Unraveling the Electrooxidation Mechanism of 5-(Hydroxymethyl)furfural at a Molecular Level via Nickel-Based Two-Dimensional Metal-Organic Frameworks Catalysts

Electrochemical conversion of biomass can mitigate environmental issues while providing a substitute for fossil products, yet it is challenging to construct efficient catalysts due to the limited understanding of the reaction mechanism. Here, two well-defined Ni-O₄ and Ni-(NH₂)₄ centers supported on two-dimensional conductive metal organic frameworks (2D MOFs, Ni-HHTP and Ni-HITP) catalysts were reported for the exploration of 5-(hydroxymethyl) furfural (HMF) electrochemical oxidation (e-HMFOR). The single Ni-O₄ site in Ni-HHTP exhibited superior catalytic activities with high turnover frequencies (TOF, 0.219 s^-1) and stability (5 cycles, ∼20 h) in the alkaline electrolyte. By virtue of the 2D MOFs model electrocatalysts combined with the ex situ ESR characteristics and oxidation products online tracking in different reaction systems, we identified that the coordination atoms with Ni played a key role on the electrocatalytic performance. The higher its electronegativity, the stronger dehydrogenation capacity of hydroxymethyl, aldehyde, and H₂O, which could efficiently promote the conversion of HMF. Moreover, the clear reaction pathway of e-HMFOR, especially the specific interaction process between HMF and the active sites, was also disclosed. This study offers well-defined and stable 2D MOFs electrocatalysts for systematically studying the distinct e-HMFOR mechanism and provides a theoretical guidance for the design of efficient aldehyde and hydroxymethyl oxidation electrocatalysts.