Size effects on reactivity of Pt nanoparticles in CO monolayer oxidation: The role of surface mobility

Abstract

In the present paper we study the reactivity of model Pt nanoparticles supported on glassy carbon. The particle size effect is rationalized for CO monolayer oxidation exploring electrochemical methods (stripping voltammetry and chronoamperometry) and modelling. Significant size effects are observed in the particle size interval from ca. 1 to 4 nm, including the positive shift of the CO stripping peak with decreasing particle size and a pronounced asymmetry of the current transients at constant potential. The latter go through a maximum at low COads conversion and exhibit tailing, which is the longer the smaller the particle size. Neither mean field nor nucleation & growth models give a coherent explanation of these experimental findings. We, therefore, suggest a basic model employing the active site concept. With a number of reasonable simplifications a full analytical solution is obtained, which allows a straightforward comparison of the theory with the experimental data. A good correspondence between experiment and theory is demonstrated. The model suggests restricted COads mobility at Pt nanoparticles below ca. 2 nm size, with the diffusion coefficient strongly dependent on the particle size, and indicates a transition towards fast diffusion when the particle size exceeds ca. 3 nm. Estimates of relevant kinetic parameters, including diffusion coefficient, reaction constant etc. are obtained and compared to the literature data for extended Pt surfaces.

Dependence of CO oxidation on Pt nanoparticle shape: a shape‐selective approach to the synthesis of PEMFC catalysts

“…[36] However, until now, no study has been reported that distinguishes between different types of adsorptive behaviour during cyclic voltammetry in a conclusive manner. While on the one hand this is understandable because the catalysts studied in the past have shown in contact with liquid phases a certain degree of CO-mobility after adsorption (see Maillard et al [17] and literature cited therein) or a tendency to agglomerate, [37] on the other hand this lack is somewhat remarkable because cyclic voltammetry is usually a very powerful tool to provide this kind of information. We have tried here to clarify the origin of these peaks based upon geometrical and morphological data of Pt nanoparticles.…”

“…[14 -16] While most efforts in real fuel cell (FC) systems are devoted to studying the size selectivity of polycrystalline nanocatalysts of different sizes, no study on shape dependence has been reported. [17] However, we consider that the key to optimizing electrode catalysis is the study of model catalyst systems that have a well-controlled composition of their surfaces defined by surface analytical techniques. [18] Although new synthetic approaches for tailoring the size and shape of nanoparticles continue to be the subject of intense investigation, it remains a challenge to synthesize nanoparticles within well-defined geometric constraints.…”

Retraction: Assembling Interconnected Pt Nanoparticles on Multiwalled Carbon Nanotubes and Their Electrocatalytic Activity for Fuel Cells

“…The high Pt loading on MWCNTs increases the density of Pt nanoparticles, leading to the increase in the magnitude of the interconnection of adjacent Pt nanoparticles and thus providing more adjacent sites for the intermixing and reaction of CO ad and OH ad on the surface of Pt nanoparticles. On the other hand, Savinova and co-workers [31] found surface mobility of CO ad and OH ad significantly influenced the electrochemical CO oxidation on the Pt surface. Here, it is shown by the CV results that Pt/MWCNTs show a reduced oxophilicity with the increased Pt loading (Fig.…”

“…The results indicate that the electrocatalytic activity for CO electro-oxidation is related to the loading and /or interconnectivity of Pt nanoparticles on CNTs. The S-shaped dependence of the electrocatalytic activity of Pt/ MWCTs on Pt loading can be explained by the reaction scheme for the electrochemical CO oxidation, which can be given by the following equations: [31] …”

A review of plasma–liquid interactions for nanomaterial synthesis

“…Although Au is chemically stable, AuNPs were found to have fascinating catalytic ability for many oxidation reactions [128,129] when AuNPs are supported by Co3O4, Fe2O3, or TiO2, and the catalytic ability is closely correlated with the size of AuNPs. Pt and Pd NPs also possess unique catalytic ability for CO oxidation [130,131], hydrogenation [132,133] etc. The NPs of these noble metals will play pivotal role in the development of new technologies.…”