Fig. 4: Mechanism of HMFOR on Ni²⁺-O-Pd interfaces.

a The catalytic cycle for HMFOR to FDCA on Ni²⁺-O-Pd interfaces derived from DFT calculations, including the intermediates and transition states. b Comparison of the energy barriers for different transition states on the Pd(111) surface and Ni²⁺-O-Pd interface. c Comparison of the energy barriers of the transition states for decarbonylation and CO oxidation on Pd(111) surface and Ni²⁺-O-Pd interface. d Proposed synergistic reaction process of HMFOR at Ni²⁺-O-Pd interfaces. Pd(111) favors aldehyde group electrooxidation, while the Ni²⁺-O-Pd interface favors HMFCA electrooxidation. e Electrochemical impedance spectroscopy measurements for HMFCA oxidation. f Kinetic studies of HMFCA oxidation over different catalysts. Polarization curves were measured in 1 M KOH + 50 mM HMFCA solution with a scanning rate of 5 mV/s with 95% iR corrected.