Elucidating spin-dependent electronic modulation and activity enhancement of Fe/Ni-doped Co3O4 catalysts for alkaline HER

Understanding the catalytic mechanisms of the alkaline hydrogen evolution reaction (HER) is essential for the rational design of efficient catalysts. In this work, Fe/Ni-doped Co 3 O 4 systems were investigated by combining DFT+U calculations with experimental validation. Theoretical simulations reveal that both dopants induce spin-state transitions in Co 3+ , tune orbital hybridization, and redistribute reaction energy barriers across elementary steps rather than uniformly lowering them on the Co 3 O 4 (110) surface. Hydrothermally synthesized Fe-Co 3 O 4 and Ni-Co 3 O 4 microflower spheres confirm these predictions: Ni doping lowers the overall reaction barrier by optimizing the electronic structure and adsorption energetics associated with high-spin Co 3+ , leading to a reduced onset overpotential, whereas Fe doping facilitates water dissociation via enhanced spin polarization, thereby lowering the rate-determining barrier and improving kinetics at high current densities. Further analyses identify reliable descriptors for different catalytic advantages: the overall reaction barrier, d -band center, and covalent bonding degree of water adsorption serve as indicators of thermodynamically favorable catalysts with low overpotential, whereas the rate-determining step barrier and d-p coupling are key descriptors of kinetically favorable catalysts with enhanced current-density performance. This study clarifies the step-specific roles of spin-state modulation and provides a framework for catalyst design based on energy barrier redistribution.