Development Of Proton Exchange Membranes Research Articles

A one-dimensional and two-phase flow model of a proton exchange membrane fuel cell

BACKGROUND Mathematical models are very important tools for the development of proton exchange membrane (PEM) fuel cells. In this work, a one-dimensional, steady-state and two-phase flow model of a PEM fuel cell is presented. RESULTS The present two-phase flow model is able to predict the experimental results more accurately than its single-phase counterpart, especially for high current values. In addition, the model presented here also allows calculation of the threshold current density defining the boundary between single and two-phase regimes, which can be used to provide a set of operating conditions avoiding a high content of liquid water and the resulting negative effects on cell performance. CONCLUSIONS Owing to its low demand on computational time, the proposed model can be used for PEM fuel cells system simulations, offering many advantages over empirical models. © 2015 Society of Chemical Industry

Nickel Nanowire Oxidation and Its Effect on Platinum Galvanic Displacement and Methanol Oxidation

The cost of platinum (Pt) catalysts is a significant barrier in the commercial development of proton exchange membrane fuel cells (PEMFCs). Carbon supported Pt nanoparticles (Pt/HSC) are typically used in PEMFCs due to their high surface area and moderate ORR mass activity. Pt/HSC currently produces roughly half the activity of the U.S. Department of Energy (DOE) target (440 mA mgPGM ‒1, 2017‒2020 mass activity target) in membrane electrode assemblies. Improving catalytic activity by 4 times will allow for the use of less than 10 g of Pt in a 10 kW stack. Such a reduction in catalyst cost can enable the commercial deployment of automotive fuel cell vehicles.Extended Pt structures have previously been studied for oxygen reduction (ORR) activity and have been found to have specific activity and durability benefits to Pt nanoparticles.1-3 Although extended catalysts can produce high specific activities, they generally lack the surface area to produce high mass activity. Catalysts formed by galvanic displacement are poised to produce high mass activities for ORR by maintaining the high specific activities demonstrated by extended Pt surfaces and by allowing for the deposition of thin Pt layers.Nickel (Ni) nanowires were previously used as a template for galvanic displacement, producing Pt coated Ni nanowires with an outer diameter of 200‒300 nm and a length of 100‒200 µm.4 Electrochemical measurements taken in rotating disk electrode (RDE) half-cells found that the Pt coated Ni nanowires produced surface areas as high as 91.3 m2 gPGM ‒1 and mass ORR activities as high as 917 mA mgPGM ‒1. These materials (Ni nanowires and Pt coated Ni nanowires) have been treated in oxygen at elevated temperatures. By heat treating in oxygen: the effects of an increasing Ni nanowire oxide layer on Pt displacement were examined; and durability losses (surface area and activity) of Pt coated Ni nanowires were reduced.As-received Ni nanowires contain a thin oxide layer and a Ni metal core. Galvanic displacement of the untreated Ni nanowires was limited to less than 17 wt % Pt without the inclusion of additional acid to remove the oxide layer. Further heat treatment of the Ni nanowires with oxygen served to grow the oxide layer. At relatively low temperatures, oxide content near the nanowire surface increased; at higher temperatures, a NiO phase grew and consumed the metal nanowire core. Increasing the oxide layer served to limit and eventually shut off Pt displacement entirely.Although Pt coated Ni nanowires produce high mass activities, losses (similar to Pt/HSC) were observed following RDE durability testing (30,000 potential cycles, 0.6‒1.0 V vs. RHE, similar protocol to DOE working group).5,6 While extended Pt structures have previously been found to offer durability benefits to Pt/HSC, the benefit is likely lessened by the presence of Ni metal. By heat treating Pt coated Ni nanowires in oxygen, the oxide layer thickness was increased thereby stabilizing the catalysts in potential cycling. Treated catalyst produced initial surface areas and activities that were lower than the untreated Pt coated Ni nanowires, presumably since Ni near the surface could not be removed electrochemically during break-in. With potential cycling, however, treatment of the nanowires dramatically improved retention of surface area and activity (Figure 1).Following durability testing, treated Pt coated Ni nanowires produced a mass ORR activity of 680 mA mgPGM ‒1, or a 9 % improvement of initial activity. Compared to conventional Pt electrocatalysts and fully displaced Pt nanotubes, Pt coated Ni nanowires appear to provide significant activity and durability advantages.ReferencesDebe, M.; Department of Energy, U. S., Ed. http://www.hydrogen.energy.gov/pdfs/review08/fc_1_debe.pdf, 2008.Chen, Z.; Waje, M.; Li, W.; Yan, Y. Angew. Chem. Int. Ed. 2007, 46, 4060-4063.Papandrew, A. B.; Atkinson, R. W.; Goenaga, G. A.; Wilson, D. L.; Kocha, S. S.; Neyerlin, K. C.; Zack, J. W.; Pivovar, B. S.; Zawodzinski, T. A. ECS Transactions 2013, 50, 1397-1403.H. A. Gasteiger, S. S. Kocha, B. Sompalli, F. T. Wagner, Applied Catalysis B-Environmental 2005, 56, 9.Alia, S. M.; Larsen, B. A.; Pylypenko, S.; Cullen, D. A.; Diercks, D. R.; Neyerlin, K. C.; Kocha, S. S.; Pivovar, B. S. ACS Catalysis 2014, 4, 1114-1119.M. Uchimura, S. Sugawara, Y. Suzuki, J. Zhang, S. S. Kocha, ECS Transactions 2008, 16, 225.S. S. Kocha, Electrochemical Degradation: Electrocatalyst and Support Durability. In M. Mench, E. C. Kumbur, T. N. Veziroglu, Polymer Electrolyte Fuel Cell Degradation, pp. 89-185, 2011.

An Isothermal Model for Predicting Performance Loss in PEMFCs Due to Contamination Mechanisms

In the development of proton exchange membrane fuel cells (PEMFCs), contamination can affect the performance on PEMFCs at a slow rate and thereby influence the apparent durability. The extent to which contamination is reversible may improve the potential for commercialization.1-3Mechanistic models may allow for understanding the differences between contamination, durability, and reversibility of performance loss.To understand contamination mechanisms and their impact on PEMFCs, experimental studies were conducted for relatively low levels of contamination. These studies have served as the basis for the development of a simple isothermal model for initial performance losses7 and a technique for correlating ex-situ and in-situ measurement.8These experiments and model highlighted three mechanisms of contamination: adsorption on the Pt catalyst, absorption into the membrane, and ion-exchange with ionomeric components.The new model presented here allows for prediction of the distribution of performance loss (i.e., voltage change) for the long-term ion-exchange which was superficially treated in the previous model.7 That is, the simple model could only predict the initial slope and a final slope of voltage losses (solid lines) in Figure 1. The simplification could not predict, a-priori, the time when the rate limiting mechanisms changed and the change in slopes of voltage loss. For example, Figure 1 shows a discrete peak point at 20 h, rather than a gradual transition between curves. This point represents the change of the governing mechanism from contamination of the ionomer in the catalyst layer to contamination of the ionomer in the membrane.The long-term ion exchange in the new model is a result of the membrane acting as a reservoir for the cation and this reservoir decreases the effect of the ionomer contamination on voltage (i.e., performance) loss. Further, the new model allows more precise predictions for the contamination by functional group (e.g. cationic, aromatic, aliphatic etc.). The new model also shows that under some circumstances, the reaction plane approximation of the simple model is valid; however, since the membrane is attached to the catalyst ionomer the two entities interact through diffusion of the cation and ion-exchange. The model predictions are shown for three sources of voltage loss and the model accounts for time dependent two-dimensional contamination along the channel and into the membrane. The ability of the new model to predict the reversibility shown in Figure 1 after 105 h, is also discussed.Figure 1. Comparison of model7,8 predictions (lines) and in-situ voltage loss (open circles) for 125 ppm of 2,6-diaminotoluene (2,6-DAT) at an infusion rate = 0.03ccm in a 50 cm2 cell. (T = 80°C, I = 0.2A/cm2, stoic=2.0/2.0, back pressure =150 /150 kPa.) Acknowledgements The authors gratefully acknowledge support for this work by the DOE EERE Fuel Cell Technologies Office (DE-AC36- 08GO28308) under a subcontract from NREL (ZGB-0-99180-1) to the University of South Carolina R eferences [1] R. Borup, J. Meyers, B. Pivovar, Y. Kim, R. Mukundan, N. Garland, D. Myers, M. Wilson, F. Garzon, D. Wood, P. Zelenay, K. More, K. Stroh, T. Zawodzinski, J. Boncella, J. E. McGrath, M. Inaba, K. Miyatake, M. Hori, K. Ota , Z. Ogumi, S. Miyata, A. Nishikata, Z. Siroma, Y. Uchimoto, K. Yasuda, K. Kimijima and N. Iwashita, Chem. Rev. 107, 3904-3951, 2007.[2] Proton Exchange Membrane Fuel Cell: Contamination and Mitigation Strategies edited by H. Li, S. Knights, Z. Shi, J. W. Van Zee, J. Zhang, CRC press, New York, 2010.[3] J. St-Pierre, Air impurities: Polymer electrolyte fuel cell durability edited by F. Buchi, M. Inaba, T. J. Schmit, p. 289-321, Springer, New York, 2009.[4] H. N. Dinh, H. Wang, C. S. Macomber, K. O’Neil, and KC Neyerlin, Paper #34 presented at the 243rd ACS National Meeting, San Diego, CA 2012.[5] Md. Opu, M. Ohashi, H. Cho, C. S. Macomber, H. N. Dinh, J. W. Van Zee, ECS Trans. 50(2), 619-634 (2013).[6] H. Cho, Md. Opu, M. Ohashi, and J. W. Van Zee, Paper #1295, presented at the 222nd ECS Meeting & Honolulu PRiME 2012, HI, Oct. 09, 2012.[7] H. Cho and J. W. Van Zee, Paper #1260, presented at the 224th ECS Meeting 2013, San Francisco, CA, Oct. 27, 2013.[8] H. Cho and J. W. Van Zee, Paper #656, presented at the 225th ECS Meeting 2014, Orlando, FL, May. 14, 2014.

Statistical and Block Copolymers for Anion-Exchange Membranes with High Local Concentrations of Quaternary Ammonium Groups

Cationic polymers in the form of anion-exchange membranes (AEMs) may enable a route towards low platinum or even platinum-free alkaline membrane fuel cells with the potential to oxidize more complex fuels than hydrogen and methanol [1-4]. The main challenges for the AEMs are currently to enhance the alkaline stability of the cationic group and to improve the ion conductivity. In this context, there have been many attempts to enhance the properties by varying the backbone polymer structure and the nature and content of the cations [1-4]. However, clearly promising strategies to prepare high-performance AEMs have not yet been described. While several lessons can be learnt from the development of proton-exchange membranes (PEMs), the cationic polymers in AEMs have different characteristics. For example, the organic cations of AEMs, such as quaternary ammonium (QA) groups, are larger and have a lower propensity to cluster and form a distinct ionic phase in the polymer matrix in comparison with the sulfonic groups of PEMs. This characteristic may seriously limit the transport properties of AEMs.We have recently developed synthetic strategies where single phenylene rings in aromatic polymers can be directly functionalized with precisely two, three, or four QA groups, allowing an excellent and systematic control over the local density and distribution of ionic groups along the polymer backbone. We have used this approach to prepare several series of statistical and multiblock copolysulfones with very high local QA concentrations to promote membrane properties. Small angle X-ray scattering of AEMs based statistical copolymers containing phenylene rings functionalized with two, three and four QA groups, respectively, showed clear ionomer peaks to indicate efficient ionic clustering. The clustering was promoted by an increasing density of QA on the single phenylene rings. Corresponding randomly functionalized copolymer membranes showed no ionomer peaks. At moderate ion-exchange capacities, the Br- conductivity of the densely functionalized copolymers was higher than that of randomly functionalized copolymers, despite a significantly higher water uptake of the latter. In the current presentation, we will discuss selected results on the synthesis and structure-property relationships of the copolymers and AEMs.

Oxygen evolution in Co-doped RuO2 and IrO2: Experimental and theoretical insights to diminish electrolysis overpotential

Development of proton exchange membrane (PEM) water electrolysis systems has been held back by the cost of membrane and precious metal electrocatalyst components, and by the high overvoltage for water splitting. Since non-noble metal electrocatalysts with satisfactory activities are not currently available, costs must be reduced by improving performance and durability of noble metal electrocatalysts. Moreover, it is mandatory to understand the mechanisms of oxygen evolution and find out how the reaction kinetics could be improved. Here the kinetic pathway for oxygen evolution reaction (OER) on RuO2, IrO2 and RuIrCoOx surfaces is analyzed with electrochemical polarization and Density Functional Theory (DFT) analyses of the changes occurring when pure oxides are doped with Co and their effect during the first stages of oxygen evolution. Experimental electrochemical methods are used to find indicators of electrocatalyst quality: the lower the Tafel slope, the faster the reaction kinetics and the more active the electrocatalyst. It is found that RuIrCoOx surfaces show the lowest Tafel slope value, 0.068 V dec−1, and the rate determining step at low overpotential is the second H–O breaking. Changes in electronic structure responsible of the sluggish second reduction step in comparison to the first are identified by the theoretical study.

Correlating Ex-Situ and In Situ Measurement for Proton Exchange Membrane Fuel Cells

In the development of proton exchange membrane fuel cells (PEMFCs), the contamination effect on PEMFC durability can retard commercialization.1-4 To understand contamination mechanisms and their impacts on PEMFCs, experimental studies conducted and found the sensitivity of performance to the low levels of contamination. 1-9 Also, a simple isothermal model for contamination of a PEMFC which includes adsorption on the Pt catalyst, absorption into the membrane, and ion-exchange with ionomeric components was developed and presented. 8-9 In this paper, we discuss the relationship between ex-situ measurements using thin film electrodes and the in-situ performance of PEMFCs. The isotherms from ex-situ measurements for each mechanism provide a quantitative effect of coverage by contaminants and are shown to predict in-situvoltage losses when the proper dimensionless variables are used. For the Pt coverage the ex-situ measurements are performed on thin-film electrodes, which have typically lower Pt loadings (e.g., 0.02mg/cm2 vs. 0.4mg/cm2) and smaller geometric electrode areas (e.g., 0.24cm2 vs. 50cm2). As shown in Figure 1, these ex-situ Pt coverage data can be obtained with contaminants in the liquid phase. In contrast, for the in-situ performance, transport of contaminants can be through the gas phase. To establish the relationship between the coverage measured with ex-situ liquid concentration and the coverage corresponding to in-situ gas phase concentration, scaling techniques are required. Data are presented and discussed to test the scaling and the dimensionless groups. Acknowledgements The authors gratefully acknowledge support for this work by the DOE EERE Fuel Cell Technologies Office (DE-AC36- 08GO28308) under a subcontract from NREL (ZGB-0-99180- 1) to the University of South Carolina R eferences [1] R. Borup, J. Meyers, B. Pivovar, Y. Kim, R. Mukundan, N. Garland, D. Myers, M. Wilson, F. Garzon, D. Wood, P. Zelenay, K. More, K. Stroh, T. Zawodzinski, J. Boncella, J. E. McGrath, M. Inaba, K. Miyatake, M. Hori, K. Ota , Z. Ogumi, S. Miyata, A. Nishikata, Z. Siroma, Y. Uchimoto, K. Yasuda, K. Kimijima and N. Iwashita, Chem. Rev. 107, 3904-3951, 2007.[2] K. O’Leary and B. Lakshmanan Paper #1036 presented at the 220th ECS Meeting & Electrochemical Energy Summit in Boston, MA, Oct. 13, 2011. [3] Proton Exchange Membrane Fuel Cell: Contamination and Mitigation Strategies edited by H. Li, S. Knights, Z. Shi, J. W. Van Zee, J. Zhang, p. 100, CRC press, New York, 2010.[4] J. St-Pierre, Air impurities: Polymer electrolyte fuel cell durability edited by F. Buchi, M. Inaba, T. J. Schmit, p. 289-321, Springer, New York, 2009.[5] H. N. Dinh, H. Wang, C. S. Macomber, K. O’Neil, and KC Neyerlin, Paper #34 presented at the 243rd ACS National Meeting, San Diego, CA 2012.[6] Md. Opu, M. Ohashi, H. Cho, C. S. Macomber, H. N. Dinh, J. W. Van Zee, ECS Trans. 50(2), 619-634 (2013).[7] H. Cho, Md. Opu, M. Ohashi, and J. W. Van Zee, Paper #1295, presented at the 222nd ECS Meeting & Honolulu PRiME 2012, HI, Oct. 09, 2012.[8] H. Cho and J. W. Van Zee, Paper #1260, presented at the 224th ECS Meeting 2013, San Francisco, CA, Oct. 27, 2013.[9] H. Cho and J. W. Van Zee, under review, Journal of the Electrochemical Society, 2013.

Incorporation of benzimidazolium ionic liquid in proton exchange membranes ABPBI-H3PO4

This paper presents the development of proton exchange membranes (PEM) from the incorporation of poly (2,5-benzimidazole) (ABPBI) in phosphoric acid (H3PO4) and ionic liquid (IL) 1-butyl-3-ethylbenzimidazolium dihydrogen phosphate (BEBzIm-H2PO4). We show structural, physicochemical and electrochemical characterization of synthesized IL and prepared membranes. The addition of IL in composite membranes of ABPBI-H3PO4 increases thermal stability. Also, the conductivity of membranes increases with temperature and the amount of absorbed mixture. Conductivity at a range of 10−4S/cm was achieved at 150°C by 50% IL and 50% phosphoric acid impregnation. This conducting composite membrane shows promise for operation in temperature proton exchange membrane fuel cells at working temperatures up to 100°C.

Mass Transport and Oxygen Reduction Kinetics at an Anion Exchange Membrane Interface: Microelectrode Studies on Effect of Carbonate Exchange

Development of proton exchange membrane fuel cells, have to be tempered with the cost, a significant portion of which is due to the so called ‘stability criterion’ restricting the choice to Pt and Pt alloy materials.Fuelcellsoperating inalkaline media havepotential advantage of facile kinetics of oxygen reduction reaction on non-precious group metals and stability at high pH values. In addition, the hydrodynamics of alkaline membrane fuel cells is potentially beneficial considering the problems associated with water management in a conventional PEM fuel cell. Further, highly stable PTFE based membranes are not required under alkaline conditions as the membranes are less prone to attack by peroxide ions. Even though AEMFCs alleviate most of the hurdles associated with PEM fuel cells, state of art performance of H2/air does not exceed half of the performance shown by H2 fed PEM fuel cells using Pt based catalysts (compare 700 mW cm −2 for PEMFCs 1 at 0.65 V

Ligand-Mediated Electrocatalytic Activity of Pt Nanoparticles for Oxygen Reduction Reactions

High-performance electrocatalysts for oxygen reduction reactions (ORR) are crucial for the development of proton exchange membrane fuel cells (PEMFCs). In this study, a novel method was developed by which the ORR activity of Pt nanoparticles was deliberately manipulated by selective organic capping ligands. By coreduction of diazonium salts and H2PtCl4, a series of Pt nanoparticles (core size 2.0–2.5 nm) stabilized by para-substituted (R = −CH3, −F, −Cl, −OCF3, and −CF3) phenyl groups were synthesized. The experimental results demonstrated that the electron-withdrawing capability of the substituent moieties, as manifested by the Hammet substituent constant (σ), plays a key role in controlling the ORR activity, where the higher σ, the higher ORR activity. Within the present experimental context, Pt nanoparticles stabilized by trifluoromethylphenyl groups (Pt–Ar–CF3) exhibit the highest catalytic activity among the series, with an ORR specific activity 3.2 times higher than that of commercial Pt/C catalysts...

Voltage loss and fluctuation in proton exchange membrane fuel cells: The role of cathode channel plurality and air stoichiometric ratio

Water management is a critical issue in the development of proton exchange membrane (PEM) fuel cells with robust operation. Liquid water can accumulate and flood the gas delivery microchannels and the porous electrodes within PEM fuel cells and deteriorate performance. Since the liquid distribution fluctuates in time for two-phase flow, the rate of oxygen transport to the cathode catalyst layer also fluctuates, resulting in unstable power density and efficiency. This paper reports experimental data on the mean voltage loss and the voltage fluctuations during constant current operation as a function of both the number of parallel microchannels and the air flow rate stoichiometric ratio. We define channel plurality as a flow field design parameter to describe the number of channels per unit of active area. The voltage loss was found to scale proportionally to channel plurality divided by the air stoichiometric ratio. The amplitude of the voltage fluctuations was found to be linearly proportional to channel plurality and inversely proportional to the air stoichiometric ratio squared. By analyzing pressure drop data and power spectra, we conclude that the voltage fluctuations are well-correlated with two-phase flow instabilities in the cathode's parallel microchannels. Finally, a scaling analysis is presented for generalizing the results for fuel cells having different active area and channel cross-section.

Electrospray ionization mass spectrometric analyses of rhodium tetraphenylporphyrin complexes as electrocatalysts for CO oxidation by tandem mass spectrometry and hyphenated method with capillary electrophoresis

Carbon monoxide (CO) poisoning of platinum (Pt)-based electrocatalysts is a huge obstacle in the development of proton-exchange membrane fuel cells. Fuel cell performance can be improved by removing CO through electrolytic oxidation. Yamazaki et al. synthesized several rhodium (Rh) tetraphenylporphyrin complexes as electrocatalysts to reduce CO poisoning. Experimental results showed that these complexes display higher electrochemical CO oxidation activity than previously synthesized Rh octaethylporphyrin complex and that the differences in the structures of p-substituted groups influence their activity. To confirm the formation of these Rh tetraphenylporphyrin complexes, analyses were performed using electrospray ionization mass spectrometry (ESI-MS), electrospray ionization tandem mass spectrometry (ESI-MS/MS), and capillary electrophoresis-electrospray ionization mass spectrometry (CE-ESI-MS). In ESI-MS, peaks other than that of the Rh tetraphenylporphyrin complex were occasionally detected at different m/z values. The ESI-MS/MS and CE-ESI-MS results suggest that these peaks correspond to the complexes coordinating CO or other ions, or to remaining uncoordinated tetraphenylporphyrins. Coordination of CO is supported by the ESI-MS/MS results for the Rh octaethylporphyrin complex. Separation of the uncoordinated tetraphenylporphyrin from Rh tetraphenylporphyrin complex was achieved by CE-ESI-MS.

Proton conductivity and stability of low-IEC sulfonated block copolyimide membrane

The proton conductivity and membrane stability of sulfonated block copolyimide membranes with a low ion exchange capacity (IEC) synthesized by chemical imidization using a two-pot procedure were investigated. The proton conductivity of the low-IEC block copolyimide membrane at 80 °C and 98% relative humidity was 16 times larger than that measured for the low-IEC random copolyimide membrane, while that of the high-IEC block copolyimide membrane at the humidity was 4 times than that of the high-IEC random copolyimide membrane, suggesting that the protons in the low-IEC block copolyimide membrane were effectively transported. In addition, the hydrolytic and oxidative stabilities of the low-IEC sulfonated block copolyimide membranes were estimated in detail from FT-IR and 1H NMR. These stabilities of the low-IEC membranes were significantly enhanced compared to those of the high-IEC membranes. The oxidative stability problem in the low-IEC block copolyimide membranes was found to be primarily caused by a decrease in the sulfonic acid groups rather than by polyimide chain scission. These findings indicate that a sulfonated block copolymer consisted of a small amount of sulfonic acid groups is desirable for the development of proton exchange membranes, when considering the balance between the proton conductivity and membrane stability of the proton exchange membranes.

Quantum-beam technology: A versatile tool for developing polymer electrolyte fuel-cell membranes

This paper describes the versatile application of quantum beam-based technology to the development of proton exchange membranes (PEMs) for fuel-cell applications. The γ-ray or electron-beam induced radiation grafting offers a way to prepare PEMs; typically, the radical-initiated polymerization of a styrene or styrene-derivative monomer on a base polymer is followed by a sulfonation step. Novel PEMs were previously obtained using radiation-crosslinked fluoropolymers as the base material. Interestingly, combining this radiation-crosslinking process with the well-known chemical crosslinker method enabled one to obtain the “multiply”-crosslinked PEMs, in which both the main and grafted chains have covalently bridged structures leading to a high durability. The bombardment of heavy ions accelerated to MeV or higher energies produces a continuous trail of excited and ionized molecules in polymers, which is known as a latent track. The approach using this ion-track technology is based on the chemical etching and/or modification of each track with diameters of tens to hundreds of nanometers. The resulting “nano-structure controlled” PEM was found to have perfect one-dimensional proton-conductive pathways parallel to its thickness direction, while, in contrast, other existing PEMs mostly exhibited proton transport in the three-dimensional random media. The hierarchical structures of the PEMs, ranging from nanometers to micrometers, were revealed by small-angle neutron scattering experiments using a cold or thermal neutron beam. The information in such a wide length scale led to a deep insight into the dynamic properties inside the PEM from a molecular to macroscopic level, which can provide feedback for the reconsideration and optimization of the preparation procedure. As demonstrated above in the author's studies, it is important to understand that every quantum beam is different, thereby making the right beam choice.

Performance evaluation of platinum-based catalysts for the development of proton exchange membrane fuel cells

Platinum-based catalysts are considered the most efficient catalysts for triggering electrochemical reactions in proton exchange membrane (PEM) fuel cells. In the present study, commercial catalysts containing 10% and 30% Pt supported on Vulcan XC-72 carbon were studied to assess their performance in PEM fuel cells. Both catalysts consisted of Pt particles of almost the same size. The utility of these catalysts in PEM fuel cells was studied by finding the real surface area and rate of electro-oxidation of methanol in 0.5 M H_2SO_4 by using cyclic voltammetry. The methanol oxidation reaction was used for characterization of catalysts of PEM fuel cells due to the liquid nature of methanol and the close resemblance of basic electrochemical features of direct methanol fuel cells and PEM fuel cells. Comparison of the data of real surface area and rate of electro-oxidation of methanol showed that 30% Pt catalyst having higher Pt loading is more suitable for PEM fuel cells as compared with 10% Pt catalyst. The PEM fuel cell components were designed and fabricated for testing of membrane electrode assemblies (MEAs). The importance of an additional gas diffusion layer in the form of carbon paper was also emphasized for improving gas diffusion and electrical contact of electrodes of MEAs with the flow field area of monopolar/bipolar plates of PEM fuel cells. The MEAs prepared from 10% and 30% Pt catalysts with Pt loading of 0.5 mg cm^{-2} gave the maximum power density of 119 and 185 mW cm^{-2}, respectively. It was concluded that nanosize carbon supported Pt catalysts having higher Pt loading are more suitable catalysts for preparing high performance MEAs of PEM fuel cells and the cyclic voltammetric data of real surface area and rate of methanol oxidation may be utilized to assess the performance of a given catalyst prior to its use in the preparation of MEAs of PEM fuel cells.

MnO 2/SiO 2–SO 3H nanocomposite as hydrogen peroxide scavenger for durability improvement in proton exchange membranes

Membrane durability was a key problem to the development of proton exchange membrane fuel cells (PEMFCs). A novel nanocomposite MnO 2/SiO 2–SO 3H was prepared to mitigate the hydrogen peroxide attack to the membranes at fuel cell condition. The nanocomposites were synthesized by the wet chemical method and three-step functionalization. The crystal structure was characterized by X-ray powder diffraction (XRD), the crystallite size and the distribution of the nanocomposites were investigated by TEM. SEM-EDX was used to analyze the elemental distribution on the surface of the nanocomposite. And the surface functional groups (–SO 3H) were evaluated by FT-IR. The amount of sulfonic acid groups introduced onto the silica surface was determined by titration method. The radical scavenging ability was estimated by UV–VIS spectroscopy using dimethyl sulfoxide (DMSO) as the trapping agent. The membrane durability was investigated via ex situ Fenton test and in situ open circuit voltage (OCV) accelerated test. In these tests, the fluoride emission rate (FER) reduced by nearly one order of magnitude with the dispersion of MnO 2/SiO 2–SO 3H nanocomposites into Nafion membrane, suggesting that MnO 2/SiO 2–SO 3H nanocomposites had a promising application to mitigate the degradation of the proton exchange membrane.

Heat and Mass Transport in Proton Exchange Membrane Fuel Cells—A Review

This review brings out those aspects of the development of proton exchange membrane (PEM) fuel cells over the last two to three decades that are of interest to the heat and mass transfer community. Because the heat transport and mass transport in proton exchange membrane fuel cells are very important from the efficiency point of view, an emphasis is given here to these transports and their influence on operating cell parameters. The works are classified as models with either isothermal or non-isothermal conditions of various assumed dimensionality and with either single-phase or two-phase flow. Along with modeling, a few experimental studies available are also reported here. Researchers in the area of PEM fuel cells are involved in activities such as development of new and low-cost materials, modeling the relevant physical processes, and electrochemical experimentation. These collective efforts may lead to making this technology viable to meet world needs for clean and cheap energy. This review brings out the fact that computational fluid dynamics (CFD) has become an inevitable tool in fuel cell analysis, as the detailed interactions between the flow structure geometry, fluid dynamics, multiphase flow, heat transfer, mass transfer, and electrochemical reaction can be modeled simultaneously, given the present state of the art in CFD. Through the predictive capability of CFD, it will be possible for fuel cell designers to better optimize the design and operating parameters of fuel cells before testing them in laboratory.

A Simple New Route to Covalent Organic/Inorganic Hybrid Proton Exchange Polymeric Membranes

The development of proton exchange membranes as electrolytes for polymer electrolyte fuel cells operating at intermediate temperatures has been achieved combining two approaches: the preparation of a cross-linked polymer and the formation of covalent organic/inorganic hybrids. A covalently cross-linked sulfonated polyetheretherketone with elevated degree of sulfonation (DS = 0.8) was prepared by reaction with HSO3Cl (SOPEEK). No degradation of PEEK was detected upon sulfonation, but only cross-linking via sulfonic groups with formation of SO2 moieties was observed. The extent of ramification was calculated by analyzing the 1H nuclear magnetic resonance (NMR) spectra of the products and resulted in 20% of the total amount of −SO3H groups present in the polymer. The solubility of the −SO2Cl precursor in organic solvents allowed easy carrying out of functionalization reactions in homogeneous conditions by lithiation and subsequent reaction with SiCl4, thus introducing covalenly linked silicon moieties (SOSiPEEK) at the ratios 1:0.25 and 1:0.50 per monomeric unit. The products were characterized by 1H and 13C NMR, attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry.

Proton Exchange Membranes: The View Forward and Back

The development of proton exchange membrane (PEM) fuel cells is largely tracked by the history of the membranes. Because fuel cells of various types were known prior to PEM technologies, the catalysts, fuels, and oxidants used in PEM fuel cells were reasonably well-established materials.

The direct borohydride fuel cell for UUV propulsion power

The development of proton exchange membrane and direct methanol fuel cell stacks is now well advanced for many applications. However, the significant performance advantages that these have over the battery for small to moderate scale applications will not be realised until a credible fuel source has been developed. The deficiencies of the PEMFC and DMFC can be eliminated by cation or anion-conducting membranes incorporated into a direct sodium borohydride fuel cell (DSBFC). The characterisation of membranes for the DSBFC is discussed. Novel membranes have been prepared which have resistance of an equal magnitude to the commercially available Nafion ® membrane.

Structural characterization and surface modification of sulfonated polystyrene–(ethylene–butylene)–styrene triblock proton exchange membranes

Structural characteristics and membrane performance of polystyrene- block-poly(ethylene- ran-butylene)- block-polystyrene (sSEBS) copolymer proton exchange membranes in water-swollen and different ratio of water/methanol-swollen are studied by small angle X-ray scattering (SAXS), ATR FT-IR, AFM. SAXS profile of sSEBS membrane showed that microstructure was a hexagonally cylindrical structure and it was maintained in the existence of methanol in water until 30 wt.%. As the main interest was on the development of proton exchange membranes for fuel cells operating at lower temperature with liquid methanol feed, a selective thin layer was introduced on the top of sSEBS membrane by simple plasma treatment in the presence of maleic anhydride in order to prevent methanol crossover. Both methanol permeability and proton conductivity gradually decreased with increasing loading amounts of maleic anhydride. Hydrophobic anhydride properties on the top of sSEBS membrane act as a barrier for methanol but also for proton, resulting in decreasing methanol permeability and proton conductivity. The hydrolysis of anhydride groups to carboxylic acid provides a facilitated transport site for the proton. After hydrolysis, the proton conductivity was recovered and the recovery rate of proton conductivity by hydrolysis was higher than that of methanol permeability.