Single-atom photocatalysts for CO₂ reduction: Insights from the periodic table

Single-atom catalysts (SACs) have garnered tremendous and continuous attention in photocatalytic CO₂ reduction reactions (CO₂RR), due to their compelling potential in broadening the light-harvesting range, elevating the charge separation/transfer efficiency, and enhancing surface reaction. Despite the surge in research and the expanding range of potential central metal candidates—including d-block, p-block, and rare metal elements, etc.—the comprehension of the structure–function relationships between the central metal and its performance remains elusive. Hence, categorized by different areas of the central metal element from periodic table, we outline the recent progress and challenges on SACs for photocatalytic CO₂RR. We begin by describing various synthetic strategies employed for SACs. Subsequently, a clear classification of the SACs applications in photocatalytic CO₂RR is provided, according to the central metal elements in different blocks of the periodic table. We also discussed how isolated metal single-atom sites from different blocks of the periodic table improve the performance of photocatalytic CO₂ reduction from the perspective of charge separation and transfer. Finally, we end this review with some perspectives and challenges associated with SACs for photocatalytic CO₂ reduction. Through this review, we aim to enrich the element diversity of SACs for photocatalytic CO₂RR, reveal trends in element evolution, and propose directions for future development in this flourishing field.