A novel cesium hydrogen sulfate-zeolite inorganic composite electrolyte membrane for polymer electrolyte membrane fuel cell application

A new type of CsHSO₄-HZSM-5 inorganic composite electrolyte membrane is prepared by mechanically mixing CsHSO₄ (CHS) and nanometer-scale HZSM-5 zeolite powders. The effects of HZSM-5 on the crystallite structure, proton conductivity, and thermal stability of the CsHSO₄ electrolyte are investigated. Incorporation of HZSM-5 is found to significantly increase the low-temperature proton conductivity of the CsHSO₄ electrolyte, extending its operating temperature down to 100 °C. The composite electrolyte with 40 mol% HZSM-5 shows the highest proton conductivity in the measured temperature range. The low-temperature activation energy of the composite with 40 mol% HZSM-5 is lower than that of the CHS-SiO₂ composite. The improvement of the proton conductivity can be attributed to the enhanced interfacial interaction between the two phases. And the small HZSM-5 particles lead to a change in the bulk properties of the ionic salts. The melting point of the CHS-HZSM-5 composite electrolyte is lower than that of the pure CHS electrolyte. The CHS-HZSM-5 composite electrolyte is suitable for polymer electrolyte membrane fuel cells operated at 100-200 °C.     

Synthesis and characterization of polysulfone/layered double hydroxides nanocomposite membranes for fuel cell application

In the present study, sulfonated polysulfone (SPSU)/layered double hydroxide (LDH) composite membranes for use in proton exchange membrane fuel cells (PEMFCs) were investigated. Polysulfone (PSU) was sulfonated with trimethylsilyl chlorosulfonate in 1,2 dichloroethane at room temperature.     

Cross-linked sulfonated poly(phathalazinone ether ketone)s for PEM fuel cell application as proton-exchange membrane

The cross-linkable sulfonated ploy(arylene ether)s derived from 3,3′-diallyl-4,4′-dihydroxybiphenyl, bisphthalazinone, 4,4′-difluorobenzophenone (DFBP) and sulfonated 4,4′-diflourobenzophenone (SDFBP) were synthesized over a wide range of DFBP/SDFBP molar ratios. The resulting sulfonated poly(arylene ether)s with high inherent viscosity (1.02–1.29 dL g⁻¹) are soluble in polar organic solvents and can form flexible and transparent membranes by casting from their solution. Cross-linking reaction was carried out using the thermal activated radical cross-linking agent (TARC) at 140 °C. The comprehensive properties of the virgin and the cross-linked membranes were compared accordingly. The results showed that the cross-linked membranes revealed the better mechanical, oxidative and dimensional stabilities together with high proton conductivity (9.675 × 10⁻³ S cm⁻¹) at 25 °C under 100% relative humidity.     

Stability enhancement of polymer electrolyte membrane fuel cells based on a sulfonated poly(ether ether ketone)/poly(vinylidene fluoride) composite membrane

Most proton-conducting membranes based on sulfonated aromatic polymers exhibit significant dimensional change by hydration, and this leads to degradation of fuel cell performance on prolonged operation. In this study, as a means of improving the stability of a polymer electrolyte membrane fuel cell, composite membranes employing a porous poly(vinylidene fluoride) (PVdF) substrate and sulfonated poly(ether ether ketone) (sPEEK) electrolyte are prepared and their hydration behaviours, including water uptake and dimensional change, are examined. The electrochemical characteristics of membrane/electrode assemblies using the sPEEK/PVdF composite membrane are also analyzed. The initial cell performance is comparable with that of a cell based on a pure sPEEK membrane. Furthermore, the stability of the cell using the sPEEK/PVdF composite membrane is considerably improved during a humidity cycle test wherein hydration and dehydration are periodically repeated.     

Chitosan/graphene complex membrane for polymer electrolyte membrane fuel cell: A molecular dynamics simulation study

Chitosan has been considered attractive in polymer electrolyte membrane fuel cells (PEMFCs) due to its excellent film forming and fuel barrier properties. Reflecting the limitation of its low proton conductivity, various materials were used to improve the proton conductivity of chitosan, through combination with inorganic materials like graphene oxide. We present an ideal molecular model for bio-nanocomposites and their mechanism of proton conductivity in PEMFCs. In this study, the diffusion behavior of hydronium ions in chitosan/graphene complex systems at various temperatures, concentrations and pH values were studied systematically using 3 ns long molecular dynamics (MD) simulations with an aim to provide the mechanisms of proton conductivity of chitosan/graphene composite at an atomistic scale. Various amounts of water content (10%, 20%, 30% and 40%), pH values (achieved by adjusting the protonation degree of amino groups of chitosan by 20%, 40%, 60%, 80% and 100%) and numbers of graphene sheets (1, 2, and 3) were considered during MD simulations at 4 temperatures (298 K, 320 K, 340 K and 360 K). Our results indicated that the chitosan system containing 40% water was the most suitable polymer electrolyte membrane and temperature was a key factor affecting diffusion proton. Adding graphene to the chitosan system and adjusting the pH values of chitosan were demonstrated to have a significant effect on improving the proton conductivity of the membrane.     

A polytetrafluoroethylene/quaternized polysulfone membrane for high temperature polymer electrolyte membrane fuel cells

A polytetrafluoroethylene (PTFE)/quaternized polysulfone (QNPSU) composite membrane has been fabricated for use in proton exchange membrane fuel cells (PEMFCs). The composite membrane is made by immobilizing a QNPSU solution into a hydrophobic porous PTFE membrane. The structure of the composite membrane is examined by SEM and EDX. The ionic conductivity of the PTFE/QNPSU membrane, at a relative humidity lower than 0.5% and a temperature of 180 °C, is greater than 0.3 S cm⁻¹, when loaded with 400% H₃PO₄. A hydrogen fuel cell with this membrane operating at 2.0 atmosphere absolute (atma) pressure and 175 °C gives voltages >0.4 V at current densities of 1.0 A cm⁻² using oxygen.     

Synthesis of sulfonated poly(diketonephenylene)s containing dibenzoyl moiety via Ni/Zn catalyst

The new monomer, 1,2-bis(4-chlorobenzoyl)-3,6-diphenylbenzene, was synthesized from the Frieldel–Craft reaction of chlorobenzene and fumaryl chloride followed by the Diels–Alder reaction. Poly(diketonephenylene)s containing the dibenzoyl moiety in the side chains were synthesized from 1,2-bis(4-chlorobenzoyl)-3,6-diphenylbenzene and 1,4-dichloro-2,5-dibenzoylbenzene as a reactive monomer. The polymerization was performed employing a Ni/Zn catalyzed carbon–carbon coupling reaction followed by a sulfonation reaction with chlorosulfuric acid. These polymers consisted of diketone in the main chain and dibenzoyl in the side chain, which consisted of four active phenyl groups for sulfonation. A series of membranes was studied via ¹H NMR spectroscopy, ion exchange capacity (IEC), water uptake, and proton conductivity analyses. The thermal and chemical stability of the prepared membrane is then characterized through a thermogravimetric investigation.     

Analysis and control of a hybrid fuel delivery system for a polymer electrolyte membrane fuel cell

A polymer electrolyte membrane fuel cell (PEM FC) system as a power source used in mobile applications should be able to produce electric power continuously and dynamically to meet the demand of the driver by consuming the fuel, hydrogen. The hydrogen stored in the tank is supplied to the anode of the stack by a fuel delivery system (FDS) that is comprised of supply and recirculation lines controlled by different actuators. Design of such a system and its operation should take into account several aspects, particularly efficient fuel usage and safe operation of the stack.     

Synthesis and characterization of sulfonated poly (arylene ether ketone sulfone) block copolymers containing multi-phenyl for PEMFC

Sulfonated multi-block copolymers (SMBPs) were successfully synthesized from precursors of hydrophilic and hydrophobic block oligomers. The hydrophilic block oligomer was synthesized using 1,2-bis(4-fluorobenzoyl)-3,4,5,6-tetraphenylbenzene (BFBTPB) and 4,4′-(2,2-diphenylethenylidene) diphenol (DHTPE). The hydrophobic block oligomer was prepared by bis(4-hydroxyphenyl) sulfone and bis(4-fluorophenyl) sulfone. The sulfonation was taken selectively on hydrophilic block segment as well as para position of the pendant phenyl groups with concentrated sulfuric acid. To control the IEC the stoichiometry mole ratios were changed with hydrophilic blocks of 10, 13 and 17 mol%. The structural properties of SMBPs were studied by FT-IR, ¹H NMR spectroscopy, thermogravimetric analysis (TGA), and atomic force microscope (AFM). The water uptakes were 9.7–42.3% at 30 °C and 14.3%–70.4% at 80 °C with changing the ion exchange capacities. The resulted ion exchange capacities (IEC) were 1.09–1.63 meq./g. The highest power density of a fuel cell using SMBP 17 (IEC = 1.63 meq./g) and Nafion 211 was 0.41 and 0.45 W/cm², respectively, at 0.6 V.     

A review of polymer electrolyte membranes for direct methanol fuel cells

This review describes the polymer electrolyte membranes (PEM) that are both under development and commercialized for direct methanol fuel cells (DMFC). Unlike the membranes for hydrogen fuelled PEM fuel cells, among which perfluorosulfonic acid based membranes show complete domination, the membranes for DMFC have numerous variations, each has its advantages and disadvantages. No single membrane is emerging as absolutely superior to others. This review outlines the prospects of the currently known membranes for DMFC. The membranes are evaluated according to various properties, including: methanol crossover, proton conductivity, durability, thermal stability and maximum power density. Hydrocarbon and composite fluorinated membranes currently show the most potential for low cost membranes with low methanol permeability and high durability. Some of these membranes are already beginning to impact the portable fuel cell market.     

Externally cooled high temperature polymer electrolyte membrane fuel cell stack

One key issue in high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) stack development is heat removal at the operating temperature of 140–180 °C. Conventionally, this process is done using coolants such as thermooil, steam or pressurized water. In this contribution, external liquid cooling designs are described, which are avoiding two constraints. First, in the cell active area, no liquid coolant is present avoiding any sealing problems with respect to the electrode. Secondly, the external positioning allows high temperature gradients between the heat removal zone and the active area resulting in a good adjustability of appropriate reformate conversion temperatures (e.g. 160 °C) and a more compact cell design. Different design concepts were investigated using modeling techniques and a selection of them has also been investigated experimentally. The experiments proved the feasibility of the external cooling design and showed that the temperature gradients within the active area are below 15 K under typical operating conditions.     

Fabrication of polymer electrolyte membrane fuel cell MEAs utilizing inkjet print technology

Utilizing drop-on-demand technology, we have successfully fabricated hydrogen–air polymer electrolyte membrane fuel cells (PEMFC), demonstrated some of the processing advantages of this technology and have demonstrated that the performance is comparable to conventionally fabricated membrane electrode assemblies (MEAs). Commercial desktop inkjet printers were used to deposit the active catalyst electrode layer directly from print cartridges onto Nafion^® polymer membranes in the hydrogen form. The layers were well-adhered and withstood simple tape peel, bending and abrasion tests and did so without any post-deposition hot press step. The elimination of this processing step suggests that inkjet-based fabrication or similar processing technologies may provide a route to less expensive large-scale fabrication of PEMFCs. When tested in our experimental apparatus, open circuit voltages up to 0.87 V and power densities of up to 155 mW cm⁻² were obtained with a catalyst loading of 0.20 mg Pt cm⁻². A commercially available membrane under identical, albeit not optimized test conditions, showed about 7% greater power density. The objective of this work was to demonstrate some of the processing advantages of drop-on-demand technology for fabrication of MEAs. It remains to be determined if inkjet fabrication offers performance advantages or leads to more efficient utilization of expensive catalyst materials.     

A review of polymer electrolyte membrane fuel cell durability test protocols

Durability is one of the major barriers to polymer electrolyte membrane fuel cells (PEMFCs) being accepted as a commercially viable product. It is therefore important to understand their degradation phenomena and analyze degradation mechanisms from the component level to the cell and stack level so that novel component materials can be developed and novel designs for cells/stacks can be achieved to mitigate insufficient fuel cell durability. It is generally impractical and costly to operate a fuel cell under its normal conditions for several thousand hours, so accelerated test methods are preferred to facilitate rapid learning about key durability issues. Based on the US Department of Energy (DOE) and US Fuel Cell Council (USFCC) accelerated test protocols, as well as degradation tests performed by researchers and published in the literature, we review degradation test protocols at both component and cell/stack levels (driving cycles), aiming to gather the available information on accelerated test methods and degradation test protocols for PEMFCs, and thereby provide practitioners with a useful toolbox to study durability issues. These protocols help prevent the prolonged test periods and high costs associated with real lifetime tests, assess the performance and durability of PEMFC components, and ensure that the generated data can be compared.     

Detailed thermodynamic analysis of polymer electrolyte membrane fuel cell efficiency

It is common knowledge that efficiency of fuel cells is highest when no electric current is produced while when the fuel cell is really working, the efficiency is reduced by dissipation. In this paper the relation between efficiency and dissipation inside the fuel cell is formulated within the framework of classical irreversible thermodynamics of mixtures. It is shown that not only dissipation influences the efficiency but that there are also some other terms which become important if there are steep temperature gradients inside the fuel cell. Indeed, we show that the new terms are negligible in polymer-electrolyte membrane fuel cells while they become important in solid oxide fuel cells. In summary, this paper presents a formulation of non-equilibrium thermodynamics of fuel cells and provides analysis of efficiency in terms of processes inside the fuel cells, revealing some new terms affecting the efficiency.     

Three-layered electrolyte membranes with acid reservoir for prolonged lifetime of high-temperature polymer electrolyte membrane fuel cells

High-temperature polymer electrolyte membrane fuel cells with phosphoric acid doped polybenzimidazole (PBI) are made with three-layered membranes. The central membrane layer is meant as an acid reservoir made from direct cast PBI with a higher acid content than the outermost layers, which are post doped membranes acting as barrier layers to limit the acid transport out of the central layer. Cells with three-layered membranes and others with normal single layered membranes are tested at 170 and 180 °C. At both temperatures, the cells with three-layered membranes show significantly lower voltage decay rates than the corresponding cells with single-layered membranes. Post doped PBI membranes based on linear or thermally crosslinked PBI are used for the barrier layers of the three-layered membranes and for the single-layered membranes in the test series at 180 °C. The acid loss rates assessed by acid collection at the fuel cell exhaust, are rather comparable. At 180 °C, the cells are tested for up to 10,000 h and voltage decay rates of 2.3 and 4.1 μVh^-1 are measured for the cells with three-layered membranes and 14 and 11 μVh^-1 for cells with single-layered membranes.     

Silicon carbide fiber-reinforced composite membrane for high-temperature and low-humidity polymer exchange membrane fuel cells

Currently, efforts are being made to commercialize a fuel cell system through research on fuel cell material enhancements. In particular, improvements in the membrane-electrode assembly, a key component of polymer electrolyte membrane (PEM) fuel cells, are essential to increase the performance of a fuel cell, in addition to accelerating its commercialization. Therefore, in this study, we used silicon carbide (SiC) fibers (web type) by electrospinning, which possess superior material, thermal, and chemical properties, as a structural material for the composite electrolyte membrane in the membrane-electrode assembly by impregnating it with the polymer electrolyte ionomer of short-side chain (SSC). In addition, we enhanced the ion-exchange capability of functionalized SiC fibers by introducing the hydroxyl (OH) group and phosphoric acid. The resulting functionalized composite electrolyte membrane exhibited a 70% better ion-exchange capability than the conventional cast electrolyte membrane and SiC webs composite electrolyte membranes was observed to excellent mechanical strength. We characterized and illustrative modeled the functionalized silicon carbide fibers, on the basis of which we further developed composite membrane. We then fabricated a unit cell of PEMFC based on this composite electrolyte membrane, and evaluated its single-cell performance, electrochemical properties, and accelerated voltage life-time durability test of operating 35 h according to the electro- and physic-chemical characteristics of the MEA under high-temperature and low humidity (120 °C/RH 40%).     

GO-nafion composite membrane development for enabling intermediate temperature operation of polymer electrolyte fuel cell

Increasing Polymer Electrolyte Fuel Cells’ (PEFCs) operating temperature has benefits on the performance and the ease of utilisation of the heat generated; however, efforts for high temperature PEFCs have resulted in high degradation and reduced life time. In the literature, conventional low temperature (T < 80 °C) and high temperature (140–200 °C) regimes have been extensively studied, while the gap of operating at intermediate temperature (IT) (100–120 °C) has been scarcely explored.The main bottleneck for operating at IT conditions is the development of a suitable proton exchange membrane with comparable performance and lifetime to the commercially used Nafion operating at conventional conditions. In this work, composite membranes of Graphene Oxide (GO) and Nafion of varied thickness were fabricated, characterised and assessed for in-situ single cell performance under automotive operating conditions at conventional and intermediate temperatures.The material characterisation confirmed that a composite GO-Nafion structure was achieved. The composite membrane demonstrated higher mechanical strength, enhanced water uptake, and higher performance. It was demonstrated that by utilising GO-Nafion composite membranes, an up to 20% increase in the maximum power density at all operating temperatures can be achieved, with the optimum performance is obtained at 100 °C. Moreover, the GO-Nafion membrane was able to maintain its open circuit voltage values at increased temperature and reduced thickness, indicating better durability and potentially higher lifetime.     

Diagnosis of contamination introduced by ammonia at the cathode in a polymer electrolyte membrane fuel cell

Contamination introduced by impurities from feed streams can impact polymer electrolyte membrane fuel cell performance dramatically. The presence of unwanted trace species, such as CO, H₂S, and NH₃, can adversely affect the function of a fuel cell. It has been reported that the major impact of CO and H₂S contamination on fuel cell performance is kinetic, while the effect of NH₃ contamination is speculated to be mainly membrane conductivity reduction. In this paper, the effect of NH₃ contamination from the cathode side was investigated. The mechanisms of NH₃ contamination were diagnosed based on degradation tests using electrochemical impedance spectroscopy and cyclic voltammetry. The contamination factors investigated included ammonia concentration, operating current, temperature, and relative humidity. The results show that the severity of the adverse effect caused by ammonia contamination was enhanced by increased ammonia concentration, decreased operating temperature, and decreased relative humidity. The performance decay induced by ammonia is attributable to reduced membrane/ionomer conductivity and ammonia adsorption on the catalyst surface, which blocks the active sites and hinders mass transfer.     

Composite S-PEEK membranes for medium temperature polymer electrolyte fuel cells

Sulphonated-PEEK polymers with two different sulphonation degrees (DS) were obtained by varying the sulphonation parameters. Ionomeric membranes were prepared as a reference. Composite membranes were obtained by mixing different percentage of 3-aminopropyl functionalised silica to the polymers dissolved in DMAc. The resulting membranes were characterised in terms of water uptake, IEC and proton conductivity in different conditions of temperature and relative humidity.