(521am) Selective Water Oxidation to H2O2 on Mn-Alloyed TiO2 Surfaces

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. Herein, we report a synergistic theoretical and experimental study showing that TiO₂ electrodes embedded with subsurface redox-active Mn atoms enable water oxidation to H₂O₂ at low overpotentials. Mn-alloyed TiO₂ is fabricated using a Ultratech Fiji G2 ALD system with tetrakisdimethylamido-titanium. bis(ethylcyclopentadienyl)manganese, and water as the coreactant at 150 °C with pne MnO_x ALD cycle applied for every eight TiO₂ cycles.

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 surface adsorbed H₂O* to HO* enhancing the selectivity for H₂O₂.

The electrochemical behavior of TiMnO_x electrodes was measured using a Bio-Logic S200 potentiostat system, a saturated calomel reference electrode, and a Ti foil counter electrode in a .5M phosphate buffer solution at pH 7.4. Product quantification was carried out in an H-cell configuration with a Nafion 117 membrane separating the TiMnO_x working electrode from the Ti foil counter electrode. H₂O₂ concentration was quantified by KMnO₄ spectrophotometric titration.

Electrochemical analysis of ALD grown Mn-alloyed TiO₂ electrodes confirm the theoretical predictions, showing enhanced selectivity for H₂O₂ generation (>90%) due to a significant shift of the onset potential (1.8 V vs RHE), a 500mV cathodic shift when compared to pristine TiO₂ (2.3 V vs RHE). These findings show that alloying metal oxides with subsurface redox-active sites represent a promising strategy for the design of catalytic materials due to the uncoupling of substrate binding and catalytic redox-state transitions.