Low Humidity Proton Exchange Membrane Research Articles

Heteroatom-Doped Defects Anchoring Nano-Pt for High-Stability and Low-Humidity Proton Exchange Membrane Fuel Cell.

To meet the ever-increasing demand of proton exchange membrane fuel cell (PEMFC), it is necessary to carry out structure optimization for low-cost and high-stability oxygen reduction reaction (ORR) catalysts. Herein, a zeolitic imidazolate framework (ZIF)-derived carbon material with a mass of heteroatoms and defects is developed and serves as advanced support for nano-Pt-based ORR catalysts. This unique structure enhances the interaction between nano-Pt and support, leading to higher ORR intrinsic activity. During fuel cell applications, it demonstrates impressive water-retaining capacity and electrochemical stability. Under H2-O2 supply without cathode humidification, this catalyst achieves high mass activity of 0.475 A mgPt -1, with only 7.4% attenuation in maximum power density after 20 000 cycles of accelerated durability test, highlighting its remarkable potential for fuel cell applications. Physicochemical characterization and theoretical simulation reveal the crucial anchoring effect of heteroatom-doped defects to nano-Pt, providing valuable insights for further ORR catalyst design and PEMFC applications.

Enhancement of comprehensive performance of high-temperature and low-humidity proton exchange membranes: Crosslinking of trifunctional proton conductor with branched polybenzimidazole

In order to improve the proton conductivity and antioxidant stability of proton exchange membranes (PEMs) at wide relative humidity (RH), composite membranes cross-linked with tribranched polybenzimidazole (TaPBI) and poly(azido-1-propanesulfonic acid −2,2′- methylsulfonic acid −5,5′-bis-benzimidazole) polyphosphazenes (PSBI) (TaPBI-PSBI) are prepared. TaPBI, as a branched polybenzimidazole, exhibits a large free volume. The trifunctional proton conductor PSBI-Na incorporates abundant flexible acidic groups and basic sites to enhance proton conductivity, and cross-linking groups to increase its binding strength with PBI. By casting and cross-linking, the proton conductivity, mechanical properties, and oxidation resistance of the TaPBI-PSBI membranes are significantly improved. The generation of cross-linked structures in the membranes is demonstrated by FT-IR. SEM shows that the surface of composite membrane is smooth and free of through holes. The elements are uniformly distributed. The TEM shows microphase separation occurs in the TaPBI-PSBI membrane, facilitating the formation of the continuous proton channels. The proton conductivity of TaPBI-PSBI (40) composite membrane reaches 0.170, 0.081, 0.059, and 0.037 S cm−1 at 180 °C, 100%, 50%, 30%, and 0% RH, respectively. The composite membrane is demonstrated the outstanding stability with the small decrease of proton conductivity and mass after durability testing of 96 h. The composite membrane exhibits high comprehensive performances as HT-PEM.

High-temperature low-humidity proton exchange membrane with "stream-reservoir" ionic channels for high-power-density fuel cells.

The perfluorosulfonic acid (PFSA) proton exchange membrane (PEM) is the key component for hydrogen fuel cells (FCs). We used in situ synchrotron scattering to investigate the PEM morphology evolution and found a "stream-reservoir" morphology, which enables efficient proton transport. The short-side-chain (SSC) PFSA PEM is fabricated under the guidance of morphology optimization, which delivered a proton conductivity of 193 milliSiemens per centimeter [95% relativity humidity (RH)] and 40 milliSiemens per centimeter (40% RH) at 80°C. The improved glass transition temperature, water permeability, and mechanical strength enable high-temperature low-humidity FC applications. Performance improvement by 82.3% at 110°C and 25% RH is obtained for SSC-PFSA PEM FCs compared to Nafion polymer PEM devices. The insights in chain conformation, packing mechanism, crystallization, and phase separation of PFSAs build up the structure-property relationship. In addition, SSC-PFSA PEM is ideal for high-temperature low-humidity FCs that are needed urgently for high-power-density and heavy-duty applications.

All sprayed fluorine-free membrane electrode assembly for low-platinum and low-humidity proton exchange membrane fuel cells

We propose an all-sprayed fluorine-free membrane electrode assembly for low-platinum and low-humidity proton exchange membrane fuel cell application.

Simultaneous improvement of power density and durability of sulfonated poly(ether ether ketone) membrane by embedding CeO 2 ‐ATiO 2 : A comprehensive study in low humidity proton exchange membrane fuel cells

Simultaneous improvement of power density and durability of sulfonated poly(ether ether ketone) membrane by embedding <scp> CeO ₂ ‐ATiO ₂ </scp> : A comprehensive study in low humidity proton exchange membrane fuel cells

Construction of Novel Proton Transport Channels by Triphosphonic Acid Proton Conductor-Doped Crosslinked mPBI-Based High-Temperature and Low-Humidity Proton Exchange Membranes

High proton conductivity and sufficient stability of the polybenzimidazole membrane are important for the application of high-temperature proton exchange membrane fuel cells (HT-PEMFCs). A series of composite membranes based on crosslinked mPBI (cPBI) with cerium 2,4,6-triphosphono-1,3,5-triazine (CeTPT) were resoundingly fabricated. Novel cPBI networks with tetrafunctional N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) were synthesized. It is noteworthy that a new high-temperature proton conductor CeTPT was added. CeTPT contained three phosphonic acid groups, which offered good proton conductivity at moderate-to-low humidity and had good thermal stability. Tetrafunctional crosslinker TGDDM had multiple functional groups. With a relatively low crosslinking degree (CLD), the mechanical properties, dimensional stability, and oxidative resistance of the membranes were efficiently improved. The low CLD and good physicochemical stability also allowed high doping levels of CeTPT (up to 50%) and consequently high proton conductivity. At 180 °C and 50% RH, the proton conductivity of cPBI-5-CeTPT-50 and cPBI-10-CeTPT-50 was 0.072 and 0.068 S cm–¹, respectively. The cPBI-CeTPT membranes showed good methanol resistance and membrane selectivity, and thus the membranes were suitable for direct methanol fuel cells.

Poly-hydroxyethylidene-1,1-diphosphonic acid (PHEDP) as a highly effective water-retentive and proton-conductive material for low-humidity proton exchange membranes

To improve the proton conductivity and fuel cell performance of a perfluorosulfonic acid (PFSA) membrane under low-humidity conditions, a series of poly-hydroxyethylidene-1,1-diphosphonic acid (PHEDP) materials are designed and synthesized through a self-polycondensation reaction. Self-humidifying proton exchange membranes are fabricated by combining PHEDP with commercial PFSA resin, then optimized by using various amounts of PHEDP. The experimental results show that the PHEDP/PFSA composite membrane provides a proton conductivity of up to 28.2 mS cm−1 at 30% RH and up to 13.6 mS cm−1 at 10% RH, which are respectively 5.6 and 13.6 times higher than a pristine PFSA membrane, and 4.5 and 6.8 times higher than a commercial Gore 740 membrane. In addition, the PHEDP/PFSA composite membrane exhibits superior fuel cell performance and low ohmic resistance under low relative humidity. The results show that the PHEDP/PFSA composite membrane's superior performance arises from its ability to absorb and retain more water in the membrane, enhance water transport from cathode to anode, and form new proton transport channels, indicating that the PHEDP/PFSA composite membrane has great potential for application in low relative humidity.

Composite Nafion Membranes with CaTiO3-δ Additive for Possible Applications in Electrochemical Devices.

A composite membrane based on a Nafion polymer matrix incorporating a non-stoichiometric calcium titanium oxide (CaTiO3−δ) additive was synthesized and characterized by means of thermal analysis, dynamic mechanical analysis, and broadband dielectric spectroscopy at different filler contents; namely two concentrations of 5 and 10 wt.% of the CaTiO3−δ additive, with respect to the dry Nafion content, were considered. The membrane with the lower amount of additive displayed the highest water affinity and the highest conductivity, indicating that a too-high dose of additive can be detrimental for these particular properties. The mechanical properties of the composite membranes are similar to those of the plain Nafion membrane and are even slightly improved by the filler addition. These findings indicate that perovskite oxides can be useful as a water-retention and reinforcing additive in low-humidity proton-exchange membranes.

Preparation and properties of ZrPA doped CMPSU cross-linked PBI based high temperature and low humidity proton exchange membranes

Poly[4,4′-(diphenyl ether)-5,5′-bibenzimidazole] (oPBI) based high temperature proton exchange membranes are prepared by covalent cross-linking with chloromethylated polysulfone (CMPSU) and doping with zirconium phytate (ZrPA). ZrPA is synthesized as the proton conductor through a facile method from zirconyl chloride and phytic acid which is abundant and readily available. oPBI is cross-linked by CMPSU and that hydrogen bonds are formed between ZrPA and oPBI-CMPSU. The composite membranes are dense without through holes when doping with ZrPA. The composite membranes exhibit good thermal stability below 140 °C. Meanwhile, the composite membranes reveal good mechanical strength and methanol resistance. The oxidative stability is improved because of cross-linking and the doping of ZrPA. Conductivities of oPBI-CMPSU/ZrPA at different temperatures and relative humidity (RH) are investigated. At 100% RH, 50% RH and 0 RH, the conductivity of oPBI-CMPSU(20%)/ZrPA(30%) can reach 0.072 S/cm, 0.025 S/cm and 0.012 S/cm at 140 °C, respectively. Although the proton conductivity of the composite membrane was not particularly high at 100% RH, the composite membrane comparatively exhibited good proton conductivity at high temperature and at 50% RH and 0 RH.

Sulfonated graphene oxide/Nafion composite membranes for high temperature and low humidity proton exchange membrane fuel cells.

Iron oxide (Fe3O4) nanoparticles anchored over sulfonated graphene oxide (SGO) and Nafion/Fe3O4–SGO composites were fabricated and applied as potential proton exchange membranes in proton exchange membrane fuel cells (PEMFCs) operated at high temperature and low humidity. Fe3O4 nanoparticles bridge SGO and Nafion through electrostatic interaction/hydrogen bonding and increased the intrinsic thermal and mechanical stabilities of Nafion/Fe3O4–SGO composite membranes. Nafion/Fe3O4–SGO composite membranes increased the compactness of ionic domains and enhanced the water absorption and proton conductivity while restricting hydrogen permeability across the membranes. The proton conductivity of Nafion/Fe3O4–SGO (3 wt%) composite membrane at 120 °C under 20% relative humidity (RH) was 11.62 mS cm−1, which is 4.74 fold higher than that of a pristine recast Nafion membrane. PEMFC containing the Nafion/Fe3O4–SGO composite membrane delivered a peak power density of 258.82 mW cm−2 at a load current density of 640.73 mA cm−2 while operating at 120 °C under 25% RH and ambient pressure. In contrast, under identical operating conditions, a peak power density of only 144.89 mW cm−2 was achieved with the pristine recast Nafion membrane at a load current density of 431.36 mA cm−2. Thus, Nafion/Fe3O4–SGO composite membranes can be used to address various critical problems associated with commercial Nafion membranes in PEMFC applications.

Highly Sulfonated Diamine Synthesized Polyimides and Protic Ionic Liquid Composite Membranes Improve PEM Conductivity

A novel sulfonated diamine was synthesized from 1,4-bis(4-aminophenoxy) benzene [pBAB]. Sulfonated polyimides (SPIs) were synthesized from sulfonated pBAB, 1,4-bis(4-aminophenoxy-2-sulfonic acid) benzenesulfonic acid [pBABTS], various diamines and aromatic dianhydrides. Composite proton exchange membranes (PEMs) made of novel SPIs and a protic ionic liquid (PIL) 1-vinyl-3-H-imidazolium trifluoromethanesulfonate [VIm][OTf] showed substantially increased conductivity. We prepared an SPI/PIL composite PEM using pBABTS, 4,4′-(9-fluorenylidene) dianiline (9FDA) as diamine, 3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride (DSDA) as dianhydride and 40 wt % [VIm][OTf] with a high conductivity of 16 mS/cm at 120 °C and anhydrous condition. pBABTS offered better conductivity, since the chemical structure had more sulfonated groups that provide increased conductivity. The new composite membrane could be a promising anhydrous or low-humidity PEM for intermediate or high-temperature fuel cells.

Synthesis and characterization of sulfonated polymers containing triazoles as low-humidity proton exchange membranes

A series of copolymers, sulfonated poly (aryl ether ketone sulfones) containing triazoles (SPAEKST), were synthesized by direct polycondensation reactions. The content of sulfonic acid and triazole groups was controlled by adjusting the molar ratio of feeding. The structures of triazole monomer and SPAEKST copolymers were confirmed by their 1H NMR and FTIR spectral analyses. The performance of membranes such as thermal and oxidative stabilities was clearly improved with increasing content of triazole groups. The morphology of SPAEKST membranes was investigated by TEM analyses, and the results indicate that the sulfonic acid groups were dispersed evenly. No clear phase separation was observed. The contact angle tests showed that the presence of triazoles clearly improved the hydrophilicity of membranes. The water desorption curves showed that the water retention of membranes increased with increasing content of triazole groups. The proton conduction of membranes exhibited a low dependence on relative humidity. At 80 °C, the proton conductivity of SPAEKST-30 % reached to 1.1 mScm−1 under 20 % RH.

Fe0.4Ta0.5P2O7-based composite membrane for high-temperature, low-humidity proton exchange membrane fuel cells

An inorganic–organic composite membrane composed of Fe0.4Ta0.5P2O7 (FTPO) and sulfonated polystyrene-b-poly(ethylene/butylene)-b-polystyrene (sSEBS) is prepared and characterized. To gain satisfaction of both the proton conductivity and mechanical strength in composite membranes, the optimal content of sSEBS was determined to be 30wt%, which resulted in high proton conductivities of approximately 0.01Scm−1 between 50 and 150°C even under an unhumidified condition, a tensile strength of 4.1MPa, and an elongation at break of 613%. A homogeneous distribution of the FTPO particles in the matrix was achieved at the composite membrane thickness greater than 50μm, providing gas-impermeability and low area-specific resistance (ASR) of the membrane (0.17Ωcm2 at 150°C and H2O vapor concentration of 30.8vol%). Fuel cell tests using the composite membrane provided peak power densities of 265 and 303mWcm−2 at 150°C under an unhumidified condition and at a H2O vapor concentration of 30.8vol%, respectively.

Quantitative estimation of water vapor distribution in low-humidity proton exchange membrane fuel cell using humidity test paper

To prevent performance degradation due to membrane dryout in proton exchange membrane fuel cells (PEMFCs) under low-humidity conditions, fundamental understanding of water transport and reaction mechanism on anode side in operating fuel cell is required. In this study, the water vapor distribution along the anode flow channel of a low-humidity PEMFC was quantitatively evaluated by using humidity test paper (HTP), and the effects of inlet gas humidification and flow configuration on the water distribution in the anode were investigated. HTP is a test paper for detecting water vapor in the range of 20–90% RH, and makes it possible to directly visualize the water distribution in the gas flow channel of the transparent PEMFC during operation. Furthermore, the locally resolved current density was also measured using segmented cell structure concept. It was found that the high humidification of the anode inlet gas increases the water vapor concentration in the anode channel and prevents the membrane dehydration. In addition, the counter-flow configuration effectively improves the water management near the anode inlet region of the low-humidity PEMFC and enhances the proton conductivity in the electrolyte membrane.

Sulfonated SBA-15 mesoporous silica-incorporated sulfonated poly(phenylsulfone) composite membranes for low-humidity proton exchange membrane fuel cells: Anomalous behavior of humidity-dependent proton conductivity

Sulfonated SBA-15 mesoporous silica (SM-SiO2)-incorporated sulfonated poly(phenylsulfone) (SPPSU) composite membranes are fabricated for potential application in low-humidity proton exchange membrane fuel cells (PEMFCs). The SM-SiO2 particles are synthesized using tetraethoxy silane (TEOS) as a mechanical framework precursor, Pluronic 123 triblock copolymer as a mesopore-forming template, and mercaptopropyl trimethoxysilane (MPTMS) as a sulfonation agent. A distinctive feature of the SM-SiO2 particles is the long-range ordered 1-D skeleton of hexagonally aligned mesoporous cylindrical channels bearing sulfonic acid groups. Based on a comprehensive characterization of the SM-SiO2 particles, the effect of SM-SiO2 (as a functional filler) addition on the proton conductivity of the SPPSU composite membrane is examined as a function of temperature and relative humidity. An intriguing finding is that the proton conductivity of the SPPSU composite membrane exhibits a strong dependence on the relative humidity of measurement conditions. This anomalous behavior is further discussed with an in-depth consideration of the characteristics and dispersion state of SM-SiO2 particles, which affect the tortuous path for proton movement, water uptake, and state of water. Notably, at low-humidity conditions, the SM-SiO2 particles in the SPPSU composite membrane serve as an effective water reservoir to tightly retain water molecules and also as a supplementary proton conductor, whereas they behave as a barrier to proton transport at fully hydrated conditions.

Effect of PTFE content in gas diffusion layer based on Nafion ®/PTFE membrane for low humidity proton exchange membrane fuel cell

This research was carried out to prepare high performance membrane-electrode assembly for proton exchange membrane fuel cell at low humidity condition. It had investigated the effect of the Nafion ®/PTFE proton exchange membrane, impregnating porous PTFE membrane with Nafion ® solution, in the gas diffusion medium and microporous layer on the cell performance under various humidity conditions. The Nafion ®/PTFE decreases the back diffusion distance of product water from cathode to anode side at low humidity condition, caused by the property of high tensile strength. It is found that the optimum PTFE content is 40 wt% of the gas diffusion medium and 30 wt% of the microporous layer at low humidity condition, respectively. The optimum PTFE treatment in the two layers can facilitate the reactant gas and the back diffusion of product water from cathode side to anode side to provide sufficient proton conductivity of membrane. The highest current density was 955 mA/cm 2 occurred at the cell potential of 0.6 V.

In situ hybrid Nafion/SiO 2–P 2O 5 proton conductors for high-temperature and low-humidity proton exchange membrane fuel cells

A proton-conducting membrane demonstrating excellent proton conductivity at high-temperature/low-humidity conditions as well as at fully hydrated states is an urgent demand for proton exchange membrane fuel cells (PEMFC). In this study, in a bid to achieve this goal, we develop a new hybrid membrane, which is based on incorporating SiO 2–P 2O 5 glass electrolytes into hydrophilic channels of Nafion115 by in situ sol–gel synthesis of tetraethoxysilane (TEOS) and trimethylphosphate (TMP). The effect of SiO 2–P 2O 5 content on the morphology, state of water, and water uptake of the hybrid membranes is quantitatively identified. Not only the well-connected/enlarged hydrophilic channels but also the increase in the number of free/bound water molecules is observed in the hybrid membranes. These interesting features are expected to enable the hybrid membranes to present the higher proton conductivity than the pristine Nafion115, which becomes more noticeable at high-temperature/low-humidity conditions.

High Temperature, Low Humidity Proton Exchange Membrane Based on an Inorganic–Organic Hybrid Structure

A high temperature and low humidity composite membrane consisting of Sn 0.95 Al 0.05 P 2 O 7 and sulfonated polystyrene-b-poly(ethylene/butylene)-b-polystyrene (sSEBS) as inorganic and organic materials, respectively, was prepared and characterized. A homogeneous distribution of the Sn 0.95 Al 0.05 P 2 O 7 particles in the matrix was accomplished in the thickness range of 25―80 μm, providing an elongation at break above 400%, which is approximately two times higher than that for Nafion. Moreover, moderate proton conductivities of sSEBS improved proton transfer between the Sn 0.95 Al 0.05 P 2 O 7 particles in the matrix, resulting in a proton conductivity of approximately 0.01 S cm ―1 at 130°C without any humidification, which is 3 or more orders of magnitude higher than that for Nafion under the same conditions.

New sulfonated polybenzimidazole (SPBI) copolymer-based proton-exchange membranes for fuel cells

The synthesis and characterization of sulfonated polybenzimidazole (SPBI) copolymers as proton-exchange membranes (PEMs) for fuel cells are described in this paper. A one-step high temperature polymerization method was used to synthesize the SPBI copolymers from 3,3′-diaminobenzidine (DABD), 4,4′-oxybis(benzoic acid) (OBBA), and two sulfonated dicarboxylic acids, i.e., 5-sulfoisophthalic acid (SIPA) and 4,8-disulfonyl-2,6-naphthalenedicarboxylic acid (DSNDA), using polyphosphoric acid (PPA) as the solvent. The pure SPBI copolymer membrane was prepared by the traditional solution-casting technique (technique 1), and the SPBI/H 3PO 4 blend membrane was prepared through a new direct hot-casting and in situ phase inversion technique (technique 2). The membranes prepared from both techniques possessed desirable mechanical, chemical, thermal, and hydrolytic stability. However, the pure SPBI copolymer membranes from technique 1 exhibited very poor proton conductivities since most of the sulfonated groups in SPBIs were neutralized by the basic imidazole groups and became deprotonated sulfonated groups. On the other hand, the SPBI/H 3PO 4 blend membrane from technique 2 showed extremely high conductivities (>0.1 S/cm) at high temperatures (>120 °C) and low relative humidities (RHs) (even at anhydrous conditions), which has great potential to be used as high temperature and low humidity PEMs for fuel cells.

Synthesis and characterization of poly(arylene ether sulfone)-b-polybenzimidazole copolymers for high temperature low humidity proton exchange membrane fuel cells

Multiblock copolymers based on poly(arylene ether sulfone) and polybenzimidazole (PBI) with different block lengths were synthesized by coupling carboxyl functional aromatic poly(arylene ethers) with ortho diamino functional PBI oligomers in NMP, selectively doped with phosphoric acid, and evaluated as a high temperature proton exchange membrane (PEM). Transparent and ductile membranes were produced by solvent casting from DMAc. From dynamic mechanical analysis (DMA), the neat copolymer membranes showed two distinct glass transition temperatures which implies the existence of a nanostructured morphology in the membranes. These two nanophases became more distinct with increasing block length. The membranes were immersed in various concentrations of phosphoric acid solution to produce the proton conductivity. The doping level increased with increasing concentration of the acid solution and a maximum doping level of 12 was achieved when 14.6M phosphoric acid solution was used. The acid doped membranes showed significantly reduced swelling behavior compared to a control conventional phosphoric acid doped PBI homopolymer system which appears to be related to the selective sorption into the PBI phase. The ionic conductivity of the doped samples at 200°C afforded up to 47mS/cm without external humidification. The protonic conductivity was found to increase with block length at a given doping level, reflecting the sharpness of the nanophase separation and the effect was even more prominent at a low doping level of 6–7. It is suggested that the phosphoric acid doped multiblock copolymer system would be a strong candidate for high temperature and low relative humidity PEM applications such as those required for stationary power.