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 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.