Investigating the Contamination Effect of Various Contaminants on Pt Surface during Fuel Cell Operating Conditions by <i>Operando</i> X-Ray Absorption Spectroscopy

As a clean energy technology, Proton Exchange Membrane Fuel Cells (PEMFC) have been widely applied in transportation and stationary power systems. However, during fuel cell operation, impurities present in air or fuel accumulate on the electrodes, leading to poisoning of the platinum (Pt) catalyst. This poisoning reduces catalytic activity, accelerating the deterioration of fuel cell performance. These contaminants infiltrate the fuel cell system through various routes, including impurities in fuel supplies, degradation products from aging sealing materials, and organic pollutants from the ambient air. In this study, we focus on five representative organic contaminants: 1-propanol, propionic acid, acrylic acid, methyl acrylate, and benzoic acid. These substances belong to the classes of alcohols, fatty acids, unsaturated acids, esters, and aromatic acids, respectively. [1] Upon penetrating the fuel cell cathode, they strongly adsorb onto Pt active sites, hindering the oxygen reduction reaction (ORR) and causing a reduction in fuel cell voltage and efficiency. Therefore, elucidating the mechanisms by which these organic contaminants affect reactions on the Pt catalyst surface is critical for improving the contaminant tolerance of fuel cells. Initially, a three-electrode rotating disk electrode (RDE) setup was employed to systematically evaluate the impact of the aforementioned contaminants on the oxygen reduction reaction (ORR) performance of the Pt catalyst under half-cell conditions in a 0.1 M perchloric acid solution. Subsequently, varying concentrations of 1-propanol, propionic acid, acrylic acid, methyl acrylate, and benzoic acid were individually introduced into the electrolyte solution, and changes in polarization curves under each condition were monitored. Cyclic voltammetry was also performed to investigate the catalyst poisoning on the Pt surface and its recovery behavior. We found that all these contaminants significantly block the Pt surface and lead to reduced ORR activity. To understand the blocking effect of various contaminants the High-Energy Resolution Fluorescence (HERFD-XANES (Pt L₃-edge)) measurements were conducted to monitor the changes in the local electronic structure of the Pt catalyst (e.g., changes in the number of Pt 5d vacancies and oxidation states) under each contamination condition by comparing the changes in white line peak intensity. There is an obvious decrease in white line intensity due to the blocking effect of various contaminants on the Pt surface, which resembled the CV results. (Fig.1) The more strongly absorbed contaminants showed a significant decrease in white line intensity. To elucidate the adsorption behavior of contaminants on the Pt under a practical conditions various contaminants were sprayed on MEA and change in the electronic environment was recorded. We observed a significant decay in electrochemical performance and decrease in white line intensity with various contaminant. However, after 60 min’s aging at 60 °C and larger airflow, we record the XANES again, and found that electrochemical performance as well as white line intensity improved remarkably due to the removal of contaminant and approaching to the contaminant free Pt behavior for some of the contaminant which can be removed easily However the more strongly adsorbed molecules still showed a significant decay in performance and decrease in white line intensity. Acknowledgment This work is supported by the NEDO aging project commissioned by the New Energy and Industrial Technology Development Organization (NEDO) References: [1] Junjie Ge, Jean St-Pierre, Yunfeng Zhai. PEMFC cathode catalyst contamination evaluation with a RRDE-methyl methacrylate . Int. J. Hydrogen Energy, 2014 , 39.32: 18351-18361. Figure 1