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.