Acid Doped Polybenzimidazole Membranes Research Articles

Imidazole and triazine framed porous aromatic framework with rich proton transport sites for high performance high-temperature proton exchange membranes

Phosphoric acid-doped polybenzimidazole (PA-PBI) membranes for high-temperature proton exchange membranes (HT-PEMs) exhibit low proton conductivity under low phosphoric acid loading and poor mechanical properties under high phosphoric acid loading. In order to overcome these disadvantages, a novel kind of porous aromatic framework framed with imidazole and triazine groups (PAF-227) was designed and synthesized, phosphoric acid (PA) was incorporated into PAF-227 by utilizing vacuum-assisted infusion to yield the product PAF-227-PA. Subsequently, this dopant was combined with polybenzimidazole (OPBI) to create the PAF-227-PA/OPBI composite high-temperature proton exchange membranes (HT-PEMs). The PAF-227-PA/OPBI exhibited high proton conductivity (0.24 S cm-1) at 200 °C, as well as a favorable mechanical property (6.73 MPa) and a high PA absorption rate (250.2%), and the peak power density of the fabricated fuel cells was significantly increased to 678.21 mW cm-2 at 200 °C with the Pt loading of 0.3 mg cm-2. The basic sites of PAF-227 framed with rigid imidazole and triazine groups can anchoring the PA to achieve a high PA retention rate through the acid-basic interaction with PA, and provide sufficient proton conduction sites by forming hydrogen bonds with PA, and synergized with OPBI membranes to form a multiple hydrogen bond and proton transfer network for enhanced mechanical properties and dimensional thermal stability. Thus, this work provided a novel approach to the preparation of HT-PEMs, which exhibited excellent overall performance for HT-PEMs fuel cells.

Stability and performance of in-situ formed phosphosilicate nanoparticles in phosphoric acid-doped polybenzimidazole composite membrane fuel cells at elevated temperatures

One of the effective strategies to pursue the highly durable high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) is to introduce inorganic fillers to the phosphoric acid-doped polybenzimidazole (PA/PBI) membranes. Among the inorganic fillers, phosphates such as phosphosilicate are effective in mitigating acid loss at elevated temperatures (200–300 °C). In this paper, the effect of in situ formed phosphosilicate on the performance and stability of SiO2/PA/PBI composite membranes is studied in detail. The mechanical properties and electrochemical performances of the in situ formed SiO2/PA/PBI membranes depend strongly on the content of in situ formed Si5P6O25 fillers and its distribution and microstructure in the membrane. Such in situ formed SiO2/PA/PBI composite membranes show a high conductivity of 53.5 mS cm−1 at 220 °C. The assembled single cell shows a maximum peak power density (PPD) of 530.6 mW cm−2 and excellent stability at elevated temperature of 220 °C for over 130 h. The exceptional stability at 220 °C is most likely due to the existence of predominant amorphous phosphosilicate phases in the in situ formed SiO2/PA/PBI composite membranes, which inhibits the evaporation and leaching of PA at elevated temperatures. The results indicate the practical application of in situ formed SiO2/PA/PBI composite membranes for HT-PEMFCs.

Core-shell tin pyrophosphate-based composite membrane for fuel cell with durability enhancement at elevated temperatures

Tin pyrophosphate has been employed as a proton conductor in polymer electrolyte membranes (PEMs) at temperatures over 200 °C. However, neither the aggregation of the SnP2O7 nanoparticles nor the proton conduction mechanism of the material has been clearly clarified in PEM. The present work reports a polybenzimidazole (PBI)/SnP2O7 composite membrane with homogeneous distribution of the inorganic phase. The membrane is successfully fabricated by in-situ transformation of SnO2 nanoparticles to core-shell SnP2O7 nanoparticles in the PBI matrix during fuel cell operation. Further in-depth analysis shows that the core-shell SnP2O7 contains a crystalline SnP2O7 core, an amorphous SnP2O7 intermediate layer and a gel-like outer layer mainly containing H4P2O7. In addition, the crystal growth of the SnP2O7 nucleus consumes ions from the amorphous SnP2O7 layer, where the reacted ions are compensated by the diffusion of Sn4+ and P2O74− ions from the gel-like outer layer. Also, the fuel cell with the composite membrane shows superior proton conductivity and durability compared to the pristine phosphoric acid-doped PBI membrane at 240 °C for over 50 h. That is due to the presence of H4P2O7 in the outer layer, which contributes to high and stable proton conductivity of the core-shell SnP2O7 at 220–260 °C.

The anion conductivity of acid-doped polybenzimidazole membrane and utilization in mitigating the capacity decay of vanadium redox flow battery stacks

The anion conductivity of acid-doped polybenzimidazole membrane and utilization in mitigating the capacity decay of vanadium redox flow battery stacks

Investigation of water effects on hydrogen dissolution, diffusion, and reaction in high temperature proton exchange membrane fuel cell

High-temperature proton exchange membrane fuel cell with phosphoric acid-doped polybenzimidazole membrane is typically utilized with a methanol steam reformer due to its high CO tolerance. However, methanol reformate commonly contains 20 % water, and its effect on the high temperature fuel cell is unclear. A comprehensive 3D multiphase non-isothermal model with an enhanced electrochemical kinetics model considering the water influence mechanism is developed. The water influence mechanism includes the proton conductivity, hydrogen dissolution on the pore-ionomer interface, hydrogen diffusion inside the ionomer, and hydrogen surface reaction on the platinum. The sensitivity analysis found that hydrogen dissolution on the pore-ionomer and hydrogen surface reaction on the platinum significantly affect cell performance. The influences of water on ionomer hydrogen concentration, platinum surface hydrogen concentration, and surface reaction rates are investigated under the voltage range of 0.9–0.4 V. The increase of water content can improve the net adsorption rate and benefit electrochemical reaction. Besides, the anode water is better for the uniformity of surface reaction rate distributions while not affecting the hydrogen distributions inside the ionomer and on the platinum surface. Additionally, the positive influence of water on CO poisoning is investigated in terms of surface reaction. The water's beneficial effect on decreasing platinum loading is also discussed. The results show that 20 % water can reduce the platinum loading by 20 %.

Experimental Analysis of Catalyst Layer Operation in a High-Temperature Proton Exchange Membrane Fuel Cell by Electrochemical Impedance Spectroscopy

High-temperature proton exchange membrane fuel cells (HT-PEMFC) directly convert hydrogen and oxygen to produce electric power at a temperature significantly higher than conventional low-temperature fuel cells. This achievement is due to the use of a phosphoric acid-doped polybenzimidazole membrane that can safely operate up to 200 °C. PBI-based HT-PEMFCs suffer severe performance limitations, despite the expectation that a higher operating temperature should positively impact both fuel cell efficiency and power density, e.g., improved ORR electrocatalyst activity or absence of liquid water flooding. These limitations must be overcome to comply with the requirements in mobility and stationary applications. In this work a systematic analysis of an HT-PEMFC is performed by means of electrochemical impedance spectroscopy (EIS), aiming to individuate the contributions of components, isolate physical phenomena, and understand the role of the operating conditions. The EIS analysis indicates that increases in both the charge transfer and mass transport impedances in the spectrum are negatively impacted by air humidification and consistently introduce a loss in performance. These findings suggest that water vapor reduces phosphoric acid density, which in turn leads to liquid flooding of the catalyst layers and increases the poisoning of the electrocatalyst by phosphoric acid anions, thus hindering performance.

A Comparative Study of CCM and CCS Membrane Electrode Assemblies for High-Temperature Proton Exchange Membrane Fuel Cells with a CsH5(PO4)2-Doped Polybenzimidazole Membrane.

Membrane electrode assemblies (MEAs) are critical components in influencing the electrochemical performance of high-temperature proton exchange membrane fuel cells (HT-PEMFCs). MEA manufacturing processes are mainly divided into the catalyst-coated membrane (CCM) and the catalyst-coated substrate (CCS) methods. For conventional HT-PEMFCs based on phosphoric acid-doped polybenzimidazole (PBI) membranes, the wetting surface and extreme swelling of the PA-doped PBI membranes make the CCM method difficult to apply to the fabrication of MEAs. In this study, by taking advantage of the dry surface and low swelling of a CsH5(PO4)2-doped PBI membrane, an MEA fabricated by the CCM method was compared with an MEA made by the CCS method. Under each temperature condition, the peak power density of the CCM-MEA was higher than that of the CCS-MEA. Furthermore, under humidified gas conditions, an enhancement in the peak power densities was observed for both MEAs, which was attributed to the increase in the conductivity of the electrolyte membrane. The CCM-MEA exhibited a peak power density of 647 mW cm-2 at 200 °C, which was ~16% higher than that of the CCS-MEA. Electrochemical impedance spectroscopy results showed that the CCM-MEA had lower ohmic resistance, which implied that it had better contact between the membrane and catalyst layer.

Effect of cooling surface temperature difference on the performance of high-temperature PEMFCs

Internal temperature distribution of the high-temperature proton exchange membrane fuel cell (HT-PEMFC) is affected by the cooling temperature, heat generation and reactant gas flow. Reasonable temperature control is helpful to improve the fuel cell performance and durability. In this work, a three-dimensional model that couples the reactant flows, species transport, heat transfer, charge transfer, and electrochemical reaction, was developed to simulate the HT-PEMFC operation. A solid mechanics model was established to analyze the stress distribution of the fuel cell. The polarization curves, distributions of temperature, membrane proton conductivity, current density and stress are investigated for different cooling surface temperature. Furthermore, the effect of assembly temperature on the stress of phosphoric acid-doped polybenzimidazole (PBI) membrane is discussed. Results reveals that the peak power density and uniformity of current density decrease with the increase of cooling surface temperature difference. The peak power density decreases by 9.14% when the temperature difference increases from 0 K to 40 K. The cooling surface temperature difference of less than 10 K and the voltage range in 0.5–0.7 V can achieve better current density uniformity and smaller current density change rate. In addition, the membrane in fuel cell has the highest stress, and increasing the assembly temperature is helpful to reduce the membrane stress. When the assembly temperature increases from 293.15 K to 343.15 K, the max and min compressive stresses in membrane in-plane decrease from 39.436 MPa to 31.416 MPa–24.934 MPa and 17.369 MPa at the temperature difference of 30 K, which decreases by 36.77% and 44.7%, respectively.

Construction of high-density proton transport channels in phosphoric acid doped polybenzimidazole membranes using ionic liquids and metal-organic frameworks

Introducing metal-organic frameworks (MOFs) into phosphoric acid (PA) doped polybenzimidazole (PBI) membranes to form proton transfer channels is an effective strategy to reduce the dependence of proton conductivity on PA. However, excessive MOF loading inevitably leads to reduced mechanical properties and damaged membrane structure. Ionic liquids (ILs) are reported as good plasticizers that can obviously improve the interface performance. Along this line, IL is introducing into the branched poly[2,2′-(p-oxydiphenylene)-5,5′-benzimidazole] (BOPBI) cross-linked by KH-560. The interface performance between the MOF and PBI in the cross-linked BOPBI (CBOPBI)@MOF composite system is improved. The high MOF loading (50 wt%) composite membranes are prepared with acceptable mechanical properties for the first time. High density proton transport channels are constructed based on the high MOF loading in the PA doped CBOPBI@MOF membranes. For instance, the CBOPBI@MOF50%-IL30 shows an excellent proton conductivity (0.135 S cm−1), and a power density about a 26.9% increase (736 mW cm−2) compared with that of the CBOPBI@MOF40% membrane. Furthermore, the load voltage of the membrane with 50 wt% MOF is also well maintained. The membranes with high density proton transport channels exhibit high potential application prospects as high-temperature proton exchange membranes (HT-PEMs).

Alkyl-substituted poly(arylene piperidinium) membranes enhancing the performance of high-temperature polymer electrolyte membrane fuel cells

Alkyl-substituted poly(arylene piperidinium) membranes can modulate the content and distribution of phosphoric acid. The peak power density of HT-PEMFCs reaches 1.5 W cm−2, the maximum performance reported under 120 °C.

Low Pt loading for high-performance fuel cell electrodes enabled by hydrogen-bonding microporous polymer binders.

A key challenge for fuel cells based on phosphoric acid doped polybenzimidazole membranes is the high Pt loading, which is required due to the low electrode performance owing to the poor mass transport and severe Pt poisoning via acid absorption on the Pt surface. Herein, these issues are well addressed by design and synthesis of effective catalyst binders based on polymers of intrinsic microporosity (PIMs) with strong hydrogen-bonding functionalities which improve phosphoric acid binding energy, and thus preferably uphold phosphoric acid in the vicinity of Pt catalyst particles to mitigate the adsorption of phosphoric acid on the Pt surface. With combination of the highly mass transport microporosity, strong hydrogen-bonds and high phosphoric acid binding energy, the tetrazole functionalized PIM binder enables an H2-O2 cell to reach a high Pt-mass specific peak power density of 3.8 W mgPt-1 at 160 °C with a low Pt loading of only 0.15 mgPt cm-2.

(Invited) HT-PEMFC Based on Acid Doped Polybenzimidazoles of the Past Quarter Century

High-temperature proton exchange membrane (HT-PEM) fuel cells based on phosphoric acid-doped polybenzimidazole (PBI) membranes were invented in 1994 by professor Bob Savinell and his coworkers at Case Western Reserve University [1]. The membrane electrolyte is a unique material that is capable of practical proton conductivity at temperatures of up to 200oC under anhydrous conditions. This ground-breaking invention has led to the start of a frontier research area for fuel cells and related technologies, as indicated by an annual publication of ca. 200 items and citation of 10,000 times in the last decade.Based on this type of membrane materials, the HT-PEM technology has developed, with operating features including little humidification, high CO tolerance, easy thermal management and thermal integration with methanol reformer.[2] Significant efforts from international industries are currently made towards commercialization and products are now on the market. Research institutions and industries in Denmark have been active and leading in the research and development of the area. Further, the PBI membrane has also emerged as a promising membrane material for redox flow batteries (RFB).This presentation is devoted to a brief summary of the fundamental understanding and technological deployment of this technology [3], as a remark of the extraordinary contributions of Professor Savinell to the electrochemistry and electrochemical engineering research.

Two-Dimensional Model of a High-Temperature Proton Exchange Membrane Hydrogen Pump for Efficient, Single-Stage Separation of Fuel Cell Quality Hydrogen Gas from Hydrogen-Enriched Natural Gas

A key component of the emerging hydrogen energy economy is the distribution system which facilitates the movement of hydrogen energy between production and end-use. There is interest in valorization of existing gas systems, which today are dedicated to natural gas movement, to facilitate the co-transportation of hydrogen via blending of hydrogen gas into these gas systems at concentrations up to 20% H2 by volume [1]. Fuel cell quality hydrogen, at a purity of 99.97%> H2, is required for the most valuable energy end-uses of hydrogen gas and thus the ability to efficiently extract H2 gas at such high purity is critical to the adoption of natural gas infrastructure as a means of co-transportation and distribution.Electrochemical hydrogen pump (EHP) utilizes a proton conducting membrane to separate hydrogen from mixtures by driving the electrochemical process of oxidation of hydrogen at an anode and subsequent evolution of hydrogen gas at a cathode, while other gaseous impurities are ideally unable to permeate through the membrane. HT-PEM EHP based on polybenzimidazole (PBI) membranes doped with phosphoric acid exhibit high proton conductivities at temperatures in the range of 160C Celsius while also exhibiting characteristics that are complimentary to their application in gas separation processes. These characteristics include a limited tolerance to common sources of platinum catalyst inhibition such as CO [1] and the presence of an aqueous phosphoric acid phase inhibits gas cross-over, providing better product purity although at the cost of performance in the form of catalyst inhibition.A two-dimensional model based on an HT-PEM system employing a phosphoric acid doped PBI membrane and free phosphoric acid as the proton conducting phase of the catalyst layer is developed to better understand the underlying processes governing the performance of the EHP. The model is validated with experimental measurements with mixtures as low as 2% H2 by volume in methane. In-operando micro-CT imaging of an HT-PEM EHP cell taken at the LBNL Advanced Light Source (ALS) is used to further validate physical parameters and assumptions of the model.The influence of differential pressure, relative humidity of the feed, and concentration of feed gases on separation performance are investigated. Losses due to back-permeation of hydrogen under pressure are accounted for. Power-loss voltage breakdown analysis indicates appreciable losses due to proton transport in the relatively thick catalyst layer, and the dependence of these losses on the volume fraction of acid present (Figure 1). The influence of CO2 as a catalyst inhibiting contaminant as was previously observed in low temperature EHP [3] is examined. The model and experiments show that a specific energy of separation of 5.1 kWh/kg H2 at a hydrogen recovery factor (HRF) of 50% can be achieved in a single stage with the EHP, producing 99.995% > H2 from a 2% H2 in CH4 blend, while pressurizing the product H2 at a product pressure ratio of 1.3 relative to feed pressure. Bibliography [1] C. J. Quarton and S. Samsatli, "Power-to-gas for injection into the gas grid: What can we learn from real-life projects, economic assessments and systems modelling?," Renewable and Sustainable Energy Reviews, vol. 98, pp. 302-316, 2018. [2] K. Perry and B. B. Eisman G.A., "Electrochemical hydrogen pumping using a high-temperature polybenzimidazole (PBI) membrane," Journal of Power Sources, pp. 478-484, 2008. [3] N. e. al., "Effect of CO2 on the performance of an electrochemical hydrogen compressor," Chemical Engineering Journal, vol. 329, 2020. Figure 1

(Invited, Digital Presentation) Polybenzimidazole and Its Use in Energy Storage and Conversion

Polybenzimidazole (PBI) is a unique polymer. It has high mechanical strength and stability, and is not conductive. However, in contact with acids, the imidazole rings are protonated, and PBI becomes proton conductive. In contact with alkaline solutions, the amine groups are deprotonated, and PBI becomes hydroxide conductive. Control of the doping process allows to adjust the uptake and hence allows to control conductivity and permeability of PBI membranes. Therefore, PBI can be used in various ways for several applications. Phosphoric acid doped PBI blends were tested in the HT PEMFC, and showed more than >2000 hours stable, high performance operation at very challenging high current density of 800 mA/cm2 (one of world-best results).[1] Sulfuric acid doped PBI membranes were developed for use in the vanadium redox flow battery. We show that stable performances with an energy efficiency >91% and coulomb efficiency >99% @ 80 mA/cm2 can be achieved, which is one of the highest reported performances.[2, 3] By using a newly developed membrane fabrication process, hydroxide conducting membranes with a conductivity of > 310 mS/cm2 were be obtained. Porous supports enhanced the mechanical stability of these membranes, and PEM-water electrolyser-like performance was achieved in an alkaline water electrolyser, which was successfully operated for 1000 hours without failure.[4] A common way to increase the mechanical stability of membranes is reinforcement with a porous support. The drawback is that different swelling ratios of matrix and support can form voids, which results in unacceptably high gas crossover in electrolyzers and fuel cells. To tackle this issue, we pore filled an electrospun PBI fiber mat with a bomoalkylated polymer and reacted it with the imidazole groups available on the PBI fiber surface, thus forming a covalently bonded interface. In a final step, the remaining bromoalkyl groups were quaternized. The membrane was tested for 200 hours in an electrolyzer, and showed no signs of degradation. [5] [1] N. Nambi Krishnan, N.M.H. Duong, A. Konovalova, J.H. Jang, H.S. Park, H.J. Kim, A. Roznowska, A. Michalak, D. Henkensmeier, Polybenzimidazole / tetrazole-modified poly(arylene ether) blend membranes for high temperature proton exchange membrane fuel cells, J. Membr. Sci., 2020, 614, 118494. https://doi.org/10.1016/j.memsci.2020.118494[2] C. Noh, D. Serhiichuk, M. Najibah, Y. Kwon, D. Henkensmeier, Optimizing the performance of meta-polybenzimidazole membranes in vanadium redox flow batteries by adding an alkaline pre-swelling step, Chem. Eng, J., 405 (2021) 126574. https://doi.org/10.1016/j.cej.2020.126574[3] unpublished results[4] under review[5] Malikah Najibah, E. Tsoy, H. Khalid, Y. Chen, Q. Li, C. Bae, J. Hnát, M. Plevová, K. Bouzek, J.H. Jang, H.S. Park, Dirk Henkensmeier, PBI nanofiber mat-reinforced anion exchange membranes with covalently linked interfaces for use in water electrolysers, J. Membr. Sci., 2021, 640, 119832. https://doi.org/10.1016/j.memsci.2021.119832

Construction of highly conductive PBI-based alloy membranes by incorporating PIMs with optimized molecular weights for high-temperature proton exchange membrane fuel cells

There is a great challenge to fabricate the phosphoric acid-doped polybenzimidazole (PA-PBI) membranes simultaneously having high proton conductivity and good mechanical strength through a simple and scalable preparation approach. In this study, the polymers of intrinsic microporosity (PIMs) with two different molecular weights (MWs) are incorporated into an aryether-type PBI (OPBI) matrix to form some novel alloy membranes containing a special intrinsic “porous” structure. It is the first time to observe the great effect of the PIMs’ MWs on the miscibility and properties of the PBI/PIM alloy membranes, and indicate that an obvious improvement on the performance can be achieved by incorporating PIMs with optimized MWs into OPBI matrix. The PIMs addition can bring a large “free volume” into the alloy membranes, which is expected to enhance the PA doping levels (ADLs) and therefore proton conductivity. It may provide an efficient way to overcome the major obstacles of the existing PA-PBI membranes; that is the mechanical stability of the PBI membranes always sharply decreases with the increase of ADLs. Most importantly, a very high proton conductivity of 313 mS cm−1 can be obtained at 200 °C and a peak power density of 438 mW cm−2 is reached at 160 °C, without humidification.

An effective strategy to enhance dimensional-mechanical stability of phosphoric acid doped polybenzimidazole membranes by introducing in situ grown covalent organic frameworks

Poor dimensional-mechanical stability and severe acid leakage have been the crucial issues restraining the practical applications of phosphoric acid-doped polybenzimidazole (PA−PBI) as high-temperature proton exchange membranes (HT-PEMs). In view of their robust, ordered, and tunable porous structures, chemically stable covalent organic frameworks (COFs) show great promise to enhance the performance of PA-doped PBI membrane. In this work, the in situ synthesized COF sheets are introduced to the PBIs for the first time and form a unique composite structure. The composite structure comprising soft PBIs matrix and rigid COF sheets can obviously improve dimensional-mechanical stability of the membranes under high acid doping level. Importantly, the rigid COF sheets help to construct proton transport channel in the membrane, resulting in high proton conductivity and excellent fuel cell performance. Among them, the 40%–COF–OPBI membrane shows the best overall performance, such as excellent proton conductivity (177.7 mS cm−1), desirable mechanical tensile strength (12.1 MPa), and high power density (774.7 mW cm−2) at 160 °C without humidification in H2/O2 fuel cell tests. These results suggest that introducing COFs to PBI is an effective strategy for fabricating high-performance proton exchange membranes for fuel cell applications.

Characterization of PBI/Graphene Oxide Composite Membranes for the SO2 Depolarized Electrolysis at High Temperature

In this work, polybenzimidazole (PBI) membranes with different graphene oxide (GO) contents (0.5, 1.0, 2.0, and 3.0 wt %) as organic filler have been prepared. The X-ray diffraction confirms the incorporation of the filler into the polymeric membrane. The composite GO-based PBI membranes show better proton conductivity at high temperature (110–170 °C) than the pristine one. Moreover, the hydrophobicity of the PBI membranes is also improved, enhancing water management. The chemical stability demonstrates the benefit of the incorporation of GO in the PBI matrix. What is more, the composite PBI-based membranes show better phosphoric acid retention capability. For the first time, the results of the SO2-depolarized electrolysis for hydrogen production at high temperature (130 °C) using phosphoric acid-doped polybenzimidazole (PBI) membranes with the different GO contents are shown. The benefit of the organic filler is demonstrated, as H2SO4 production is 1.5 times higher when the membrane with a content of 1 wt % of GO is used. Moreover, three times more hydrogen is produced with the membrane containing 2 wt % of GO compared with the non-modified membrane. The obtained results are very promising and provide open research for this kind of composite membranes for green hydrogen production by the Westinghouse cycle.

Thermodynamic Modeling and Performance Analysis of Vehicular High-Temperature Proton Exchange Membrane Fuel Cell System.

Since the high temperature proton exchange membrane fuel cells (HT-PEMFC) stack require a range of auxiliary equipments to maintain operating conditions, it is necessary to consider operation of related components in the design of HT-PEMFC systems. In this paper, a thermodynamic model of a vehicular HT-PEMFC system using phosphoric acid doped polybenzimidazole membrane is developed. The power distribution and exergy loss of each component are derived according to thermodynamic analysis, where the stack and heat exchanger are the two components with the greatest exergy loss. In addition, ecological functions and improvement potentials are proposed to evaluate the system performance better. On this basis, the effects of stack inlet temperature, pressure, and stoichiometric on system performance are analyzed. The results showed that the energy efficiency, exergy efficiency and net output power of the system achieved the maximum when the inlet gases temperature is 406.1 K. The system performance is better when the cathode inlet pressure is relatively low and the anode inlet pressure is relatively high. Moreover, the stoichiometry should be reduced to improve the system output performance on the basis of ensuring sufficient gases reaction in the stack.

An Effective Strategy to Enhance Dimensional-Mechanical Stability of Phosphoric Acid Doped Polybenzimidazole Membranes by Introducing in Situ Grown Covalent Organic Frameworks

An Effective Strategy to Enhance Dimensional-Mechanical Stability of Phosphoric Acid Doped Polybenzimidazole Membranes by Introducing in Situ Grown Covalent Organic Frameworks

Durability Studies on PBI Based High Temperature PEMFC

HT-PEMFC based on phosphoric acid-doped polybenzimidazole membranes are a technology characterized by simplified construction and operation along with methanol reformers. Durability issues including acid loss, platinum sintering and carbon corrosion are recognized for both steady state and start-stop cycling operations. This work reports experimental studies on the degradation of PBI-based fuel cells operating with synthetic reformate fuel and air. Degradation stressors include elevated temperatures, pressures, current densities, and start-stop cycles. An average degradation rate of 9.3 mV/h is observed for continuous operation at 0.4 A/cm2 and 160 ˚C for 12,000 hours. High pressure (1.5 bara) operation at 170 oC and 0.8 A/cm2 shows an average degradation rate of 12.6 µV/h during a period of 2,000 hours. A start-stop test from 50 oC consisting of 240 cycles between temperatures of 165 and 175 oC and current density of 0.31 and 0.55 A/cm2 reveals a performance decay by 0.48-0.58 mV/cycle.