Oxygen Reduction Reaction Measurements on Platinum Electrocatalysts Utilizing Rotating Disk Electrode Technique II. Influence of Ink Formulation, Catalyst Layer Uniformity and Thickness

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/mgpt and SA 864 +/- 56 mu A/cm(2)pt while Pt/V had MA 706 +/- 42 mA/mgpt and SA 1120 +/- 70 mu A/cm(2)pt when measured in 0.1 M HClO4, 20 mV/s, 100 kPa O-2 and 23 +/- 2 degrees C. An enhancement factor of 2.8 in the measured SA was observable on eliminating Nafion ionomer and employing extremely thin, uniform films (similar to 4.5 mu g/cm(pt)(2)) of Pt/HSC. The ECA for Pt/HSC (99 +/- 7 m(2)/g(pt)) and Pt/V (65 +/- 5 m(2)/gpt) 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. (C) The Author(s) 2015. Published by ECS. All rights reserved.