Electrocatalytic Activity and Durability of Li x Ni2-x O2/Ni Electrode Prepared by Oxidation with LiOH Melt for Alkaline Water Electrolysis

Abstract

Alkaline water electrolysis (AWE) is suitable for hydrogen production to develop a fluctuating and uneven-distributed renewable energy-based energy system, because hydrogen is a secondary energy which is suitable to large-scale storage and transportation, and the AWE has a simple configuration using low-cost materials. In this system, the anode typically using Ni and Ni alloys is degraded during the fluctuation of electricity from renewable energy. This degradation is related to the surface hydrous oxide layer which contains Ni(II) and Ni(III). During potential cycling, the hydrous oxide layer grows and increases the electronic resistance due to the redox of Ni(II)/Ni(III) and Ni(III)/Ni(IV). In order to improve the durability and catalytic activity by stabilization of the surface using an electroconductive oxide, a Li x Ni2-x O2/Ni has been developed. The surface oxide was prepared by the oxidation of Ni with a LiOH melt. The Li-doped amount for the surface oxide prepared at 1000 °C was homogeneous with a cubic crystalline structure. On the other hand, the crystalline structure prepared at 800 °C was a mixture of the trigonal and cubic Li-doped NiO phases, which has a high and low Li content, respectively. The oxide layer conductivity increased with the Li-doped amount. The excess Li-doped amount increased not only the conductivity of the oxide layer but also the deactivation of the oxygen evolution reaction (OER) electrocatalytic activity. The durability of the Li x Ni2-x O2/Ni under potential cycling was higher than that of Ni for both the OER activity and redox change of Ni(II)/Ni(III) and Ni(III)/Ni(IV).