Progress in Photoelectrocatalytic Reduction of Carbon Dioxide

Carbon dioxide is the most common compound. As a potential source of carbon, it can be used to prepare a variety of high value-added chemicals, such as carbon monoxide, methane, methanol, and formic acid. The traditional method of thermal catalytic conversion of CO2 requires high energy consumption and harsh reaction conditions. Therefore, the efficient conversion of CO2 to value-added chemicals under mild conditions has long been an area of great interest in the field of catalysis. Photocatalysis usually takes place under mild reaction conditions and is environmentally friendly. However, pure photocatalytic reactions generally have a limited solar energy utilization efficiency and low separation efficiency of photogenerated charge carriers. In view of the above problems, the introduction of electrocatalysis on the basis of photocatalysis can improve the charge separation efficiency. At a lower overpotential, multi-electrons and protons can be transferred to CO2, thus improving the catalytic reaction efficiency. Photoelectrochemical catalysis combines the advantages of photocatalysis and electrocatalysis to improve the efficiency of the catalytic reduction of CO2, offering a new method for the clean utilization of CO2. According to the principle of photocatalysis, the absorption capacity of a semiconductor is governed by its band structure. Optimization of the band structure is a major strategy to enhance the absorptivity of photocatalysts. In addition, the loading of light-absorbent materials on photocatalysts is an effective way to enhance the photocatalytic absorption of a photocatalytic system. During photoelectrocatalytic CO2 reduction, numerous photogenerated charge carriers recombine in bulk and on the surface of the catalyst, greatly reducing the efficiency of the catalytic reaction. Therefore, increasing the separation efficiency of charge carriers is an important means to improve the photoelectrocatalytic efficiency. In photoelectrocatalytic CO2 reduction, heterojunction construction and electric field formation often lead to the efficient separation of charge carriers. The interfacial reaction is a crucial step in the photoelectrocatalytic process. After generation, the photogenerated charge carriers need to migrate to the surface of the catalyst to participate in the redox reaction. In photoelectrocatalytic CO2 reduction, electrons participate in the reduction of CO2, while holes participate in the oxidation of water. Studies show that acceleration of the interfacial reaction process is of paramount importance for improving the efficiency of the photoelectrocatalytic reduction of CO2. This review summarizes the basic enhancement strategies of photoelectrocatalytic CO2 reduction from three aspects: light absorption, charge separation, and surface reaction, based on the basic mechanism of the reduction. The future prospects and research areas are also proposed.