Interstitial Doping in Ultrafine Nanocrystals for Efficient and Durable Water Splitting

Transition metal-based catalysts with high efficiency and stability for overall water splitting (OWS) offer significant potential for reducing green hydrogen production costs. Utilizing sputtering deposition technology, we propose a deposition-diffusion strategy to fabricate heterojunction coatings composed of ultrafine FeCoNi-C-N transition metal interstitial solid solution (TMISS) nanocrystals and amorphous nitrided carbon (NC) on the pre-deposited NC micro column arrays. The diffusion of C and N atoms results in the formation of uniformly distributed TMISS nanocrystals, with an average diameter of ~1.9 nm, thus maximizing atomic utilization. The unique crystalline-amorphous heterojunction interface enhances electrocatalytic stability. Furthermore, the electronic regulation of metal sites by interstitial C and N atoms not only optimizes the adsorption-dissociation process in hydrogen evolution reaction (HER), but also accelerates the surface reconstruction of hydroxyl oxides to enhance the oxygen evolution reaction (OER) activity. As a result, the as-prepared coating achieved overpotentials of only 62 mV and 237 mV for the HER and OER at 10 mA cm^-2 in alkaline electrolytes, and exhibited excellent OWS performance and long-term stability at high current densities. This work presents a new perspective for synthesizing TMISS nanocrystals and promotes their application in bifunctional electrocatalysts.