Role of oxygen-containing species at Pt(111) on the oxygen reduction reaction in acid media

Abstract

Abstract:The oxygen reduction reaction (ORR) is one of the fundamental reactions in electrochemistry and has been widely studied, but the mechanistic details of ORR still remain elusive. In this work, the role of electrochemical oxygenated species, such as adsorbed hydroxide, OH ads , adsorbed oxygen, O ads , and Pt (111) oxide, PtO, in the ORR dynamics is studied by employing electrochemical techniques, i.e. combining rotating disk mass-transport control with potential sweep rate perturbation. In this framework, a reduction peak at 0.85 V, E ORR , is detected. This peak shows a different electrochemical dynamics than that of Pt (111) oxides. The data analysis suggests that neither OH ads nor O ads are the main bottleneck in the mechanism. Instead, results support the reduction of a soluble intermediate species as the rate determining step in the mechanism. On the other hand, PtO species, which are generated at relatively high potentials, and are responsible of surface disordering, strongly inhibit the ORR as long as they are adsorbed in the electrode surface.

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

“…[107,108], Eqn. (16), is also similar to experimental activation energies reported for the ORR on Pt basal planes and Pt(poly) in both acid and alkaline solutions [7,19], and even on bimetallic surfaces of Pt 3 -Ni and Pt 3 Co [7].…”

“…Despite decades of research, the reaction occurs at a significant rate only at high overpotentials, and the highest reported improvement in the activity is a ~100 mV reduction in the overpotential on Platinum-based alloys relative to Pt, the most active pure metal [1][2][3]. This fact is commonly attributed to an inhibiting role of surface oxygen-containing species, such as adsorbed oxygen, O ads , and/or hydroxyl, OH ads [1,2,[4][5][6][7][8][9][10], though their exact nature has not been undoubtedly established yet [11][12][13][14][15][16].…”

“…On the other hand, ORR studies at Pt (111) , has been proposed to be the most probable species, Eqn. (4) [13,15,16,33,34]. ܱ ଶ + ‫ܪݐܲ2‬ ଶ ܱ ௗ௦ ⇄ ‫ܪܱݐܲ‬ ௗ௦ + ‫ܱܪݐܲ‬ ଶ,ௗ௦ *…”

Mobility and Poisoning of Mass-Selected Platinum Nanoclusters during the Oxygen Reduction Reaction

“…It is known that hydrogen adsorbs in Pt at E ≤ 0.3 V and that, in this potential range, the 4e -ORR is no longer possible due to adsorbed hydrogen. 6,15,[73][74][75][76][77] In this potential range, a 2eprocess would be expected, in line with the currents measured. For the LD samples, the maximum current densities measured before H2 evolution proceeds are, approximately, 0.3 mA/cm 2 .…”

“…The superoxide anion radical (O2•-) [87][88][89][90] hydroxyl radical (•OH), [91][92][93] and hydroperoxyl radical (•OOH) 94 have all been detected as products from the ORR in PEMFCs 91,95,96 or in aqueous alkaline or neutral solutions. 89,90,94,[97][98][99] They have also been detected directly 88,94 or indirectly 99 in small concentrations and suggested 75,76,100 as ORR reaction intermediates in acidic solutions.…”