A dynamic Ni(OH)2-NiOOH/NiFeP heterojunction enabling high-performance E-upgrading of hydroxymethylfurfural

Facilely upgrading 5-Hydroxymethylfurfural (HMF) via controllable oxidation of aldehyde and hydroxymethyl groups has attracted increasing attention since one of the products, 2,5-Furandicarboxylic acid (FDCA), is of great industrial value. Herein, the surface reconstruction of NiFeP and underlying dynamic Ni(OH)2-NiOOH transformation are characterized under electro-anodic HMF oxidation reaction (HMFOR). The Ni(OH)2-NiOOH/NiFeP heterojunction presents extraordinary HMFOR performance and produces FDCA with a yield over 99% and a Faradaic efficiency over 94%. The reconstructed NiOOH is suggested to chemically (not electrochemically) oxidize HMF while itself is reduced back to Ni(OH)2; The applied anodic potential then drives the oxidation of Ni(OH)2 to NiOOH, to circlize the HMF oxidation process. Meanwhile, the deeper oxidation of NiOOH to NiO(OH)2 or beyond can drive the oxygen evolution reaction (OER). Therefore, a NiOOH-centered dual-circle mechanism is unraveled to understand the entangled and competitive HMFOR and OER, which will be helpful to design better HMFOR electrocatalysts.