Photocatalytic CO₂ Reduction

Previous chapters address the production of hydrogen and/or oxygen via water splitting. Photocatalytic reduction of CO₂ to form hydrocarbon fuels is also economical, recyclable, and safe and provides an ideal way to addressing worldwide energy and environmental problems. Such a transformation process usually involves solar energy absorption, photoexcitation, surface molecule adsorption and activation, surface redox reactions, and detachment of product molecules. The multiple and complex steps usually result in the limited energy conversion efficiency for CO₂ reduction. In principle, in addition to developing or modifying photocatalysts with high activity, selectivity, and stability, the spatiotemporal divergences involved in the entire energy and mass transfer process should also be focused. In this chapter, the whole processes of photocatalytic CO₂ reduction are analyzed from the perspectives of energy and mass flow. The flow of solar energy through concentrator, reactor, reaction solution, and photocatalyst and the mass flow from the adsorption and activation of reactants (such as CO₂ ^-) on the surface of the photocatalysts to the formation of CO, CH₄, and other products through photocatalytic reaction are all discussed in detail. Furthermore, the energy loss and obstacles contained in the transformation processes and the possible strategies to improve the overall reaction efficiency are analyzed as well.