Optimization of Two-step Thermal Decomposition Condition for Durable NiCo Oxide Anode in Alkaline Water Electrolysis Using Start/Stop Simulated ADT (Supporting Information)

The long-promised lifespan of alkaline water electrolysis is due to its stable power system. However, when used for hydrogen production with renewable energy, electrode degradation caused by an intermittent power supply must be predicted. In alkaline water electrolysis, where all cells are connected in series, intermittent shutdowns create a reverse current. This results in the reduction of anode material during the stopping time, and the repeated oxidation-reduction process due to intermittent power causes degradation. Electrodes coated with thermally decomposed electrocatalysts on a nickel substrate have demonstrated high durability in industrial alkaline electrolysis applications. However, their durability decreases when exposed to reverse currents due to the detachment of the catalyst layer. In this study, we aimed to improve durability and catalytic performance by using stepwise temperature control during the coating heat treatment and reducing the annealing duration. This two-step process formed an intermediate NiOx-rich layer between the catalyst and substrate. This might strengthen interfacial adhesion and improve the durability of the catalyst layer. However, at high temperatures, as the heat treatment time increases, the intermediate oxide layer becomes more pronounced, subsequently increasing the NiO proportion. The low electrical conductivity of NiO leads to increased resistance and decreased initial performance. The most appropriate heat treatment conditions were 300 °C decomposition followed by 500 °C annealing with a relatively short time. The performance interval, maintained at approximately 1.7 V vs. RHE, increased by about three times compared to conventional consistent heat treatment. This improvement is believed to be due to optimal formation of the catalyst structure via thermal decomposition and of the intermediate oxide layer via annealing.