Polymer electrolyte membrane water electrolyser with Aquivion short side chain perfluorosulfonic acid ionomer binder in catalyst layers

The Aquivion^® short-side-chain (SSC) perfluorosulfonic acid (PFSA) ionomer was adopted in catalyst layers (CL) of polymer electrolyte membrane water electrolysers (PEMWE) instead of long-side-chain (LSC) Nafion^® ionomer. The effects of SSC ionomer content in CL for oxygen evolution reaction were studied in half cell with cyclic voltammetry and steady state linear sweep. In a single cell test the MEA with SSC-PFSA Aquivion^® ionomer exhibited better thermal stability than the one with LSC-PFSA Nafion^® ionomer at 90 °C. The cell voltage at a current density of 1 A cm⁻² was 1.63 V at 90 °C using the SSC-PFSA Aquivion^® ionomer binder, Nafion^® 117 membrane, and without back pressurizing. In a continuous operation the cell voltage degradation rate of the MEA using Aquivion^® ionomer binder was only about 0.82 mV h⁻¹.     

A novel catalyst coated membrane embedded with Cs-substituted phosphotungstates for proton exchange membrane water electrolysis

Catalyst coated membrane (CCM) is the core component of proton exchange membrane (PEM) water electrolysis and the main place for electrochemical reaction and mass transfer. Its properties directly affect the performance of PEM water electrolysis. Aiming at decreasing the polarization loss and the ohmic loss, a novel CCM embedded with Cs_1.5HPA in the skeleton of the Nafion^® ionomer and the Nafion^® membrane was prepared and possessed functionality of improved protonic conductivity. Meanwhile, the Cs_1.5HPA-Nafion ionomer content in the catalyst layers was further optimized. The SEM, EDS and pore volume distribution measurement showed that the Cs_1.5HPA embedded in the CCM without agglomeration and the micropore and mesopore were well distributed in the catalyst layer. Furthermore, CCMs were tested in a PEM water electrolyser at 80 °C, beneficial effects on both the Tafel slope and the iR loss were obtained due to the improved protonic conductivity as well as the appropriate pore structure and increased specific pore volume. The performance of the electrolyser cell was obviously improved with the novel CCM. The highest cell performance of 1.59 V at 2 A cm⁻² was achieved at 80 °C. At 35 °C and 300 mA cm⁻², the cell showed good durability within the test period of up to 570 h.     

Study of catalyst sprayed membrane under irradiation method to prepare high performance membrane electrode assemblies for solid polymer electrolyte water electrolysis

In this work, a catalyst sprayed membrane under irradiation (CSMUI) method was investigated to develop high performance membrane electrode assembly (MEA) for solid polymer electrolyte (SPE) water electrolysis. The water electrolysis performance and properties of the prepared MEA were evaluated and analyzed by polarization curves, electrochemistry impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The characterizations revealed that the CSMUI method is very effective for preparing high performance MEA for SPE water electrolysis: the cell voltage can be as low as 1.564 V at 1 A cm⁻² and the terminal voltage is only 1.669 V at 2 A cm⁻², which are among the best results yet reported for SPE water electrolysis with IrO₂ catalyst. Also, it is found that the noble metal catalysts loadings of the MEA prepared by this method can be greatly decreased without significant performance degradation. At a current density of 1 A cm⁻², the MEA showed good stability for water electrolysis operating: the cell voltage remained at 1.60 V without obvious deterioration after 105 h operation under atmosphere pressure and 80 °C.     

Antimony doped tin oxides and their composites with tin pyrophosphates as catalyst supports for oxygen evolution reaction in proton exchange membrane water electrolysis

Proton exchange membrane water electrolysers operating at typically 80 °C or at further elevated temperatures suffer from insufficient catalyst activity and durability. In this work, antimony doped tin oxide nanoparticles were synthesized and further doped with an inorganic proton conducting phase based on tin pyrophosphates as the catalyst support. The materials showed an overall conductivity of 0.57 S cm⁻¹ at 130 °C under the water vapor atmosphere with a contribution of the proton conduction. Using this composite support, iridium oxide nanoparticle catalysts were prepared and characterized in sulfuric and phosphoric acid electrolytes, showing much enhanced catalytic activity. Electrolyzer tests were conducted at both 80 °C with an Aquivion^™ membrane and at 130 °C with a phosphoric acid doped Aquivion^™ membrane. Significant improvement in the anodic kinetics was achieved on the composite supported catalysts at 130 °C although the electrolyzer cells showed higher ohmic resistance primarily from the membrane and catalyst layer. A durability test of electrolyzer cells was carried out at 130 °C under a current density of 400 mA cm⁻² in a period of up to 760 h, showing rather good stability of the system.     

Phosphoric acid doped membranes based on Nafion, PBI and their blends - Membrane preparation, characterization and steam electrolysis testing

Proton exchange membrane steam electrolysis at temperatures above 100 °C has several advantages from thermodynamic, kinetic and engineering points of view. A key material for this technology is the high temperature proton exchange membrane. In this work a novel procedure for preparation of Nafion^® and polybenzimidazole blend membranes was developed. Homogeneous binary membranes covering the whole composition range were prepared and characterized with respect to chemical and physiochemical properties such as water uptake, phosphoric acid doping, oxidative stability, mechanical strength and proton conductivity. An MEA based on phosphoric acid doped Nafion^® was operated at 130 °C at ambient pressure with a current density of 300 mA cm⁻² at 1.75 V, with no membrane degradation observed during a test of 90 h. The PBI based MEAs showed better polarization curves (500 mA cm⁻² at 1.75 V) but poor durability.     

Effect of crosslinking on the durability and electrochemical performance of sulfonated aromatic polymer membranes at elevated temperatures

End-group crosslinked sulfonated poly(arylene sulfide nitrile) (XESPSN) membranes are prepared to investigate the effect of crosslinking on the properties of sulfonated aromatic polymer membranes at elevated temperatures (>100 °C). The morphological transformation during annealing and crosslinking is confirmed by atomic force microscopy. The XESPSN membranes show outstanding thermal and mechanical properties compared to pristine and non-crosslinked ESPSN and Nafion^® up to 200 °C. In addition, the XESPSN membranes exhibit higher proton conductivities (0.011–0.023 S cm⁻¹) than the as-prepared pristine ESPSN (0.004 S cm⁻¹), particularly at elevated temperature (120 °C) and low relative humidity (35%) conditions due to its well-ordered hydrophilic morphology after crosslinking. Therefore, the XESPSN membranes demonstrate significantly improved maximum power densities (415–485 mW cm⁻²) compared to the ESPSN (281 mW cm⁻²) and Nafion^® (314 mW cm⁻²) membranes in single cell performance tests conducted at 120 °C and 35% relative humidity. Furthermore, the XESPSN membrane exhibits a much longer duration than the ESPSN membrane during fuel cell operation under a constant current load as a result of its improved mechanical and thermal stabilities.     

Preparation and characterization of partial-cocrystallized catalyst-coated membrane for solid polymer electrolyte water electrolysis

A novel catalyst-coated membrane (CCM) for solid polymer electrolyte water electrolysis was fabricated by together crystallizing partial-crystallized Nafion membrane and catalyst layers. The properties and performance of the partial-cocrystallized CCM (PCCCM) were evaluated and analyzed by destructive soaking test, scanning electron microscope, mercury intrusion and single cell test. The results revealed that the optimum annealing temperature and time for fabricating partial-crystallized Nafion membrane and PCCCM was 100 °C for 4 h and 120 °C for 4 h, respectively. The PCCCM not only possessed much stronger cohesion between membrane and catalyst layers, but also had higher porosity than conventional CCM. The electrolysis voltage of the SPE water electrolyser with the new CCM was as low as 1.748 V at 2000 mA cm⁻² under 80 °C and atmospheric pressure. Moreover, there was no obvious increase of electrolysis voltage during stability test conducted under 2000 mA cm⁻² for about 180 h.     

Membrane electrode assemblies with low noble metal loadings for hydrogen production from solid polymer electrolyte water electrolysis

High performance membrane electrode assemblies (MEAs) with low noble metal loadings (NMLs) were developed for solid polymer electrolyte (SPE) water electrolysis. The electrochemical and physical characterization of the MEAs was performed by I–V curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Even though the total NML was lowered to 0.38 mg cm⁻², it still reached a high performance of 1.633 V at 2 A cm⁻² and 80 °C, with IrO₂ as anode catalyst. The influences of the ionomer content in the anode catalyst layer (CL) and the cell temperature were investigated with the purpose of optimizing the performance. SEM and EIS measurements revealed that the MEA with low NML has very thin porous cathode and anode CLs that get intimate contact with the electrolyte membrane, which makes a reduced mass transport limitation and lower ohmic resistance of the MEA. A short-term water electrolysis operation at 1 A cm⁻² showed that the MEA has good stability: the cell voltage maintained at ∼1.60 V without distinct degradation after 122 h operation at 80 °C and atmospheric pressure.     

Efficient multi-metallic anode catalysts in a PEM water electrolyzer

Anode catalysts synthesized by the thermal decomposition method were used for splitting water in PEM electrolysis cells. Although the area resistance of the ternary anode materials increased, the Ti content in the ruthenium and iridium based catalysts have led to an energy consumption of 4.5 kWh/Nm³(H₂) at 60 °C. The Membrane Electrode Assemblies have given information on the strong dependence of the membrane thickness. The crossover of hydrogen through Nafion^®117 is two-fold lower than that measured in the presence of Nafion^®115. Life testing was attempted with supplying the electrolyzer by solar power source. Importantly, the proton exchange membrane water electrolyzer (PEMWE) cell has involved a constant cell voltage at 1 A cm⁻² over 800 h durability tests.     

Nanosphere-structured composites consisting of Cs-substituted phosphotungstates and antimony doped tin oxides as catalyst supports for proton exchange membrane liquid water electrolysis

Proton exchange membrane liquid water electrolyser operated blow 80 °C suffers from insufficient catalyst activity and durability due to the slow oxygen evolution kinetics and poor stability. Aiming at enhancing oxygen electrode kinetics and stability, composite materials consisting of antimony doped tin oxide and Cs-substituted phosphotungstate were synthesized as the support of iridium oxide and possessed functionality of mixed electronic and protonic conductivity. At 80 °C under dry ambient atmosphere, the materials showed an overall conductivity of 0.33 S cm⁻¹. The supported IrO₂ catalysts were characterized in sulfuric acid electrolyte, showing significant enhancement of the oxygen evolution reaction (OER) activity. Electrolyser tests of the catalysts were conducted at 80 °C with a Nafion membrane. At an IrO₂ loading of 0.75 mg cm⁻² and a Pt loading of 0.2 mg cm⁻², the cell performance of a current density of 2 A cm⁻² at 1.66 V was achieved. The cell showed good durability at 35 °C under a current density of 300 mA cm⁻² in a period of 464 h.     

Properties and morphology of Nafion/polytetrafluoroethylene composite membrane fabricated by a solution-spray process

The Nafion/polytetrafluoroethylene (Nafion/PTFE) composite membrane is fabricated by a solution-spray process. The performance and morphology of the composite membrane are studied in terms of the mechanical properties, conductivity, and permeability. The results of TEM and X-ray studies show that the morphologies of crystalline and ion cluster of the perfluorosulfonated acid (PFSA) in composite membrane are apparently similar to that of Nafion^® NR211 membrane. The composite membrane has higher stiffness and strength and lower swelling than that of Nafion^® NR211. The conductivity at 85 °C of 0.375 S cm⁻¹ is relatively high in comparison to that of 0.300 S cm⁻¹ for Nafion^® NR211. The 20 kW stack with the composite membranes is evaluated. The mean single cell voltage is 0.67 V @1000 mA cm⁻². The stack has behaved performance uniformity and steadily operated under low humidifying condition. In consideration of the integration of complex structure and perfect morphology, the solution-spray process is feasible for composite proton exchange membrane manufacture.     

High performance membrane-electrode assembly based on a surface-modified membrane

A surface-modified membrane is prepared using a sputtering technique that deposits gold directly on a Nafion^® 115 membrane surface that is roughened with silicon carbide paper. The surface-modified membranes are characterized by means of a scanning electron microscope (SEM), differential scanning calorimetry (DSC), and water contact-angle analysis. A single direct methanol fuel cell (DMFC) with a surface-modified membrane exhibits enhanced performance (160 mW cm⁻²), while a bare Nafion^® 115 cell yields 113 mW cm⁻² at 0.4 V and an operating temperature of 70 °C. From FE-SEM images and CO_ad stripping voltammograms, it is also found that the gold layer is composed of clusters of porous nodule-like particles, which indicates that an anode with nodule-like gold leads to the preferential oxidation of carbon monoxide. These results suggest that the topology of gold in the interfacial area and its electrocatalytic nature may be the critical factors that affect DMFC performance.     

Temperature-dependent performance of the polymer electrolyte membrane fuel cell using short-side-chain perfluorosulfonic acid ionomer

We report on polymer electrolyte membrane fuel cells (PEMFCs) that function at high temperature and low humidity conditions based on short-side-chain perfluorosulfonic acid ionomer (SSC-PFSA). The PEMFCs fabricated with both SSC-PFSA membrane and ionomer exhibit higher performances than those with long-side-chain (LSC) PFSA at temperatures higher than 100 °C. The SSC-PFSA cell delivers 2.43 times higher current density (0.524 A cm⁻¹) at a potential of 0.6 V than LSC-PFSA cell at 140 °C and 20% relative humidity (RH). Such a higher performance at the elevated temperature is confirmed from the better membrane properties that are effective for an operation of high temperature fuel cell. From the characterization technique of TGA, XRD, FT-IR, water uptake and tensile test, we found that the SSC-PFSA membrane shows thermal stability by higher crystallinity, and chemical/mechanical stability than the LSC-PFSA membrane at high temperature. These fine properties are found to be the factor for applying Aquivion™ E87-05S membrane rather than Nafion^® 212 membrane for a high temperature fuel cell.     

Protonic conductivity and viscoelastic behaviour of Nafion membranes with periodic mesoporous organosilica fillers

Benzene-bridged periodic mesoporous organosilicas functionalised with sulfonic acid (S-Ph-PMO) are explored as fillers to improve the protonic conductivity and the viscoelastic properties of Nafion^®. Homogeneous membranes with 5, 10 and 20 wt.% submicrometric S-Ph-PMO particles (roughly corresponding to 11, 20 and 36 vol.%) were obtained by control of the casting suspensions. The three composite membranes have acid loads and water uptake values similar to Nafion^®. The storage modulus of the 20 wt.% S-Ph-PMO composite (0.2 GPa at 100 °C and 0.05 GPa at 140 °C) is 2.5–15 times higher than for pure Nafion^® (respectively 0.08 and 0.005 GPa), denoting a positive effect of the fillers on the mechanical resistance of the membranes, also observed for lower filler fractions. The protonic conductivity of the composite membranes at 20% relative humidity (RH) and 40 °C is up to 1.5 orders of magnitude higher than for Nafion^®. The magnitude of the effect decreases with increasing humidity, with the best composite attaining 0.03 S cm⁻¹ at 120 °C/40% RH, 3 times more than Nafion^®. All membranes have similar behaviour at 98% RH, showing a maximum of 0.2 S cm⁻¹ at 94 °C, with the composites still showing slightly better performance. The results are discussed in terms of the effect of the fillers on reducing the internal swelling pressure and the activation energy for proton migration.     

Development and testing of a novel catalyst-coated membrane with platinum-free catalysts for alkaline water electrolysis

A stable, platinum-free catalyst-coated anion-exchange membrane with a promising performance for alkaline water electrolysis as an energy conversion technology was prepared and tested. A hot plate spraying technique used to deposit electrodes 35 or 120 μm thick on the surface of an anion-selective polymer electrolyte membrane. These thicknesses of 35 and 120 μm corresponding to the catalyst load of 2.5 and 10 mg cm⁻². The platinum free catalysts based on NiCo₂O₄ for anode and NiFe₂O₄ for cathode were used together with anion selective polymer binder in the catalyst/binder ratio equal to 9:1. The performance of the prepared membrane-electrode assembly was verified under conditions of alkaline water electrolysis using different concentrations of liquid electrolyte ranging from 1 to 15 wt% KOH. The electrolyser performance was compared to a cell utilizing a catalyst-coated Ni foam as the electrodes. The prepared membrane-electrode assembly stability at a current load of 0.25 A cm⁻² was verified by a 72-hour electrolysis test. The results of the experiments indicated the possibility of a significant reduction of the catalyst loading compared to a catalyst-coated substrate approach.     

Double cross-linked polyetheretherketone proton exchange membrane for fuel cell

The proton exchange membrane based on polyetheretherketone was prepared via two steps of cross-linking. The properties of the double cross-linked membrane (water uptake, proton conductivity, methanol permeability and thermal stability) have been investigated for fuel cell applications. The prepared membrane exhibited relatively high proton conductivity, 3.2 × 10⁻² S cm⁻¹ at room temperature and 5.8 × 10⁻² S cm⁻¹ at 80 °C. The second cross-linking significantly decreased the water uptake of the membrane. The performance of direct methanol fuel cell was slightly improved as compared to Nafion^® 117 due to its low methanol permeability. The results indicated that the double cross-linked membrane is a promising candidate for the polymer electrolyte membrane fuel cell, especially for the direct methanol fuel cell due to its low methanol permeability and high stability in a methanol solution.     

Use of in situ polymerized phenol-formaldehyde resin to modify a Nafion membrane for the direct methanol fuel cell

Commercial Nafion^®-115 (trademark registered to DuPont) membranes were modified by in situ polymerized phenol formaldehyde resin (PFR) to suppress methanol crossover, and SO₃⁻ groups were introduced to PFR by post-sulfonatation. A series of membranes with different sulfonated phenol formaldehyde resin (sPFR) loadings have been fabricated and investigated. SEM-EDX characterization shows that the PFR was well dispersed throughout the Nafion^® membrane. The composite membranes have a similar or slightly lower proton conductivity compared with a native Nafion^® membrane, but show a significant reduction in methanol crossover (the methanol permeability of sPFR/Nafion^® composite membrane with 2.3 wt.% sPFR loading was 1.5 × 10⁻⁶ cm² s⁻¹, compared with the 2.5 × 10⁻⁶ cm² s⁻¹ for the native Nafion^® membrane). In direct methanol fuel cell (DMFC) evaluation, the membrane electrode assembly (MEA) using a composite membrane with a 2.3 wt.% sPFR loading shows a higher performance than that of a native Nafion^® membrane with 1 M methanol feed, and at higher methanol concentrations (5 M), the composite membrane achieved a 114 mW cm⁻² maximum power density, while the maximum power density of the native Nafion^® was only 78 mW cm⁻².     

Composite membranes based on a sulfonated poly(arylene ether sulfone) and proton-conducting hybrid silica particles for high temperature PEMFCs

The organic-inorganic composite membranes are prepared by inserting poly(styrene sulfonate)-grafted silica particles into a polymer matrix of sulfonated poly(arylene ether sulfone) copolymer. The first step consisted in using atom transfer radical polymerization method to prepare surface-modified silica particles grafted with sodium 4-styrenesulfonate, referred to as PSS-g-SiO₂. Ion exchange capacities up to 2.4 meq/g are obtained for these modified silica particles. In a second step, a sulfonated poly(arylene ether sulfone) copolymer is synthesized via nucleophilic step polymerization of sulfonated 4,4′-dichlorodiphenyl sulfone, 4,4′-dichlorodiphenyl sulfone and phenolphthalin monomers in the presence of potassium carbonate. The copolymer is blended with various amounts of silica particles to form organic-inorganic composite membranes. Esterification reaction is carried out between silica particles and the sulfonated polymer chains by thermal treatment in the presence of sodium hypophosphite, which catalyzed the esterification reaction. The water uptake, proton conductivity, and thermal decomposition temperature of the membranes are measured. All composite membranes show better water uptake and proton conductivity than the unmodified membrane. Moreover, the membranes are tested in a commercial single cell at 80 °C and 120 °C in humidified H₂/air under different relative humidity conditions. The composite membrane containing 10%(w/w) of PSS-g-SiO₂ particles, which have ester bonds between polymer chains and silica particles, showed the best performance of 690 mA cm⁻² at 0.6 V, 120 °C and 30 %RH, even higher than the commercial Nafion^® 112 membrane.     

Development and characterization of covalently cross-linked SPEEK/Cs-TPA/CeO2 composite membrane and membrane electrode assembly for water electrolysis

Covalently cross-linked SPEEK/Cs-TPA/CeO₂ composite membrane was prepared for the polymer electrolyte membrane water electrolysis. Tungstophosphoric acid (TPA) with a cesium was added to the SPEEK to increase proton conductivity. CeO₂ was used to scavenge free radicals which attack the membrane in the water electrolysis and to improve the durability of the membrane. The composite membrane featured the electrochemical characteristics, such as 0.130 S/cm of proton conductivity at 80 °C, and 2.324 meq./g-dry-memb. of ion-exchange capacity. Pt(NH₃)₄Cl₂, Pd(NH₃)₄Cl₂, RhCl₃ and Co(NH₆)₄Cl₃ were used to prepare a variety of the membrane electrode assemblies (MEAs) as electrocatalytic precursors. Electrochemical activity surface area (ESA) of the Pt–Pd electrode prepared with 2 mM Pt(NH₃)₄Cl₂ and 2 mM Pd(NH₃)₄Cl₂ showed the best properties of 26.2 m²/g with CL-SPEEK/Cs-TPA/CeO₂ membrane. In water electrolysis performance, the cell voltage of Pd/PEM/Pt–Pd MEA with CL-SPEEK/Cs-TPA/CeO₂(1%) composite membrane showed cell property of 1.82 V at 1 A cm⁻² and 80 °C.     

Preparation and performance of nano silica/Nafion composite membrane for proton exchange membrane fuel cells

Composite membranes made from Nafion ionomer with nano phosphonic acid-functionalised silica and colloidal silica were prepared and evaluated for proton exchange membrane fuel cells (PEMFCs) operating at elevated temperature and low relative humidity (RH). The phosphonic acid-functionalised silica additive obtained from a sol–gel process was well incorporated into Nafion membrane. The particle size determined using transmission electron microscope (TEM) had a narrow distribution with an average value of approximately 11 nm and a standard deviation of ±4 nm. The phosphonic acid-functionalised silica additive enhanced proton conductivity and water retention by introducing both acidic groups and porous silica. The proton conductivity of the composite membrane with the acid-functionalised silica was 0.026 S cm⁻¹, 24% higher than that of the unmodified Nafion membrane at 85 °C and 50% RH. Compared with the Nafion membrane, the phosphonic acid-functionalised silica (10% loading level) composite membrane exhibited 60 mV higher fuel cell performance at 1 A cm⁻², 95 °C and 35% RH, and 80 mV higher at 0.8 A cm⁻², 120 °C and 35% RH. The fuel cell performance of composite membrane made with 6% colloidal silica without acidic group was also higher than unmodified Nafion membrane, however, its performance was lower than the acid-functionalised silica additive composite membrane.