Designing a Glycerol Oxidation Electrocatalyst through Active Site Identification and Optimisation in Co₃O₄

Precise identification of active sites in electrocatalysts is pivotal for rational design and performance breakthroughs. Co₃O₄ has been extensively studied as an promising glycerol oxidation catalyst, yet its true active sites remain unidentified. This study systematically elucidates that the GOR activity of Co₃O₄ is critically governed by the geometric coordination environment of cobalt sites, achieved through the precise synthesis of three spinel-structured catalysts: Co₃O₄, MgCo₂O₄, and CoAl₂O₄. It further demonstrates that GOR predominantly occurs at octahedral Co sites (Co³⁺_Oh) rather than tetrahedral Co sites (Co²⁺_Td). Building upon this insight, to further enhance the intrinsic activity of Co³⁺_Oh, we successfully constructed the CuCo₂O₄/NF catalyst by replacing inert Co²⁺_Td with Cu²⁺ cations. This catalyst exhibits outstanding GOR performance in alkaline media, delivering 10 mA cm^-2 at only 1.16 V vs RHE and sustaining stable performance over 120 h under galvanostatic conditions. Notably, CuCo₂O₄/NF attains a Faradaic efficiency of 98.04% for formic acid conversion at 1.40 V vs RHE. This work not only clarifies the structure-activity relationship between cobalt oxidation state in Co₃O₄ and GOR activity but also develops a superior catalyst through cation substitution strategies. It provides a pioneering and effective strategy for designing highly robust and stable spinel electrocatalysts.