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

Hydrogenated TiO2/MnOx nanowires (NWs) with a diameter of 50-80 nm and a length of 0.5-0.8 mm supported on carbon cloth have been successfully prepared. The entire surface of the H-TiO2 NWs is covered uniformly by amorphous MnOx with an average thickness of 7.0 nm. The H-TiO2 NWs are poorly active for the oxygen evolution reaction (OER) and the MnOx 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 MnOx support on the H-TiO2 NWs, but also by a synergistic effect between TiO2 and MnOx. The presence of three manganese oxides with different valences such as MnO, Mn2O3 and MnO2 in the H-TiO2/MnOx NWs is apt to effect the OER due to electron transfer. The percentage of Mn2+ increases and the percentages of Mn3+ and Mn4+ decrease after the test, which proves the assumption that Mn4+ is first reduced to Mn3+ by electron injection from H2O, and then Mn3+ is further reduced to Mn2+ when the O-2 evolution occurs during the OER in alkaline media at pH >= 9.