The solar‐to‐chemical energy conversion of greenhouse gas CO₂ into carbon‐based fuels is a very important research challenge, with implications for both climate change and energy security. Herein, the key attributes of hydroxides and oxygen vacancies are experimentally identified in non‐stoichiometric indium oxide nanoparticles, In₂O_3‐x(OH)_y, that function in concert to reduce CO₂ to CO under simulated solar irradiation.

Gaseous CO₂ is transformed photochemically and thermochemically in the presence of H₂ to CH₄ at millimole per hour per gram of catalyst conversion rates, using visible and near‐infrared photons. The catalyst used to drive this reaction comprises black silicon nanowire supported ruthenium. These results represent a step towards engineering broadband solar fuels tandem photothermal reactors that enable a three‐step process involving i) CO₂ capture, ii) gaseous water splitting into H₂, and iii) reduction of gaseous CO2 by H₂.

The reverse water gas shift (RWGS) reaction driven by Nb₂O₅ nanorod‐supported Pd nanocrystals without external heating using visible and near infrared (NIR) light is demonstrated. By measuring the dependence of the RWGS reaction rates on the intensity and spectral power distribution of filtered light incident onto the nanostructured Pd@Nb₂O₅ catalyst, it is determined that the RWGS reaction is activated photothermally. That is the RWGS reaction is initiated by heat generated from thermalization of charge carriers in the Pd nanocrystals that are excited by interband and intraband absorption of visible and NIR light. Taking advantage of this photothermal effect, a visible and NIR responsive Pd@Nb₂O₅ hybrid catalyst that efficiently hydrogenates CO₂ to CO at an impressive rate as high as 1.8 mmol gcat⁻¹ h⁻¹ is developed. The mechanism of this photothermal reaction involves H₂ dissociation on Pd nanocrystals and subsequent spillover of H to the Nb₂O₅ nanorods whereupon adsorbed CO₂ is hydrogenated to CO. This work represents a significant enhancement in our understanding of the underlying mechanism of photothermally driven CO₂ reduction and will help guide the way toward the development of highly efficient catalysts that exploit the full solar spectrum to convert gas‐phase CO₂ to valuable chemicals and fuels.