Engineering Gradient D-d Orbital Occupancy to Boost Substrate Adsorption for Efficient Electrocatalytic Biomass...

Electrocatalysis provides a green and sustainable approach for the upgrading of biomass-derived 5-hydroxymethylfurfural (HMF) to the polymer monomer 2,5-furandicarboxylic acid (FDCA). Precisely tuning the electronic structure, specifically the electron gradient orbitals and spin state of key active sites, is crucial for achieving high catalytic performance, as it directly influences the adsorption strength of the reactive substrate. Herein, by introducing Mn^4+/3+ with low 3d filling, the e^--e^- repulsion between bridging O^2- and Ni²⁺ is weakened due to π-donation function. Corresponding energy level splitting and partial occupancy of the spin-up state orbital determine the location and state density of the Fermi level. Based on this, an ultra-high current density of 1.2 A cm^-2 at the potential of only 1.42 V versus RHE can be achieved with a well-designed Mn-modified porous metallic skeleton Ni for HMF electrooxidation. Furthermore, continuous flow electrolysis experiments confirmed the stable FDCA production capacity, yielding 88.3% FDCA after approximately 300 h of operation. This insight into the electron gradient orbitals-activity relationship can provide valuable guidance for developing electrocatalysts for biomass upgrading.