Effect of Electrode Pt Loading on the Oxygen Reduction Reaction Evaluated by Rotating Disk Electrode and Its Implication on the Reaction Kinetics

Abstract

The oxygen reduction reaction (ORR) activity was evaluated over film electrodes prepared from different Pt catalysts using rotating-disk electrode (RDE) and rotating-ring-disk electrode (RRDE) systems. The ORR activity as a function of Pt loading using the same catalyst was examined first, and it is concluded to be strongly influenced by mass transfer limitation. Two types of mass transfer limitation were identified. One is the external diffusion as described by the rotating-speed-dependent Levich equation. The other one is the internal diffusion within the electrode in which the electrode thickness is the governing parameter. The electrode thickness is closely related to the catalyst loading of the electrodes. After corrections of these mass transfer limitations, all the tested Pt catalysts under the conditions of this study show similar specific ORR activity with a Tafel slope near −120 mV/dec This result suggests that the ORR over Pt catalysts is a structure-insensitive reaction and the overall electrode performance can be limited by the mass transfer.

Effect of praseodymium oxide and cerium–praseodymium mixed oxide in the Pt electrocatalyst performance for the oxygen reduction reaction in PAFCs

“…Therefore, the diffusion-free intrinsic catalytic activity for ORR can be evaluated here. [18,23,24]. Two typical Tafel slopes of -125.1 and -64.2 mV dec -1 can be observed on the Tafel plot for Pt/C, which can be ascribed to a combination of both ''energetic effects'' (changing of adsorption isotherm for reaction intermediate from Temkin to Langmuir adsorption) [11,[25][26][27] and ''blocking effects'' (surface coverage of oxygen containing species controlling availability of O 2 adsorption) [11,27].…”

Evaluation of the intrinsic kinetic activity of nanoparticle ensembles under steady-state conditions

“…When a monolayer of NPs cannot be assumed, the Koutecky-Levich equation must be modified to reflect non-linear diffusion to the NPs within the convection layer so that the description of electrode area becomes important (i.e. geometric area vs. electrochemical active area) [18,50,51]. This is similar to the modification of the KouteckyLevich equation for an electrode covered with thin films such as Nafion or conductive polymers [52][53][54][55][56][57][58][59][60][61][62].…”

The electrochemical behavior of PtRu- and Pt-modified zeolite X in alkaline solution

“…The increase in the electrode rotation rate has a stronger effect on 13XPtRu as compared with 13XPt. Shih et al [28] noticed that the recorded ORR current obviously increases as a function of both the electrode rotating speed and the Pt loading. The noticed difference in response of our investigated electrode could be consequence of combined effect of Fig.…”