The Origin of High Overpotentials: Catalyst Reconstruction into High-Energy State Governs Organic Electrooxidation

The substantial overpotentials in organic electrooxidation remain poorly understood, as conventional static catalyst models overlook dynamic reconstruction and its associated energy cost. Here, we demonstrate that catalyst reconstruction, not molecular conversion kinetics, governs the overpotential, using the Ni(OH) 2 /NiOOH model system. The Ni(OH) 2 → NiOOH transition imposes a phase transformation barrier of 1.87 eV, substantially exceeding the rate-determining barrier for urea conversion (0.93 eV). Correspondingly, the Ni 2+ (t 2g 6 e g 2 ) → Ni 3+ (t 2g 6 e g 1 ) transition involves a 2.45 eV Fermi level jump, creating a high-energy NiOOH state with an unoccupied e g orbital that drives electron transfer from the substrate's orbitals. Kinetically, urea oxidation on this potential-maintained Ni 3+ state is facile, with a near-zero apparent activation energy. Consequently, the high applied potential is expended to generate and sustain the high-energy Ni 3+ state, whose unoccupied e g orbital enables direct electron transfer with a low kinetic barrier. Collectively, these converging lines of evidence establish catalyst reconstruction as the dominant step governing overpotential, redefining catalyst design toward minimizing or avoiding the energy cost of accessing such high-energy catalytic states.