Ru-modified CoMoOx catalyst on carbon cloth for efficient HER in alkaline seawater electrolysis at high current densities

• First report on ternary Ru/CoMoO x catalysts coated on carbon cloth (CC) for the HER. • Simple hydrothermal method enables scalable fabrication of Ru/CoMoO x @CC electrodes. • Low Ru content significantly enhanced the HER performance. • Ru/CoMoO x @CC maintained stable operation for over a month at 500 mA/cm 2 in alkaline seawater. • Ru/CoMoO x @CC exhibited superior stability, surpassing other Ru-based catalysts supported on CC. Seawater electrolysis with low energy consumption at high current densities is a promising strategy for sustainable hydrogen production. However, the hydrogen evolution reaction (HER) under alkaline conditions is a major challenge owing to its sluggish reaction kinetics. Although Co-based catalysts supported on carbon cloth (CC) have been widely used in the HER, their catalytic activity and durability are insufficient at industrially relevant current densities. In this study, we introduce a Ru-modified CoMo catalyst immobilized on CC (Ru/CoMoO x @CC), a catalyst configuration that has not been previously reported. The incorporation of a small amount of Ru significantly enhanced the HER performance, possibly by modulating the hydrogen adsorption behavior, while maintaining cost-effectiveness. Consequently, the Ru/CoMoO x @CC electrode achieved an overpotential of only 78 mV in alkaline seawater at 10 mA/cm 2 , outperforming conventional CoMoO x @CC electrodes. Furthermore, at an industrially relevant current density of 500 mA/cm 2 , Ru/CoMoO x @CC demonstrated remarkable stability, maintaining its performance for over a month. These findings highlight the unique synergy between Ru, Co, Mo, and CC, demonstrating the potential of Ru/CoMoO x @CC as a highly efficient, durable, and scalable catalyst for HER in alkaline seawater electrolysis. These advancements will pave the way for cost-effective hydrogen production with reduced reliance on precious metals.