Stabilizing the High Spin Cobalt Atoms by Local Magnetic Asymmetry in p-Block Metals-Doped Spinel MnCo₂O₄ Catalysts for Efficient Oxygen Reduction.

Abstract

Spinel MnCo₂O₄ (MCO) is often used for electrocatalytic oxygen reduction reaction (eORR), limited kinetically by the electronic spin state of surface cobalt (Co) centers. In this work, the rate-determining step of eORR is unlocked by doping p-block metals, including Ga, In, and Pb, into MCO catalysts to stabilize the high-spin state of surface octahedral Co atoms, where the high-spin electrons are rapidly injected into triplet O₂ adsorbates. The optimal Pb-doped MCO catalyst (denoted as 0.2MCPO) as an air electrode is used to setup a solid oxide fuel cell (SOFC) device, achieving a significantly-enhanced peak power density of 1.53 W cm^-2 and remarkable stability over 210 h. The M─2O─Co covalencies make the high-spin state of surface octahedral Co atoms more stable by the p-d orbital coupling mechanism, and thus boost kinetically the electron transfer from surface Co sites to O₂ adsorbates. A combination of experimental and theoretical analysis reveals that the stable high-spin state of Co atoms enhances O₂ adsorption and activation, lowering the energy barriers for the homolytic cleavage of O₂ into two *O atoms. These findings offer fundamental insights into spin-selected electrocatalysis for ORR and a general guidance to construction of high-performance SOFC devices for energy conversion and storage.