Investigating the Influence of MEA Conditioning on Commercial Pt/C and State-of-the-Art Pt-Alloy/C Electrocatalysts in a PEMFC

Abstract

Fuel cells are one of the most the most promising energy conversion devices for both residential and transportation applications due to their high electrical efficiencies, low operating temperatures, and zero tailpipe emissions.1-2 Significant advancements have been made in the development of ORR electrocatalysts to enable attainment of the DOE catalyst activity target of 440 mA/mgPt at 0.9V and 150 kPa. Specifically, utilizing nanostructured carbon materials with internal porosity resulted in increased platinum dispersion, higher electrochemically available surface areas, and higher mass acitivites.3 Additionally, transition metal Pt alloys, specifically, Ni and Co, have shown to increase the activity per Pt site, enabling improvements in mass acitivity.4 However, when these different sets of Pt or PtM/Carbon materials are incorporated into dispersed PEMFC electrodes the time, potential and environmental parameters, also known as “break-in” or “conditioning”, required to achieve optimum performance can be vastly different. While several publications have presented baseline electrocatalyst performance values,5-7 and/or demonstrated different methods for fabricating electrodes and standardizing MEA performance,8-9 the impact of MEA conditioning on performance has rarely been discussed in detail. The absence of a detailed discussion of lab-scale MEA fabrication methods in conjunction with conditioning can lead to the reporting of erroneous experimental observations related to purported improvements in electrocatalytic activity or device design. Previous studies by Neyerlin et. al.10 have demonstrated the importance of MEA conditioning on observed mass activity and high current density performance alike. In this study, we expand upon our previous findings, examining the influence of conditioning on 4 different commercially available catalysts: (i) 50wt.% Pt/Vulcan (TKK), (ii) 50 wt% Pt/HSC (TKK), (iii) 30 wt.% PtCo (Umicore) and (iv) 30 wt.% Pt/HSC (Umicore) at three different loadings (0.05, 0.1 and 0.15 mgPt cm-2). The objective was to determine the influence of the break-in processes on oxygen reduction reaction (ORR) mass and specific activity (MA, SA), electrochemical surface area (ECA) and H2-Air polarization curves to formulate a fair and comparative assessment of state-of-the-art electrocatalysts. Ex-situ techniques such as, SAXS, XAFS, nano-CT, and microscopy will be utilized along with operando effluent collection and performance data to glean the fundamental impact of the conditioning process. Preliminary results have shown that the conditioning procedures might need to be re-considered based on the particular catalyst and catalyst layer loading in order to obtain peak performances. The results from this study will not only provide possible pathways towards improving the performance of low loaded high activity catalysts that is needed to meet DOE targets for fuel cell commercialization, but also demonstrate the importance of implementing systematic protocols. References M. K Debe, Nature, 2012, 486, 43−51.Handbook of Fuel Cells: Advances in Electrocatalyst, Materials, Diagnostics, and Durability; Vielstich, W., Yokokawa, H., Gasteiger, H.A., Eds.; John Wiley & Sons: Hoboken, NJ, 2009.S. H. Joo, S. J. Choi, I. Oh, J. Kwak, Z. Liu, O. Terasaki, R. Ryoo, Nature, 2001, 412(6843), 169-172.D. Wang, H. L. Xin, R. Hovden, H. Wang, Y. Yu, A. Muller, F. J. DiSalvo, H. D. Abruña, Nature materials, 2013, 12(1), 81-87.H. A. Gasteiger, S. S. Kocha, B. Sompalli, and F. T. Wagner, Appl. Catal. B: Env., 2005, 56, 9.H. A. Gasteiger, J. E. Panels, and S. G. Yan, J. Power Sources, 2004, 127, 162.Y. Garsany, O. A. Baturina, K. E. Swider-Lyons, S. S. Kocha, Anal. Chem., 2010, 82 (15), 6321-6328.M. B. Sassin, Y. Garsany, B. D. Gould, K. E. Swider-Lyons, Anal. Chem., 2017, 89 (1), 511–518