Multi-heterojunction engineering in FeCoW–S/NF for ultra-low-overpotential hydrogen and oxygen evolution reactions

The pursuit of cost-effective, highly active, and durable non-precious metal electrocatalysts is pivotal for advancing next-generation sustainable energy technologies. In this study, we introduce a bifunctional FeCoW–S/NF electrocatalyst, fabricated on a conductive nickel foam (NF) substrate through an innovative electrodeposition-etching-sulfidation approach. The catalyst features engineered multi-heterojunctions, including CoFe 2 O 4 /WS 2 , WS 2 /Ni 3 S 2 , Ni 0.96 S/Ni 3 S 2 , WS 2 /Ni 0.96 S, and CoFe 2 O 4 /Ni 3 S 2 , synergistically integrated within a 3D porous architecture. This unique structural design maximizes exposed active sites, enhances electronic conductivity, and facilitates rapid charge transfer and mass transport, leading to superior electrocatalytic performance in both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Remarkably, the FeCoW–S/NF catalyst exhibits outstanding activity in alkaline media (1 M KOH), achieving industrially relevant current densities of 10 mA cm −2 at ultralow overpotentials of 52 mV for HER and 105 mV for OER. When deployed as a bifunctional catalyst for overall water splitting, the system delivers 10 mA cm −2 at a remarkably low cell voltage of 1.50 V, while maintaining exceptional stability (about 95 % retention) over 100 h of continuous operation, surpassing most recently reported state-of-the-art non-precious metal electrocatalysts. This work not only presents a highly efficient and stable electrocatalyst but also establishes a novel synthetic strategy for designing advanced metal sulfide-based bifunctional catalysts, paving the way for scalable and sustainable hydrogen production. • The co-doping of Fe/Co/W/Ni/S establishes abundant exposed active sites. • Low overpotential of 52 mV for HER and 105 mV for OER. • Remarkable current density of 10 mA cm −2 at 1.5 V for water splitting. • S doping induced defect-engineered heterojunctions, which is key to its properties.