Nanostrctured nickel chalcogenide electrocatalysts for the selective electro-oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA)

Composite materials based on nickel sulphide (Ni 3 S 2 ) and selenide (Ni 3 Se 2 ) with nanowire morphology were synthesised on Ni foam, modified by low-temperature hydrothermal treatment with or without Fe incorporation, and evaluated as electrocatalysts for the 5-hydroxymethylfurfural oxidation reaction (HMFOR) to 2,5-furandicarboxylic acid (FDCA), a key monomer for the production of bio-based plastics. The nickel selenide-based electrocatalysts outperformed their sulphide counterparts. Particularly, the selenide composite prepared by hydrothermal treatment at 40 °C without introducing Fe (H 2 O-Ni 3 Se 2 /Ni-foam-40) achieved nearly complete HMF conversion within 90 min at 1.6 V vs RHE (1.0 M KOH, room temperature), with 96 % yield and 94 % Faradaic efficiency towards FDCA. Under identical conditions, the benchmark Ni foam showed only 36 % HMF conversion and 7 % FDCA yield. Fe incorporation in the electrocatalyst was found to be detrimental for the HMFOR selectivity as it promoted the competing oxygen evolution reaction. In-situ Raman spectroscopy allowed identifying NiOOH as the key catalytic intermediate operating through an indirect mechanism in which HMF is oxidised by Ni(III) species that are continuously regenerated at the applied potential. The promising HMFOR performance shown by H 2 O-Ni 3 Se 2 /Ni-foam-40 was achieved with a much higher initial HMF concentration (100 mM) than generally used, bringing this electrochemical route closer to application.