This supporting online material provides detailed information on the materials and methods used in the study of high-flux solar-driven thermochemical dissociation of CO₂ and H₂O using nonstoichiometric ceria. The materials section describes the preparation of the ceria-based catalyst, including ball-milling, drying, and heat-treatment processes. The experimental methods section outlines the design and operation of the solar reactor, which is a cavity-receiver that efficiently captures concentrated solar radiation. The reactor's components, such as the reflective parabolic concentrator and the porous alumina insulation, are detailed. The efficiency calculation section explains the theoretical framework for determining the solar-to-fuel energy conversion efficiency, considering both the fuel production rate and the incident solar radiation power. The reactor energy balance section provides a detailed analysis of the power losses and heat transfer mechanisms within the reactor. Additionally, figures S1 to S3 are included to support the material and method sections, showing X-ray diffraction patterns, equilibrium oxygen nonstoichiometry, and the evolution of ceria morphology after heat-treatment.This supporting online material provides detailed information on the materials and methods used in the study of high-flux solar-driven thermochemical dissociation of CO₂ and H₂O using nonstoichiometric ceria. The materials section describes the preparation of the ceria-based catalyst, including ball-milling, drying, and heat-treatment processes. The experimental methods section outlines the design and operation of the solar reactor, which is a cavity-receiver that efficiently captures concentrated solar radiation. The reactor's components, such as the reflective parabolic concentrator and the porous alumina insulation, are detailed. The efficiency calculation section explains the theoretical framework for determining the solar-to-fuel energy conversion efficiency, considering both the fuel production rate and the incident solar radiation power. The reactor energy balance section provides a detailed analysis of the power losses and heat transfer mechanisms within the reactor. Additionally, figures S1 to S3 are included to support the material and method sections, showing X-ray diffraction patterns, equilibrium oxygen nonstoichiometry, and the evolution of ceria morphology after heat-treatment.