Electrocatalytic enhancement of formic acid oxidation reaction by acetonitrile on well-defined platinum surfaces

Catalysis and Surface Chemistr

Shape-dependent electrocatalysis: ammonia oxidation on platinum nanoparticles with preferential (100) surfaces

A shape-dependent electrocatalysis for the ammonia oxidation reaction is reported. Pt nanoparticles with different (100) preferentially oriented surface structures were synthesised. Cyclic voltammetry of the Pt nanoparticles is presented and the “so-called” hydrogen adsorption/desorption process is used as structure sensitive reaction to obtain qualitative information about the surface structure of the nanoparticles. While Pt nanoparticles prepared in microemulsion show a voltammetric profile very similar to that characteristic of a polyoriented surface, colloidal Pt nanoparticles appear to be (100) preferentially oriented. The electrochemical activity of these nanoparticles for ammonia oxidation in basic medium was studied. The results show that the anodic current density is very sensitive to the existence of Pt(100) domains. Thus oxidation current densities seven times higher can be obtained among the different nanoparticles, showing the importance of controlling the surface structure of the nanoparticles for the development of an active electrocatalyst for ammonia oxidation. Keywords: Nanoparticles, Ammonia oxidation, Shape-dependent, Electrocatalysi

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

MICINN of Spain [CTQ2010-16271]; China Scholarship Council; NSFC [20833005, 21021002]; European Social FundingIn 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 0.5MH(2)SO(4). 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

Bi-modified Pt Electrodes toward Glycerol Electrooxidation in Alkaline Solution: Effects on Activity and Selectivity

Herein we investigate the effect of irreversibly adsorbed bismuth on polycrystalline platinum (Ptp) on the electrooxidation of glycerol in alkaline media by combining electrochemical, spectroscopic (in situ FTIR), and analytical (HPLC on line) techniques. We found that the activity of Ptp increases by about 5-fold when the optimal quantity of Bi ions is added to the solution. Besides, the adatom strongly impacts the reaction products by suppressing the pathways with C-C bond breaking, hindering the formation of CO (and other unknown intermediates) and enhancing the production of glycerate. Different from the results in acid media for Ptp-Bi systems where Bi blocks the oxidation pathway through the primary carbon, glycerate is the main product in alkaline media, and dihydroxyacetone is either produced in extremely low quantities or not produced. Besides, comparing our results with those in acid media, the peak current recorded at 1 mV·s-1 in this work was 1 order of magnitude higher. These results show the strong impact of the pH in the reaction rate and selectivity

Pt/C nanocatalysts for methanol electrooxidation prepared by water-in-oil microemulsion method

Pt nanoparticles supported on Vulcan XC-72R were synthesized by water-in-oil microemulsion method. By incorporating different amounts of HCl as a capping agent in the precursor-containing water phase, nanoparticle shape was varied. Influencing the growth of certain facets leads to the changes of the particle shape depending on the preferential facets. As a result, nanoparticles exhibit some of the electrochemical features typical for single crystals. Commonly employed synthesis procedure for water-in-oil microemulsion method was altered with the addition of catalyst support in the system and changing the catalyst cleaning steps. Prepared catalysts were characterized by thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and electrochemical methods. Activity and stability for methanol oxidation reaction (MOR), a structure-sensitive reaction, were tested. Electrochemical results reveal the influence of particle size, shape and exposed facets on the electrochemical processes. TEM investigations confirm electrochemical findings, while TGA verifies Pt loading in catalyst powder. Based on the results, optimal HCl concentration for cubic particle formation is determined, and structural effect on MOR activity and stability was tested. Cuboidal NPs show very good reaction activity and fair stability under applied experimental conditions