Development of Pseudo-Homogeneous Three-Dimensional Reaction Anode Structure for Proton Exchange Membrane Water Electrolysis

Abstract

Solid Polymer Electrolyte (SPE) diaphragm such as Nafion🄬 has been applied to proton exchange membrane water electrolysis (PEMWE) due to the high efficiency and response. The structure of PEMWE consists of a catalyst layer, diffusion layer, current collector, flow-field, etc. In addition to the membrane, these elements and structural parameters were adapted from the proton exchange membrane fuel cell (PEMFC) technology due to the time series factors in the development process and are still strongly influenced by that technology today. Although PEMFC technology is applied to these elements in PEMWE, the material composition, structure, and various parameters are not fully optimized, and the basic structure and technology are diverted from various PEMFC conditions, although the main object of fluid has greatly changed from the gas phase to the liquid phase. As the above background, PEMWE technology needs to go back to the basic level of structural design, mainly from the viewpoint of mass transfer, and reconstruct the component structure.In this study, we focused on the mass transfer characteristics that most affect the performance of PEMWE and investigated a new structure for gas-liquid two-phase fluids for the electrode structure, which is the most important element of PEMWE.Figure 1 shows the two and three-dimensional reaction electrode structures in PEMWE. Figure 1(a) is the electrode structure of a conventional general PEMWE, which is the catalyst reaction in the catalyst layer on the rate-limiting electrode side proceeds in a heterogeneous two-dimensional reaction area. In this current method, sufficient diffusion cannot be maintained from the viewpoint of mass transfer, which leads to performance decrease due to the inability to remove obstacles such as bubbles to mass transport to the catalyst layer. Figure 1 (b) shows the pseudo-homogeneous three-dimensional reaction electrode structure developed in this study. The catalyst is supported on the porous current collector itself. This structure dramatically increases the reaction area from two-dimensional to three-dimensional, and it is expected to greatly improve electrolytic performance by optimizing various parameter conditions.The experimental was performed as following. The anode catalyst IrOx was synthesized from H2IrCl6-nH2O and NaNO3 by the Adams method1). Catalyst Ink, which mixed with the synthesized catalyst and Nafion🄬 dispersion solution, was dropped onto a Ti-web current collector and dried. The anode catalyst loading current collector was evaluated in a 1 cm2 component evaluation electrolyzer2).In this development, the essential issue is the establishment of the conditions to support the catalyst in the three-dimensional reaction area and to maintain the supply path of the proton from the SPE membrane efficiently.References T. Saida, S. Hirano, E. Niwa, F. Sato, and M. Maruyama, ECS Trans., 85, 865 (2018). K. Nagasawa, T. Ishida, H. Kashiwagi, Y. Sano, S. Mitsushima, Int. J. Hydrog. Energy, 46, 36619 (2021). Figure 1