Platinum oxidation-reduction cycles

Figure 13. Schematic representation of the setup used for the infrared characterization of liquid-solid interfaces [63], The main cell consists of a platinum disk used for adsorption and reaction, a Cap2 prism for guidance of the infrared beam, and a liquid solution trapped between those two elements. The overall arrangement includes gas and liquid sample introduction stages as well as the electronics used for the electrochemical oxidation-reduction cycles needed to preclean the platinum surface.

Similarly to the catalysts in H -air fuel cells, DMFC catalysts lose their ECS A over time, predominantly owing to catalyst particle agglomeration. Once again, the performance loss is more pronounced at the platinum cathode, which tends to undergo frequent oxidation-reduction cycles, than at the anode (possible protective role of oxophilic ruthenium). 

The Pt(0) electrodeposition markedly affects further scans on the same surface as shown in Figure 5 in the case of JM 8. Indeed, we may see by reversing after cathodic steps II or III a new redox couple formation Epa2 and Epca which corresponds to the catalytic oxidation and reduction of species II and III at the platinum microparticles. Oxidation of species I, which possess no halide ligand in its structure, is not detected at the platinum particles. In the case of cis-platin, several oxidation-reduction cycles conducted on the same surface produce the same electrode modification process as observed for JM 8, but to a greater extent since cis-platin itself is reducible. The shape of the quasi-reversible couple Epa /Epc is particularly well marked in the presence of chloride ions. With continued cycling, the peaks increase and the reversibility of the reaction and available potential ranges become restricted. 

Miyaura and co-workers reported the platinum-catalyzed diboration of allenes with bis(pinacolato)diboron (Scheme 16.52) [57]. The catalytic cycle involves a sequence of oxidative addition of bis(pinacolato)diboron to Pt(0), insertion of an allene into the B-Pt bond and reductive elimination of an allylic boronate, re-producing the Pt(0) species. (Z)-Allylic boronates are formed stereoselectively in the reaction with monosubstituted allenes, which strongly suggests a pathway via a vinylplatinum species rather than a Jt-allylplatinum species. 

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