Estimation of adsorbed anion charge density from the electrode charge-potential relationship

A correlation, based upon available data for a number of electrolytes at 0.1 and 1.0 N concentrations, may permit adsorbed anion charge densities to be estimated as a function of electrode potential by comparing the experimentally-determined charge-potential relationship for a previously uninvestigated electrolyte with a semihypothetical curve representing no anion adsorption. The results are believed sufficiently precise to permit the calculation of approximate [psi]0-potentials for use in kinetic studies. The correlation indicates that the adsorption of fluoride ion may be substantial at sufficiently positive potentials.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33376/1/0000774.pd

Transient study of the oxygen reduction reaction on reduced Pt and Pt alloys microelectrodes: evidence for the reduction of pre-adsorbed oxygen species linked to dissolved oxygen

Using chronoamperometry at preconditioned oxide-free Pt microdisc electrodes in aqueous media, we investigated the oxygen reduction reaction (ORR) on the millisecond timescale and obtained results consistent with the reduction of oxygen species which adsorb on the electrode before the ORR is electrochemically driven. Furthermore these adsorbed species are clearly linked to oxygen in solution. At long times, the amperometric response is solely controlled by the diffusion of dissolved oxygen towards the microelectrode. However, at short times, typically below 50 ms, the reduction of pre-adsorbed oxygen produces a large extra current whose magnitude depends on the oxygen concentration in solution, deliberate electrode poisoning and the rest time before the potential step. Using sampled current voltammetry we show that this extra current affects the entire potential range of the ORR. Using microdisc electrodes made with Pt alloys we find that the amperometric response is sufficiently sensitive to distinguish oxygen coverage differences between Pt, Pt0.9Rh0.1 and Pt0.9Ir0.1 microdiscs. These unexpected and, to our knowledge, never previously reported results provide new insight into the oxygen reduction reaction on Pt. The existence over a wide potential range of irreversibly adsorbed oxygen species arising from dissolved oxygen and different from Pt oxide is particularly relevant to the development of oxygen reduction catalysts for low temperature fuel cells

Oxygen Reduction at Carbon Supported Lanthanides:The Role of the B-site

The kinetics of the oxygen reduction reaction (ORR) at carbon supported transition metal oxides in alkaline solutions is systematically investigated as a function of the nature of the B-site. The study is focused on LaBO3 (B = Cr, Co, Fe, Mn and Ni) nanoparticles synthesized by an ionic liquid route, offering fine control over phase purity and composition. Activity towards the ORR was compared with commercial Pt/Etek catalyst. Detailed electrochemical analysis employing a rotating ring-disc electrode provides conclusive evidences that the carbon support plays an important contribution in the faradaic responses. Decoupling the contribution of the carbon support uncovers that the reactivity of LaMnO3 towards the 4e- ORR pathway is orders of magnitude higher than for the other lanthanides. We rationalise these observations in terms of changes in the redox state at the B-site close to the formal oxygen reduction potential