Ligand-Mediated Self-Terminating Growth of Single-Atom Pt on Au Nanocrystals for Improved Formic Acid Oxidation Activity

Decreasing the ensemble size of Pt to isolated single atoms is the key to enhance the electrocatalytic formic acid oxidation reaction (FAOR) by bypassing the indirect reaction path that involves the poisoning by the CO intermediate. However, it is challenging to construct isolated Pt single atoms on a foreign metal substrate, especially at high Pt loadings, because Pt tends to form large ensembles due to the high Pt–Pt bond energy. Herein, a ligand-mediated self-terminating growth strategy is reported for reliably controlling the ensemble size of Pt on an Au substrate. The key is to introduce a ligand of sulfite (SO₃²⁻) into the synthesis, which preferentially adsorbs at Pt sites, thus substantially increasing the kinetic barrier toward Pt–Pt bond formation. This strategy enables reliable formation of isolated Pt single atoms even at high Pt loadings (up to 26% coverage on Au), which is difficult to achieve by regular syntheses. The resulting catalyst exhibits a high FAOR activity of 38.6 A mg_Pt⁻¹ in 0.5 m H₂SO₄+0.25 m HCOOH, 370 times greater than that of the commercial Pt/C. It is believed this strategy is general and potentially applicable to the fabrication of a wide range of noble metal catalysts with tailored ensemble sizes for energy conversion.