A Molecular-Based Water Electrolyzer Consisting of Two Mesoporous TiO₂ Electrodes Modified with Metalloporphyrin Molecular Catalysts Showing a Quantitative Faradaic Efficiency

To achieve a molecular-based water electrolyzer promoting water splitting into H2 and O2 with a quantitative Faradaic efficiency, it is crucial to develop efficient molecular water reduction and oxidation catalysts that can work well under a common pH condition. Here we report a molecular-based water electrolyzer consisting of the mesoporous TiO2 anode and cathode respectively modified with a cobalt porphyrin O2 evolution catalyst and a platinum porphyrin H2 evolution catalyst. Under the weakly basic condition (pH 9.0), the reported molecular-based water electrolyzer evolves H2 and O2 in a 2:1 molar ratio by using the overall applied overpotential of ca. 1.0 V, and the Faradaic efficiencies for both reactions are found to be nearly quantitative (>90%). This is the first example of a molecular-based water electrolyzer promoting the overall water splitting.