Role of surface defect sites: from Pt model surfaces to shape-controlled nanoparticles

Abstract

In the present paper, preferentially oriented (111) Pt nanoparticles (mostly octahedral and tetrahedral, namely {111}Pt nanoparticles) have been characterized and compared with a Pt(554) single-crystal electrode as their voltammetric features are quite similar in 0.5 M H₂SO₄. The anion and Bi adsorption behaviours suggest that the {111}Pt nanoparticles contain relatively wide hexagonal domains and also isolated sites which could adsorb solely hydrogen. Bi step decoration has been successfully extended to modify the defects of {111}Pt nanoparticles without blocking terrace sites. CO charge displacement has been applied to determine the potential of zero total charge (pztc) of non-decorated and Bi decorated surfaces. It has found that the positive shift of pztc on defect-decorated {111}Pt nanoparticles is not so significant in comparison with that of Pt(554) due to the relative short mean length of (111) domains on the {111}Pt nanoparticles. CO stripping demonstrates that {111}Pt nanoparticles exhibit higher reactivity toward CO oxidation. This reflects the role of the defect sites in nanoparticles, evidenced by the disappearance of the “pre-wave” in the stripping voltammogram once the defects were blocked by Bi. The stripping peaks shift to higher potential on Bi decorated surfaces, indicating the active role of both steps and defects for CO oxidation. By comparing the CO stripping charge and the change in hydrogen adsorption charge of surfaces with and without Bi decoration, including reasonable deconvolution, the local CO coverage on defect and terrace sites were obtained for the first time for the {111}Pt nanoparticles, and the results are in good agreement with those obtained on Pt(554). Chronoamperometry studies show tailing in all current–time transients of CO oxidation on all surfaces studied. The kinetics of CO oxidation can be satisfactorily simulated by a modified Langmuir–Hinshelwood model, demonstrating that CO oxidation on all studied surfaces follows the same mechanism.