Atomically well-mixed quad-metallic sulfide as multi-functional electrocatalyst for overall water electrolysis and zinc-air battery

A non-precious-metal medium entropy sulfide (MES) embedded in sulfur-doped polyacrylonitrile-derived carbon fiber (SPAN-FCNM) has been successfully designed to maximize the synergistic effects among the atomically well-mixed constituents and exhibits superior trifunctional electrocatalytic performances toward the overall alkaline water electrolysis and oxygen reduction reactions. This catalyst achieves low overpotentials (η) for the oxygen evolution reaction (η10 = 210 mV) and hydrogen evolution reaction (η10 = 55 mV) with a minor efficiency decay of 7.5% under 100-h continuous operation in 1 M KOH at 500 mA cm−2. In addition, a zinc-air battery with the SPAN-FCNM-coated air electrode exhibits an extraordinary energy efficiency (1st cycle = 60.9%; 90th cycle = 58.9%) at the industrially relevant discharge/charge current density of 50 mA cm−2 for over 60 h. Therefore, rational design to maximize the synergistic effects through atomically well-mixed composition, as realized in entropy-maximized materials, successfully demonstrates the breakthrough in the catalyst design.