# Hydroxylated Rh Single‐Atom Antennas Assembled on Carbon Nitride Toward Stable Photocatalytic Hydrogen Evolution

## TL;DR

A new Rh-based single-atom catalyst on carbon nitride improves hydrogen production efficiency and stability significantly compared to existing benchmarks.

## Contribution

Hydroxylated Rh single-atom antennas with dual oxygen-bridges enhance structural stability and photocatalytic performance.

## Key findings

- PCN-Rh-0.5 achieves a PHE rate 32.5 times higher than the PCN/Pt benchmark.
- The catalyst operates stably for 192 hours, outperforming other high-stability catalysts.
- A dual-cycle reaction path is enabled by improved charge separation and protonation capability.

## Abstract

Polymeric carbon nitride (PCN)‐based single‐atom catalysts represent the most promising catalysts for photocatalytic hydrogen evolution (PHE), which, however, still suffer from reduced thermodynamic stability because of the metal‐induced heptazine skeleton distortion. Herein, hydroxylated Rh single‐atom antennas (Rh‐SAAs) connected by dual oxygen‐bridges are constructed on the surface of PCN matrix, which brings great structural advantages in avoiding skeleton distortion and increasing stability compared to the traditional direct coordination of metal atoms onto PCN. The optimal PCN‐Rh‐0.5 delivers an average PHE rate of 3409 µmol g−1 h−1, 32.5 times that of the PCN/Pt benchmark. More importantly, it achieves an ultralong stable operation time (192 h) with a higher amount of hydrogen production per unit mass than those of the state‐of‐the‐art single‐atom catalysts and other high‐stability catalysts (≥50 h) under the same conditions. Insights into the mechanism reveal the key role of the electron pump effect induced by interband trap states composed of hybridized Rh 4d/O 2p orbitals that can propel the directed electron transfer toward Rh‐SAAs. As a result, the improved charge separation efficiency and lifetime, along with the strong protonation capability with dual oxygen‐bridges, trigger a dual‐cycle reaction path, thereby achieving high PHE activity and stability.

PCN‐Rh single‐atom catalyst shows a dual‐cycle reaction path for photocatalytic hydrogen evolution (PHE). PCN‐Rh‐0.5 achieves 32.5 times the PHE rate of PCN/Pt, which exhibits a longer operation time (192 h) with a higher amount of hydrogen production (654.5 mmol g−1) than the reported PCN‐based single‐atom catalysts and other high‐stability catalysts with operation time ≥50 h under the same conditions.