(Poster Award - 1st Place) Liquid Water Permeability in a Hydrophobic Microporous Layer for the Anode Interdigitated Flow Field of a Gas-Liquid Separating Polymer Electrolyte Membrane Water Electrolyzer
Authors: Kubota Shunji , Nakajima Hironori , Sato Motohiko , Shima Asuka , Sakurai Masato , Sone Yoshitsugu 
Published: February 2024

A novel interdigitated flow field for polymer electrolyte membrane (PEM) water electrolyzers (polymer electrolyte electrolysis cells) composed of oxygen exhaust channels apart from liquid water feed channels has been developed for ground and space applications 1, 2). This design can separate oxygen gas and liquid water between the flow channels without buoyancy, so that it dispenses with water circulators for bubble removal in electrolyzers and external separators by natural or centrifugal buoyancy.
In this electrolyzer, pressurized liquid water is injected in the in-plane direction from the water channels to the catalyst layer through a hydrophobic microporous layer (MPL) applied to the anode porous transport layer (PTL) 2). Produced oxygen gas is discharged in the through-plane direction of the MPL to the oxygen channels, taking advantage of the capillary pressure in the hydrophobic MPL 2),3). Extreme leakage of the liquid water to the oxygen channels has not been found.
This study conducted liquid water permeability tests for an MPL (SIGRACET 29BC, SGL Carbon Inc.) with pressurized liquid water by weighing liquid water penetrated through the MPL-coated PTL to the PTL surface under ambient air pressure. We find gradual permeability decreases with time for different liquid water pressures 4). This permeability is a useful parameter for optimal structure designs of this electrolyzer. Similar tendencies were also observed for a hydrophobic PTL without MPL (SIGRACET 29BA, SGL Carbon Inc., substrate of the MPL-coated PTL). The same test on the hydrophobic MPL dried after the test revealed that the permeability partially recovered. The liquid water networks inside the MPL and the PTL substrate possibly lead to decreases in the permeability. This phenomenon is a critical issue for this electrolytic cell as well as PEM fuel cells, and thus discussed further.
References
1) Y. SONE, O.S. HERNANDEZ-MENDOZA, A. SHIMA, M. SATO, H. NAKAJIMA, H. MATSUMOTO, Water Electrolysis by the Direct Water Supply to the Solid Polymer Electrolyte through the Interdigitated Structure of the Electrode, Electrochemistry. 89 (2021) 138–140. https://doi.org/10.5796/electrochemistry.20-00145.
2) H. NAKAJIMA, V. VEDIYAPPAN, H. MATSUMOTO, M. SATO, O.S. MENDOZA-HERNANDEZ, A. SHIMA, Y. SONE, Water Transport Analysis in a Polymer Electrolyte Electrolysis Cell Comprised of Gas/Liquid Separating Interdigitated Flow Fields, Electrochemistry. 90 (2022) 017002. https://doi.org/10.5796/electrochemistry.21-00097.
3) H. Nakajima, S. Iwasaki, T. Kitahara, Pore network modeling of a microporous layer for polymer electrolyte fuel cells under wet conditions, J. Power Sources. 560 (2023) 232677. https://doi.org/10.1016/j.jpowsour.2023.232677.
4) S. KUBOTA, H. NAKAJIMA, M. SATO, A. SHIMA, M. SAKURAI, and Y. SONE, Liquid Water Permeability Test for a Microporous Layer Applied to a Gas-Liquid Separating Polymer Electrolyte Membrane Water Electrolyzer, the 42nd Symposium of the Hydrogen Energy Systems Society of Japan (2022) 12H06.
Acknowledgments
This study is based on results obtained from a project, JPNP21014, commissioned by the New Energy and Industrial Technology Development (NEDO).