Curvature‐Engineered Co Single Atoms on Hydrogen Bonded Organic Frameworks for Efficient Photo Assisted Electrocatalytic Nitrate Reduction to Ammonia

ABSTRACT The photo assisted electrocatalytic nitrate reduction reaction (PEC‐NO 3 RR) for ammonia synthesis presents a green pathway for ammonia production from nitrate pollutants. Curved coordination environments in metal single atoms (SAs) based catalysts offer unique opportunities for tuning local electronic structures and thus improve their catalytic activity, yet has not been explored in PEC‐NO 3 RR. In this work, curvature‐engineered Co SAs active sites supported on HOFs matrix (CDs@Co SAs ‐HOFs) is designed. The atomically dispersed Co sites naturally adopt a curved Co‐N/O configuration. Compared to planar Co SAs sites, this curved Co SAs have higher d ‐band center, facilitating the adsorption towards NO 3 − and relative intermediates during NO 3 RR. Moreover, the energy barriers for * NO hydrogenation, which is considered as the rate‐determining step, has been significantly reduced on the curved Co SAs sites. With the incorporated carbon dots as light harvesting units, CDs@Co SAs ‐HOFs delivers a high ammonia yield of 135.12 µmol h −1 cm −2 and Faradaic efficiency of 92.01% at −0.4 V versus reversible hydrogen electrode (vs. RHE) under light irradiation. This work demonstrates a route for optimizing and boosting photo assisted electrocatalytic activity of the single atom catalysts by regulating the local geometric configurations, which may be applied in other catalytic reactions.