Review and Outlook on Photoelectrocatalytic CO ₂ Conversion: A Synergistic Approach to Coupled Catalyst Design and Reactor Innovation

The rising atmospheric CO 2 concentration resulting from fossil fuel combustion has intensified global climate challenges, positioning photoelectrocatalytic CO 2 reduction (PEC CO 2 RR) conversion as a pivotal technology for advancing a carbon circular economy and enabling sustainable energy transitions. However, its practical deployment is constrained by cross-scale bottlenecks spanning from atomic-scale active sites to macroscopic reactor systems, while current research efforts remain largely fragmented, focusing on discrete optimization rather than systematic, integrated innovation. Herein, we present a holistic review and outlook of PEC CO 2 RR across the entire value chain, emphasizing the synergistic interplay among design, mechanistic understanding, and reactor engineering. We systematically discuss strategies for developing high-performance catalysts, including band engineering of semiconductor light absorbers, atomic-level modulation of active sites for selective product control, and heterojunction and interface engineering to enhance charge separation. We then elucidate the fundamental mechanisms governing CO 2 initial activation via proton-coupled electron transfer (PCET) and the critical C–C coupling pathways that dictate multicarbon product formation, establishing intrinsic structure–activity relationships. Furthermore, we compare mainstream reactor configurations, reveal the microenvironmental regulation effects of electrolytes and ion-exchange membranes, and review advances in bias-free solar-driven integrated systems. Finally, we highlight the necessary shift from isolated component optimization toward cross-scale integrated design and outline key research directions to overcoming remaining challenges related to long-term stability, scalability, the trade-off between Faradaic efficiency (FE) and current density, and techno-economic feasibility. This review provides a comprehensive and systematic framework to accelerate the development of efficient, stable, and industrially scalable PEC CO 2 RR technologies.