Medium‐Entropy Metal Selenides Nanoparticles with Optimized Electronic Structure as High‐Performance Bifunctional Electrocatalysts for Overall Water Splitting

Abstract Development of low‐cost and high‐efficiency electrocatalysts for overall water splitting is of great significance in the sustainable hydrogen economy. Herein, Fe_1.2(CoNi)_1.8Se_x medium‐entropy metal selenides (MESes) nanoparticles are prepared via the selenylation of metal‐organic frameworks (MOFs) precursors. The optimal Fe_1.2(CoNi)_1.8Se₆ MESe exhibits an outstanding electrocatalytic performance in alkaline media, offering low overpotentials of 66 and 216 mV at 10 mA cm⁻² for the hydrogen evolution reaction and oxygen evolution reaction, respectively. A full electrolysis apparatus with Fe_1.2(CoNi)_1.8Se₆ MESe as both cathode and anode displays an excellent performance, achieving 10 mA cm⁻² at a potential of 1.55 V. Furthermore, density functional theory calculations demonstrate that the formation of MESe enhances the surface charge density and brings the d‐band center closer to Fermi level, as compared with that of the MOF precursor. Overall, the proposed strategy of medium‐entropy materials presents a low‐cost approach to fabricate energy storage and conversion devices.