Constructing built-in electric field in crystalline-amorphous heterostructure bifunctional electrocatalysts for highly efficient overall water splitting at high current density

• • The FNS/HEOXY(In) heterostructure electrocatalyst achieves overpotentials of 180 mV for OER and 230 mV for HER at 100 mA cm−2 in alkaline solution, outperforming conventional Ni3S2-based catalysts and approaching noble metal benchmarks. • • The catalyst sustains stable operation for 2000 hours at industrial current densities of 0.5, 1, and 2 A cm−2, demonstrating exceptional durability critical for commercial electrolysis. • • An AEMWE assembled with FNS/HEOXY(In) electrodes requires only 1.86 V to deliver 1 A cm−2 at 80 °C, with continuous operation for 400 hours, meeting industrial voltage and stability targets. • • The built-in electric field, induced by a large work function difference between crystalline FNS and amorphous HEOXY, optimizes adsorption energies of reaction intermediates, as confirmed by experimental and theoretical analyses.