Metal Single-Atom Cocatalyst on Carbon Nitride for the Photocatalytic Hydrogen Evolution Reaction: Effects of Metal Species

摘要

Single-atom (SA) catalysts exhibit high activity in various reactions becausethere are no inactive internal atoms. Accordingly, SA cocatalysts are also anactive research fields regarding photocatalytic hydrogen (H_2) evolution whichcan be generated by abundant water and sunlight. Herein, it is investigatedwhether 10 transition metal elements can work as an SA on graphitic carbonnitride (g-C_3N_4; i.e., gCN), a promising visible-light-driven photocatalyst. Amethod is established to prepare SA-loaded gCN at high loadings (weight of≈3 wt.% for Cu, Ni, Pd, Pt, Rh, and Ru) by modulating the photoreductionpower. Regarding Au and Ag, SAs are formed with difficulty withoutaggregation because of the low binding energy between gCN and the SA. Anevaluation of the photocatalytic H_2-evolution activity of the prepared metalSA-loaded gCN reveals that Pd, Pt, and Rh SA-loaded gCN exhibits relativelyhigh H_2-evolution efficiency per SA. Transient absorption spectroscopy andelectrochemical measurements reveal the following: ⅰ) Pd SA-loaded gCNexhibits a particularly suitable electronic structure for proton adsorption andii) therefore they exhibit the highest H_2-evolution efficiency per SA than othermetal SA-loaded gCN. Finally, the 8.6 times higher H_2-evolution rate peractive site of Pd SA is achieved than that of Pd-nanoparticles cocatalyst.