Development of electrocatalysts capable of efficiently oxidizing biomass-derived 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA) is critically important for production of degradable plastics via non-fossil routes. Herein, we report a facile and scalable immersion synthetic approach to in situ grow ultrathin nickel hydroxide nanosheets on commercial nickel foam (Ni(OH)2/NF) as an anode to electrocatalytically oxidize HMF to FDCA with complete HMF conversion, 100% FDCA yield and > 99% Faraday efficiency at 1.39 V (vs RHE) within 90 min. The mechanistic studies unveil that the initial oxidation of HMF takes place on its carbonyl group and FDCA is yielded through two further oxidation steps. Impressively, the synthesized Ni(OH)2/NF can also be used to electrocatalytically oxidize other alcohol/aldehyde containing compounds to the targeted products in alkaline medium with 100% yield and > 94% faradic efficiency under a low oxidation potential of 1.39 V (vs. RHE) within short reaction times.