The Contamination Mechanism and Behavior of Amide Bond Containing Organic Contaminant on PEMFC

Abstract

This paper presents a study of the effects of an organic contaminant containing an amide bond (-CONH-), ε-caprolactam, on polymer electrolyte membrane fuel cells (PEMFCs). The ε-caprolactam has been detected in leachates from polyphthalamide materials that are being considered for use as balance-of-plant structural materials for PEMFCs. Contamination effects from ε-caprolactam in Nafion membranes are shown to be controlled by temperature. A possible explanation of the temperature effect is the endothermic ring-opening reaction of the amide bond (-NHCO-) of the cyclic ε-caprolactam. UV-vis and ATR-IR spectroscopy studies confirmed the presence of open ring structure of ε-caprolactam in membranes. The ECSA and kinetic current for the ORR of the Pt/C catalyst were also investigated and were observed to decrease upon contamination by the ε-caprolactam. By comparison of the CVs of ammonia and acetic acid, we confirmed the adsorption of carboxylic acid (-COOH) or carboxylate anion (-COO-) onto the surface of the Pt. Finally, a comparison of in situ voltage losses at 80 • C and 50 • C also revealed temperature effects, especially in the membrane, as a result of the dramatic increase in the HFR. Although research efforts have been made to reduce system costs and improve efficiency of polymer electrolyte membrane fuel cells (PEMFCs), cost and durability issues continue to delay their commercialization.1 In addition, because contamination of the stack can affect performance and durability, studies designed to elucidate these effects and mechanisms have been receiving more attention. 1-41In general, three fundamental contamination mechanisms are known: conductivity loss by ion exchange in the membrane/ionomer, Pt contamination by adsorption, and water/mass transport issues induced by changes in the gas diffusion layer (GDL) properties. Alkali, alkaline-earth, or transitional-metal cations such as Li + , Na + , K + , Cs + , Ni 2+ , Cu 2+ , Ca 2+ , and Fe 3+ are well known contaminants that undergo ion exchange [2][3][4][6][7][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] with the proton exchange membrane (PEM) in a PEMFC. Changes in the oxygen reduction reaction (ORR) kinetics at a Pt electrode covered with a Nafion ionomer [20][21][22][23][24] have also been reported. In addition to the decrease in PEM conductivity due to the reaction with cationic contaminants, a structural change also occurs in the ionomer. This structural change appears to be related to the degradation of Pt/C catalyst activity. Catalyst contamination by an adsorption mechanism from feed-gas contaminants such as SO 2 , [8][9] CO, 10 and H 2 S 11 are well known. In addition, we have reported that aniline adsorbs onto the Pt/C electrode because it contains an aromatic ring and a nitrogen atom in the form of an amine group. 31,35 In a recent cost analysis, 36,37 the need for cost reduction of balanceof-plant (BOP) materials increased relative to the need for cost reduction of the stack in PEMFCs. Using off-the-shelf materials ...

Effect of System Contaminants on the Performance of a Proton Exchange Membrane Fuel Cell

“…46 The concentration of O 2 in the catalyst layer is eliminated in Equation 3, as it was assumed constant throughout the experiment. 29,37 The reaction rate is assumed to be a 1.5 order with respect to the proton concentration as proposed previously. 47 δ is the catalyst layer thickness assumed equal to 2.5 and 10 μm for 0.1 and 0.4 mg/cm 2 respectively.…”

“…[29][30][31][32][33][34][35] These results showed that despite the contamination caused by fuel and air side impurities that can effect only the catalyst (e.g., CO) or the membrane (e.g. metal cations), organic contaminants (e.g., those from BOP materials) can have severe effects on the catalyst, ionomer and membrane at the same time.…”

Fluorescence-Based Detection of Benzene, Toluene, Ethylbenzene, Xylene, and Cumene (BTEXC) Compounds in Fuel-Contaminated Snow Environments

“…Gas chromatography -mass spectrometry (GC-MS) was used to characterize the undoped (i.e., analyte-free) snow melt samples (Figure 4), with all samples showing peaks in the chromatograms corresponding to long-chain alkanes [43] and amides [44] that are typically found in fuel and other environmental contamination sources. Snow melt from Newport showed the lowest number of peaks, corresponding to the fewest organic contaminants, likely due to the sampling location selected (Newport sample from parking lot; Providence and Kingston samples from street).…”

Effects of Ethylene Glycol and Caprolactam on the ORR and HOR Performances of Pt/C Catalysts

“…Caprolactam adsorbates are also responsible for the activity loss. In addition, the aminocaproic acid hydrolysis produces a quaternary amine (−NH 3 + ) in acidic conditions, 28 which displaces the ionomer proton (ion exchange), decreases the water content, 48 diminishes the oxygen permeability 49,50 and increases the mass transport resistance. This explanation is consistent with the large decrease in diffusion-limited current for caprolactam (Fig.…”

“…Both EG and caprolactam poison the ORR Pt/C, 28,32,33 but the H 2 O 2 yield has not been measured. In contrast to the slow ORR kinetics, the HOR kinetics on Pt/C catalysts is so fast that the cell voltage losses are negligible even for notably low Pt loadings.…”