Valence-tuned electron bridge enables high-yield multi-electron HMF oxidation over spinel catalysts

The catalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid is a key step in the production of bio-based plastics but remains limited by sluggish multi-electron transfer kinetics across multiple reaction intermediates. In this study, we address this long-standing challenge by introducing a Mn-O-Co electron bridge within spinel CoMn₂O₄ to mediate and accelerate electron transfer. Through precise valence state regulation, we engineer a heterogeneous electron bridge dominated by Mn⁴⁺-O^2--Co³⁺ linkages, enabling more efficient electron flow. Experimental characterization and theoretical calculations reveal that the incorporation of Mn⁴⁺ significantly enhances electron delocalization across the bridge. The empty e_g orbitals of Mn⁴⁺ (t_2g³e_g⁰) serve as efficient electron acceptors, creating an energy-level gradient with Co³⁺ (t_2g⁴e_g²) that favors directional electron transfer. Simultaneously, Mn⁴⁺ strengthens metal-oxygen covalency, further improving electron mobility. This engineered electron bridge structure enables highly efficient cooperation across the full six-electron transfer pathway in 5-hydroxymethylfurfural oxidation, driven by a dynamic electron compensation mechanism. As a result, an 2,5-furandicarboxylic acid yield of 98.1% is achieved. This work offers a valuable theoretical foundation for understanding cooperative electron transfer in heterogeneous catalysis and provides a rational strategy for designing efficient electron bridge structures.