Adams Metal Oxide Catalysts for Solar Driven Water Splitting

The widespread utilisation of solar driven water is hindered by the use of expensive and unstable materials. Herein, we show that highly active earth abundant metal oxide oxygen and hydrogen evolution electrocatalysts can be synthesised using the Adams method, in which the metal salts are oxidised in a melt of sodium nitrate and that such oxides are usually highly crystalline powders with high specific surface areas. Disc electrodes of the Adams method metal oxides: RuO2, Mn2O3, Co3O4 and NiO are prepared using a recently reported mechanical, solvent-free method, involving pressing a mixture of the metal oxide and a small amount (5 wt%) of PTFE powder. Each electrode is tested as an electrode for the hydrogen evolution reaction, HER, and oxygen evolution reaction, OER, in 1 M NaOH. In the former role, Mn2O3 appears better than a platinum wire electrode (overpotential at 10 mA cm-2, 10, = 61 mV, cf. 70 mV, for Pt). In the OER study, although RuO2 is the best electrocatalyst, 10, = 267 mV, Co3O4 is also very effective, 10, = 330 mV. Using Mn2O3 as the cathode and Co3O4 as the anode, a silicon solar cell is used to photocleave water into H2 and O2. The wide spread utilisation of solar driven water is hindered by the use of expensive and unstable materials. Herein, we show that highly active earth abundant metal oxide oxygen and hydrogen evolution electrocatalysts can be synthesised using the Adams method, in which the metal salts are oxidised in a melt of sodium nitrate and that such oxides are usually highly crystalline powders with high specific surface areas. Disc electrodes of the Adams method metal oxides: RuO2, Mn2O3, Co3O4 and NiO are prepared using a recently reported mechanical, solvent-free method, involving pressing a mixture of the metal oxide and a small amount (5 wt%) of PTFE powder. Each electrode is tested as an electrode for the hydrogen evolution reaction, HER, and oxygen evolution reaction, OER, in 1 M NaOH. In the former role, Mn2O3 appears better than a platinum wire electrode (overpotential at 10 mA cm-2, 10, = 61 mV, cf. 70 mV, for Pt). In the OER study, although RuO2 is the best electrocatalyst, 10, = 267 mV, Co3O4 is also very effective, 10, = 330 mV. Using Mn2O3 as the cathode and Co3O4 as the anode, a silicon solar cell is used to photocleave water into H2 and O2.