Adstructures of platinum-complex precursors and platinum nanoparticles formed on low-index single-crystal Au surfaces for oxygen reduction reaction

We investigated the adlayer structures of Pt complexes, PtCl42− and PtBr42−, by using in situ scanning tunneling microscopy (STM) and the electrochemical behavior on the Pt nanoparticles deposited from the PtCl42− and PtBr42− precursors on Au(100), Au(111), and Au(110) surfaces in 0.1 M HClO4. The STM investigation revealed that the PtCl42− and the PtBr42− adlayers had very similar structures on Au(111) and Au(110) surfaces: the (√7 × √7)R19.1° structure on Au(111), and the c(2 × 4) structure on Au(110). On Au(100), PtCl42− formed a (√5 × √5)R26.7° structure, whereas PtBr42− was adsorbed randomly in a flat configuration. High-resolution STM images also revealed pinwheel features of the Pt complexes, resulting from the flat-lying adsorption configurations. The electrochemical reduction of the PtBr42− adlayer proceeded at a more negative potential than the PtCl42− adlayer to form metallic Pt nanoparticles. The average size of the Pt particles varied on the different Au surfaces. The cyclic voltammograms and the catalytic activities for the oxygen reduction reaction were different on the Pt complexes and the three Pt-modified Au(hkl) electrodes. The structures of deposited Pt nanoparticles depended on the substrate Au electrodes. The order of the ORR activity of Pt nanoparticles on Au substrates, Pt/Au(111) > Pt/Au(100) ≥ Pt/Au(110), corresponded to the relative ease of specific adsorption of anions on Pt single-crystal electrodes, Pt(111) > Pt(110) > Pt(100).