Fundamental Insights into Photoelectrochemical Carbon Dioxide Reduction: Elucidating the Reaction Pathways

Abstract

The photoelectrochemical (PEC) reduction of carbon dioxide (CO 2 ) to produce solar fuels presents a sustainable strategy to mitigate CO 2 emissions and alleviate the global energy crisis. While significant research efforts have been dedicated to optimizing cell system configurations and designing efficient photoelectrocatalysts, there remains a lack of in-depth understanding of the CO 2 reduction pathway. This review provides a comprehensive overview of the fundamental insights of PEC CO 2 reduction with a focus on CO 2 reduction pathways from the perspectives of final products and adsorption modes. First, key challenges are identified and analyzed, including the initial activation of CO 2, the competitive hydrogen evolution reaction (HER), and the complex carbon–carbon (C–C) coupling process. The review then examines the fundamental aspects of the reduction process, covering state-of-the-art cell devices, their operational principles, and methodologies for capturing reaction intermediates. The initial activation of CO 2 through concerted or sequential proton–electron transfer mechanisms is discussed in detail. Furthermore, potential PEC CO 2 reduction pathways are systematically identified and categorized on the basis of the final products and distinct adsorption modes that drive the reduction process, including CO 2 insertion, carbon-coordinated and oxygen-coordinated monodentate adsorption, oxygen-coordinated bidentate adsorption, and adsorption on oxygen vacancies. Detailed pathways leading to the formation of C 1, C 2, and C 3 compounds are elucidated, with an emphasis on strategies that enhance selectivity toward C 1 and C 2+ products. In particular, understanding the CO 2 reduction pathways aids in catalyst design. For C 1 production, catalyst design focuses on promoting adsorption and activation, as the rate-determining step (RDS) is the initial CO 2 activation. In contrast, for C 2+ formation, catalyst design strategies aim to increase intermediate concentration, thereby enhancing the lateral interaction of intermediates, which is crucial for C–C coupling. Finally, the review summarizes potential future breakthroughs from electron, interfacial, and ionic pathways, thereby offering insights into the ongoing evolution of PEC reduction technologies.

Topics & Concepts