The Particle Size Effect on the Oxygen Reduction Reaction Activity of Pt Catalysts: Influence of Electrolyte and Relation to Single Crystal Models

Abstract

The influence of particle size on the oxygen reduction reaction (ORR) activity of Pt was examined in three different electrolytes: two acidic solutions, with varying anionic adsorption strength (HClO(4) < H(2)SO(4)); and an alkaline solution (KOH). The experiments show that the absolute ORR rate is dependent on the supporting electrolyte; however, the relationship between activity and particle size is rather independent of the supporting electrolyte. The specific activity (SA) toward the ORR rapidly decreases in the order of polycrystalline Pt > unsupported Pt black particles (~30 nm) > high surface area (HSA) carbon supported Pt nanoparticle catalysts (of various size between 1 and 5 nm). In contrast to previous work, it is highlighted that the difference in SA between the individual HSA carbon supported catalysts (1 to 5 nm) is rather trivial and that the main challenge is to understand the significant differences in SA between the polycrystalline Pt, unsupported Pt particles, and HSA carbon supported Pt catalysts. Finally, a comparison between measured and modeled activities (based on the distribution of surface planes and their SAs) for different particle sizes indicates that such simple models do not capture all aspects of the behavior of HSA carbon supported catalysts.

Key Factors Affecting the Performance and Durability of Cathode Electrocatalysts in Polymer Electrolyte Fuel Cells Characterized by In Situ Real Time and Spatially Resolved XAFS Techniques

“…Figure 3 (bottom A) shows the variation of the Pt L IIIedge XANES white line peak heights at 0.4 V with the specific power density [51], which is in agreement with the linear relationship between ORR activity and d-band center shift for Pt 3 Co, Pt 3 Ni, and Pt [70][71][72]. Although we did not investigate the particle size effect on the structural kinetics, the ORR kinetics may not be affected by the particle size of Pt cathode electrocatalysts (below 5 nm size) [73,74]. The enhancements of the rate constants by the Co and Ni addition to Pt/C are shown in Fig.…”

Exploring the phase space of time of flight mass selected PtxY nanoparticles

“…Most, albeit not all, theoretical and experimental studies seem to suggest that the surface specific activity for oxygen reduction should decrease with a decrease in particle size. 12,[22][23][24][25][26][27][28] However, this notion is in conflict with the experimental observation that extended single crystal stepped Pt surfaces sometimes exhibit higher oxygen reduction activity than unstepped surfaces. [29][30][31] One strategy to improve the activity of Pt is to alloy it with other metals.…”

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

“…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.…”