Rotating Ring-Disk Electrode Method for the Detection of Solution Phase Superoxide as a Reaction Intermediate of Oxygen Reduction in Neutral Aqueous Solutions

Abstract

A method is herein described that allows for solution phase superoxide generated via the reduction of dioxygen in neutral aqueous solutions at a rotating disk electrode to be oxidized at a concentric Au ring electrode bearing a covalently linked monolayer of 3-mercapto-1-propanol, a modified surface that blocks the oxidation of solution phase of hydrogen peroxide. Experiments were performed in which the potential of a glassy carbon disk electrode was linearly scanned in the oxygen reduction region and the ring voltage was poised at a value at which superoxide oxidation ensued yielded bell-shaped ring currents. This behavior is consistent with changes in the relative rates constant for the processes involved in the mechanism of oxygen reduction on this carbonaceous material induced by the applied potential which so far had remained undetected using other techniques.

Synthesis and Characterizations of PdNi Carbon Supported Nanomaterials: Studies of Electrocatalytic Activity for Oxygen Reduction in Alkaline Medium

“…Equation (13) [ 35 ] can be used to compute the proportion of H 2 O 2 in percent. where i r is the current measured in the ring, i d is the current measured on the disk and N is the collection efficiency of the ring-disk electrode, which depends on the dimensions of the gap between the disk and the ring [ 36 ]. Figure 6 and Table 3 show that the production of H 2 O 2 is higher in the case of Pd/C and Pt/C but reduces as the amount of Ni in the catalyst increases, implying that the addition of Ni favors the ORR via near 4 electrons.…”

Adsorbed Intermediates in Oxygen Reduction on Platinum Nanoparticles Observed by In Situ IR Spectroscopy

“…It is well established from rotating ring disk electrode (RRDE) experiments, which detect species at an outer ring electrode as they diffuse away from a central disk electrode, that the mechanism on Pt proceeds via H 2 O 2 as an intermediate . Recently, a RRDE was further used to detect solution‐phase superoxide at a Au ring electrode, while scanning electrochemical microscopy with a nanopipette tip was used to detect desorbed superoxide at the polycrystalline Pt surface during ORR in neutral aqueous solution . However, these electrochemical techniques are not species‐specific and cannot give any direct structural information or report on ORR intermediates that remain adsorbed on the electrode surface.…”

Adsorbed Intermediates in Oxygen Reduction on Platinum Nanoparticles Observed by In Situ IR Spectroscopy

“…[7][8][9][10][11][12] However,t his effort is hindered by the poor understanding of the ORR mechanism, especially at real supported Pt nanoparticle electrodes.The complete reduction of O 2 to H 2 O is afour-electron process (O 2 + 4e À + 4H + !2H 2 O) and must therefore be composed of an umber of elementary electron transfer steps and intermediate species.S everal different mechanistic pathways have been proposed for acidic conditions.One possibility is the initial dissociative adsorption of O 2 to form Pt À Os pecies,w hich subsequently undergo reduction and protonation. [18][19][20][21] Recently,aRRDE was further used to detect solution-phase superoxide at aA ur ing electrode, [22] while scanning electrochemical microscopy with an anopipette tip was used to detect desorbed superoxide at the polycrystalline Pt surface during ORR in neutral aqueous solution. H 2 O 2 ).…”