Proton exchange membrane water electrolysis system-membrane electrode assembly with additive

In proton exchange membrane water electrolysis system, the performance is highly affected by the anode materials and the operation modes. In addition, high voltages are for higher hydrogen production and also ozone for disinfection. After switching off of the power and restarted, a decrease in electric conductivity may lead to a performance drop in further hydrogen/ozone/generation. In this study, three different additives, A, Z and V are adopted which respectively mixed with the PbO₂ and to become anode catalyst ink. The characteristics of the anode catalysts are determined by interruptive power supply, electrochemical impedance spectroscopy, and cyclic voltammetry tests. The results show that additives A and Z have batter current efficiency than the other groups. Additionally, anode catalyst withadditive V possess the most outstanding durability among all groups.     

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.     

On the influence of the anodic porous transport layer on PEM electrolysis performance at high current densities

In this study, the influence of the anodic porous transport layer (PTL) on the performance of a proton exchange membrane (PEM) electrolysis laboratory test cell was investigated up to a current density of 5 A*cm⁻². Operation parameters such as water volume flow rate (0.2–0.8 l*min⁻¹), temperature (40–80 °C) and pressure (1–30 barg) have been varied to study their influence on the polarisation curve. Special attention has been paid to the appearance of mass transport losses (MTL) and their dependency on the operation parameters. Two stack designs that are commercially in use - one with and one without flow channels underneath the PTL - were tested and evaluated. Fundamental differences in performance have been observed between the two cell designs. Operation parameters only show impact on performance for the configuration without flow channels. Here, MTL were observed in several cases already for current densities around and above 1.0 A*cm⁻². An increase in pressure, temperature or water flow rate reduces MTL for these configurations.     

Investigations on high performance proton exchange membrane water electrolyzer

In order to improve proton exchange membrane water electrolyzer (PEMWE) performance, some factors related to the processes of preparing the Membrane Electrode Assemblies (MEAs), such as iridium (Ir) electrocatalyst loading and Nafion^® content at the anode, thicknesses of proton exchange membrane and gas diffusion layers (GDLs), were examined. In addition, a home-made supported Ir/titanium carbide (Ir/TiC, 20% Ir by weight) was developed for the anode. With best commercial Ir catalyst loading of 1.5 mg cm⁻² Ir at the anode, the cell's current densities of 1346 mA cm⁻², 1820 mA cm⁻² and 2250 mA cm⁻² were achieved at the cell potentials of 1.80 V, 1.90 V and 2.00 V, respectively. A PEMWE with 0.3 mg cm⁻² Ir loading of Ir/TiC anode catalyst was comparatively stable and gave current densities of 840 mA cm⁻², 1130 mA cm⁻² and 1463 mA cm⁻² at the cell potentials of 1.80 V, 1.90 V and 2.00 V, respectively. Based on catalysis efficiency of Amperes per milligram of Ir, the Ir/TiC catalyst is found to be more active than unsupported Ir catalyst.     

N/C doped nano-size IrO2 catalyst of high activity and stability in proton exchange membrane water electrolysis

It is highly desirable to synthesize and deploy low-cost and highly efficient catalysts for the oxygen evolution reaction (OER) to catalyze water splitting. We show that N/C doped amorphous iridium oxide combines the benefits of nano-size (approximately 2 nm), which results in exposure to large active surface areas and features of oxygen defects, which make for an electronic structure suitable for the OER. Systematic studies indicate that the OER activity of the iridium oxide catalyst is accelerated by the effect of the structure and chemical state of the iridium element. Remarkably, the N/C doped amorphous iridium oxide catalyst shows a lower cell voltage of 1.774 V at 1.5 A cm⁻², compared with IrO₂ (1.847 V at 1.5 A cm⁻²), and it can maintain such a high current density for over 200 h without noticeable performance deterioration. This work provides a promising method for the improving OER electrocatalysts and the construction of an efficient and stable PEM water cracking system.     

Mathematical modeling of novel porous transport layer architectures for proton exchange membrane electrolysis cells

Thin foil based porous transport layers (PTLs) that contain highly structured pore arrays have shown promise as anode PTLs in proton exchange membrane electrolysis cells. These novel PTLs, fabricated with advanced manufacturing techniques, produce thin, tunable, multifunctional layers with reduced flow and interfacial resistances and high thermal and electric conductivities. To further optimize their design, it is important to understand their fundamental impact on the transport of protons, electrons, and liquid/vapor mixtures in the electrode. In this work, we develop a two-dimensional multiphysics model to simulate the coupled electrochemistry and multiphase transport in an electrolysis cell operated with the novel PTL architecture. The results show that larger pores improve access of water to the anode catalyst layer, which is beneficial for both the oxygen evolution reaction and membrane hydration. Larger pore sizes also improve oxygen gas transport from the catalyst layer, because generated oxygen gas is forced to travel in-plane through the anode catalyst layer until it reaches a pore opening that is connected to a channel. The discussed results confirm that the proposed thin foil based PTLs are fundamentally different from conventional PTLs, such as felts or layered meshes. The model developed in this work also provides generalizable insight into fundamental PEMEC phenomena, such as the competition between liquid and gas phase transport, membrane hydration and water management, and nonuniform electrochemical reactions, which are processes relevant to all PEMEC designs.     

An analysis of PEM water electrolysis cells operating at elevated current densities

Recent developments related to the operation of PEM water electrolysis cells at elevated current density are reported. First, a cost analysis has been performed to discuss the interest of extending the range of operating current density of these cells, towards the 10 A cm⁻² range and above. Then the technical impact this may have on the cell design has been analyzed, and the practical conditions required to remove the extra-heat and to facilitate fluid transport across the porous transport layers have been identified. Experimental current-voltage polarization curves have been measured using a pressurized laboratory cells equipped with PFSA (perfluoro-sulfonic acid) membranes of various thicknesses, operating at 80 °C and current densities up to 10 A cm⁻². These experimental polarization curves have been fitted using model equations. Key cell parameters such as internal cell resistance, charge transfer exchange current densities and roughness factors have been determined from these fits. The impact of the cell design on the performance and efficiency of PEM water electrolysis cells operated in the multi A cm⁻² range of current density has been analyzed, with a focus on the situation that prevails above 5 A cm⁻².     

Hydrogen production performance of a photovoltaic thermal system coupled with a proton exchange membrane electrolysis cell

As one of the cleanest energies, hydrogen has attracted much attention over the past decade. Hydrogen can be produced using water electrolysis in a Proton Exchange Membrane Electrolysis Cell (PEMEC). In the present study, the performance of the PEMEC, powered by the Photovoltaic-Thermal (PVT) system, is scrutinized. It is considered that the PVT system provides the required electrical power of the PEMEC and preheats the feedwater. A comprehensive numerical model of the coupled PVT-PEMEC system is developed. The model is used to investigate the effect of various operating parameters, including solar radiation intensity, inlet feedwater temperature, and feedwater mass flow rate, on the hydrogen production and operating voltage of the PEMEC at various Exchange Current Densities (ECDs). Furthermore, the effect of integration of Phase Change Material (PCM) and Thermoelectric Generator (TEG) on the hydrogen production of the system is evaluated. According to the obtained results, the PVT-TEG-PEMEC system outperforms other systems in hydrogen production. However, integration of the PVT-PEMEC system with PCM has a negligible effect on its hydrogen production.     

Transient behavior of water generation in a proton exchange membrane fuel cell

The effect of water generation on the performance of proton exchange membrane fuel cell (PEMFC) was investigated by using a periodical linear sweep method. Three different kinds of I–V curves were obtained, which reflected different amount of water uptake in the fuel cell. The maximum water uptake that could avoid flooding in the fuel cell and the hysteresis of water diffusion were also discussed. Quantitative analysis of water uptake and water transport phenomena in this study were conducted both experimentally and theoretically. Results showed that the water uptake capacity for the fuel cell under no severe flooding was 27.837 mg cm⁻². The transient response of the internal resistance indicated that the high frequency resistance (HFR) lagged the current with a value of about 20 s. The effect of purging operation on the internal resistance of the fuel cell was also explored. Experimental data showed that the cell experienced a continuous 8-min purging process can maintain at a relatively steady and dry state.     

Simulation and experiment of heat and mass transfer in a proton exchange membrane electrolysis cell

A full-scale, two-phase, single-channel model of proton exchange membrane electrolysis cell is established. The electrochemical model and the thermal model are coupled to explore the mass transfer of the channel, catalytic layer and diffusion layer, and the heat transfer of the entire electrolysis cell. Two different calculation models are compared, and it is found that the calculation results of the model with bipolar plates are closer to the actual values. Simultaneously, effective water and thermal management strategies are proposed: The temperature of the electrolysis cell can be reduced effectively by supplying water to the cathode side. The Counter-flow mode has a lower temperature than the Co-flow mode, but the temperature gradient in the Counter-flow mode is greater. Reducing the channel depth and increasing the channel width can improve the water transmission in the electrolysis cell and reduce the temperature of the electrolysis cell, but a larger channel width will increase the electrical loss. Therefore, the selection of appropriate channel size is of great significance to the long-term stable operation of the electrolysis cell.     

Performance of a high temperature polymer electrolyte membrane water electrolyser

A high temperature polymer electrolyte membrane water electrolyser (PEMWE) was investigated at temperatures between 80 and 130 °C and pressures between 0.5 and 4 bar. Nanometer size Ru_0.7Ir_0.3O₂ and Pt/C were employed as anode and cathode catalysts respectively. The catalyst coated on membrane (CCM) method was used to fabricate the membrane electrode assemblies. The membrane, oxygen evolution catalysts and MEAs were characterized with SEM, XRD and TEM. The influence of high temperature and pressure was investigated using in situ electrochemical measurements. Increasing temperature and pressure produced higher current densities for oxygen evolution, and smaller terminal voltages. The high temperature PEMWE achieved a voltage of 1.51 V at a current density of 1 A cm⁻², at 130 °C and 4 bar pressure.     

Water transport analysis during cathode dry operation of anion exchange membrane water electrolysis

The effect of water diffusion through an anion exchange membrane (AEM) on the concentration overpotential (η_conc) during cathode dry operation of AEM water electrolysis was experimentally examined using electrolytic cells with different membrane electrode assemblies (MEAs). The specially designed MEAs were used in the cells to obtain reliable and reproducible data to clarify the influence of membrane thickness (t_mem) and porosity of cathode catalyst layer (CL). The relative humidity of generated hydrogen (?_H2) during electrolysis was also measured based on dew point measurements of the hydrogen. The η_conc analysis for cells with single- and double-AEM MEAs revealed that water diffusion through the membrane was the main contributor to η_conc. The quantitative agreement between ?_H2 data and η_conc revealed that the difference in η_conc between the two types of MEAs is explained by the water concentration difference between anode and cathode via the Nernst equation. The effect of the porosity of the cathode CL on cell performance and on water transport was also examined experimentally. The results revealed that a high-porosity cathode CL tended to keep the cathode in a drier state during electrolysis compared with a low-porosity cathode CL. When ?_H2 is lower than a threshold value in the range from 0.5 to 0.6, the ion conductivity of AEM and ionomer would decrease, and the cell performance would deteriorate due to an increase in cell resistance (R_cell) and/or activation overpotential (η_act).     

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.     

PEM steam electrolysis at 130 °C using a phosphoric acid doped short side chain PFSA membrane

Steam electrolysis test with a phosphoric acid doped Aquivion™ membrane was successfully conducted and current densities up to 775 mA cm⁻² at 1.8 V was reached at 130 °C and ambient pressure. A new composite membrane system using a perfluorosulfonic acid membrane (Aquivion™) as matrix and phosphoric acid as proton conducting electrolyte was developed. Traditional perfluorosulfonic acid membranes do not possess sufficient dimensional stability and proton conductivity to be used at elevated temperatures and ambient pressures. The elevated temperature, high potentials and acidic conditions implied that a new and highly corrosion resistant construction material was needed. Tantalum coated stainless steel felt was tested and found suitable as the anode gas diffusion layer.     

Model-based decoupling control for the thermal management system of proton exchange membrane fuel cells

As one of the most promising sustainable energy technologies available today, proton exchange membrane fuel cell (PEMFC) engines are becoming more and more popular in various applications, especially in transportation vehicles. However, the complexity and the severity of the vehicle operating conditions present challenges to control the temperature distribution in single cells and stack, which is an important factor influencing the performance and durability of PEMFC engines. It has been found that regulating the input and output coolant water temperature can improve the temperature distribution. Therefore, the control objective in this paper is regulating the input and output temperature of coolant water at the same time. Firstly, a coupled model of the thermal management system is established based on the physical structure of PEMFC engines. Then, in order to realize the simultaneous control of the inlet and outlet cooling water temperature of the PEMFC stack, a decoupling controller is proposed and its closed-loop stability is proved. Finally, based on the actual PEMFC engine platform, the effectiveness, accuracy and reliability of the proposed decoupling controller are tested. The experimental results show that with the proposed decoupling controller, the inlet and outlet temperatures of the PEMFC stack cooling water can be accurately controlled on-line. The temperature error range is less than 0.2 °C even under the dynamic current load conditions.     

Assessment of the FAA3-50 polymer electrolyte in combination with a NiMn2O4 anode catalyst for anion exchange membrane water electrolysis

A commercial FAA3-50 membrane was investigated as a solid polymer electrolyte in an alkaline water electrolysis. An improved chemical treatment based on alkaline KOH solution was carried out. A limited degradation of the functional groups was observed allowing to maintain a good anion conductivity approaching 55 mS cm-1 at 100 °C. Thermal stability up to 200 °C was assessed by thermal analysis.A specific membrane-electrodes assembly based on FAA3-50 anionic membrane and NiMn₂O₄ anode catalyst was developed and investigated in a single cell for water electrolysis at a moderate temperature (50 °C).Performance stability was assessed by a potential cycling-based durability test for 1000 h by varying the cell potential between 1 and 1.8 V for the FAA3-50 and NiMn₂O₄ based-MEA.According to this evaluation, both the FAA3-50 membrane and the NiMn₂O₄ catalyst appear sufficiently stable for electrolysis operation under mild operating temperatures.     

High-performance and cost-effective membrane electrode assemblies for advanced proton exchange membrane water electrolyzers: Long-term durability assessment

Improved activity and durability performance of a two-cell (86 cm²) proton exchange membrane water electrolyzer (PEMWE) stack is reported for the first time. Both membrane electrode assemblies (MEAs) contain one order of magnitude lower platinum group metal (PGM) loadings compared to the state-of-the-art PEMWEs and incorporate novel Pt recombination layers. The high-performance and cost-effective MEAs are fabricated by the unique reactive spray deposition technology (RSDT). This advanced methodology allows for one-step fabrication of MEAs and ensures precise control and distribution of the catalyst composition and loading. The RSDT-fabricated MEAs contain only 0.2 and 0.3 mg_PGM cm^?2 loading in the cathode and anode electrodes, respectively, and demonstrate excellent activity and durability for over 3000 h of operation at industrially-relevant operating conditions without showing significant loss in performance. This novel work shows that a significant cost reduction for PEMWEs is achieved while maintaining excellent durability, high catalysts activities, and low hydrogen cross-over.     

Design and characterization of compact proton exchange membrane water electrolyzer for component evaluation test

In this study, we designed and developed a compact electrolyzer for the evaluation of components in proton exchange membrane (PEM) water electrolysis. First, this electrolyzer features a precise pressure-control system that controls the active electrode area and facilitates setting the desired clamping pressure. This mechanism makes it possible to optimize the electrolyzer performance. Second, it has two reference electrodes that are connected on the faces of the active electrode area of the anode and the cathode on the PEM. The polarizations at the anode and the cathode, the membrane resistivity, and the porous transport layer (PTL) overpotential were measured. The details of the design are described, and the electrochemical performance was measured. The optimized clamping pressure for this electrolyzer component was obtained as the specific value. A new measurement method was developed for estimating polarizations at the anode and the cathode, membrane resistance, and PTL overpotential using two reference electrodes.