Modulating the d-band centers by coordination environment regulation of single-atom Ni on porous carbon fibers for overall water splitting

The coordination environment of metal atoms is at the center of designing high-performance single-atom catalysts (SACs), which deserves to provide appropriate metal–support interaction. Herein, we propose a coordination environment regulation strategy to modulate the d-band center of Ni by introducing different heteroatoms, such as N, N-B, N-P, N-S, into porous carbon nanofibers (CNFs), which enables to optimize the geometrical and electronic structures of isolated Ni atoms, thus tunes the interaction between Ni center and intermediates for effective water splitting. The experimental and theoretical results indicate the d-band center of Ni atoms coupled with three N atoms and one P atom is tailored to moderate position to create favorable binding with H/O-containing intermediates, thus leading to benefitting thermodynamics and kinetics for both hydrogen and oxygen evolution. As a proof, the designed Ni-N,P/CNFs with Ni-N₃-P moiety shows extraordinary overall water splitting ability, superior to other coordination configurations. Notably, the acidic hydrogen evolution reaction upon Ni-N,P/CNFs present ultralow overpotential of 38 mV to afford 10 mA cm⁻² and Tafel slope of 24 mV dec⁻¹, placed at the top of reported single-atom-based catalysts. Such concept of modulating d-band center could provide in-depth insight into the design and performance optimization of SACs.