Selective Water Oxidation to H₂O₂ on TiO₂ Surfaces with Redox-Active Allosteric Sites

Generation of hydrogen peroxide (H₂O₂) by electrocatalytic water oxidation is a promising approach for renewable energy utilization that motivates the development of selective catalytic materials. Here, we report a combined theoretical and experimental study, showing that alloyed TiO₂ electrodes embedded with subsurface redox-active transition metals enable water oxidation to H₂O₂ at low overpotentials. Density functional theory calculations show that first-row transition metals (Cr, Mn, Fe, and Co) serve as reservoirs of oxidizing equivalents that couple to substrate binding sites on the surface of redox-inert metal oxides. The distinct sites for substrate binding and redox state transitions reduce the overpotential of the critical first step of water oxidation, the oxidization of H₂O* to HO* (“*” = adsorbed), enhancing the selectivity for H₂O₂. Electrochemical analysis of alloyed TiO₂ electrodes with subsurface Mn fabricated by atomic layer deposition confirms the theoretical predictions, showing enhanced selectivity for H₂O₂ generation (>90%) due to a significant shift of the onset potential (1.8 V vs reversible hydrogen electrode (RHE)), a 500 mV cathodic shift when compared to pristine TiO₂ (2.3 V vs RHE). These findings show that otherwise inert metal oxides with subsurface redox-active sites represent a promising class of catalytic materials for a wide range of applications due to the uncoupling of substrate binding and catalytic redox-state transitions.