Phase and Composition Engineering of Mn-Doped TiO2 for Hydrogen Peroxide Synthesis through Ion-Mediated Water Oxidation

Abstract

An electrochemical two-electron (2e^–) water oxidation process provides a promising approach for on-site H₂O₂ synthesis. The design of an efficient electrocatalyst with high selectivity and productivity is crucial. In this work, manganese atoms are introduced into titanium dioxide (i.e., Mn_xTi_1–xO_y) with rutile and anatase phases for H₂O₂ synthesis through the two-electron water oxidation reaction. The anatase phase Mn_0.08Ti_0.92O_y exhibits promising activity with a low overpotential of 290 mV at 10 mA cm^–2 and Faradaic efficiency of 58% for H₂O₂ synthesis, which is twice higher than that (∼30%) of the rutile phase counterpart. Moreover, the H₂O₂ production rate on the anatase Mn_0.08Ti_0.92O_y electrode is around 51.2 μmol min^–1 cm^–2, along with 600 ppm of H₂O₂ accumulation within an 8 min reaction. Operando infrared spectroscopic analysis combined with theoretical calculations reveals that carbonate ions in the electrolyte could effectively mediate and promote active oxygen in water oxidation on Mn_0.08Ti_0.92O_y for H₂O₂ synthesis through the peroxocarbonate intermediate pathway. Compared to the rutile phase Mn_0.08Ti_0.92O_y, the much lower energy barrier for the rate-determining step (oxidation of carbonate to peroxocarbonate) of the mediated two-electron water oxidation process on the anatase phase Mn_0.08Ti_0.92O_y is achieved for boosting the catalytic H₂O₂ synthesis. This work highlights an innovative phase modulation strategy and electrolyte ion assisted electrochemical process for improving the efficiency of H₂O₂ synthesis.