Uniting Heat and Light in Heterogeneous CO₂ Photocatalysis: Optochemical Materials and Reactor Engineering

ConspectusThe rapid increase in atmospheric CO2 concentration (∼420 ppm) has become one of the significant issues threatening human survival. As an effective measure to solve this major problem, renewable energy-powered catalytic CO2 conversion technologies have received vast attention in both academia and industry. Among these techniques, photothermal catalysis is a rising star with promising potential for CO2 conversion even under milder conditions. Indium oxide was among the first to be used in photothermal CO2 catalysis, and through its various forms, stoichiometries, and surface chemistry, it has become one of the most well-studied photothermal catalyst systems. Indium oxide is a highly tunable semiconductor for CO2 photocatalysis, which can be driven by both light photochemically and heat photothermally, thereby serving as an archetype for understanding how to optimize its performance for storing solar as chemical energy, through creative materials chemistry.Our solar fuel cluster discovered photothermal CO2 catalysis over indium oxide in 2014 and has long been committed to the study of this field. Photothermal catalysis by semiconductors like indium oxide can be deconstructed into three key processes: photochemistry, thermochemistry, and surface chemistry. To be specific, photoexcited electron–hole pairs can enable redox and acid–base surface chemical reactions. Phonons and plasmons can drive these reactions photothermally. Surface active sites, such as surface frustrated Lewis pairs and oxygen vacancies, can amplify product activity and selectivity. Designer synergism between all of these effects ultimately determines the overall performance metrics of photothermal CO2 catalysis. Thus, to design and optimize a photothermal catalyst, the three aforementioned key processes should be considered synergistically.In this Account, indium oxide-based catalysts are selected as an archetype to introduce the process of photothermal CO2 catalysis and the advancements of indium oxide-based catalysts mainly from our solar fuel cluster are summarized. In detail, the strategies of material design are introduced systematically with the three key processes: photochemistry, thermochemistry, and surface chemistry. Moreover, a foreseeable future of the emerging field of optochemical engineering of photothermal catalysis, ranging from potential reactions to reactor design, is included as the perspective as well. In other words, this Account is dedicated to exploring how chemically tailored indium oxide-based catalyst has served as a platform material for understanding photothermal CO2 catalysis and how this know-how is enabling the design of high quantum efficiency photocatalysts and photoreactors. A comprehensive understanding of these points is the key to the development of the emerging field of optochemical materials and reactor engineering of heterogeneous CO2 photocatalysis.