Metal-enhanced strategies for photocatalytic and photoelectrochemical CO2 reduction

Using abundant solar energy resources to mitigate the negative impact of CO2 provides an effective way for the green development of human society. Photocatalytic and photoelectrochemical CO2 reduction still face certain difficulties because of the unfavorable thermodynamics and slow kinetics of CO2 reduction. In recent years, the combination of metal and photocatalyst is a promising strategy to improve the performance of photocatalyst and photocathode and made exciting progress in the field of CO2 photoreduction. Here, we summarize recent advances on the role of metals in photocatalysis and photoelectrochemical CO2 reduction. The main fundamentals and principles of CO2 reduction are first introduced, and the three major functions of metal in the CO2 photoreduction system, that are co-catalysts, single atom catalysts, and electronic media in all-solid-state Z-scheme junction, are then thoroughly summarized. In general, metal is most commonly used as co-catalyst and the loading is straightforward, and single atom performs more prominently in enhancing reactivity, while the role of electronic media in Z-system junction offers a more optimal method for building multiple composite catalysts. Finally, challenges and outlooks for developing mechanism-guided photocatalysts and photocathodes with high performance are proposed. This review is expected to facilitate the understanding on diverse functions of metal and rational design of efficient photocatalytic and photoelectrochemical systems.