Hydrothermal CO2 Reduction with Zinc to Produce Formic Acid

Using sunlight as an energy source to split water for CO₂ reduction, artificial photosynthesis is considered as one of the most promising methods for CO₂ conversion. However, a high efficient and rapid solar-to-fuel conversion with a direct use of solar energy remains a great and fascinating challenge. The use of an integrated technology could be expected to have a high potential for improving solar-to-fuel efficiency. The abiotic synthesis of organics from CO₂ suggests that highly efficient dissociation of H₂O and subsequent reduction of CO₂ into organics could be achieved with metals under hydrothermal conditions. Thus, an integrated technology of interest for high-efficiency artificial photosynthesis could be developed by coupling the geochemical reactions involved in the dissociation of H₂O and the reduction of CO₂ in the presence of metals with the solar-driven thermochemical reduction of metal oxides into metals. In this chapter, we summarize the recent advance in highly efficient H2O dissociation with Zn for CO₂ reduction into formic acid. The content mainly includes (1) formic acid syntheses from CO₂ with water-derived hydrogen, (2) hydrogen production from water with Zn, (3) reaction mechanism study and density function theory calculation for formic acid synthesis from CO₂ and water with Zn, and (4) solar to chemical energy conversion efficiency estimation. The estimated solar–fuel efficiency of around 5% shows great potential in the proposed strategy.