A Highly Conjugated Nickel(II)-Acetylide Framework for Efficient Photocatalytic Carbon Dioxide Reduction

The incorporation of transition-metal single atoms as molecular functional entities into the skeleton of graphdiyne (GDY) to construct novel two-dimensional (2D) metal-acetylide frameworks, known as metalated graphynes (MGYs), is a promising strategy for developing efficient catalysts, which can combine the tunable charge transfer of GDY frameworks, the catalytic activity of metal and the precise distribution of single metallic centers. Herein, four highly conjugated MGY photocatalysts based on Ni^II, Pd^II, Pt^II, and Hg^II were synthesized for the first time using the 'bottom-up' strategy through the use of M-C bonds (-C≡C-M-C≡C-). Remarkably, the Ni^II-based graphyne (TEPY-Ni-GY) exhibited the highest CO generation rate of 18.3 mmol g^-1 h^-1 and a selectivity of 98.8 %. This superior performance is attributed to the synergistic effects of pyrenyl and -C≡C-Ni(PBu₃)₂-C≡C- moieties. The pyrenyl block functions as an intramolecular π-conjugation channel, facilitating kinetically favorable electron transfer, while the -C≡C-Ni(PBu₃)₂-C≡C- moiety serves as the catalytic site that enhances CO₂ adsorption and activation, thereby suppressing competitive hydrogen evolution. This study provides a new perspective on MGY-based photocatalysts for developing highly active and low-cost catalysts for CO₂ reduction.