Toward High-Selectivity CO2 Photoelectroreduction: Mechanistic Foundations, Recent Advances and Challenges

Photoelectrochemical carbon dioxide reduction reaction (PEC CO2RR) is a promising strategy for converting CO2 into high-value chemicals that contribute to carbon neutrality. However, CO2 reduction is often accompanied by a variety of competitive reaction paths in the actual reaction process, which may generate a variety of products. The selective regulation of different products not only directly affects the yield and separation cost of the target product, but also relates to the energy efficiency and economic feasibility of the whole process. Improving product selectivity is essential for increasing product yield and understanding reaction mechanism. This review systematically summarizes recent advances and challenges in achieving high selectivity in PEC CO2RR. Firstly, the basic concept and principle of PEC CO2RR are summarized. Next, the key factors affecting product selectivity are discussed, including catalyst design (catalyst type, modification, composition, morphology), reaction conditions (applied voltage, light intensity and wavelength, reaction temperature, electrolyte type) and reactor design (photoelectrode area, synergistic oxidation effect, geometric structure, gas diffusion electrode). In addition, kinetic and thermodynamic aspects such as the CO2 adsorption model, band gap structure, and reaction free energy are also explored. Then, the recent five years of research progress in different products is described in detail, focusing on the current status and challenges in the study of C1 products and C2 products. Subsequently, the primary factors leading to the failure of PEC CO2RR were summarized, and various cooperative strategies were introduced to achieve long-term stability in product selectivity. Finally, the challenges and future directions of developing PEC systems with enhanced selectivity are introduced. In particular, the importance of innovative catalyst design, reaction stability, reaction environment optimization, advanced equipment structure and reaction mechanism analysis for promoting PEC CO2RR in industrial applications is emphasized.