Efficient and cost-effective production of clean energy carriers such as hydrogen is of critical importance for sustained growth of the modern economy. Among the various approaches for sustainable hydrogen generation, solar-thermal water-splitting represents a potentially attractive and environmentally friendly option. Typical solar-thermal water-splitting schemes involve cyclic redox reactions of transition metal oxides to indirectly convert solar energy and water into separate streams of hydrogen and oxygen. In its simplest configuration, a solar-thermal water-splitting cycle involves two redox steps. In the first step, solar energy is used to decompose a metal oxide at high temperature. In the subsequent step, the decomposed metal/metal oxide is reoxidized with water, producing hydrogen. The key for the aforementioned process is the metal oxide decomposition step. To date, the endothermic decomposition reaction for most, if not all, solar-thermal water-splitting processes are conducted at temperatures above 1300 °C. Therefore, novel solar-thermal schemes that can effectively promote metal oxide reduction at lower temperatures are highly desired in order to achieve improved efficiency and economic attractiveness for solar-thermal hydrogen generation.
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