Engineering single-atom rhodium-CN sites on covalent organic frameworks for boosting photocatalytic hydrogen evolution.

Developing efficient and stable photocatalysts for solar hydrogen (H) energy conversion is meaningful but challenging. Herein, a novel photocatalyst with Rh single atoms (Rh SAs) anchoring in β-ketoimine-linked covalent organic frameworks (TpPa-1) via RhCN sites is proposed for achieving highly efficient H production in phosphate buffer saline (PBS) solution with sodium ascorbate (SA) as sacrificial agent under visible light. TpPa-1 with abundant N and C-chelate sites provides a reliable basis for anchoring Rh single atoms. The optimized Rh SAs/TpPa-1 exhibits an outstanding hydrogen evolution activity (1836.81μmol h g), 9.34 and 2.27 folds enhancement than that of pristine TpPa-1 and Rh NPs/TpPa-1. X-ray absorption fine structure (XAFS) combined with density functional theory (DFT) calculations reveal that the significant improvement in H evolution performance on Rh SAs/TpPa-1 originates from the unique RhCN coordination environment, promoting the charge separation and migration at the atomic interface, and thus decreasing the energy barrier for H* formation. Notably, in situ Raman technique confirmed Rh SAs was the main active sites (RhH) for proton reduction.