Double cross-linked polyetheretherketone proton exchange membrane for fuel cell

The proton exchange membrane based on polyetheretherketone was prepared via two steps of cross-linking. The properties of the double cross-linked membrane (water uptake, proton conductivity, methanol permeability and thermal stability) have been investigated for fuel cell applications. The prepared membrane exhibited relatively high proton conductivity, 3.2 × 10⁻² S cm⁻¹ at room temperature and 5.8 × 10⁻² S cm⁻¹ at 80 °C. The second cross-linking significantly decreased the water uptake of the membrane. The performance of direct methanol fuel cell was slightly improved as compared to Nafion^® 117 due to its low methanol permeability. The results indicated that the double cross-linked membrane is a promising candidate for the polymer electrolyte membrane fuel cell, especially for the direct methanol fuel cell due to its low methanol permeability and high stability in a methanol solution.     

Covalent-ionically cross-linked polyetheretherketone proton exchange membrane for direct methanol fuel cell

In this paper, the proton exchange membrane prepared by covalent-ionically cross-linking water soluble sulfonated-sulfinated poly(oxa-p-phenylene-3,3-phthalido-p-phenylene-oxa-p-phenylene-oxy-phenylene) (SsPEEK-WC) is reported. Compared with covalent cross-linked PEEK-WC membrane, this covalent-ionically cross-linked PEEK-WC membrane exhibits extremely reduced water uptake and methanol permeability, but just slightly sacrificed proton conductivity. The proton conductivity of the covalent-ionically cross-linked PEEK-WC membrane reaches to 2.1 × 10⁻² S cm⁻¹ at room temperature and 4.1 × 10⁻² S cm⁻¹ at 80 °C. The methanol permeability is 1.3 × 10⁻⁷ cm² s⁻¹, 10 times lower than that of Nafion^® 117 membrane. The results suggest that the covalent-ionically cross-linked PEEK-WC membrane is a promising candidate for direct methanol fuel cell because of low methanol permeability and adequate proton conductivity.     

Microstructured membranes for improving transport resistances in proton exchange membrane fuel cells

Proton exchange membrane fuel cells (PEMFCs) have been identified as one of the most promising renewable energy system for use in automotive applications. However, due to the wide range of weather conditions around the world, the PEMFCs must be stable for operating under these variable conditions. One of the inefficiencies of PEMFCs in automotive applications is during vehicle warm-up, where the low hydration level within the PEMFC can lead to a low performance of the fuel cell. In this study, a proton exchange membrane (PEM) was prepared with regular, microstructured features tuned over a range of aspect ratios. These microstructured membranes were incorporated into MEAs and analyzed for their membrane, proton, and oxygen transport resistances. These fuel cells were tested under different conditions to simulate vehicle start-up, normal operating conditions, and hot operating conditions. It was determined that microstructured PEMs improved performance over planar PEMs under both the start-up and hot conditions. Despite the improved performance of the microstructured PEMs, a high hydrogen cross-over and short-circuit current were also observed for these samples. Adjusting the preparation techniques and tuning the dimensions of the microstructures may provide avenues for further optimization of PEMFC performance.     

Dynamic modeling and simulation of air-breathing proton exchange membrane fuel cell

Small fuel cells have shown excellent potential as alternative energy sources for portable applications. One of the most promising fuel cell technologies for portable applications is air-breathing fuel cells. In this paper, a dynamic model of an air-breathing PEM fuel cell (AB-PEMFC) system is presented. The analytical modeling and simulation of the air-breathing PEM fuel cell system are verified using Matlab, Simulink and SimPowerSystems Blockset. To show the effectiveness of the proposed AB-PEMFC model, two case studies are carried out using the Matlab software package. In the first case study, the dynamic behavior of the proposed AB-PEMFC system is compared with that of a planar air-breathing PEM fuel cell model. In the second case study, the validation of the air-breathing PEM fuel cell-based power source is carried out for the portable application. Test results show that the proposed AB-PEMFC system can be considered as a viable alternative energy sources for portable applications.     

Novel epoxy-based cross-linked polybenzimidazole for high temperature proton exchange membrane fuel cells

An approach has been proposed to prepare the reinforced phosphoric acid (PA) doped cross-linked polybenzimidazole membranes for high temperature proton exchange membrane fuel cells (HT-PEMFCs), using 1,3-bis(2,3-epoxypropoxy)-2,2-dimethylpropane (NGDE) as the cross-linker. FT-IR measurement and solubility test showed the successful completion of the crosslinking reaction. The resulting cross-linked membranes exhibited improved mechanical strength, making it possible to obtain higher phosphoric acid doping levels and therefore relatively high proton conductivity. Moreover, the oxidative stability of the cross-linked membranes was significantly enhanced. For instance, in Fenton’s reagent (3% H₂O₂ solution, 4 ppm Fe²⁺, 70 °C), the cross-linked PBI-NGDE-20% membrane did not break into pieces and kept its shape for more than 480 h and its remaining weight percent was approximately 65%. In addition, the thermal stability was sufficient enough within the operation temperature of PBI-based fuel cells. The cross-linked PBI-NGDE-X% (X is the weight percent of epoxy resin in the cross-linked membranes) membranes displayed relatively high proton conductivity under anhydrous conditions. For instance, PBI-NGDE-5% membrane with acid uptake of 193% exhibited a proton conductivity of 0.017 S cm⁻¹ at 200 °C. All the results indicated that it may be a suitable candidate for applications in HT-PEMFCs.     

Parallel serpentine-baffle flow field design for water management in a proton exchange membrane fuel cell

In a proton exchange membrane fuel cell (PEMFC) water management is one of the critical issues to be addressed. Although the membrane requires humidification for high proton conductivity, water in excess decreases the cell performance by flooding. In this paper an improved strategy for water management in a fuel cell operating with low water content is proposed using a parallel serpentine-baffle flow field plate (PSBFFP) design compared to the parallel serpentine flow field plate (PSFFP). The water management in a fuel cell is closely connected to the temperature control in the fuel cell and gases humidifier. The PSBFFP and the PSFFP were evaluated comparatively under three different humidity conditions and their influence on the PEMFC prototype performance was monitored by determining the current density–voltage and current density–power curves. Under low humidification conditions the PEMFC prototype presented better performance when fitted with the PSBFFP since it retains water in the flow field channels.     

Incorporation of H3PO4 into three-dimensional polyacrylamide-graft-starch hydrogel frameworks for robust high-temperature proton exchange membrane fuel cells

To enhance the anhydrous proton conductivities of proton exchange membranes, we report here the incorporation of H₃PO₄ into three-dimensional (3D) framework of polyacrylamide-graft-starch (PAAm-g-starch) hydrogel materials using extraordinary absorption of hydrogels to H₃PO₄ aqueous solution. Intrinsic microporous structure can close to seal H₃PO₄ molecules in the interconnected 3D frameworks of PAAm-g-starch after suffering from dehydration. The hydrogel membranes are thoroughly characterized by morphology observation, thermal stability, swelling kinetics, proton-conducting performances as well as electrochemical behaviors. The results show that the H₃PO₄ loadings and therefore the proton conductivities of the hydrogel membranes are dramatically enhanced by employing PAAm-g-starch matrix. H₃PO₄ loading of 88.68 wt% and an anhydrous proton conductivity as high as 0.046 S cm⁻¹ at 180 °C are recorded. A fuel cell using a thick membrane shows a peak power density of 517 mW cm⁻² at 180 °C by feeding with H₂/O₂ streams. The high H₃PO₄ loading, reasonable proton conductivity in combination with simple preparation, low cost and scalable matrix demonstrates the potential use of PAAm-g-starch hydrogel membranes in high-temperature proton exchange membrane fuel cells.     

Investigation and analysis of proton exchange membrane fuel cell dynamic response characteristics on hydrogen consumption of fuel cell vehicle

The number of working points and response speed are two essential characteristics of proton exchange membrane fuel cell (PEMFC). The improper setting of the number of working points and response speed may reduce the life of PEMFC and increase the hydrogen consumption of the vehicle. This paper explores the impact of the response speed as well as the working points of the PEMFC on the hydrogen consumption in the real-system level. In this paper a dynamic model of the PEMFC system is established and verified by experiments. The model is able to reflect the dynamic response process of PEMFC under a series different number of working points and different response speed. Based on the proposed model, the influence of working points and the response speed of PEMFC on the hydrogen consumption in the vehicle under different driving cycles is analyzed and summarized, for the first time, in the open literature. The results highlight that the hydrogen consumption will decreases in both cases that with the increase of working point number and increase of response speed. However, the reduction range of hydrogen consumption trends to smaller and may reach to an optimal level considering the trade-off between the hydrogen saving and the other costs, for example the control cost. Also, with a more complex driving cycle, the working points and response speed have a greater the impact on the hydrogen consumption in the vehicle applications.     

Poly(ethylene glycol) modified activated carbon for high performance proton exchange membrane fuel cells

A high water retention membrane is developed by co-assembling poly(ethylene glycol) (PEG) grafted activated carbon (AC-PEG) with Nafion. The AC-PEG is prepared via a sol–gel process. The use of PEG as a transporting medium in AC-PEG shows a largely improved water retention ability, a higher proton conductivity and a reduced swelling ratio, making it well suited for proton exchange membrane fuel cells (PEMFCs). Further, the composite membranes show improved mechanical properties at high temperature, thus ensuring the structural stability of membranes during the fuel cell operation. Compositional optimized AC-PEG/Nafion composite membrane (15 wt% compared to Nafion) demonstrates a better performance than the commercially available counterpart, Nafion 212, in fuel cell measurements. To identify the key factor of the improved performance, current interrupt technique is used to quantitatively verify the changes of resistance under different relative humidity environment.     

Modeling and simulation of a proton exchange membrane fuel cell using computational fluid dynamics

An isothermal, three dimensional, single phase model was presented to evaluate a proton exchange membrane fuel cell (PEMFC) with serpentine flow. The mass, momentum and electrochemical equations were solved simultaneously for the steady state condition using computational fluid dynamics (CFD) software based on the finite element method. The model considered reactions as mass source/sink terms, and electron transport in the catalyst layers and GDLs. To validate the model, the numerical results were compared to the experimental data collected from the fabricated membrane electrode assemblies. The exchange current density parameter of the catalysts was fitted by the model to calibrate the results. The model showed good agreement with experimental data and predicted a higher current density for the catalyst with a higher surface area and Pt content. The oxygen, hydrogen and water mass fraction distribution, velocity magnitude and pressure distribution were estimated by the model. Moreover, the effect of pressure and temperature, as two important operating conditions, on the current density was predicted by the validated model.     

Control of a heat-integrated proton exchange membrane fuel cell system with methanol reforming

This work presents a novel heat-integrated fuel cell stack system with methanol reforming. Its configuration is composed of fuel processing units (FPUs), proton exchange membrane (PEM) fuel cell stack, and heat exchangers (HEXs). Well mixed methanol and oxygen flows in contact with countercurrent flowing water dominates the production of hydrogen at the exit of FPUs and influences the stack temperature. The heat exchange connections can enhance the utilization of energy of FPUs. To ensure the stable steady-state operation, the model-free fuzzy incremental control scheme within the multi-loop feedback control framework is developed. Finally, the proposed system integration and control configuration are verified by closed-loop simulations.     

The computer-aided analysis for the driving stability of a plug-in fuel cell vehicle using a proton exchange membrane fuel cell

In order to analyze the driving stability of a plug-in fuel cell vehicle (PFCV), a computer-aided simulator for PFCVs has been developed. PFCVs have been introduced around the world to achieve early commercialization of an eco-friendly and highly efficient fuel cell vehicle. The plug-in option, which allows the battery to be recharged from the electricity grid, enables a reduction in size of the fuel cell system (FCS) and an improvement of its durability. As such, the existing limitations of the fuel cell - such as its high cost, poor durability, and the insufficient hydrogen infrastructure – can be overcome. During the design phase of PFCV development, simulation-based driving stability test is necessary to determine the sizes of the electric engine of the FCS and the battery. The developed simulator is very useful for analyzing the driving stability of the PFCV with respect to the capacities of the FCS and battery. The simulation results are in fact very close to those obtained from a real system, since the estimation accuracy of PFCV component models used in this simulator, such as the fuel cell stack, battery, electric vehicle, and the other balance of plants (BOPs), are verified by the experiments, and the simulator uses the newly-proposed power distribution control logic and the pre-confirmed real driving schedule. Using these results, we can study which one will be the best in terms of driving stability.     

Development of a proton exchange membrane fuel cell cogeneration system

A proton exchange membrane fuel cell (PEMFC) cogeneration system that provides high-quality electricity and hot water has been developed. A specially designed thermal management system together with a microcontroller embedded with appropriate control algorithm is integrated into a PEM fuel cell system. The thermal management system does not only control the fuel cell operation temperature but also recover the heat dissipated by FC stack. The dynamic behaviors of thermal and electrical characteristics are presented to verify the stability of the fuel cell cogeneration system. In addition, the reliability of the fuel cell cogeneration system is proved by one-day demonstration that deals with the daily power demand in a typical family. Finally, the effects of external loads on the efficiencies of the fuel cell cogeneration system are examined. Results reveal that the maximum system efficiency was as high as 81% when combining heat and power.     

Three-dimensional two-phase flow model of proton exchange membrane fuel cell with parallel gas distributors

A non-isothermal, steady-state, three-dimensional (3D), two-phase, multicomponent transport model is developed for proton exchange membrane (PEM) fuel cell with parallel gas distributors. A key feature of this work is that a detailed membrane model is developed for the liquid water transport with a two-mode water transfer condition, accounting for the non-equilibrium humidification of membrane with the replacement of an equilibrium assumption. Another key feature is that water transport processes inside electrodes are coupled and the balance of water flux is insured between anode and cathode during the modeling. The model is validated by the comparison of predicted cell polarization curve with experimental data. The simulation is performed for water vapor concentration field of reactant gases, water content distribution in the membrane, liquid water velocity field and liquid water saturation distribution inside the cathode. The net water flux and net water transport coefficient values are obtained at different current densities in this work, which are seldom discussed in other modeling works. The temperature distribution inside the cell is also simulated by this model.     

Water content diagnosis for proton exchange membrane fuel cell based on wavelet transformation

The fuel cell reliability and durability are still the main factors limiting the large scale commercialization. To a certain degree, water content, transportation, distribution and state in the fuel cell influence the fuel cell State of Health (SOH). However, it's very difficult to measure water content inside fuel cell directly. The PEMFC system voltage fluctuate during hydrogen purging process, due to the removal of liquid water will affect the reactants transformation. Different internal water content will cause different voltage fluctuations. For this characteristic, The Energy Intensity of Reconstructed Vibrating Voltage (EIV) based on wavelet transformation is proposed and validated in this paper. The boundary value of EIV is determined to be 0.1 through experiments. The results show that the fuel cell voltage drop is reduced to 0.32 V/h from 1.39 V/h by using this method to avoid anode flooding. By several PEMFC system experiment results in test bench, this method can diagnosis the water content in PEMFC properly.     

A high efficient assembly technique for large proton exchange membrane fuel cell stacks: Part II. Applications

A high efficient assembly technique for large proton exchange membrane fuel cell (PEMFC) stacks is proposed for obtaining the optimal clamping load. Using the equivalent stiffness model proposed in Part I of this study, we show how to design the structure components for a large PEMFC stack. First, we give a design demonstration based on the structural strength of the stack. We then discuss how to obtain the optimal clamping load for a given PEMFC stack according to the requirements of the interface contact resistance and permeability of the gas diffusion layer. Finally, we discuss the effects of the equivalent stiffness of the spring washer on the structure thermal stress.     

Preparation and characterization of sulfonated amine-poly(ether sulfone)s for proton exchange membrane fuel cell

Sulfonated amine-poly(ether sulfone)s (S-APES)s were prepared by nitration, reduction and sulfonation of poly(ether sulfone) (ultrason^®-S6010). Poly(ether sulfone) was reacted with ammonium nitrate and trifluoroacetic anhydride to produce the nitrated poly(ether sulfone), and was followed by reduction using tin(II)chloride and sodium iodide as reducing agents to give the amino-poly(ether sulfone). The S-APES was obtained by reaction of 1,3-propanesultone and the amino-poly(ether sulfone) (NH₂-PES) with sodium methoxide. The different degrees of nitration and reduction of poly(ether sulfone) were successfully synthesized by an optimized process. The reduction of nitro group to amino was done quantitatively, and this controlled the contents of the sulfonic acid group. The films were converted from salt to acid forms with dilute hydrochloric acid. Different contents of sulfonated unit of the S-APES were studied by FT-IR, ¹H NMR spectroscopy, differential scanning calorimetry (DSC), and thermo gravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymers with water and methanol. The ion exchange capacity (IEC), a measure of proton conductivity, was evaluated. The S-APES membranes exhibit conductivities (25 °C) from 1.05 × 10⁻³ to 4.83 × 10⁻³ S/cm, water swell from 30.25 to 66.50%, IEC from 0.38 to 0.82 meq/g, and methanol diffusion coefficients from 3.10 × 10⁻⁷ to 4.82 × 10⁻⁷ cm²/S at 25 °C.     

Dynamic modeling of a high-temperature proton exchange membrane fuel cell with a fuel processor

A dynamic model of a high-temperature proton exchange membrane fuel cell with a fuel processor is developed in this study. In the model, a fuel processing system, a fuel cell stack, and an exhaust gas burner are modeled and integrated. The model can predict the characteristics of the overall system and each component at the steady and transient states. Specifically, a unit fuel cell model is discretized in a simplified quasi-three-dimensional geometry; therefore, the model can rapidly predict the distribution of fuel cell characteristics. Various operating conditions such as the steam-to-carbon ratio, oxygen-to-carbon ratio, and autothermal reforming inlet temperature are varied and investigated in this study. In addition, the dynamic characteristics exhibited during the transient state are investigated, and an efficiency controller is developed and implemented in the model to maintain the electrical efficiency. The simulation results demonstrate that the steam-to-carbon ratio and the oxygen-to-carbon ratio affect the electrical and system efficiency and that controlling the fuel flow rate maintains the electrical efficiency in the transient state. The model may be a useful tool for investigating the characteristics of the overall system as well as for developing optimal control strategies for enhancing the system performance.     

Recent advances in designing and tailoring nanofiber composite electrolyte membranes for high-performance proton exchange membrane fuel cells

As the critical component of proton exchange membrane fuel cell (PEMFC), proton exchange membrane (PEM) determine its overall performance. Current PEMs hardly meet the operating requirements of fuel cells, limiting their commercial applications. With the development of nanocomposite technology, nanofibers introduced into PEMs to prepare nanofiber composite proton exchange membranes (NCPEMs) have been widely studied. In an NCPEM, nanofibers can form long-range channels for proton transport, and reinforced skeleton to reach the target performance of PEMFCs. Focusing on NCPEM, this paper reviews on recent progresses in nanofiber preparation and NCPEM preparation techniques. Furthermore, different types of nanofibers incorporated into NCPEMs are reviewed in terms of fiber composition. The challenges and future perspectives regarding NCPEMs are also discussed.