Co-Ligand-Induced Electronic Modulation Controls Substrate Adsorption and Selectivity in Biomass Electrooxidation

The electrooxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is often limited by competitive adsorption between HMF and surface-bound hydroxyl species (OH_ads), which governs both activity and selectivity, yet independent control over these interfacial adsorption processes remains a fundamental challenge. Here, we report a molecular design strategy that introduces distinct anionic co-ligands into Cu-based catalysts to modulate the electronic density of the metal center and, consequently, its interaction with both OH_ads and HMF. This approach enables differential tuning of competing adsorption processes on the same active sites, effectively reshaping their intrinsic coupling under fixed reaction conditions. As a result, the optimized catalyst achieves catalyst-controlled pathway selectivity together with efficient FDCA production, delivering a Faradaic efficiency of 99%, a selectivity of 98%, and a high partial current density of 351 mA cm^-2 at 1.6 V vs. RHE. In situ attenuated total reflectance (ATR) infrared spectroscopy reveals distinct adsorption behaviors and reaction intermediates, providing molecular-level insight into the origin of selectivity. This work establishes co-ligand engineering as an effective strategy for precise interfacial adsorption control in electrocatalysis, enabling catalyst-controlled pathway selectivity beyond conventional regulation by pH and applied potential.