Influence of Ammonia Contamination on HT-PEM Fuel Cell Platinum Catalyst

Abstract

High temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are considered as one of the promising types of power sources for automobile and stationary application. They have several advantageous characteristics, including high power density and efficiency, high tolerance against CO poisoning as well as zero-emission when using hydrogen and air as fuel and oxidant, respectively[1]. In the last decades HT-PEM fuel cells have been investigated extensively with the aim to introduce them into the market for commercial use.Gas impurities are one of the factors which can limit their durability and life time. Among them ammonia is a feed stream gas impurity which may contaminate the cathode as well as the anode of fuel cells. The main sources of ammonia traces come from hydrogen fuel produced from ammonia and from reforming of fossil fuel that contain species of nitrogen compounds[2]. Moreover, traces of ammonia in ambient air can occur in agricultural areas. The presence of ammonia traces was shown to decrease the performance of low temperature PEM fuel cells [3]. The ammonia species can effect on hydrogen oxidation reaction as well as oxygen reduction reaction affecting the catalyst and leading to reduced efficiency of fuel cells.[3] To the best of our knowledge, the effect of ammonia contamination on HT-PEM fuel cells and in particular on the carbon-supported platinum catalyst has not been fully explored yet. Therefore, the first aim of the present work is to investigate the effect of NH4 + poisoning on carbon-supported platinum in 0.5 mol L-1 H3PO4 in order to simulate the environment of HT-PEMFCs. The oxygen reduction reaction was studied in the presence of 10 ppm NH4 + ions using the rotating ring disk electrode (RRDE). In particular, activity of the Pt/C catalyst was determined before and after poisoning to evaluate the degradation. The effect of contamination on the performance loss, reduction of electrochemical active area and increase of H2O2 formation has been defined by RRDE measurements. In the second part, a commercially available membrane electrode assembly (MEA) was exposed to 10 ppm NH3 inside the air stream using a HT-PEM single cell test bench and applying a constant load of 0.3 A cm-2. Polarization curves and electrochemical impedance spectroscopy were used to investigate changes of the MEA performance. The RRDE study in H3PO4 electrolyte of the catalyst provides in combination with HT-PEM fuel cell testing an increased understanding of the NH3 impact on HT-PEMFC systems.Figure: CVs of Pt/C catalyst in 0.5 M H3PO4 at 50 mV/s in the potential range 0.05 – 1.5 V vs RHE in the absence and in the presence of 10 and 100 ppm NH4 +, respectively.[1] X. Cheng, Z. Shi, N. Glass, L. Zhang, J. Zhang, D. Song, Z.-S. Liu, H. Wang, J. Shen, J. Power Sources 2007, 165, 739-756.[2] X. Zhang, U. Pasaogullari, T. Molter, Int. J. Hydrogen Energy 2009, 34, 9188-9194.[3] F. A. Uribe, S. Gottesfeld, T. A. Zawodzinski, J. Electrochem. Soc. 2002, 149, A293-A296; R. Halseid, P. J. S. Vie, R. Tunold, J. Power Sources 2006, 154, 343-350. Figure 1