Cyclic voltammetric studies of adsorption of cetyltrimethylammonium bromide and HBr on Pt(100) towards understanding their effects in shape-controlled synthesis of nanomaterials

Abstract

Adsorption of CTAB and HBr on Pt(100) in acid solutions were studied by using cyclic voltammetry (CV). The effects of bromide anion (Br−), and cetyltrimethylammonium cation (CTA+) together with Br− (CTAB) on the long-range ordered structure of Pt(100) were investigated systematically and analyzed quantitatively. It has demonstrated that adsorption of both CTA+ and Br− can protect the long-range ordered structure of Pt(100). The upper limit potential of CV below which the long-range ordered structure of Pt(100) is starting to be disturbed was measured at 0.6V in 0.1M H2SO4, and it was shifted positively to 0.9V in 0.1M H2SO4+1mM HBr; this potential has been further postponed to even a higher potential of 1.1V in 0.1M H2SO4+1mM CTAB solution, demonstrating that the ability of protecting the long-range ordered structure of Pt(100) is CTAB>HBr. The adsorbed Br− can desorb simultaneously with proton adsorption, while the CTA+ has adsorbed firmly on Pt(100). It has demonstrated that the irreversibly adsorbed CTA+ could be mostly removed by CO adsorption/stripping. The results revealed that the origin of protecting the long-range ordered (100) structure by HBr is mainly through the inhibition of oxygen adsorption, while that by CTAB comes from both the inhibition of oxygen adsorption and the CTA+ irreversible adsorption. The study has thrown insights in understanding the interaction of Br− and CTA+ with Pt(100), and interpreted that using CTAB as shape-tuning agent is more favorable to yield Pt nanomaterials with long-range ordered (100) surface structure.