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.碱性水电解（alkaline water electrolysis）长久以来被寄予厚望的长使用寿命，得益于其稳定的供电系统。然而当其应用于可再生能源制氢场景时，必须对间歇性供电引发的电极劣化进行预测。在所有电解槽呈串联连接的碱性水电解体系中，间歇性停机会产生反向电流（reverse current）。停机阶段阳极材料会发生还原反应，而间歇性供电引发的反复氧化还原循环会进一步加剧电极劣化。在镍基底（nickel substrate）上负载热分解型电催化剂（thermally decomposed electrocatalysts）的电极，在工业碱性电解应用中展现出优异的耐久性。但当暴露于反向电流环境时，由于催化剂层（catalyst layer）脱落，其耐久性会出现显著下降。本研究通过在涂层热处理过程中采用阶梯式温控（stepwise temperature control）并缩短退火时长（annealing duration），旨在提升电极的耐久性与催化性能。该两步工艺可在催化剂与基底之间形成富氧化镍中间层（intermediate NiOx-rich layer），或可强化界面结合力，进而提升催化剂层的耐久性。但在高温环境下，随着热处理时长增加，中间氧化层的厚度会愈发显著，随之提升NiO的占比。NiO较低的电导率会导致体系内阻上升，初始性能下降。最适宜的热处理工艺为：先在300℃下进行分解，随后在500℃下进行短时退火。相较于传统恒温热处理工艺，维持在约1.7 V（相对于可逆氢电极（Reversible Hydrogen Electrode））的性能区间提升了约三倍。该性能提升被认为得益于：热分解过程实现了催化剂结构的最优构筑，而退火工艺则促成了中间氧化层的理想形成。