The spin-coupling-dependent oxygen reduction mechanism in dual-atom catalysts

The role of electronic spin in electrocatalysis has led to the emerging field of "spin-dependent electrocatalysis". While spin effects in individual active sites have been well understood, spin coupling among multiple sites remains underexplored in electrocatalysis, which will bring forth new active sites and mechanisms. In this work, we propose a general theory to understand the spin coupling in electrocatalysis. Inspired by spintronics, the energy of the spin-polarized bond of catalyst-adsorbate can be effectively tuned by exchange splitting, resulting in a spin-dependent mechanism. To validate this hypothesis, we take the Fe₂N₆ dual-atom-catalyst (DAC) with parallel and antiparallel spin (PS/APS) alignments as an example. Our calculation demonstrates that spin exchange splitting significantly determines the ORR mechanism, leading to a huge discrepancy in ORR activity in APS-Fe₂N₆ (<i>U</i> _L = 1.04 V <i>vs.</i> SHE) and PS-Fe₂N₆ (<i>U</i> _L = 0.67 V <i>vs.</i> SHE). We further reveal that PS alignment enhances exchange splitting and strengthens OH/O₂ adsorption, while APS alignment reduces exchange splitting and weakens OH/O₂ adsorption. This mechanism is further validated with other bi-metallic DACs. Our work first unravels how spin exchange splitting alters the catalytic activity and mechanism, offering significant mechanistic insights into spin-related electrocatalysis.