A ball milling method for highly dispersed Ni atoms on g-C₃N₄ to boost CO₂ photoreduction

Atomically dispersed active sites can effectively enhance the catalytic activity, but the synthesis of highly dispersed single-atom active sites remains challenging. Herein, we report for the fabrication of single-atom Ni on g-C₃N₄ (CN) catalysts for photocatalytic CO₂ reduction reaction (CO₂RR) using a high-energy ball milling method. The uniformly loaded single-atomic Ni on the surface of the substrate suggests the improvement of synthetic methods. After optimizing the Ni loading, the photocatalyst containing 0.5 at% (0.32 wt%) single-atomic Ni (Ni/CN-0.5) exhibited the highest CO₂ reduction performance (∼19.9 μmol·g^-1·h^-1) without any co-catalyst or sacrificial agent. As visualized by aberration-corrected high-angle annular darkfield scanning transmission electron microscopy (AC HAADF-STEM), the Ni atoms in the Ni/CN-0.5 photocatalyst are most uniformly dispersed for different loadings (0.1, 0.3, 0.5, 0.7, 1.0, 3.0 and 5.0 at%). These results suggest that the uniformity of the single-atom active sites plays a decisive role rather than the loading amount in the highly enhanced performance. This work provides insight into the design of photocatalysts with highly dispersed single-atom catalytic active sites for enhancing activity.