Spin-state engineering of octahedral Co via tetrahedral Ni in NiCo2O4 for electrocatalytic glucose oxidation to formate

Abstract

Electrocatalytic glucose oxidation to high-value chemicals provides a sustainable route for biomass valorization. NiCo-based catalysts have emerged as promising candidates for glucose oxidation reaction owing to the intrinsic activity of Ni and Co catalytic centers. However, the dynamic evolution and atomic-scale synergy between these centers remain elusive. Herein, we fabricated NiCo₂O₄ nanosheets supported on nickel foam, where Ni preferentially occupies tetrahedral sites to regulate the electronic configuration of octahedral Co. Experimental and theoretical results demonstrate that the incorporation of tetrahedral Ni induces low-to-intermediate spin transition in octahedral Co, thereby optimizing e_g orbital occupancy and stabilizing active sites. This spin-state engineering establishes Ni-Co synergistic catalytic centers for the selective oxidation of glucose to formate (FA). At higher potential (≥1.4 V vs. RHE), octahedral Co undergoes reconstruction into excessive active CoOOH and CoO₂ species, resulting in glucose overoxidation to CO₂ and intensified competitive oxygen evolution. In contrast, at lower potentials (<1.4 V vs. RHE), tetrahedral Ni facilitates electron delocalization across the Ni–O–Co lattice, thereby stabilizing octahedral Co for glucose adsorption and oxidation. Subsequently, a coupled electrocatalytic system was constructed, achieving 80.7 % FA yield with 91.3 % Faradaic efficiency (FE) at NiCo₂O₄ anode and H₂ evolution rate of 696 μmol h⁻¹ with 99.9 % FE at Pt cathode for 2 h under 1.35 V vs. RHE. This work provides a deep insight into spin-state regulation of the catalytic center, offering valuable guidance for rational catalyst design.