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

Abstract

Platinum electrocatalysts supported on high surface area and Vulcan carbon blacks (Pt/HSC, Pt/V) were characterized in rotating disk electrode (RDE) setups for electrochemical area (ECA) and oxygen reduction reaction (ORR) area specific activity (SA) and mass specific activity (MA) at 0.9 V. Films fabricated using several ink formulations and film-drying techniques were characterized for a statistically significant number of independent samples. The highest quality Pt/HSC films exhibited MA 870 ± 91 mA/mg Pt and SA 864 ± 56 μA/cm 2 Pt while Pt/V had MA 706 ± 42 mA/mg Pt and SA 1120 ± 70 μA/cm 2 Pt when measured in 0.1 M HClO 4 , 20 mV/s, 100 kPa O 2 and 23 ± 2 • C. An enhancement factor of 2.8 in the measured SA was observable on eliminating Nafion ionomer and employing extremely thin, uniform films (∼4.5 μg/cm 2 Pt ) of Pt/HSC. The ECA for Pt/HSC (99 ± 7 m 2 /g Pt ) and Pt/V (65 ± 5 m 2 /g Pt ) were statistically invariant and insensitive to film uniformity/thickness/fabrication technique; accordingly, enhancements in MA are wholly attributable to increases in SA. Impedance measurements coupled with scanning electron microscopy were used to de-convolute the losses within the catalyst layer and ascribed to the catalyst layer resistance, oxygen diffusion, and sulfonate anion adsorption/blocking. The ramifications of these results for proton exchange membrane fuel cells have also been examined.

Perovskite Electrocatalysts for the Oxygen Reduction Reaction in Alkaline Media

“…It disperses the catalyst particles, electrically connects the catalyst particles, enhances the conductivity locally and can act as a co-catalyst in some cases [92][93][94][95]. Most notably, the activity enhancement after Vulcan carbon addition to a conductive La 0.8 Sr 0.2 CoO 3 strongly suggests a co-catalytic role of the used carbon [96], which is also likely on conductive LaCoO 3 and La 0.8 Sr 0.2 MnO 3 as supported by kinetic modeling [95,97].…”

“…It should be noted here that both i m and the apparent i k of composite electrodes depend on the dispersion and loading of the catalytic particles [91,93,94,[104][105][106][107][108][109][110][111], which calls for optimization. Kinetic currents should be reported in the range of 10 to 80% of the limiting current and ideally below 50% [91].…”

“…The most active composite electrodes [22] are also included for reference. The currents of the composites are equal or higher than those of the single crystalline surfaces because carbon can act as a co-catalyst [92,95,[137][138][139] and disperses the catalyst [92,93].…”

Experimental Methodologies to Understand Degradation of Nanostructured Electrocatalysts for PEM Fuel Cells: Advances and Opportunities

“…The assessment of the ECSA losses in an MEA configuration by CV is less straightforward than for RDE studies, as both the method based on integration of the H UPD charge and on the CO stripping procedure are affected by the measuring conditions. [35,61] EIS has been often coupled to I-V analyses in order to interpret the evolution of the diffusion overpotential as well as to study the ionomer degradation in the CL. [62] Young et al, for instance, monitored the CL ionic conductivity during an ADT as a function of relative humidity.…”

“…It is acknowledged that the quality of the film can substantially affect the measurement of the kinetic properties. [35] Therefore, it is possible to expect that it may affect also stability studies, although, to the authors' knowledge, no extensive work on the subject has been reported in the literature. The impact of the catalyst loading and rotation rate were studied for instance by Nagai et al, [14b] who showed that the rate of ECSA losses decreases with increasing the catalyst loading ( Figure 5) and by decreasing the rotation rate.…”