Effect of chloride ligands removal on the oxidation state and electrochemical reactions of platinum single-atom catalysts

Abstract

Single-atom catalysts have been studied extensively for heterogeneous catalytic reactions because they use precious metals the most efficiently with 100% atom utilization and they possess unique selectivity due to the lack of ensemble sites. Chloride ligands often help to stabilize Pt single-atoms, but their effect on the catalytic reactions has not been studied. In this study, sinlge atomic Pt supported on TiC was prepared from chloride Pt precursors, then chloride ligand was intentionally removed by increasing reduction temperature. As the reduction temperature increased from 100 $^\circ C$ to 300, 500, 700 $^\circ C$, the chloride ligand was gradually peeled off. In the 0.2 wt% Pt/TiC, the catalyst reduced at 100 $^\circ C$ possessed highly oxidized Pt single-atoms, whereas the catalyst reduced at 300 $^\circ C$ had more reduced Pt single-atoms with a little Pt nanoparticles. The catalyst reduced at 300 $^\circ C$ exhibited the highest currents for $H_2O_2$ formation in electrochemical oxygen reduction reaction. When the catalyst was reduced at higher than 300 $^\circ C$, the Pt single-atoms were aggregated and the currents for $H_2O_2$ formation decreased significantly. Controlling the oxidation state of the single-atoms is very important to maximize the activity of the single-atom catalysts.