Crystalline/amorphous heterostructure CoNi/MoO3-x electrocatalyst for alkaline seawater hydrogen evolution at ultra-high current density of 4000 mA/cm2

Designing highly efficient nonprecious metal electrocatalyst for the hydrogen evolution reaction (HER) in seawater electrolyte, particularly under ultra-high current density conditions, remains a formidable challenge. In this study, we successfully synthesized a crystalline/amorphous heterostructured CoNi/MoO 3-x electrocatalyst through a facile hydrothermal method followed by a calcination-reduction process. The as-prepared CoNi/MoO 3-x catalyst exhibited remarkable HER catalytic performance in both alkaline water and seawater electrolytes. Notably, the catalyst achieved impressively low overpotentials of 343 mV in 1 M KOH aqueous solution and 294 mV in alkaline natural seawater electrolyte at an ultra-high current density of 4000 mA/cm 2 . Furthermore, the CoNi/MoO 3-x electrocatalyst demonstrated outstanding long-term stability, maintaining robust performance at current densities of 3000 and 2000 mA/cm 2 . Density functional theory calculations revealed that the synergetic effect between crystalline CoNi and amorphous MoO 3-x accelerates water dissociation kinetics and optimizes hydrogen adsorption. These findings not only provide a promising strategy for developing cost-effective, nonprecious metal electrocatalysts with superior HER performance at ampere-level current densities, particularly for seawater splitting applications.