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

Abstract

Conspectus The 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.

Wettability Engineering of Solar Methanol Synthesis

“…8 The generation of heat arises from the nonradiative relaxation of light-induced charge carriers on In 2 O 3 . 26,27 The presence of alkylsilanes establishes a thermal insulating layer, effectively curbing thermal conduction and augmenting the local temperature of S2 by approximately 12 °C. 28,29 Nonetheless, even when compared to the S0 sample tested in the dark at 242 °C, the S2 sample tested at 200 °C under light still exhibits a significantly higher methanol production rate, with an increase of ∼464 μmol g cat −1 h −1 (Figure S14C).…”

Synergistic Modulation between Non-thermal and Thermal Effects in Photothermal Catalysis based on Modified In2O3

“…Meanwhile, the thermal effect is manifested through an increase in system temperature, which may be attributed to non-radiative relaxation of semiconductors, 14,15 localized heating induced by plasma, 16−18 thermal vibration of molecules, 19 as summarized in our previous work. 20 It is noteworthy to distinguish the subtle differences from the definitions of "photochemistry" and "thermochemistry," "photochemical" and "photophysical" effects, and "photochemical" and "photothermal" effects in other studies. 13,21−24 Obviously, there is currently growing evidence that synergistic mechanisms in non-thermal and thermal effect are of particular interest.…”

“…It is concluded that light excitation generates highenergy carriers to participate in the reaction, thereby promoting the activation of reactants, reducing the reaction energy barrier, adjusting the reaction paths, and maintaining catalytic activity. 20 Nevertheless, thermal and non-thermal effects do not always synergistically promote the reaction. In the photoexcitation process of semiconductors, without effective carrier transfer path, the temperature increased by the thermal effect will accelerate the carrier recombination, which is not conducive to the photothermal synergistic reaction.…”

“…In this paper, we present our findings on the successful enhancement of the absorption and utilization of various solar radiation effects achieved through the implementation of transition metal double doping. Indium oxide, as one of the most influential catalysts, ,, has been previously studied as a potential photocatalyst for water splitting to produce hydrogen . Nevertheless, In 2 O 3 is a relatively wide bandgap n-type semiconductor that leads to the rapid recombination of photogenerated charge carriers.…”

Regulation of frustrated Lewis pairs on CeO2 facilitates tandem transformation of styrene and CO2

“…13,14 Inspired by these observations, FLP sites have been created on CeO 2 and In 2 O 3 surfaces to activate H 2 , CO 2 , H 2 O, etc. 7,15,16 However, the rigid solid lattice and lack of effective strategies to manipulate Lewis acid-base interaction have restricted the optimization of heterogeneous FLPs.…”