Coupling sunlight and carbon cycle: advances and challenges in solar-driven Ca-based CO₂ capture and thermochemical conversion into fuels

Abstract The accelerating global transition toward carbon neutrality calls for transformative technologies capable of tightly coupling renewable energy with carbon reduction. Among next-generation approaches, solar-driven calcium-based CO₂ capture (SCa-CC) and thermochemical conversion (TC) constitutes a promising pathway by utilizing solar energy to directly facilitate the conversion of CO₂ into value-added hydrocarbon fuels. This approach addresses the high energy consumption associated with conventional CO₂ capture technologies, thereby mitigating the critical efficiency bottleneck and enhancing economic viability. However, the practical deployment of SCa-CC-TC remains constrained by a series of scientific and engineering challenges. These include the progressive degradation of functional material, the complex coupling of irradiation, thermal, flow, and reaction fields, the dynamic match of solar flux, particle transport, and reaction kinetics, and the constraints of techno-economic feasibility. Breakthroughs in both theoretical insight and practical inquiry are urgently required to enable reliable scale-up. This review offers a comprehensive analysis of full technical framework, encompassing solar energy harvesting, CO₂ capture, and coupled heat-mass conversion. Recent advances are discussed in the of solar concentrator development, multifunctional materials modification, photothermal reactor configurations, coupling characteristics, and techno-economic assessments. Emerging multimodal activation strategies, including plasmonic, pyroelectric, and piezoelectric effects, are highlighted for their potential to improve reaction kinetics and product selectivity. Key scientific and engineering bottlenecks are analyzed, and strategic directions are proposed to accelerate the transition from laboratory-scale concepts to pilot- and industrial-scale demonstrations. These insights are expected to promote the continued development of SCa-CC-TC and facilitate the construction of a sustainable energy system with deep coupling of sunlight and carbon cycle.