Dopant-Directed Activity in NiOOH: Distinct Fe, Co, and Cu Roles in Electrocatalytic HMF Oxidation to FDCA

Electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) offers a sustainable route to bio-based plastics that can replace petroleum-derived PET. Here, we systematically compare NiOOH and Fe-, Co-, and Cu-doped NiOOH electrocatalysts synthesized by pulsed electrodeposition with matched loadings and dopant distributions, enabling a direct one-to-one assessment of dopant effects on HMFOR in alkaline media. Among all catalysts, NiFeOOH delivers the highest activity and selectivity across the full potential range, reaching an FE_FDCA of 87.42% and an FE_HMFOR of 98.85% at 1.53 V versus reversible hydrogen electrode. Scaling the electrode area fivefold achieves near-quantitative HMF conversion (99.98%) with a 95.45% FDCA yield over 6 h while maintaining excellent durability. Mechanistic investigation via potential-dependent product analysis, in situ Raman spectroscopy, spontaneous kinetics, and density functional theory reveals dopant-specific functions: Fe strongly tunes the Ni³⁺ electronic structure to weaken Ni³⁺-O bonding, enhance substrate adsorption, and accelerate charge transfer; Co primarily increases electrochemical surface area, boosting site density but not intrinsic site reactivity; and Cu alters the rate-determining step, redirecting the reaction pathway. These insights show that different dopants offer distinct design levers in Ni-based HMF oxidation reaction (HMFOR) catalysts and motivate multidopant strategies to jointly tune electronic structure, morphology, and reaction pathways for improved performance.