Electrochemical Deposition Processes for Fabrication of Cathodes/Anodes of Alkaline Water Electrolysis Device

Abstract

Water electrolysis employing anion exchange membranes (AEM) is a promising technique toward the realization of a carbon-neutral society as it facilitates the development of water electrolyzers without noble metals; generally, alkaline electrolytes do not require platinum and iridium oxides for catalysts or titanium for porous transport layers (PTL) and bipolar plates. Although coating techniques have been demonstrated to be effective in forming catalyst layers of cathodes or anodes with lowered resistances [1,2], in this paper, the authors present novel electrochemical methods to produce cathodes/anodes to be used in AEM water electrolysis devices. In the fabrication of cathodes, we use electroless deposition for the direct formation of non-noble metal alloy catalysts on the AEM. This enables ionomer-less attachment of the catalyst layer on the membrane, producing a catalyst that is sufficiently durable under high temperatures. Here, pretreatments for activating the membrane before the deposition are critical. Based on quantum chemical calculations, we found that immersing the membrane in a solution of palladium chloride, prior to its immersion in a reducing agent solution, provides sufficiently stable catalyst nuclei for electroless deposition. For the fabrication of anodes, electrolytic deposition of the catalyst on a PTL is chosen. To retain the porous structure of the PTL, the deposition of a compact film is essential. For this, pulse electrodeposition with an optimized sequence of current density is an attractive technique as it accomplishes metal deposition while retaining the substrate shape. Scanning electron microscopy images in this study proved that the pulse sequence of the current density is beneficial to depositing catalyst alloys with the porous structure of the PTL retained. This is because the pulse technique recovers the depletion of precursor ions for deposition around the electrode surface, which results in preventing the development of diffusion layers. We expect that these processes will make alkaline water electrolysis devices more efficient and cost effective.[1] H. Ito, N. Miyazaki, S. Sugiyama, M. Ishida, Y. Nakamura, S. Iwasaki, Y. Hasegawa, A. Nakano, J. Appl. Electrochem., 48, 305 (2018).[2] H. Ito, N. Kawaguchi, S. Someya, T. Munakata, N. Miyazaki, M. Ishida, A. Nakano, Int. J. Hydrogen Energy, 43, 17030 (2018).AcknowledgementsThis study was financially supported in part by the “Advancement of Hydrogen Technologies and Utilization Project” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. We would like to express the gratitude to Tokuyama Corporation for the supply of AEM.