Collective redox-shuttling properties of nanoalloys boost water electrolysis of nitrides

Interstitial transition metal catalysts (carbides, nitrides, and sulfides) represent the promising nonprecious metal bifunctional catalysts for water electrolysis. However, they still suffer from inferior activity and, particularly, stability for industrial applications. Leveraging template-free hydrothermal and reduction protocol, we report an unexpected collective effect between CoNi nanoalloy and molybdenum nitride (Mo2N) phase on Ni foam substrate (Mo2N@NiCo/NF). Distinct from the conventional promoting effect of the additives to parent metal motifs, the collective properties of local nanosized CoNi particles in Mo2N@NiCo/NF comprise differently-weighted geometric and electronic interactions, leading to remarkably enhanced hydrogen evolution reaction (HER) activity (18 and 67 mV at the current density of 10 and 100 mA cm−2, respectively) for Mo2N active sites in alkaline, relative to Pt/C@NF (87 mV at 100 mA cm−2). In-depth characterization, density functional theory (DFT) calculations, and electrocatalytic kinetics reveal that spatially located CoNi nanoalloy inside two-dimensional Mo2N nanoarrays serves as collective electron buffer, enabling the enhanced redox-shuttling properties and thus fulfilling the bifunctional catalytic activities for overall water and simulated seawater splitting with excellent durability (200 h at 50 or 100 mA cm−2). These results verify the importance of a collective properties strategy to design efficient bifunctional metal electrocatalysts for water electrolysis.