The oxygen reduction reaction (ORR) on reduced metals: evidence for a unique relationship between the coverage of adsorbed oxygen species and adsorption energy

Abstract

Using chronoamperometry and voltammetry at oxide-free microelectrodes in non-adsorbing electrolyte, KClO4, we investigated the reduction of oxygen containing species which adsorb at potentials below those where oxides are grown electrochemically when the electrode is exposed to dissolved oxygen. Their coverage is found to vary with the metal substrate as follows, Ni > Cu > Pt > Ag, and is negligible on Au microdiscs. This dependence is consistent with the adsorption energy of atomic oxygen for the respective metals predicted by DFT. Furthermore the adsorption energies derived from the stripping peak potentials for the different metals agree very well with those predicted by the DFT calculations. We exploit the oxygen coverage differences between Pt, Pt0.9Rh0.1 and Pt0.9Ir0.1 microdiscs to predict the adsorption energy of these species on the Pt alloys and demonstrate a clear correlation between the metal activity towards the ORR and the charge associated with the reduction of the adsorbed oxygen species. In effect the coverageadsorption energy relationship turns the charge associated with the reduction of the adsorbed oxygen species into a descriptor of the electrode activity towards the ORR. This study provides new insight into the oxygen reduction reaction and offers a new methodology to investigate low temperature fuel cell ORR catalysts.

PdPt-TiO2 nanowires: correlating composition, electronic effects and O-vacancies with activities towards water splitting and oxygen reduction

“…The pseudocapacitance model was not applicable, suggesting a well-established mass transport control for both materials. A linear relationship was also found for jp vs. v, in agreement with previous publications [3,34], suggesting the presence of adsorbed intermediates (i.e. HO2 -(ads)).…”

Reaction Mechanism for Oxygen Reduction on Platinum: Existence of a Fast Initial Chemical Step and a Soluble Species Different from H2O2

“…Under such a condition, j-E profiles for single electrochemical reactions at both, stationary and rotating disk electrodes, should have a current peak, j p , proportional to √v, Eqn. 5, and independent of ω in the case of RDEs [56][57][58][59][60][61][62]87] (10, -10) This result, however, does not imply that the amount of adsorbed O-containing species during the ORR would be the same as in O 2 -free solutions, and it could be higher, as indicated by X-ray photoelectron spectroscopy (XPS) [11], electrochemical quartz crystal microbalance (EQCM) measurements [14,78], and studies at microelectrodes [54,55]. ோ் at a smaller slope than the one expected for a 1etransfer, and later become independent of v. This transition depends on ω and takes place at 0.5 and 10…”

“…Moreover, because transient experiments are very sensitive to initial conditions, as it will be discussed below, a conditioning program before each experiment was applied to the electrode to get quantifiable and reproducible data. The program was similar to the one already reported [54,55] and consisted in sweeping the electrode between 1. This procedure assures that the electrode surface is in a similar state before every measurement.…”

Influence of Anion Chaotropicity on the SO2 Oxidation Reaction: When Spectator Species Determine the Reaction Pathway

“…The potential profile can be related to the SO 2 adsorption energy. In the literature, it is possible to find some experimental methods to estimate this parameter, such as the one proposed by Perry and Denuault, in which an electrode is placed in a solution containing the supporting electrolyte and the species of interest, SO 2 in the present case, for 10 min. Then, the electrode is rinsed and inserted in a SO 2 free electrolyte and subjected to a linear scanning potential perturbation.…”

“…The oxidation peak potential can be related to an energy value by substituting E 0 by E peak in ΔG=−nFE 0 , and this energy value is called |ΔG peak |, and represented in the absolute. This energy was suggested to be closely related to the adsorption energy . We carried out such experiments.…”