Engineering an Electron-Rich Microenvironment in Ni–NiWO4 Heterostructures as High-Performance Electrocatalysts for H2 Production at High Current Density

Exploration of efficient and nonprecious electrocatalysts is essential to propel water electrolysis toward developing a sustainable world. Herein, we demonstrated heterogeneous Ni–NiWO 4 nanostructures grown in situ on nickel foam (NF) (Ni–NiWO 4 /NF), serving as effective bifunctional electrocatalysts toward the hydrogen evolution reaction (HER) and urea oxidation reaction (UOR), enabling high-performance overall urea splitting reaction (OUS) in both freshwater and seawater. The favorable porous architecture provides a large electrochemically active surface area and facilitates mass transfer. The coupling between Ni nanoparticles and the NiWO 4 matrix creates an electron-rich microenvironment and modulates the electronic states of the active sites, which provides optimal chemical affinities for various reaction intermediates, as confirmed by our calculation through density functional theory calculations. Specifically, the Ni–NiWO 4 /NF electrocatalyst exhibits low overpotentials of 26 mV@10 mA cm –2 , 126 mV@100 mA cm –2 , and 156 mV@200 mA cm –2 in alkaline freshwater and 31 mV@10 mA cm –2 , 162 mV@100 mA cm –2 , and 212 mV@200 mA cm –2 in alkaline seawater for the HER. Remarkably, the overpotential is as low as 265 mV, even when the current density was evaluated to be as high as 1.0 A cm –2 . For the UOR, it demonstrates low potentials of 1.292 V@10 mA cm –2 , 1.343 V@100 mA cm –2 , and 1.374 V@200 mA cm –2 in alkaline freshwater and 1.307 V@10 mA cm –2 , 1.358 V@100 mA cm –2 , and 1.387 V@200 mA cm –2 in alkaline seawater. Notably, the recorded voltage for the OUS reaction decreases to 1.366 V in freshwater and 1.390 V in seawater. Additionally, the catalyst demonstrates excellent long-term stability in seawater for 100 h at 10 mA cm –2 . Furthermore, we successfully demonstrated solar-powered green hydrogen production at a rate exceeding 510 L h –1 m –2 , showcasing its strong potential for the practical application of direct solar-to-hydrogen conversion.