Analytical Procedure for Accurate Comparison of Rotating Disk Electrode Results for the Oxygen Reduction Activity of Pt/C

Abstract

Rotating disk electrode (RDE) voltammetry has been touted as a simple means for benchmarking the oxygen reduction reaction (ORR) activity of platinum-based electrocatalysts in proton exchange membrane fuel cells. In practice, the RDE methodology has been highly variable across laboratories, with up to 20% differences in values for the Pt electrochemical surface area and 10x differences in mass activity and area-specific activity reported from the same standard Pt/C electrocatalyst. We confirm that the same ORR activities can be replicated across laboratories when a detailed experimental protocol is followed. From our work and others', we conclude that dominant factors in the RDE experimental protocol include the ink formulation, electrocatalyst film quality and the electrochemical procedures. We make a recommendation for procedures for the reproducible characterization of Pt/C commercial catalysts, present simple metrics for researchers to use for a quick check of their results, and also propose new benchmark values for two Pt/C standards.

Oxygen Reduction Reaction Measurements on Platinum Electrocatalysts Utilizing Rotating Disk Electrode Technique

“…correction for catalysts evaluated in this work as well as that reported in literature. 4,26,74,82,83 The b.g. correction trends observed in the literature qualitatively agree with the behavior discussed above.…”

“…In order to report valid standard deviations, it is necessary to evaluate sufficient number of samples from several inks. When the standard deviation of a population is not known and only 3-8 samples are evaluated as is conventional in the RDE literature, 27,35,50,83 a 't' distribution is the more appropriate choice. A 't' distribution for a sample size of 50 approaches a normal distribution to within 2% for a 90% confidence interval (CI); for 20 samples, the 't' distribution is within 5% for the same CI.…”

The Use of C-MnO2 as Hybrid Precursor Support for a Pt/C-MnxO1+x Catalyst with Enhanced Activity for the Methanol Oxidation Reaction (MOR)

“…Glassy carbon (GC) electrodes were polished with alumina powder, ultrasonic washing and blow drying, before dropping the catalyst ink. Different GC disk electrodes were arranged by preparing the ink using an ionomer-to-catalyst (ITC) mass ratio (mg of Nafion ® over mg of catalyst) equal to 0.1 and catalyst loading of 20 μgPt·cm −2 [51].…”

Oxygen Reduction Reaction Measurements on Platinum Electrocatalysts Utilizing Rotating Disk Electrode Technique

“…[78][79][80] A common factor in a majority of the TF-RDE studies for Pt/C catalysts encountered in the literature is the incorporation of Nafion ionomer either mixed in with the catalyst ink formulation or applied as a cap over the dried catalyst film on RDE disk. 6,[13][14][15]17,[48][49][50][51]61,62,69,[81][82][83][84] However, the ORR activity values that are measured with added Nafion represent a complex, poorly defined, and variable electrochemical interface that can be represented as "Pt/C | discontinuous Nafion film soaked in 0.1 M HClO 4 , free 0.1 M HClO 4 ". We use this notation to describe two parallel interfaces, Pt/C in contact with HClO 4 soaked Nafion and Pt/C directly in contact with free HClO 4 as shown in Fig.…”

“…It is evident that values of "kinetic currents" and "activity" reported in the literature actually represent a "measured activity" that may not be completely free from losses associated with O 2 diffusion, protonic resistances 'within the catalyst layer' as well as blocking/adsorption by species at the catalyst-electrolyte interface. 15,17,69,[85][86][87] Focus of this study.-The objectives of this study are: i) to obtain the ORR activity using conventional and advanced film fabrication techniques with statistically significant number of samples using down-selected protocols established and defined in Part I, and understand the difference in measured ORR activity; 88 ii) to obtain 'true' kinetics on Nafion-free catalyst layers (Pt/C | free 0.1 M HClO 4 interface), iii) to understand the impact of Nafion ionomer on the activity, and, lastly iv) to emphasize the implications of ionomer adsorption in PEMFCs and the causes for differences in the absolute magnitude of activity between MEAs and TF-RDE.…”