Figure 1 - uploaded by Hyun-Seok Cho
Content may be subject to copyright.
Source publication
In this paper, we investigate contaminationmechanisms and quantify the effect of organicmodel 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....
Contexts in source publication
Context 1
... pressure of 150/150 kPa, and 50% RH for anode/cathode, respectively. A comparison of lines (a) no contaminants, (b) 18 μmol/h of ε-caprolactam, and (c) 78 μmol/h of ε-caprolactam in Figure 10 reveals that, as the feed rate of the ε-caprolactam under the same condi- tions increases, the voltage loss (i.e., V pristine -V contamination ) increases. The interesting aspect of this ε-caprolactam effect on performance loss is the temperature effect shown in the comparison of lines (b) 80 • C and (d) 50 • C for the same molar feed rate (i.e., 18 μmol/h) of ε-caprolactam. ...
Context 2
... we chose a 50% RH (i.e., 0.5 water vapor activity) to ensure the same water content in the PEMs at different temperatures. Two fitting curves of measured water uptake for N117 membranes at 30 • C and 80 • C 56,57 and for NRE212 membranes at 50 • C and 90 • C are shown as dots in Figure 11. The water uptake in the PEM shows consistency at RH values less than 50%, whereas significant discrep- ancies arise at RH values greater than 50%. ...
Context 3
... in situ CV measurements (not shown in this paper) before (0 h) and after infusion (14.5 h in Figure 10) revealed 40% (line c) The ECSA loss measured in situ is more comparable to the CV results measured ex situ at pH 2 rather than those measured at pH 1 (see 0.04 mM and 0.2 mM in Table IV). This comparison between ex situ and in situ CVs suggests that carboxylate anion (-COO − ) may be the main chemical structure of the amino ε-caproic acid rather than the carboxylic acid (-COOH) in PEMFCs. ...
Citations
... Additionally, when the membrane is functionalized (ionexchanged) by soaking in ammonium solution, the water content in the membrane decreases by almost half as that of a pure H þ conducting membrane. This results in a significant loss of conductivity when the cation being transferred changes from H þ to NH 4 þ [25]. ...
Ammonia is widely used in fertilizers and cleaning products, as a refrigerant in air conditioning, and in food preservation. Ammonia is also an excellent vector for hydrogen with high energy density and can be compressed for convenient transport and storage. In this paper, we examine the suitability of ammonia for electrochemical compression (ECC). Electrochemical compressors can be an ideal replacement for mechanical compressors because of noiseless operation and higher efficiencies. They also permit the use of environmentally-friendly refrigerants such as ammonia. We evaluate the performance of an ECC operated on an ammonia-hydrogen blend using a fuel cell type hardware. A perfluorosulfonic acid (PFSA) membrane is employed to facilitate the pumping of ammonia, using hydrogen as a carrier gas, by the conduction of NH4+ ions from anode to cathode. We have recently established and experimentally validated a robust formulation for the electrochemical compression of hydrogen that properly addresses the role of back-diffusion. The primary goal of this work is to assess the effect of back-diffusion during the ECC of ammonia. Our results indicate that back-diffusion plays a highly deleterious role when a PFSA membrane is employed and is the principal challenge that needs to be addressed during the ECC of ammonia-hydrogen blends.
... Based on such behaviour, they inferred that the compounds with ion exchange properties have more of an effect on the non-reversible performance degradation. Cho et al. [123] examined seven organic model contaminants i.e. aniline, diethyleneglycol monoethyl ether acetate, diethyleneglycol monoethyl ether, 4-methyl benzensulfonamide, benzyl alcohol, and 2,6-diaminotoluene, which are suspect of being originated from BOP materials on PEM fuel cell. According to their findings, the impacts of aromatic compounds are more severe rather than aliphatic compounds. ...
... 1,2 Previous experimental studies on contamination effects to the PEMFC durability including in-situ single cell and segmented cell tests were conducted, and the sensitivity of performance to the low levels of contamination was determined. The contaminants from airborne impurities (SO 2 , H 2 S, CO, NO x , and bromomethane), [3][4][5][6][7][8][9][10][11][12][13] fuel impurities in hydrogen(NH 3 , CO, hydrocarbons, glycols, and alcohols), [14][15][16][17][18][19][20][21] inorganic metal cations(sodium, calcium, potassium, iron, nickel, and silicon etc.) [22][23][24][25][26][27][28][29][30][31][32][33] from gasket, bipolar plates, catalyst alloys, and deicer etc., and also from organic leachates(aniline, toluene, alcohols, glycols, propylene, methyl methacrylate) [34][35][36][37][38][39][40][41][42][43] derived from fuel cell systems including stack, structural plastic materials, and assembly aids. ...
... As shown in Figure 1, these ex-situ Pt coverage data can be obtained with contaminants in the liquid phase. 36,39 By contrast, for the in-situ performance, the transport of contaminants can be through the gas phase. Scaling techniques are required to establish the relationship between the coverage measured with ex-situ liquid concentration and the coverage corresponding to in-situ gas phase concentration. ...
... Here, we present ex-situ and in-situ data and discuss methods to test the scaling using the dimensionless groups. The major species that were identified in previous studies in the leachate solution of off-the-shelf assembly aid materials 39,43 are chosen for study. ...
Correlating ex-situ measurements of Pt coverage using the thin film-rotating disk electrode (TF-RDE) and in-situ performance of proton exchange membrane (PEM) type fuel cells and electrolyzer is established. The TF-RDE has a smaller geometric electrode area, and, typically, lower Pt loading is used compared to the in-situ single cell of PEMs. The model equation for Pt contamination by adsorption mechanisms followed by dimensionless analysis enables us to find three important dimensionless groups, which has been shown to control the contamination phenomena. The capacity ratio of Pt loading and inlet concentration of the contaminant, the measure of the rate of reaction, and the coverage ratio of the contaminant is used to translate ex-situ to in-situ by providing the scaling factor that is key to the correlation. These scales lead to the prediction of the coverage on the Pt sites using the ex-situ adsorption isotherm. Also, dimensionless numbers are tested in in-situ performance tests of PEM fuel cells for validation.
... [1][2][3] Such species may adsorb on the Pt catalyst, penetrate into the ionomer and membrane, or compete with the main reactions, which decreases the active surface area, ionic conductivity of the catalyst layer and membrane, and cell performance. 2,[4][5][6][7][8][9] In addition, H 2 O 2 , which is a side product of the oxygen reduction reaction (ORR), and its associated yield often increases in the presence of organic contaminants such as acetylene, acetonitrile, propene, naphthalene, and methyl methacrylate. [10][11][12][13] A larger H 2 O 2 generation rate exerts an undetermined effect on the performance and durability of PEMFCs. ...
... n e can be calculated using Eq. 4 52 after subtracting the background disk and ring currents from the observed disk and ring currents during the ORR. n e = 4/ I ring /(I disk N ) + 1 [4] The meanings of I disk , I ring , and N are identical to those in Eq. 3. The electron transfer number is considered the effective number of transferred electrons per O 2 molecule, e.g., 4 or 2, depending on whether the process generates exclusively H 2 O or H 2 O 2 , respectively. As shown in Fig. 7, the electron transfer number of the ORR, which is directly related to the H 2 O 2 yield, is close to 4 on the Pt/C catalyst in 0.1 M HClO 4 when the potential is higher than 0.6 V. ...
Ethylene glycol (EG) and caprolactam are two representative contaminant species either present in the fuel cell system or released by fuel cell system materials. The contamination effects of EG and caprolactam on the electro-catalytic performances of a Pt/C catalyst toward the oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) were investigated in acid media using the rotating ring/disk electrode (RRDE) technique. The Pt surface coverage increased with EG and caprolactam concentrations. The H2O2 yield also significantly increased because of the effects of the two contaminants. The EG- and caprolactam-derived adsorbates reduce the ORR and HOR rates and modify the rate-determining step (change in Tafel slope).
... Their studies also showed the effect of individual functional groups in poisoning the fuel cell. The effects of contamination by some organic model compounds derived from the fuel cell BOP on performance in PEMFCs were examined by Cho et al. 37 Their results revealed severe impacts on performance in PEMFCs depending on functionalities which allowed multiple contamination mechanisms. In another work Cho et al. 38 developed a mathematical model for organic contaminants that come from BOP materials by considering the effect of contamination on the catalyst, electrode ionomers and membrane. ...
... 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. ...
... 48 The ion exchange reaction of 2,6-DAT in the membrane is similar to aniline and ammonia. 37 Previous studies has shown that the ionomer conductivity is exponentially related to the proton concentration 28 and can be related to y by: ...
The performance loss and recovery of the fuel cell due to Balance of Plant (BOP) contaminants was identified via a combination of experimental data and a mathematical model. The experiments were designed to study the influence of organic contaminants (e.g. those from BOP materials) on the resistance of the catalyst, ionomer and membrane, and a mathematical model was developed that allowed us to separate these competing resistances from the data collected on an operating fuel cell. For this reason, based on the functional groups, four organic contaminants found in BOP materials, diethylene glycol monoethyl ether (DGMEE), diethylene glycol monoethyl ether acetate (DGMEA), benzyl alcohol (BzOH) and 2,6-diaminotoluene (2,6-DAT) were infused separately to the cathode side of the fuel cell. The cell voltage and high frequency impedance resistance was measured as a function of time. The contaminant feed was then discontinued and voltage recovery was measured. It was determined that compounds with ion exchange properties like 2,6-DAT can cause voltage loss with non-reversible recovery, so this compound was studied in more detail. The degree of voltage loss increased with an increase in concentration, and/or infusion time, and increased with a decrease in catalyst loadings.
The diversity and complexity of the parameters involved in the modeling of proton exchange membrane fuel cells (PEMFCs) have restricted further research and applications of such cells, and the similarity theory is a promising solution to this problem. The similarity theory is an effective tool to obtain compact and generalized results with the same precision as that of the basic mathematical model. This paper presents a comprehensive review of the application of the similarity theory to most aspects of PEMFCs. The advantages of using the similarity theory, such as generality, reduction in the test effort, convenient comparisons and guidance to scale up the experiment, are discussed and analyzed. Although a number of similarity criteria have been proposed in recent years, the similarity theory is not as widely applied or well accepted in PEMFC research as in the heat transfer and fluid flow domain. The objective of this paper is to demonstrate the feasibility of performing a similarity analysis for such complex systems and encouraging researchers to present a dimensionless expression of their results in the follow up PEMFC research. A key challenge is to use the similarity analysis for a complete gas-water-electricity-heat-mechanics coupled PEMFC system and obtain the correlation between the dimensionless output voltage/current and input similarity criteria. This review indicates that none of the existing models can achieve this objective, and further research pertaining to this aspect must be performed. Several recommendations to achieve this aim, including a hierarchical classification of the criteria, are provided.
The contamination impacts of ethylene glycol (EG) and caprolactam on the electro-catalytic behavior of a Pt/C catalyst toward the oxygen reduction reaction (ORR) were investigated in acid media using a rotating ring/disk electrode (RRDE). The Pt surface coverage increased whereas the ORR diffusion-limited and kinetic currents decreased with larger EG and caprolactam concentrations. The poisoning effect of caprolactam on the ORR was more severe than EG. The Tafel slope was unchanged for EG but higher values were observed when the caprolactam concentration increased to 10⁻¹ M. The H2O2 yield greatly increased for both contaminants. The ORR performance loss due to EG was attributed to Pt active sites blocked by COad species and EG oxidation by-products. The adsorption of aminocaproic acid resulting from a caprolactam ring-opening reaction onto Pt active sites was responsible for the ORR activity and selectivity effects.
