Olga V. Cherstiouk

Model approach to evaluate particle size effects in electrocatalysis: Preparation and properties of Pt nanoparticles supported on GC and HOPG

Although metal nanoparticles are widely used in electrocatalysis, in particular for the preparation of the electrodes for fuel cells, it is still not fully understood how the size of a metal phase affects its electrochemical reactivity. In this paper, we demonstrate a possible approach to design model electrodes for studying size effects in electrocatalysis. A simple chemical deposition procedure is introduced, which allows reproducible preparation of 1.5/3.0 nm Pt nanoparticles anchored to the surface of glassy carbon (GC) or highly oriented pyrolytic graphite (HOPG). Pt nanoparticles supported on GC are stable versus potential variation and can be used for studying size effects. They are examined in electrochemical reactions relevant to low temperature fuel cells: electrooxidation of adsorbed CO and methanol. It is demonstrated that reactivity of Pt nanoparticles in these reactions is considerably decreased in comparison to bulk polycrystalline Pt.

On the effect of Cu on the activity of carbon supported Ni nanoparticles for hydrogen electrode reactions in alkaline medium

Effects of adding varied amounts of copper to carbon-supported nickel particles on their structure, composition and electrocatalytic activity for the hydrogen oxidation and evolution reactions in alkaline medium have been explored. Ni1-xCux/C catalysts were prepared by the incipient wetness impregnation. Comprehensive characterization of the catalysts included X-ray powder diffraction, X-ray photoelectron spectroscopic, transmission electron microscopic and cyclic voltammetric analyses, while atomistic Monte Carlo simulations have been undertaken to obtain further insights into the structure of the bimetallic NiCu nanoparticles. We found that compared to monometallic Ni, NiCu nanoparticles show lower propensity towards oxidation under ambient conditions. Furthermore, we report that adding Cu allows increasing the surface-weighted electrocatalytic activity, and the specific surface area of Ni1-xCux/C electrodes, both contributing to a ca four-fold enhancement of the mass-weighted activity. The nature of the synergistic interactions between Ni and Cu is proposed on the basis of the analysis of experimental data and Monte Carlo structural modelling results.

X-ray diffraction study of Pt and Pd electrolytic deposits on polycrystalline supports

Electrolytic deposits are widely used in electrochemistry and electrocatalysis. Investigation of the real structure of electrolytic deposits is of great importance as they usually posses high defectiveness that could be the reason of unusual electrocatalytic properties. The example of the exhibition of structural effects in electrocatalysis could be the dependence of the activity of Pt and Pd electrolytic deposits on the deposition potential. High-precision X-ray diffraction studies of Pt and Pd electrolytic deposits on various supports (Pt/Pt, Pd/Pt, Pt/Au) obtained at different deposition potentials were performed. The effect of the deposition potential on the structure of the deposit has been evaluated. It was shown that electrodeposited Pt and Pd have the particle size in the range from eight to twenty five nm. For the Pt electrolytic deposits systematic decrease of the Pt particle size and an increase of the concentration of the grain boundaries with the deposition potential have been found. For Pt/Pt and Pd/Pt the deposition potential influences the texture of the deposit: an increase of the deposition potential leads to the formation of more textured deposit. A decrease of the lattice parameter of nanocrystalline Pt and Pd in comparison with the value for bulk metals has been found to be the common characteristic of the electrolytic deposits. For Pt/Au systematic decrease of the Pt lattice parameter with deposition potential was observed. Thus the deposition potential is really an important variable, which could determine the structure of electrolytic deposits. The work was supported by the RFBR.