Solar-processed metals as clean energy carriers and water-splitters

Two-step solar thermochemical cycles and processes for the production of hydrogen, hydrocarbons, and synthesis gas are considered. The first step is based on the thermal, electrothermal, or carbothermal reduction of metal oxides, producing metals, metal nitrides, metal carbides, or lower-valence metal oxides. These are high-temperature highly endothermic reactions that can be driven by concentrated solar energy, reducing the consumption of fossil fuels and their concomitant emissions. The second step involves hydrolysis reactions. The thermodynamics of both reaction steps are examined and relevant experimental studies conducted using solar energy are reviewed.