperature polymer electrolyte membrane fuel cell (HT‐PEMFC) electrodes. However, the electrode fabrication needs to be adapted for this new class of catalysts. In this study, gas diffusion electrodes (GDEs) are fabricated using a commercial Fe‐N‐C catalyst and different polytetrafluorethylene (PTFE) binder ratios, varying from 10 to 50 wt % in the catalyst layer (CL). The oxygen reduction reaction performance is investigated under HT‐PEMFC conditions (160 °C, conc. H3PO4 electrolyte) in a half‐cell setup. The acidophilic character of the Fe‐N‐C catalyst leads to intrusion of phosphoric acid electrolyte into the CL. The strength of the acid penetration depends on the PTFE content, which is visible via the contact angles. The 10 wt % PTFE GDE is less capable to withdraw product water and electrolyte and results into the lowest half‐cell performance. Higher PTFE contents counterbalance the acid drag into the CL and impede flooding. The power density at around 130 mA mgCatalyst−2 increases by 34 % from 10 to 50 wt % PTFE.