(Invited) On-Line Inductively-Coupled Plasma Mass Spectrometry Characterization of Transition Metal Dissolution in Electrochemical Environments

Abstract

While in-cell studies are the best way to characterize the performance and stability of electrochemical materials, the device environment often presents challenges to the real-time measurement of degradation processes. Several techniques have been developed to mimic the device environment, but to enable the real-time characterization of degradation processes. For example, low temperature fuel cell catalysts are often characterized using an aqueous electrolyte tuned to have pH and adsorption characteristics comparable to those of the solid ionomers used in fuel cells’ membrane-electrode assemblies. The material can then be subjected to various potential waveforms typical of those encountered in the device or intended to accelerate the materials degradation and the electrolyte analyzed, ex situ, for degradation products using a number of techniques. One such technique which is particularly useful is inductively-coupled mass spectrometry (ICP-MS), as it is able to detect transition metals in solution at concentrations as low at parts-per-trillion (ppt). This method, while valuable, provides limited information regarding the mechanisms of materials degradation (e.g., potential and time-dependence of dissolution processes). Recently, techniques have been developed which couple electrochemical flow or rotating disk electrode (RDE) cells directly to an ICP-MS allowing for precise time- and potential-resolved detection of dissolved species. One iteration of this technique is that pioneered by Mayrhofer et al. 1 in which a cell is sealed to a planar substrate on which the electrode material of interest is deposited. A stream of electrolyte is pumped over the material and the effluent electrolyte analyzed by ICP-MS. This cell can be rastered over the substrate/electrode material and thus has been dubbed a “scanning flow cell”. Lopes et al. 2 developed a stationary ICP-MS probe coupled with an RDE which allows measurement of the kinetics of a reaction simultaneously with detection of dissolution products. Another version of the technique uses a commercial flow cell from BASi with the electroactive material deposited on a glassy carbon working electrode and electrolyte drawn through the cell using the peristaltic pump of the ICP-MS.3,4 An overview of the application and utility of this technique in determining the potential-dependent degradation mechanisms of platinum and platinum alloy fuel cell catalysts will be presented. Acknowledgements This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the Fuel Cell Performance and Durability Consortium (FC-PAD). Argonne National Laboratory is managed for the U.S. Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357. References O. Klemm, A. A. Topalov, C. A. Laska, K. J. J. Mayrhofer, Electrochem. Commun., 13, 1533 (2011).P. Lopes, D. Strmcnik, D. Tripkovic, J. G. Connell, V. Stamenkovic, and N.M. Markovic, Acs Catal, 6, 2536 (2016).P. Jovanovic, A. Pavlisic, V.S. Selih, M. Sala, N. Hodnik, M. Bele, S. Hocevar, and M. Gaberscek, Chemcatchem, 6, 449 (2014).R.K. Ahluwalia, D.D. Papadias, N.N. Kariuki, J.-K. Peng, X. Wang, Y. Tsai, D.G. Graczyk, and D.J. Myers, J. Electrochem. Soc., 165(6), F3024 (2018).