Spatially coupled Ni₂P/CoP-8 heterostructures with superwetting interfaces for high current density overall water...

Water electrolysis is crucial for a sustainable hydrogen economy, but stable bifunctional catalysts at high current densities remain a significant challenge. This work developed a Ni₂P/CoP-8 heterojunction catalyst featuring a spatially coupled architecture, composed of a needle-like inner layer and a sea-urchin-like outer layer. Specifically, the inner layer ensures strong adhesion and fast electron transport, while the outer layer provides abundant catalytic sites, improving electrolyte penetration and accelerating gas evolution. With a distinctive architecture, the Ni₂P/CoP-8 catalyst maintains prolonged durability, operating continuously for 400 h at an industrial-level current density of 1000 mA cm^-2. It simultaneously exhibits superior bifunctional catalytic performance for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), with minimal overpotentials of 34 mV and 196 mV, respectively. Additionally, it enables efficient overall water splitting, requiring only 1.37 V to reach a current density of 10 mA cm^-2. In addition, in situ Raman spectroscopy unveils that the electrochemically transformed surface layers (NiOOH/CoOOH) serve as active phases for enhanced OER performance. Ultraviolet photoelectron spectroscopy (UPS) and density functional theory (DFT) calculations indicate that the heterointerface induces electron transfer from Co to Ni. This optimizes the adsorption strength of H* and *OH, significantly enhancing the intrinsic activity. This work demonstrates stable and highly active electrocatalysts for overall water splitting under high current density through a spatial coupling strategy, thereby contributing to practical applications.