Boron Doping-Induced Lattice Strain Engineering in Cobalt Diselenide: Regulating Cobalt Spin States for Enhanced...

Spin polarization is a promising strategy for the oxygen evolution reaction (OER) due to the spin-dependent behaviors of intermediates, but its application in transition metal chalcogenides for anion-exchange membrane water electrolyzers (AEMWE) remains rarely reported. Here, density functional theory calculations reveal that partial substitution of selenium (Se) by boron (B) in cobalt diselenide (CoSe₂) induces lattice contraction strain, reducing the spin polarization degree of cobalt (Co) and triggering a high-spin to low-spin transition. Experimental results confirm the presence of compressive strain and enhanced catalytic performance in B-doped CoSe₂. Notably, the B2-CoSe₂ sample, featuring a lattice strain of -0.27%, achieves a current density of 50 mA cm^-2 at an overpotential of only 367 mV in 1 M KOH-35 mV lower than that of pristine CoSe₂. When applied to an AEMWE, this catalyst requires only 2.05 V to achieve a current density of 1 A cm^-2 and exhibits exceptional stability over 120 h at 25 °C in 1 M KOH electrolyte, outperforming commercial RuO₂. Collectively, these findings demonstrate that B-doping-induced lattice contraction strain plays a critical role in modulating the spin polarization and spin state of Co, thereby providing a new paradigm for designing OER catalysts through lattice strain engineering.