Amorphous-crystalline CoFeB/NiPS₃ vertical heterostructure with a built-in electric field for robust ampere-level water oxidation

Highly efficient oxygen evolution reaction (OER) electrocatalysts play a paramount role in future hydrogen energy deployment. The quest for earth-abundant OER catalysts is actively pursued for the sustainable deployment of water electrolysis. In this work, an amorphous-crystalline CoFeB/NiPS₃ heterostructure was successfully fabricated to realize highly active water electrolysis. The heterostructure delivered an overpotential as low as 285 mV at 50 mA cm⁻² and an ultrasmall Tafel slope of 96 mV dec⁻¹, with impressive stability for 24 h. This powder achieved an excellent ampere-level current density of over 1 A cm⁻². Theoretically, density functional theory (DFT) calculations exhibited that CoFeB/NiPS₃ has the smallest energy barrier for the formation of *OOH species (0.91 eV). It was also revealed that the presence of an internal polarization field (IPF) accelerates the electron transfer from CoFeB to NiPS₃. This research provides a new opportunity for the development of all transition metal-based amorphous-crystalline heterostructure electrocatalysts for large current density water splitting.