Production of Liquid Solar Fuels and Their Use in Fuel Cells

This review focuses on the production of liquid fuels using solar energy combined with their use in direct liquid fuel cells. The production of formic acid, which is the two-electron reduced product of CO2, as a solar liquid fuel as well as a hydrogen storage material is discussed together with its use in direct formate fuel cells. Other CO2 reduction products such as methanol and formaldehyde as solar liquid fuels as well as hydrogen storage materials are reviewed with the performance of the corresponding fuel cells. The production of nitrogen fixation products such as ammonia and hydrazine is also reviewed together with their fuel cells. Finally, the production of hydrogen peroxide from not only pure water but also seawater and dioxygen in the air using solar energy is discussed and combined with the recent development of one-compartment hydrogen peroxide fuel cells.