Multiscale structural optimization: Highly efficient hollow iron-doped metal sulfide heterostructures as bifunctional electrocatalysts for water splitting

Hollow iron-doped Co–Mo sulfide (H–Fe–CoMoS) heterostructures with a highly efficient water-splitting catalytic ability were achieved by applying a multiscale optimization strategy. Morphological and compositional optimization on a macroscale achieved by assembling a bimetallic Co–Mo sulfide (CoMoS) heterostructure in a hollow-structured composite (H–CoMoS) gave the electrocatalyst an ability to conduct enhanced bifunctional activities for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Intrinsic electronic structure optimization on a microscale achieved by introducing a small amount of iron (Fe) into H–CoMoS (H–Fe–CoMoS) further improved its catalytic activity and stability. Electrochemical measurements revealed that this multiscale structural optimization promoted enhanced electrical conductivity and increased the number of electrochemical active sites on the H–Fe–CoMoS, leading to its remarkable electrocatalytic performance as a bifunctional catalyst for both HER and OER in alkaline media. The H–Fe–CoMoS showed overpotentials of 282 mV and 137 mV to achieve a current density of 10 mA cm⁻² for OER and HER, respectively, which are comparable to the performance of the benchmark OER catalyst RuO₂ and HER catalyst Pt/C.