The Contamination Behavior of System Derived Organic Model Compounds on PEMFC Based upon Functional Groups

Abstract

In this paper, we investigate contamination mechanisms and quantify the effect of organic model compounds aniline, diethyleneglycol monoethyl ether acetate, diethyleneglycol monoethyl ether, 4-methyl benzensulfonamide, benzyl alcohol, and 2,6-diaminotoluene that have been observed to originate from degradation of balance of plant materials on PEMFCs. In situ voltage loss can be quantified by contamination sources such as Pt, the ionomer, and the membrane using isotherm curves that are prepared by ex situ studies considering contamination mechanisms: adsorption on Pt, ion-exchange/absorption in membranes or electrodes. Severe kinetic loss of Pt activity on oxygen reduction reaction was observed for aromatic compounds due to the greater coverage on Pt/C than aliphatic compounds. An ion-exchange reaction by amine-containing aromatic compounds results in significant conductivity losses of the membrane/ionomer, which is main contributor of the performance loss in this study. That is, controlling the voltage losses caused by the membrane/ionomer contamination is critical to ensure the stability of the system. Infusion of non-amine containing compounds into PEMFCs also increased performance loss by an absorption mechanism but reached at steady state with reversible recovery by switching into normal operations without contaminants.

An Isothermal Model for Predicting Performance Loss in PEMFCs from Balance of Plant Leachates

“…37) of DEGEE for the absorption mechanism can be estimated as 0.3 to quantify the voltage loss of the ionomer in the electrode by the model. 18,34 Membrane contamination.-In a similar fashion to that described above, the analysis of dimensionless numbers for the membrane contamination by ion-exchange reaction also shows that higher Da 3, 3 and 3 yield the fastest contamination and voltage loss, as shown in Figure 6d. The interesting aspect of membrane contamination is that 3 is a small number due to the large number of moles of ionomer in a typical membrane.…”

“…We selected the dimensionless numbers by considering the general operating variables (T, i, RH, backpressure, stoic, C A0 ), the system geometry (w, r, h), and the physical constants (N m , δ, D, K, B) used for in situ infusion experiments. 2,[14][15][16][17][18][30][31][32]34,52 Tables I to III list the variables for each contamination source (i.e., Pt = 1, ionomer = 2, membrane = 3). For the purpose of exploring the parameter space for the model predictions, we choose a 2 2 factorial design for each source in terms of the dimensionless numbers (i.e., high and low) as summarized in Table IV for each mechanism. For 1, 2, and 3 (capacity ratios), the Pt catalyst and H + ionomer and membrane concentrations change with feed contaminant concentrations for a specified membrane electrode assembly (MEA).…”

“…Finally, the (coverage ratio) can be obtained from ex situ adsorption and ion-exchange isotherms of Pt and the Nafion membrane for selected compounds. [16][17][18] Details of the calculations for Table IV can be found in Ref. 34.…”

“…Examples are also known for SO 2 , 10,11 for H 2 S, 12 and even for details of the reverse water-gas shift reaction of CO 2 . 13 The fundamental mechanism of contamination from organic contaminants such as aniline, ε-caprolactam, and diaminotoluene (DAT), [14][15][16][17][18] which have been identified as possible system contaminants, have been studied only briefly and recently, and it has been shown that their impact on PEMFC performance depends on their functional groups. For example, the ion-exchange reaction of the amine group in aniline with the Nafion membrane/ionomer causes a decrease in the number of available proton sites, thereby hindering the transport of protons and increasing ohmic losses.…”

“…Models that address the absorption mechanism, which has been shown to exist for organics, 18 are non-existent in PEMFC literature. On the other hand, for the adsorption mechanism, many contamination models [27][28][29] have been developed and introduced.…”