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 CoMn 2 O 4 to mediate and accelerate electron transfer. Through precise valence state regulation, we engineer a heterogeneous electron bridge dominated by Mn 4+ -O 2- -Co 3+ linkages, enabling more efficient electron flow. Experimental characterization and theoretical calculations reveal that the incorporation of Mn 4+ significantly enhances electron delocalization across the bridge. The empty e g orbitals of Mn 4+ ( t 2g 3 e g 0 ) serve as efficient electron acceptors, creating an energy-level gradient with Co 3+ ( t 2g 4 e g 2 ) that favors directional electron transfer. Simultaneously, Mn 4+ 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.