Surface Reconstruction Unlocks Lattice Oxygen Activity to Promote Selective Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

Oxidation of 5-hydroxymethylfurfural (HMF) has been proposed as a promising alternative to the oxygen evolution reaction to enhance hydrogen production in alkaline media. However, the mechanistic understanding of the HMF oxidation reaction (HMFOR) has remained limited. In this study, CoSe 2 -Cu 2−x Se heterostructure composites are synthesized via a two-step hydrothermal method using cobalt(II) acetate, cupric acetate, and selenium powders as the starting materials, and the sample with a 0.4 mmol initial feed of cupric acetate stands out as the best HMFOR catalyst among the series, achieving a current density of 10 mA cm −2 at a potential of +1.265 V vs RHE and a 97% Faradaic efficiency for the production of 2,5-furandicarboxylic acid at +1.5 V vs RHE. The catalytic activity is attributed to the lattice oxygen within the amorphous hydroxyl oxide layer formed via surface reconstruction of the catalyst, which can directly and indirectly participate in HMFOR during the indirect oxidation of CoOOH/CoO 2 . Such a lattice oxygen-mediated indirect oxidation mechanism of CoOOH/CoO 2 is supported by in situ spectroscopic characterizations, 18 O-isotope labeling experiments, and density functional theory calculations. The findings of this work provide new insights into the electro-oxidation of small organic molecules, an important process for advancing electrochemical energy technologies.