Silicon Nanostructure Arrays: An Emerging Platform for Photothermal CO<sub>2</sub> Catalysis

Abstract: Rapid population growth and the demand for energy, which is powered by unrestricted fossil fuel exploitation, have caused severe environmental problems. Thus, it is crucial to effectively exploit alternative clean energy sources. Solar energy, which is a sustainable renewable energy source, provides an effective strategy for mitigating the energy crisis and greenhouse effect without resulting in additional carbon emissions. The concept of converting carbon dioxide (CO2) into synthetic fuels is a promising solution towards realizing a sustainable carbon-neutral economy. Photocatalysis is a favorable approach for CO2 conversion, but it has limitations in terms of conversion rates, efficiency, and scalability. Therefore, the novel concept of photothermal catalysis has been proposed based on the photothermal effect of catalysts, which allows for the complete exploitation of the solar spectrum, especially infrared light that is typically wasted during photochemical catalysis. Photothermal catalysis, combining photochemical and photothermal effects, can effectively catalyze chemical reactions under mild conditions. Although various metal structures can serve as the light-absorbing and active centers for photothermal catalysis, they suffer from disadvantages such as insufficient light utilization, high cost, and poor stability. Recently, naturally abundant silicon has emerged as a prospective photothermal catalyst, especially silicon nanostructure arrays, which outperform other conventional silicon materials owing to their excellent light-harvesting ability and efficient catalytic performance. Compared with conventional photothermal catalysts, silicon nanostructure arrays have demonstrated unique catalytic performance advantages in the photothermal CO2 reduction reaction. As a platform, silicon nanostructure arrays exhibit an excellent light-harvesting ability, high specific surface area, and versatile hybridization possibilities. This review discusses the fundamental concepts and principles related to the theory and applications of photothermal catalytic CO2 conversion, the functionalities of silicon nanostructure arrays in conventional photothermal CO2 catalytic reduction, and the recent developments in photothermal CO2 catalysis using silicon nanostructure arrays. Ultimately, it provides a guide for the development direction of high-performance nanostructure arrays-based photothermal CO2 catalysts.