In-Situ Formation of High-Performance β-NiOOH OER Electrocatalysts Using Boron and Phosphorus-Enriched Ni Core-Shell Nanoparticles

Electrocatalytic water splitting is key to achieving UN Sustainable Development Goal 7, clean energy. However, electrocatalysts with increased activity and reasonable costs are needed. Ni-B, Ni-P, and Ni-B-P-based systems have recently been proposed as particularly promising candidates, but lacked either an active surface or sufficiently high B and P concentrations, which hindered their catalytic performance. Therefore, we developed a tailored synthesis of Ni-B-P electrocatalysts. The resulting core-shell nanoparticles featured a highly porous borate-phosphate shell and a metallic core. This design provided an abundance of active sites for the oxygen evolution reaction (OER) while ensuring high electrical conductivity. Furthermore, screening of the annealing temperature was performed, and significant changes in surface chemistry were observed, as revealed by X-ray photoelectron (XPS) and low-energy ion scattering (LEIS) spectroscopy. Comprehensive cyclic voltammetry (CV) and operando electrochemical impedance spectroscopy (EIS) measurements revealed that leaching of P and B facilitated the formation of β-NiOOH, a compound recognized for its highly active sites in the OER, leading to excellent performance. Our results present a facile and scalable chemical reduction procedure to obtain tailored mesoporous Ni-B-P core-shell nanoparticles, and we believe that their pronounced activation for the OER can inspire the development of in situ-activated electrocatalysts.