Spin-Polarization-Activated d–p Orbital Coupling Enables Optimal Oxygen Reduction Reaction of Cobalt

Abstract

The spin configuration of electrons is inherently linked to catalytic activity, particularly in the oxygen reduction reaction (ORR). Since the regulation of electron distribution in the d orbital of a metal center affects the spin state greatly, the adsorption behavior of active sites is influenced by intermediates. Herein, a straightforward adsorption-pyrolysis strategy was employed to co-anchor Co and S atoms onto amorphous carbon (CoN_xS_4–x, x = 1, 2, 3). As a result, the presence of S enhances the Co spin state (t2g4eg2). In the high-spin state, the electron back-donation effect of Co³⁺ becomes more pronounced. As this effect strengthens the Co and O orbital coupling (d–p), it facilitates the conversion of the ligand of O₂ to *OOH and remarkably improves the reaction kinetics. Consequently, the case of CoN₁S₃ has demonstrated superior catalytic performance (E_1/2 = 0.88 V), surpassing noble metal catalysts and most recently reported Co-based catalysts.