The degradation of Ni4Mo/MoO2 catalysts under fluctuating current conditions

Abstract

The development of durable electrocatalysts for hydrogen production under fluctuating current conditions is essential for advancing large-scale electrolysis systems powered by renewable energy. Ni₄Mo/MoO₂ catalysts have shown great promise for the hydrogen evolution reaction (HER) due to their cost-effectiveness and high catalytic activity. However, the behavior of catalysts under dynamic operating conditions remains poorly understood. In this study, we investigate the evolution of Ni₄Mo/MoO₂ catalysts subjected to intermittent shutdown cycling, simulating the current fluctuations typically encountered in renewable energy-driven electrolysis. Our results reveal that although Ni₄Mo/MoO₂ performs stably during continuous operation, it undergoes significant degradation upon shutdown cycling. This degradation is primarily attributed to the irreversible oxidation and dissolution of active Mo species, leading to the loss of the MoNi₄ alloy phase and the formation of Ni(OH)₂ and MoO_x on the surface. The resultant phase transformation, surface reconstruction, and blockage of active sites collectively cause a sharp decline in intrinsic catalytic activity. These findings provide valuable insights into the failure mechanisms of Ni₄Mo/MoO₂-based electrocatalysts under dynamic conditions.