High Temperature Proton Exchange Membrane Fuel Cell Research Articles

Construction of Novel Proton Transport Channels by Triphosphonic Acid Proton Conductor-Doped Crosslinked mPBI-Based High-Temperature and Low-Humidity Proton Exchange Membranes

High proton conductivity and sufficient stability of the polybenzimidazole membrane are important for the application of high-temperature proton exchange membrane fuel cells (HT-PEMFCs). A series of composite membranes based on crosslinked mPBI (cPBI) with cerium 2,4,6-triphosphono-1,3,5-triazine (CeTPT) were resoundingly fabricated. Novel cPBI networks with tetrafunctional N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) were synthesized. It is noteworthy that a new high-temperature proton conductor CeTPT was added. CeTPT contained three phosphonic acid groups, which offered good proton conductivity at moderate-to-low humidity and had good thermal stability. Tetrafunctional crosslinker TGDDM had multiple functional groups. With a relatively low crosslinking degree (CLD), the mechanical properties, dimensional stability, and oxidative resistance of the membranes were efficiently improved. The low CLD and good physicochemical stability also allowed high doping levels of CeTPT (up to 50%) and consequently high proton conductivity. At 180 °C and 50% RH, the proton conductivity of cPBI-5-CeTPT-50 and cPBI-10-CeTPT-50 was 0.072 and 0.068 S cm–¹, respectively. The cPBI-CeTPT membranes showed good methanol resistance and membrane selectivity, and thus the membranes were suitable for direct methanol fuel cells.

Proton conduction of novel calcium phosphate nanocomposite membranes for high temperature PEM fuel cells applications

This work describes the synthesis and evaluation of nanocomposite membranes based on calcium phosphate (CP)/ionic liquids (ILs) for high-temperature proton exchange membrane (PEM) fuel cells. Several composite membranes were synthesized by varying the mass ratios of ILs with respect to the CP and all supported on porous polytetrafluoroethylene (PTFE). The membranes exhibit high proton conductivities. Two ionic liquids were investigated in this study, namely, 1-Hexyl-3- methylimidazolium tricyanomethanide, [HMIM][C4N3−], and 1-Ethyl-3-methylimidazolium methanesulfonate, [EMIM][CH3O3S−]. At room temperature, the CP/PTFE/[HMIM][C4N3−] composite membrane possessed a high proton conductivity of 0.1 S cm−1. When processed at 200 °C, and fully anhydrous conditions, the membrane showed a conductivity of 3.14 × 10−3 S cm−1. Membranes based on CP/PTFE/[EMIM][CH3O3S−] on the other hand, had a maximum proton conductivity of 2.06 × 10−3 S cm−1 at room temperature. The proton conductivities reported in this work appear promising for the application in high-temperature PEMFCs operated above the boiling point of water.

Impact of N-Substituent and pKa of Azole Rings on Fuel Cell Performance and Phosphoric Acid Loss.

The influence of N-substituent and pKa of azole rings has been investigated for the performance of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). Imidazole, benzimidazole, and triazole groups were functionalized on the side chains of poly(phenylene oxide), respectively. Each azole group is categorized by their N-substituent into two types: unsubstituted and methyl-substituted azoles. The membranes with methyl-substituted azoles showed higher phosphoric acid (PA) doping levels with an average increase of 20% compared to those with unsubstituted azoles in the full-doped states. However, unsubstituted azoles more effectively improved the proton conductivity and the membrane with unsubstituted imidazole (IMPPO-H) showed a high anhydrous proton conductivity of 153 mS/cm at 150 °C. In contrast, the membranes with methyl-substituted azoles showed a higher PA retention with an average increase of 81% compared to those with unsubstituted azoles. The higher PA retention of methyl-substituted azoles also led to the higher fuel cell performance with the maximum increase of 95% in the power density. It was also revealed that higher pKa of azoles enhanced the PA retention and the fuel cell performance. Based on the experimental results of PA retention and density functional theory calculations, the PA loss mechanism was also proposed.

Combination effects of flow field structure and assembly force on performance of high temperature proton exchange membrane fuel cells

In this work, a three-dimensional, steady state model was developed by combining mechanical equations, Navier-stokes equation, Maxwell-Stefan equation, and Butler-Volmer equation. This model was used to investigate the influences of flow field structure and assembly force on porosity distribution in gas diffusion layer (GDL), species distribution in GDL, and current density distribution in GDL and membrane by extracting uneven porosity in the GDL from mechanical calculation equation to put in mass transfer calculation and electrochemical calculation equation as the known data. The optimum assembly prestress and optimum flow field structure were achieved. The results show combined effect of the assembly force and flow field makes the uneven porosity distribution and remarkable lateral current in the GDL; the channel width/rib width ratio of flow field has significant effects on the performance of the high temperature proton exchange membrane fuel cells (HT-PEMFC). These results provide the potential to promote the performance and application of HT-PEMFC.

Spatial analysis of CO poisoning in high temperature polymer electrolyte membrane fuel cells

The improved tolerance of the High Temperature-Polymer Electrolyte Membrane Fuel Cell (HT-PEMFC) to CO allows the use of reformate as an anode feed. However, the presence of several per cent of CO in the reformate, which is inevitable particularly in on-board reformation in automobiles, which otherwise demands complex systems to keep the CO level very low, will significantly lower the cell performance, especially when the HT-PEMFC is operated at 160 °C or below. In this study, a three-dimensional, non-isothermal numerical model is developed and applied to a single straight-channel HT-PEMFC geometry. The model is validated against the experimental data for a broad range of current densities at different CO concentration and operating temperatures. A significant spatial variation in current density distribution is observed in the membrane because the CO sorption is a spatially non-homogeneous process depending on local operating conditions and dilution of the H2 stream. To investigate the local spatial effects on HT-PEMFC operation, the model is applied to a real cell of size 49.4 cm2 with an 8-pass serpentine flow-field at the anode and the cathode. The membrane and anode catalyst layer are segmented into 5×5 array to investigate the spatial resolution of the polarization curves, H2 concentration, current density, and anode polarization loss. The simulation results show that the presence of CO in the anode feed reduces cell performance, however, the results reveal that uniformity in current density distribution in the membrane improves when the cell is operated in potentiostatic mode. The results are discussed in detail with the help of several line plots and multi-dimensional contours. The study also emphasizes on the importance of optimizing the reformate anode feed rate to improve cell performance.

Reticulated polyaniline nanowires as a cathode microporous layer for high-temperature PEMFCs

Traditional dense microporous layers (MPLs) are suitable for low-temperature proton exchange membrane fuel cells (PEMFCs), but they greatly hinder mass transport in high-temperature PEMFCs. Here, we report a novel cathode MPL based on reticulated polyaniline nanowires that were grown on carbon paper via in-situ electropolymerization. The maximum power density of the high-temperature PEMFC based on the new MPL was 476 mW/cm2, which was 36% higher than that based on a conventional MPL. Oxygen gain tests and electrochemical impedance spectroscopy showed that the new MPL accelerated oxygen transfer due to its unique pore size distribution, which ultimately improved the performance of the HT-PEMFC.

Impact of catalyst layer morphology on the operation of high temperature PEM fuel cells

Electrochemical impedance spectroscopy (EIS) is a well-established method to analyze a polymer electrolyte membrane fuel cell (PEMFC). However, without further data processing, the impedance spectrum yields only qualitative insight into the mechanism and individual contribution of transport, kinetics, and ohmic losses to the overall fuel cell limitations. The distribution of relaxation times (DRT) method allows quantifying each of these polarization losses and evaluates their contribution to a given electrocatalyst's depreciated performances. We coupled this method with a detailed morphology study to investigate the impact of the 3D-structure on the processes occurring inside a high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC). We tested a platinum catalyst (Pt/C), a platinum-cobalt alloy catalyst (Pt3Co/C), and a platinum group metal-free iron-nitrogen-carbon (Fe–N–C) catalyst. We found that the hampered mass transport in the latter is mainly responsible for its low performance in the MEA (along with its decreased intrinsic performances for the ORR reaction). The better performance of the alloy catalyst can be explained by both improved mass transport and a lower ORR resistance. Furthermore, single-cell tests show that the catalyst layer morphology influences the distribution of phosphoric acid during conditioning.

Synthesis and Physicochemical Characterisation of Amine Functionalised SiO<sub>2</sub>/PBI derivatives nanocomposite membrane

In this study, a series of amine functionalised silica/OPBI nanocomposite membrane for high-temperature polymer electrolyte fuel cell (HT – PEMFC) application were prepared. In order to provide a better dispersion and improving the interfacial interaction between organic/inorganic materials, polyethyleneimine was immobilised onto the surface of silica before added into poly(4,4’-diphenylether – 5, 5’-bibenzimidazole) (OPBI). Nuclear Magnetic Resonance (NMR) experiment proved the synthesised polymer while Fourier-transform infrared spectroscopy (FTIR) and EDX method used to validate the grafting of the amine derivative to the surface of silica in the polymer matrix. Although a satisfactory dispersion pattern was found on all nanocomposite membrane under scanning electron microscope (SEM) studies, agglomeration pattern was seen at higher loading of functionalised silica nanoparticles. The physicochemical characteristic of the nanocomposite membrane was investigated by using thermogravimetric analysis for high temperature PEMFC application. Lower water uptake and swelling ratio in both water and phosphoric acid (PA) showed by the OPBI / SiPEI with an increasing trend as the amount of SiPEI were increased. Addition of amine functionalised silica into OPBI shows a significant improvement compared to pure OPBI while the thermal stability of the membrane at high temperature region (100 – 200 °C) can be influenced by the loading concentration of the amine functionalised silica.

Measurement and separation of cathodic mass transport resistance in high temperature proton exchange membrane fuel cell

High oxygen transport resistance in the cathode is a main cause of the low performance of high temperature proton exchange membrane fuel cell (HT-PEMFC), and therefore to determine the contribution of different mass transport processes to the oxygen transport resistance is beneficial to the subsequent research work. In this paper, the molecular diffusion resistance (RM) in the cathode was successfully calculated by measuring the limiting currents with using different diluent gases. And the oxygen transport resistance in phosphoric acid (RPA) was analyzed by changing the humidity and temperature. It was found that the total oxygen transport resistance (Rtotal) increased obviously with the increase of the humidify, and the variation of Rtotal under different conditions was mainly related to the change of RPA. Combined with the phenomenon that the experimental value of RM was less than the calculated value at high humidity, but higher than that at high operation temperature, we speculate that the cause of that RPA increased obviously at high humidity is the occupancy or blockage of gas phase transport channel in catalyst layer (CL) by phosphoric acid due to the water absorption of phosphoric acid in CL and the swelling of membrane. This consequence indicates that it is the change of phosphoric acid distribution that dominateCis the Rtotal at high humidity.

Thermodynamic Modeling and Performance Analysis of a Combined Power Generation System Based on HT-PEMFC and ORC

Recently, the need for energy-saving and eco-friendly energy systems is increasing as problems such as rapid climate change and air pollution are getting more serious. While research on a power generation system using hydrogen energy-based fuel cells, which rarely generates harmful substances unlike fossil fuels, is being done, a power generation system that combines fuel cells and Organic Rankine Cycle (ORC) is being recognized. In the case of High Temperature Proton Exchange Membrane Fuel Cell (HT-PEMFC) with an operating temperature of approximately 150 to 200 °C, the importance of a thermal management system increases. It also produces the waste heat energy at a relatively high temperature, so it can be used as a heat source for ORC system. In order to achieve this outcome, waste heat must be used on a limited scale within a certain range of the temperature of the stack coolant. Therefore, it is necessary to utilize the waste heat of ORC system reflecting the stack thermal management and to establish and predict an appropriate operating range. By constructing an analytical model of a combined power generation system of HT-PEMFC and ORC systems, this study compares the stack load and power generation performance and efficiency of the system by operating temperature. In the integrated lumped thermal capacity model, the effects of stack operating temperature and current density, which are important factors affecting the performance change of HT-PEMFC and ORC combined cycle power generation, were compared according to operating conditions. In the comparison of the change in power and waste heat generation of the HT-PEMFC stack, it was shown that the rate of change in power and waste heat generation by the stack operating temperature was clearly changed according to the current density. In the case of the ORC system, changes in the thermal efficiency of the ORC system according to the operating temperature of the stack and the environmental temperature (cooling temperature) of the object to which this system is applied were characteristic. This study is expected to contribute to the establishment of an optimal operation strategy and efficient system configuration according to the subjects of the HT-PEMFC and ORC combined power generation system in the future.

NO/NO2 Contamination of HT-PEM Fuel Cells – A Degradation Study with Evaluation of Regeneration Strategies

In view of a sustainable energy supply, polymer electrolyte membrane fuel cell technology is used in several stationary and mobile application fields of power generation. High temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are operated at increased temperatures of around 160 °C to achieve a simplified water and heat management and to enhance the tolerable CO concentration in fuels. HT-PEMFCs are especially attractive in combination with methanol reforming in combined heat and power systems for auxiliary power units and further application fields. [1]Air pollution is a world-wide problem, whereby especially in urban areas ambient air contains nitrogen oxides (NOx) mainly originating from traffic. It has been shown in several studies that such NOx contamination affects the performance of low temperature PEMFC systems. [2] NO/NO2 enters the cathode through the supply with ambient air and reversibly adsorbs onto the platinum surface leading to catalytic deactivation. Immediate regeneration of low temperature PEM cells is possible by supplying clean air. [3] Although the HT-PEMFC system accounts for an enhanced tolerance towards CO contamination, NO/NO2 has a significant impact on its cell performance. On one hand, cell degradation is not completely understood yet, and on other hand, cell regeneration is not given by simple switching to clean air as in case of LT-PEMFCs. [4]For this purpose, systematic NOx contamination of commercially available HT-PEM single cells was carried out followed by analysing performance changes in dependence of several cell operational modes. First, the cell start-up was performed for two days at 160 °C and constant load of 0.3 A cm-2. Second, a controlled contamination using 10 ppm NO or NO2 inside the cathode air stream was applied. Last, after significant decrease of the voltage different cell operation modes were applied and tested as regeneration strategies, while the voltage change was continuously monitored. Cell operation under open circuit voltage (OCV), N2/N2 supply to both electrodes, cyclic voltammetry (CV up to 1.0, 1.2 and 1.5 VRHE) and an increased temperature of 180 °C were utilized. To evaluate the cause of voltage changes, the cells were electrochemically characterized using polarization curves, electrochemical impedance spectroscopy, cyclic voltammetry and linear sweep voltammetry at begin of test, after operation with contaminated air and after switching to the defined cell modes.Figure 1a) shows the voltage over time of cell break-in followed by operation under NO2 contamination resulting in a significant degradation of -364 µV h-1. Figure 1b) shows the voltage monitored during applying the different cell modes after cell contamination. NO2 is verified to have a dramatic impact on the HT-PEMFC without any regenerating effect by any of the cell modes. In conclusion, this study demonstrates the strong impact of NO/NO2 on HT-PEMFC systems and furthermore points out the difficulty to regenerate the cell after contamination. This is an important evidence for industry that less a suitable cell operation strategy and more a system engineering approach in view of appropriate filter systems is one possible way of solving the NOx contamination issue.[1] R. E. Rosli, A. B. Sulong, W. R. W. Daud, M. A. Zulkifley, T. Husaini, M. I. Rosli, E. H. Majlan, M. A. Haque, Int. J. Hydrogen Energy 2017, 42, 9293-9314.[2] 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.[3] A. Talke, U. Misz, G. Konrad, A. Heinzel, J. Electrochem. Soc. 2018, 165, F3111-F3117.[4] Final Project Report „HT-Kathodenluft“ 2016. Figure 1: Voltage and current density of cell break-in followed by operation under NO2 contamination (a) and voltage monitoring during applying different cell modes (b). Figure 1

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

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

Analysis of Bipolar Plate Material Properties for HT-PEM Fuel Cell Application

To meet the world’s energy requirements, advanced technologies for energy storage and provision have to be developed. Hydrogen offers a promising way to solve fluctuating electricity demands as well as the possibility of energy storage. When fed to a fuel cell, the chemical energy of the hydrogen molecule can be converted to electrical energy, which can be consumed in stationary and mobile applications.A Hydrogen-based fuel cell consists of various components, such as the membrane electrode assembly, where oxygen and hydrogen gas are reacting. To ensure a controlled conduction of electrons via an external pathway, so called bipolar plates (BPPs) are necessary. The bipolar plates have several functions inside the fuel cell as they provide the gases to the electrodes and separate the individual cells in a fuel cell stack from each other. The material itself has to be gas-impermeable and must ensure heat conductivity for heating and cooling of the cells. Moreover, it has to withstand acidic conditions under potentials ranging from 0-1.5 V and elevated temperatures up to 160 °C present in high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs).In this work, we present a detailed analysis of composite-based bipolar plate materials with application in HT-PEM fuel cells. Such bipolar plates mostly contain graphite and varying low amounts of a polymeric binder. While graphite has a low mechanical stability, it provides the required electrical conductivity. It is mixed with a binder polymer to enable mechanic flexibility and stability as well as gas tightness. From previous studies it was shown that fundamental knowledge about BPPs electrical and thermo-mechanical properties and their stability is crucial for the development of fuel cells with high power outputs1-3.Our study includes the investigation of the BPP materials properties in correlation to the nature of the different components and to their fabrication processes. Therefore, a series of different characterisation methods are applied to the composite material provided by the manufacturer. The surface morphology is analysed by scanning electron microscopy (SEM), confocal microscopy and atomic force microscopy (AFM), while X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDS) in combination with SEM will give insight in the surface composition. In addition, µ-computed tomography (µ-CT) is used to reveal inhomogeneities in the compounds volume. Those methods will enable us to analyse surface properties such as roughness and elemental composition as well as bulk composition.The electrical conductivity of the different BPPs is addressed by conductive-AFM and correlated to the materials composition. In this regard, Figure 1 shows the current distribution of two different BPP (PPS 1 and PPS 2) materials. The comparison shows significant differences in the current responses when applying a potential to the sample. While at one type of BPP already at 0.5 V high currents are observed locally, the overall current distribution for the other type of BPP is much lower (even at 1.0 V) but shows a very homogeneous distribution (Figure 1b). We will correlate such differences in current distribution to the surface morphology analysed by REM and confocal microscopy.Furthermore, the corrosion behaviour is analysed by extended chemical treatment in concentrated phosphoric acid at 160 °C and physicochemical changes of the composite material are tracked. This comprehensive study will enable us to gain new insights into the behaviour of carbon-based BPPs for HT-PEM fuel cells. Lee, D.; Lee, D. G., Journal of Power Sources 2016, 327, 119-126.Pilinski, N.; Nagappan, N. K.; Satola, B.; Rastedt, M.; Dyck, A.; Wagner, P., ECS Transactions 2018, 86, (13).Hartnig, C.; Schmidt, T. J., Electrochimica Acta 2011, 56, (11), 4237-4242. Figure 1

Strategies to Enhance the Activity and Durability of MEA for High Temperature PEMFC

High temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) using phosphoric acid (PA)-doped polybenzimidazole (PBI) membrane have advantages of enhanced electrode kinetics, improved carbon monoxide (CO) tolerance, and simplified water management [1], while poisoning of the catalysts by phosphate adsorption to deactivate them remains as an issue [2]. In addition, the deliquescence of PA (absorption of moisture when exposed to the humid atmosphere) resulted in the un-even distribution of PA [3], therefore deterioration in the MEA performance.To mitigate these issues, we have tried to optimize the structures of the commercial electrode and controlled the hydrophilicity of the electrode through additional deposition of very small amounts of Pt (anode) [4] or PtCu (cathode) using pulse electrodeposition. It was confirmed that the cell performance was improved by adjusting the hydrophilicity, improving the distribution of PA, and changing the formation of the triple phase boundary (TPB) of the catalyst layer. The performance loss due to the deliquescence of PA in the commercial PBI membrane when exposed to various humidity conditions was mitigated through an additional PA dosing method on the electrode [5].Apart from the activity, the durability of the modified MEAs exhibited different aspects. Various MEAs were fabricated by selectively combining the results of the pulse electrodeposition and PA dosing, and the durability tests for the MEAs were performed with repeated cycles of turning on (180°C) and turning off (room temperature). 40 cycles of repeated temperature variation deactivated most of the MEAs regardless of the modifications, while the amounts of the deterioration were the functions of the modification methods. Interestingly, the performance deterioration was more obvious in the observation of the peak powers while the change in the cell potential at low current density region (200 mA/cm2) was not substantial, implying the deterioration was greatly related to the mass transport management. The different behaviors in the durability according to the modification methods along with the materials characterization using electrochemical and spectroscopic analyses will be introduced at the conference.[1] I. I. Ponomarev, K. M. Skupov, A. V. Naumkin, V. G. Basu, O. M. Zhigalina, D. Y. Razorenov, I. I. Ponomarev, Y. A. Volkova, RSC Adv., 9 (2019) 257-267.[2] S. Kaserer, K. M. Caldwell, D. E. Ramaker, C. Roth, J. Phys. Chem. C, 117 (2013) 6210-6217.[3] S. Jahangiri, I. Aravi, L. I. Sanli, Y. Z. Menceloglu, E. Ozden-Yenigun, Polym. Advan. Technol., 29 (2018) 594-602.[4] D.-K. Kim, H. Kim, H. Park, S. Oh, S. H. Ahn, H.-J. Kim, S.-K. Kim, J. Power Sources, 438 (2019) 227022-227030.[5] H. Park, H. Kim, D.-K. Kim, W. J. Lee, I. Choi, H.-J. Kim S.-K. Kim, Int. J. Hydrogen Energy, (2019) DOI:10.1016/j.ijhydene.2020.03.039.

Constructing anhydrous proton exchange membranes through alternate depositing graphene oxide and chitosan on sulfonated poly(vinylidenefluoride) or sulfonated poly(vinylidene fluoride-co-hexafluoropropylene) membranes

The proton exchange membranes (PEMs) have been constructed through alternate depositing chitosan (CS) and graphene oxide (GO) on the membrane substrates of sulfonated poly(vinylidenefluoride) (SPVDF) or sulfonated poly(vinylidene fluoride-co-hexafluoropropylene) (SPVDF-HFP). Phosphoric acid (PA) doped membranes were formed owing to the intermolecular hydrogen bonds, which were expected to work as PEMs in high temperature proton exchange membrane fuel cells (HTPEMFCs). The prepared layer-by-layer (LBL) depositional composite membranes showed the fine capacity to combine PA molecules with the lower dimension swelling. As expected, SPVDF(CS/GO)50/PA and SPVDF-HFP(CS/GO)50/PA membranes respectively exhibited higher proton conductivity values of 2.34 × 10−1 S/cm and 1.56 × 10−1 S/cm at 140 °C. Furthermore, the proton conductivity values of 3.52 × 10−1 S/cm and 2.25 × 10−1 S/cm at 140 °C in a 500-hour non-stop test could correspond to the negligible leakage of the depositional layers from the composite membranes. Because the doped PA molecules entered the gaps between the depositional layers, the prepared PA doped membranes possessed the enhanced mechanical strength owing to the compacted structure. Most interestingly, the prepared LBL deposited membranes could retain the better tensile stress even if PA molecules were doped with the formation of SPVDF(CS/GO)50/PA and SPVDF-HFP(CS/GO)50/PA membranes. Meanwhile, the proper thermal stability, methanol permeability and proton conductivity stability of the prepared membranes could suggest that the strategy of alternate depositing the functional components on membrane substrates is substantially more effective at improving the grade of PEMs. In our opinion, the fine balance on proton conductivity and mechanical property could make them stand out from other candidates as PEMs for HTPEMFCs.

Exergy analysis of a polymer fuel cell and identification of its optimum operating conditions using improved Farmland Fertility Optimization

In this paper, the exergy analysis of a proposed power generation system based on high-temperature proton exchange membrane fuel cell (HT-PEMFC) has been proposed. The analyzed system includes the organic Rankine cycle to recover the wasted heat. To analyze the system, a mathematical model of the considered PEMFC has been presented and the water management system is investigated. Parametric analysis is provided to investigate the effect of the various thermodynamic and economic parameters such as exergy, irreversibility, and the work. Therefore, the three mentioned parameters have been optimized for improving the PEMFC design. To achieve an efficient optimized system, a new design of Farmland Fertility Optimization (FFO) is proposed. Final results of the algorithm are compared with experimental results, the genetic algorithm, and the basic FFO and the optimized values of irreversibility, exergy efficiency, work for the proposed algorithm are achieved 0.011, −0.446, and −0.462, respectively that are the best results toward the other compared algorithms.

Single-Atom Iron-Based Electrocatalysts for High-Temperature Polymer Electrolyte Membrane Fuel Cell: Organometallic Precursor and Pore Texture Tailoring

The oxygen reduction reaction (ORR) activity of platinum (Pt)-based catalyst is not satisfactory in high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) operating with a phosphoric ...

3D non-isothermal dynamic simulation of high temperature proton exchange membrane fuel cell in the start-up process

High temperature proton exchange membrane fuel cell (HT-PEMFC) with phosphoric acid doped polybenzimidazole (PBI) electrolyte shows multiple advantages over conventional PEMFC working at below 373 K, such as faster electrochemical kinetics, simpler water management, higher carbon monoxide tolerance. However, starting HT-PEMFC from room temperature to the optimal operating temperature range (433.15 K–453.15 K) is still a serious challenge. In present work, the start-up strategy is proposed and evaluated and a three-dimensional non-isothermal dynamic model is developed to investigate start-up time and temperature distribution during the start-up process. The HT-PEMFC is preheated by gas to 393.15 K, followed by discharging a current from the cell for electrochemical heat generation. Firstly, different current loads are applied when the average temperature of membrane reaches 393.15 K. Then, the start-up time and temperature distribution of co-flow and counter-flow are compared at different current loads. Finally, the effect of inlet velocity and temperature on the start-up process are explored in the case of counter-flow. Numerical results clearly show that applied current load is necessary to reduce start-up time and just 0.1 A/cm2 current load can reduce startup time by 45%. It is also found that co-flow takes 18.8% less time than counter-flow to heat membrane temperature to 393.15 K, but the maximum temperature difference of membrane is 39% higher than the counter-flow. Increasing the inlet gas flow velocity and temperature can shorten the start-up time but increases the temperature difference of the membrane.

Fabrication of PBI/SPOSS hybrid high-temperature proton exchange membranes using SPAEK as compatibilizer

Because of the harsh operating circumstances of high temperature over 100 °C and strong acidity, it is of great significance to explore some new methods on the developments of high-performance membrane materials using in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). In current work, with the assistance of newly designed sulfonated poly (aryl ether ketone) (SPAEK) compatibilizer, some hydrophilic and acidophilic polyhedral-oligosilsesquioxane nanoparticles bearing sulfuric acid groups (SPOSS) were successfully incorporated into a soluble arylether-type polybenzimidazole (Ph-PBI) matrix via an in situ sol-gel process to obtain a new family of hybrid membranes with an improved overall performance. As a result, these hybrid membranes exhibited enhanced acid absorption ability and doping levels at 120 °C, improved acid retention ability and attractive mechanical-dimensional stability. More importantly, the proton conductivity of a phosphoric acid doped hybrid membrane reached 126 mS cm−1 at 200 °C. This membrane was also suitable for membrane electrode assemblies (MEAs), and a maximum power density of 300 mW cm−2 could be achieved at 160 °C without humidity.

Machine Learning for Guiding High-Temperature PEM Fuel Cells with Greater Power Density

High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are enticing energy conversion technologies because they use low-cost hydrogen generated from methane and have simple water and heat management. However, proliferation of this technology requires improvement in power density. Here, we show that Machine Learning (ML) tools can help guide activities for improving HT-PEMFC power density because these tools quickly and efficiently explore large search spaces. The ML scheme relied on a 0-D, semi-empirical model of HT-PEMFC polarization behavior and a data analysis framework. Existing data sets underwent support vector regression analysis using a radial basis function kernel. Additionally, the 0-D, semi-empirical HT-PEMFC model was substantiated by polarization data; and synthetic data generated from this model was the subject to dimension reduction and density-based clustering. From these analyses, pathways were revealed to surpass 1 W cm-2 in HT-PEMFCs with oxygen as the oxidant and CO containing hydrogen.