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

Generation of hydrogen peroxide (H2O2) byelectrocatalytic water oxidation is a promising approach for renewableenergy utilization that motivates the development of selective catalyticmaterials. Here, we report a combined theoretical and experimentalstudy, showing that alloyed TiO2 electrodes embedded withsubsurface redox-active transition metals enable water oxidation toH(2)O(2) at low overpotentials. Density functionaltheory calculations show that first-row transition metals (Cr, Mn,Fe, and Co) serve as reservoirs of oxidizing equivalents that coupleto substrate binding sites on the surface of redox-inert metal oxides.The distinct sites for substrate binding and redox state transitionsreduce the overpotential of the critical first step of water oxidation,the oxidization of H2O* to HO* ("*" = adsorbed),enhancing the selectivity for H2O2. Electrochemicalanalysis of alloyed TiO2 electrodes with subsurface Mnfabricated 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 Vvsreversible hydrogen electrode (RHE)), a 500 mV cathodic shift whencompared to pristine TiO2 (2.3 V vs RHE). These findingsshow that otherwise inert metal oxides with subsurface redox-activesites represent a promising class of catalytic materials for a widerange of applications due to the uncoupling of substrate binding andcatalytic redox-state transitions.