Manganese oxides supported on hydrogenated TiO2 nanowire array catalysts for the electrochemical oxygen evolution reaction in water electrolysis

Hydrogenated TiO 2 /MnO x nanowires (NWs) with a diameter of 50-80 nm and a length of 0.5-0.8 μm supported on carbon cloth have been successfully prepared. The entire surface of the H-TiO 2 NWs is covered uniformly by amorphous MnO x with an average thickness of 7.0 nm. The H-TiO 2 NWs are poorly active for the oxygen evolution reaction (OER) and the MnO x as a major potential feasible electrocatalyst shows a considerable activity. The onset potential shifts negatively and the current density improves not only by the enlarged surface area of the MnO x support on the H-TiO 2 NWs, but also by a synergistic effect between TiO 2 and MnO x . The presence of three manganese oxides with different valences such as MnO, Mn 2 O 3 and MnO 2 in the H-TiO 2 /MnO x NWs is apt to effect the OER due to electron transfer. The percentage of Mn 2+ increases and the percentages of Mn 3+ and Mn 4+ decrease after the test, which proves the assumption that Mn 4+ is first reduced to Mn 3+ by electron injection from H 2 O, and then Mn 3+ is further reduced to Mn 2+ when the O 2 evolution occurs during the OER in alkaline media at pH ≥ 9. Manganese oxide/hydrogenated TiO 2 core-shell nanowires exhibited enhanced electrocatalytic activity toward the oxygen evolution reaction in water electrolysis.