Oxygen Reduction Reaction on Pt and Pt Bimetallic Surfaces: A Selective Review

Abstract

In this review we selectively summarize recent progress, primarily from our laboratory, in the development of the oxygen reduction reaction (ORR) catalysis on well‐defined surfaces. The focus is on two type of metallic surfaces: platinum single crystals and bimetallic surfaces based on platinum. The single crystal results provide insight into the effects of the platinum structure on the kinetics of the ORR, and create a fundamental link between the specific activity of Pt (rate per unit area) and particle size (for various particle shapes). The results show that the structure sensitive kinetics of the ORR arise primarily due to structure sensitive adsorption of anions. In the absence of specific adsorption, such as in Nafion polymer electrolyte, no particle size effect is expected. The knowledge of the electrocatalysis of the ORR on model bimetallic surfaces on Pt‐Ni and Pt‐Co bulk alloys was used to resolve the enhanced ORR kinetics on supported Pt‐Ni and Pt‐Co catalysts. Finally, we show that the ORR on platinum modified with pseudomorphic Pd metal film in alkaline solution is the best catalysts ever used in O2 reduction. For both bimetallic systems, we demonstrated that the ability to make a controlled and well characterized arrangement of two elements in the electrode surface region presage a new era of advances in the ORR electrocatalysis.

High resolution mapping of oxygen reduction reaction kinetics at polycrystalline platinum electrodes

“…Based on research on single-crystal basal planes, the adsorption of (bi)sulfate on (111) long range terraces strongly hinders the ORR, while the introduction of mono-atomic steps on 60 the surface, enhances the activity by breaking the long range order and thereby the anion adsorption strength. 10,49 Our results are consistent with this analysis, showing that facets close to (111) orientation with (100) contributions are the most active.…”

“…By solving equation 2, an average j k of 932 µA cm -2 was obtained. Evidently, the current values depicted in Figures 3B and 4A, approximate 10 well to kinetic values, with minimal mass transport contribution.…”

“…35 The mechanism and kinetics of the ORR on Pt have been studied [6][7][8] to understand the cause of the sub-optimal performance and to identify strategies to optimize the catalytic properties of Pt surfaces. [9][10][11] A common strategy is to identify the most efficient surface structure for the ORR and then try to expose these micro- 40 or nano-structures in the catalysts. 10 To do this, knowledge of the structure-dependence of the ORR activity is required.…”

“…[9][10][11] A common strategy is to identify the most efficient surface structure for the ORR and then try to expose these micro- 40 or nano-structures in the catalysts. 10 To do this, knowledge of the structure-dependence of the ORR activity is required. Previous research on a variety of Pt-based materials, spanning bulk polycrystalline electrodes, 12,13 single-crystal electrodes 14,15 and nanoparticles, 2,16 has shown that the ORR kinetics and 45 mechanism are strongly affected by the nature and the structure of electrodes.…”

“…25,26 For example, we have shown recently that the Fe 2+/3+ redox process on polycrystalline platinum electrodes in sulfuric acid is dominated by grain boundaries. 27 To evaluate whether similar 10 effects operate for the ORR, localized electrochemical measurements are needed, as reported herein.…”