Tuning the Spin Density of Cobalt Single-Atom Catalysts for Efficient Oxygen Evolution

Single-atom catalysts (SACs) with magnetic elements as the active center have been widely exploited for efficient electrochemical conversions. Understanding the catalytic role of spin, and thus modulating the spin density of a single-atom center, is of profound fundamental interest and technological impact. Here, we synthesized ferromagnetic single Co atom catalysts on TaS₂ monolayers (Co₁/TaS₂) as a model system to explore the spin-activity correlation for the oxygen evolution reaction (OER). A single Co atom adsorbed at the hollow site (Co_HS) with spin-polarized electronic states serves as the active site for OER, whose spin density can be regulated by its neighboring single Co site via tuning the Co loading. Both experimental and theoretical results reveal the spin density-dependent OER activity that an optimal spin density of Co_HS can be achieved with a neighboring hetero-single Co_Ta site (substitution of Ta by Co) for a superior OER performance, in contrast to a homo-single Co_HS site, which creates an excessive spin density over vicinal Co_HS. An optimized spin density of Co_HS results in an optimal binding energy of oxygen species for the OER. Establishing the spin-activity correlation in SACs may create a descriptor for designing efficient magnetic SACs for renewable energy conversions.