Transport effects in the oxygen reduction reaction on nanostructured, planar glassy carbon supported Pt/GC model electrodes

Abstract

The role of transport and re-adsorption processes on the oxygen reduction reaction (ORR), and in particular on its selectivity was studied using nanostructured model electrodes consisting of arrays of Pt nanostructures of well-defined size and separation on a planar glassy carbon (GC) substrate. The electrochemical measurements were performed under controlled transport conditions in a double-disk electrode thin-layer flow-cell configuration; the model electrodes were fabricated by colloidal lithography techniques, yielding Pt nanostructures of well defined and controlled size and density (diameter: 140 or 85 nm, height: 20 or 10 nm, separation: from 1-2 to more than 10 diameters). The nanostructured model electrodes were characterized by scanning electron microscopy and electrochemical probing of the active surface area (via the hydrogen adsorption charge). The electrocatalytic measurements revealed a pronounced variation of the hydrogen peroxide yield, which increases by up to two orders of magnitude with increasing separation and decreasing size of the Pt nanostructures. Similar, though less pronounced effects were observed upon varying the electrolyte flow and thus the mass transport characteristics. These effects are discussed in a reaction model which includes (i) direct reduction to H(2)O on the Pt surface and (ii) additional H(2)O(2) formation and desorption on both Pt and carbon surfaces and subsequent partial re-adsorption and further reduction of the H(2)O(2) molecules on the Pt surface.

Nanoporous Gold Catalyst for Direct Ammonia Borane Fuel Cells

“…It is also possible that the NPG active layer structure promotes an increase in the residence time of reaction intermediates at the surface leaving more time for complete oxidation to borate. Such behaviour was recently reported by Molina Concha et al for Pt and Pt/C electrodes 6,42 and for the multi-step oxygen reduction reaction at Pt nanostructure arrays at planar glassy carbon electrodes 43 .…”

Oxygen reduction reaction on stepped platinum surfaces in alkaline media

“…This fact implies that the reduction of hydrogen peroxide is not completely inhibited in this potential 35 region, so that a slow removal of the formed hydrogen peroxide from the interfacial region allows for a second interaction with the surface that can lead eventually to the reduction of the species to form OH -. 2 When the effect of the surface structure is analyzed, it can be seen 40 that the most active electrode in this medium is the Pt(111) (figure 2), since it has the lower onset for the ORR. This onset is progressively shifted to less positive potentials when steps are introduced in the (111) surface, a clear indication that the steps are less active than the terrace sites.…”

“…On the other hand, for platinum and other metals, water is readily produced, either directly or from the decomposition of the generated 30 hydrogen peroxide. 2 Additionally, the reaction is structure sensitive which implies that the reactants and/or intermediates are adsorbed in the surface. Thus, the complete understanding of the oxidation mechanism requires the use of well-defined surfaces, in order to simplify the complexity of the reaction mechanism and 35 to make explicit the role of surface structure and composition in the competitive adsorption processes that occur on the oxidation mechanism.…”

Electrochemical detection of hydrogen peroxide on platinum-containing tetrahedral amorphous carbon sensors and evaluation of their biofouling properties

“…It can be either electrochemically oxidized to O2 (E 0 = 0.695 V) or reduced to water (E 0 = 1.763 V) in diffusion controlled two-electron processes [2]. In industrial applications H2O2 and its redox reactions are closely linked to fuel cell technology as it has been proposed to be formed as reaction intermediate in the oxygen reduction reaction [2], [3]. In living organisms cells produce H2O2 mitochondria to control growth and apoptosis.…”