The Degradation Mechanism of Nonprecious Ni ₄ Mo-MoO ₂ Cathode during Intermittent Alkaline Water Electrolysis

Developing efficient and durable nonprecious cathodes for the hydrogen evolution reaction (HER) is crucial for industrial alkaline water electrolysis (AWE). NiMo-based materials are among the highly active nonprecious HER electrocatalysts at present and are expected to replace noble-metal catalysts. However, their practical application is hindered by the performance degradation under the industrial operating conditions, especially fluctuating conditions imposed by an intermittent renewable power supply. This study systematically carried out a series of experiments and elucidated the degradation mechanisms of the NiMo-based cathode (Ni 4 Mo-MoO 2 ) during intermittent AWE. First, the dissolved oxygen that inevitably diffuses from the anode to the cathode chemically corrodes the NiMo catalyst in concentrated alkaline electrolyte at high temperature, thus reducing active sites and leaching critical components, notably Mo. Simultaneously, the reverse current generated during start–stop operations induces anodic polarization of the NiMo cathode, accelerating its degradation through electrochemical oxidation. Moreover, driven by external gas–liquid flow scouring and internal stress from redox-induced phase transformation, the catalyst layer separates from the substrate, leading to serious mechanical detachment. These factors collectively cause severe degradation in the activity of the NiMo cathode. This work provides important guidelines for developing next-generation nonprecious metal cathodes with lasting stability.