Fe-Doped CoS₂ Nanocages as Bifunctional Electrocatalysts for Water Splitting

Currently, electrochemical water-splitting activity is limited by the slow intrinsic reaction kinetics and energy conversion efficiency, so designing highly efficient electrocatalysts that can facilitate electrochemical reactions remains necessary. Herein, the catalyst architecture consisting of Fe-doped CoS₂ nanocages with nitrogen-doped carbon wrapping (CN/Fe-CoS₂) was explored as an outstanding bifunctional electrocatalyst. Through density functional theory calculations, the introduction of Fe into CoS₂ would modulate the density of states, making the reduced band gap and enhanced intrinsic charge transfer efficiency of CoS₂. Simultaneously, the adsorption of intermediates during the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) processes is regulated, leading to an improvement in the intrinsic catalytic activity. The experimental results demonstrate that Fe doping significantly enhances the electron transfer, specific surface area, and electrochemical active area of CoS₂, which facilitates the efficient utilization of charge and exposes additional active sites for electrochemical reactions. In addition, the nanocage architecture and nitrogen-doped carbon wrapping in CN/Fe-CoS₂ act as a protective layer to prevent CoS₂ aggregation, thereby exposing additional active sites and enhancing the interface with the electrolyte. By optimizing the amount of Fe, CN/Fe-CoS₂ demonstrates a remarkably superior electrocatalytic performance and stability, as evidenced by the low overpotential (η₁₀) of 186 and 304 mV at the current density of 10 mA cm^-2 in 1.0 M KOH media for HER and OER, respectively. Overall, combining heteroatom doping and structure designing represents a promising approach to develop high-performance electrocatalysts for water splitting.