Impact of Polymer Electrolyte Membrane Degradation Products on the Activity of the Oxygen Reduction Reaction for Platinum Catalysts

Autor: Huyen N. Dinh, Kenneth C. Neyerlin, Jason M. Christ, Ryan M. Richards, Heli Wang
Rok vydání: 2013
Předmět:
Zdroj: ECS Transactions. 50:691-700
ISSN: 1938-6737
1938-5862
DOI: 10.1149/05002.0691ecst
Popis: Polymer electrolyte membrane fuel cells (PEMFCs) hold great promise for providing clean energy without the use of fossil fuels. A major obstacle that must be overcome before PEMFC’s can successfully compete in a commercial market is performance durability [1, 2]. The oxygen reduction reaction (ORR) occurring at the cathode is a limiting process in PEM fuel cell performance due to its high activation energy and slower kinetics compared to hydrogen reduction at the anode [3]. The catalyst layer facilitating the reaction is typically composed of carbon supported platinum or platinum alloy and is highly susceptible to poisoning from foreign compounds either entering through the fuel streams or being introduced internally through system component degradation [4]. Research has shown through studies involving commercial membranes and model compounds that when perfluorinated sulfonic acid (PFSA) membranes are exposed to peroxides, severe chemical decomposition can occur [5,6]. Two compounds in particular, perfluoro(2methyl-3-oxa-7-sulfonic heptanoic) acid (MC2) and perfluoro(4-sulfonic butanoic) acid (MC3), both shown in Figure 1, arise along with HF as the main membrane degradation compounds of Nafion and 3M commercial membranes respectively [5]. Along with losses in membrane conductivity and structural integrity, such degradation products may additionally adsorb to the Pt based electrocatalyst reducing Pt electrochemical surface area (ECA), ORR activity, or both. To date, little effort has been put forth in determining the impact PFSA degradation compounds have on catalyst performance. This work investigates the effects four membrane degradation compounds, shown in Figure 1, have on ECA and ORR activity on platinum electrodes. MC2 and MC3 were selected to represent common internally produced degradation compounds. Nonafluorobutanesulfonic acid (MC5) and trifluoroacetic acid (TFA) were used as model compounds to gain further insight into possible Pt poisoning mechanisms [5]. A rotating disk electrode electrochemical setup utilizing 0.1 M perchloric acid electrolyte (diluted from 70% HClO4 double distilled veritas grade, GFS Chemical) was used to study the effects of the aforementioned compounds on the ORR activity of polycrystalline Pt as well as commercially available carbon supported Pt electrocatalysts. After injecting the model compound into the electrochemical cell and recording adsorption effects on ECA and ORR activity, the electrode was then analyzed in clean electrolyte in order to monitor the recoverability of the activity loss for the Pt catalyst. This presentation will focus on the effects that membrane decomposition products have on the Pt ECA and ORR activity. perfluoro(2-methyl-3-oxa-7-sulfonic heptanoic) acid
Databáze: OpenAIRE
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