Crystal facet-induced reconstruction of MoN-supported Co pre-catalysts for optimized active sites and enhanced alkaline hydrogen evolution

The self-reconstruction of electrocatalysts during the cathodic hydrogen evolution reaction (HER) has garnered significant interest due to its impact on microstructure and electrocatalytic efficiency. Understanding the mechanisms driving this transformation is crucial for the development of high-performance HER pre-catalysts. In this study, an efficient Co(OH)₂ (001)/MoN (002) heterostructured catalyst is fabricated through the self-reconstruction of the Co/MoN pre-catalyst and the mechanism of facet-induced reconstruction is investigated in detail. This Co/MoN pre-catalyst exhibits an impressive 58 % reduction in overpotential at a constant current density of 100 mA cm⁻² over 5 h. It ultimately achieves a low overpotential of 339 mV at 1 A cm⁻², outperforming commercial Pt/C under similar current conditions, while maintaining high current activity with 99.4 % retention after 110 h of continuous electrolysis. Operando characterizations and theoretical simulations reveal that metallic Co dissolves rapidly under bias as H⁺ ions infiltrate the interstitial spaces, and the dissolved Co²⁺ ions preferentially deposit as Co(OH)₂ nanosheets. This deposition aligns with the (001) facet of Co(OH)₂ and the prominent (002) plane of the MoN matrix through lattice matching, exhibiting a very low interfacial formation energy. Density-functional theory analysis reveals that the alignment of the crystal facets between Co(OH)₂ (001) and MoN (002) enhances electron transfer and modulates the interface to boost the water dissociation and hydrogen adsorption activity and kinetics. Our results underscore the importance of precise control over the reconstruction process for cathodic HER and facilitate the development of advanced transition metal-based electrocatalysts for industrial alkaline hydrogen production. © 2025 Elsevier Inc.