Mechanistic insights on CO₂ fixation via electrochemical and photocatalytic reduction

The electrochemical and photochemical conversion of CO₂ into value-added chemicals and fuels has emerged as a sustainable approach to mitigate climate change and provide renewable energy carriers. Recent advances span heterogeneous and homogeneous catalysts, single- and dual-atom alloys, and MOF-derived materials, each offering unique opportunities to enhance activity, selectivity, and durability. Heterogenized molecular catalysts, such as Re^(I), Mn^(I), and Ru^(II) complexes on TiO₂, demonstrate site isolation that suppresses dimerization and side reactions, thereby improving product selectivity toward CO, formate, or syngas. Single-atom alloys (SAAs) and dual-atom catalysts (DACs) exploit synergistic electronic and geometric effects to tune the adsorption energies of key intermediates, enabling efficient formation of C₁ and C₂₊ products, including CH₄, CH₃OH, and ethylene. MOF-derived electrocatalysts offer high surface areas, tunable pore environments, and adjustable active sites, promoting CO₂ adsorption, activation, and multielectron reduction. Photocatalytic systems benefit from optimized light absorption, efficient charge separation, and surface site engineering to drive selective CO₂ reduction under visible light. Integrating mechanistic insights with rational design principles, such as electronic structure modulation, heterogenization, and cooperative bimetallic interactions, provides a framework for developing next-generation CO₂ reduction catalysts with enhanced selectivity, turnover, and durability. This review highlights recent progress and mechanistic understanding.