Engineering the axial coordination of cobalt single atom catalysts for efficient photocatalytic hydrogen evolution

Improving the catalytic activity of non-noble metal single atom catalysts (SACs) has attracted considerable attention in materials science. Although optimizing the local electronic structure of single atom can greatly improve their catalytic activity, it often involves in-plane modulation and requires high temperatures. Herein, we report a novel strategy to manipulate the local electronic structure of SACs via the modulation of axial Co–S bond anchored onto graphitic carbon nitride (C₃N₄) at room temperature (RT). Each Co atom is bonded to four N atoms and one S atom (Co-(N, S)/C₃N₄). Owing to the greater electronegativity of S in the Co–S bond, the local electronic structure of the Co atoms is available to be controlled at a relatively moderate level. Consequently, when employed for the photocatalytic hydrogen evolution reaction, the adsorption energy of intermediate hydrogen (H*) on the Co atoms is remarkably low. In the presence of the Co-(N, S)/C₃N₄ SACs, the hydrogen evolution rates reach up to 10 mmol/(g·h), which is nearly 10 and 2.5 times greater than the rates in the presence of previously reported transition metal/C₃N₄ and noble platinum nanoparticles (PtNPs)/C₃N₄ catalysts, respectively. Attributed to the tailorable axial Co–S bond in the SAC, the local electronic structure of the Co atoms can be further optimized for other photocatalytic reactions. This axial coordination engineering strategy is universal in catalyst designing and can be used for a variety of photocatalytic applications.