Electrochemical preparation of platinum nanocrystallites on activated carbon studied by X-ray absorption spectroscopy

An XAS investigation was undertaken to understand the mechanism of our platinum deposition process. This process is based on H(2)PtCl(6) impregnation onto activated carbon followed by current pulses reduction. After each step of the process and during the electrochemical reduction, ex situ and in situ dispersive X-ray absorption measurements allowed us to follow the evolution of platinum environment and its valence state. This characterization shows a first diminution in the electronic density of final states for Pt atoms when H(2)PtCl(6) is involved in the impregnation mixture, because of the simple contact of this acid with activated carbon. After the impregnation mixture spraying step onto a carbon support and thermal treatment, the platinum compound is found to be reduced to a Pt(II) form corresponding to the anionic PtCl(4)(2-) complex. The electrochemical reduction takes place in the first galvanostatic pulses. The competitive proton evolution to hydrogen on in situ generated metallic platinum particles occurs, but EXAFS analysis shows that, in our process, this evolved hydrogen does not have a major role in platinum species reduction.