(A) study on improvement of efficiency and durability of transition metal based alkaline water electrolysis electrodes

Abstract

The water electrolysis is a method that can produce hydrogen with eco-friendly energy, and since an overpotential of more than the theoretical potential (1.23 V) is required, it is necessary to improve the efficiency through a highly active electrode catalyst. In this study, the intrinsic activity enhancement and active surface area increase were induced based on the surface-controlled transition metal, and an easy synthesis method was adopted to enable practical industrial application. This study proposes a porous Sn-Co catalyst based on an electrodeposition method and a Cu$_3$P/carbon composite catalyst based on a low pollution gas phase reaction method. In addition, it proposes a Ni-P-N catalyst for seawater electrolysis electrodes, suggesting its applicability to low-grade water electrolysis. In the study of the catalyst for the oxygen evolution reaction of porous Sn-Co, using the property of dissolving tin in an alkaline environment, some of the tin on the surface is dissolved and the rest is oxidized, which leads to high active surface area and structural stability together. In the study of Cu$_3$P/carbon composite catalyst for hydrogen evolution reaction based on low pollution gas phase reaction method, copper phosphide was synthesized without the use of a large amount of phosphorus in the heat treatment process by improving the synthesis process. The surface cyclized carbon structure generated in the heat treatment process maximizes the catalytic activity through synergy with Cu$_3$P and keeps the catalyst material stably present on the electrode surface. The research on the Ni-P-N catalyst for oxygen evolution reaction for seawater electrolysis proposes a nitrogen doping process that reduces the possibility of environmental pollution and high-temperature deformation of the electrode without using toxic ammonia gas or high-temperature nitrogen gas. This catalyst showed high oxygen evolution reaction activity in seawater, and showed superior properties compared to the control group in corrosion evaluation. The surface properties of the catalyst were observed on the surface using the in-situ Raman technique according to the applied potential, and it was found that the length of the nickel-oxygen bond becomes longer. It not only improves the activity of the oxygen evolution reaction in seawater but also increases the corrosion resistance by lowering the possibility of nickel-chlorine bonding.