Sustainable hybrid photo/electro-enzyme systems for CO₂ conversion

Carbon dioxide (CO₂), as an abundant and renewable carbon feedstock, holds immense potential for sustainable biomanufacturing. However, natural carbon fixation pathways, such as the Calvin-Benson-Bassham (CBB) cycle and the reverse tricarboxylic acid (rTCA) cycle, suffer from intrinsic limitations, including low catalytic efficiency, high adenosine triphosphate (ATP) consumption, and oxygen sensitivity. Recent advances in synthetic biology and metabolic engineering have pioneered artificial pathways (e.g., the crotonyl-CoA/ethylmalonyl-CoA/hydroxybutyryl-CoA (CETCH) cycle) that bypass central metabolism, achieving higher fixation rates with reduced ATP consumption. Concurrently, photocatalytic and electrocatalytic systems have emerged as complementary strategies to address cofactor dependency and CO₂ activation thermodynamic barriers. This review summarizes breakthroughs in (ⅰ) rational design for CO₂ conversion pathway optimization, (ⅱ) photocatalysis, and (ⅲ) electrocatalysis for CO₂ activation and cofactor regeneration. By integrating these disciplines, synergistic systems achieve unprecedented efficiency in converting CO₂ to Cn compounds (e.g., ethanol, glyoxylate, sugar, and starch) and establish a foundation for scalable carbon-negative biotechnologies. However, challenges remain, including enzyme denaturation under operational stresses, inefficiencies in multi-enzyme cascades due to kinetic mismatches, and the need for sustainable metrics to ensure net-negative carbon footprints. Future research should prioritize material innovation, CO₂ assimilation system integration, and optimization to unlock higher efficiency CO₂ conversion, aligning with global decarbonization goals while producing high-value chemicals.