A review of progressive advanced polymer nanohybrid membrane in fuel cell application

This review provides a deep insight into the advanced polymer composite developed in fuel cell application. Organic polymer combined with inorganic filler has produced a new material known as a hybrid membrane or composite membrane. This combination has enhanced the various characteristics including conductivity properties, membrane permeability, and stability, cheaper, optimum water retention and mechanical properties. Properties of the hybrid membrane are influenced totally by several factors such as membrane preparation techniques as well as internal properties of particles involved, for example, inorganic fillers such as the size and type of particles, surface alkaline or acidity, shape and formation of networking between the polymer phase. The conventional membrane used in the fuel cell application is Nafion. Nafion potential is undoubtedly in obtains of high conductivity, but it faces some major problems such as CO poisoning, high cost, fuel crossover and water management that needs to be taken seriously. Hybrid composite is seen as an alternative material to addressing problems faced by a conventional membrane but promises even better potential if explored in depth. In this article, all inorganic fillers involved in the production of the composite membranes have been discussed comprehensively. Different types of polymers have been categorized with various fillers.     

Silica-related membranes in fuel cell applications: An overview

Silica is the most common inorganic filler used in fuel cells, especially for proton exchange membrane fuel cell and direct alcohol fuel cell applications. Silica has played an important role in improving the performance of fuel cells by enhancing their membrane properties. Recently, silica has been widely implemented in different types of membranes, such as fluorinated membranes (Nafion), sulfonated membranes (SPEEK, SPS, SPAES, SPI) and other organic polymer matrixes. The incorporation of silica into membrane matrices has improved the thermal stability, mechanical strength, water retention capacity and proton conductivity of the membrane. This review describes the interactions between silica and different types of polymer matrices in fuel cells and how they boost fuel cell performance. In addition, this review also discusses the current challenges of silica-related membrane-based fuel cells and predicts the future prospects of silica in membrane-based fuel cell applications.     

Cross‐linked polymer electrolyte membrane based on a highly branched sulfonated polyimide with improved electrochemical properties for fuel cell applications

Sulfonated polyimides (SPIs) are extremely suitable as polymer electrolyte membranes (PEMs) for fuel cell applications, except for their poor water stability. Cross‐linking is a method that is commonly used to improve the weak hydrolytic stability of SPI membranes. However, this strategy significantly decreases the proton conductivity of the membrane, which leads to a lower fuel cell power density. In this work, a cross‐linked SPI membrane containing a highly branched polymer main chain was fabricated as a PEM. With a similar ion‐exchange capacity value, the cross‐linked membrane containing branched main chains showed an improved proton conductivity. Also, this membrane remained 92.3% of pristine weight after a hydrolytic stability test about 120 hours. In a single direct methanol fuel cell, the cross‐linked membrane containing a branched structure showed a higher power density (53.4 mW cm^?2) than the common cross‐linked membrane (43.0 mW cm^?2), indicating that branching is effective for improving the electrochemical properties of PEM‐based cross‐linked SPIs.     

Graphene based polymer electrolyte membranes for electro-chemical energy applications

Graphene, a material with exceptional properties, has dragged an attention worldwide due to its applicability in wide range of applications particularly in energy sector. With the growing human population, an intense need has aroused to explore alternate ways to meet upsurge demand of energy, where the sources of non-renewable energy are limited. Energy conversion and storage devices e.g. fuel cell, electrolyzer, batteries use polymer electrolyte membranes (PEM) as electrolyte/separator, as an important component. PEM plays a vital role in such devices, which can be prepared by functional polymers. Various PEMs consisting of various fillers have been developed to fulfill the needs of energy devices. Graphene oxide (GO), a fascinating material, has stimulated interest among researchers due to its various applications including energy based devices. This review mainly deals with graphene oxide (GO) based polymer electrolyte membranes and their applications in energy devices. Advancements in the development of GO membranes, interaction with polymer matrix and their electrochemical properties has been summarized. This review provides a profound insight about graphene based polymer electrolyte membranes for energy related applications including polymer electrolyte membranes fuel cell (PEMFC), vanadium redox flow battery (VRB) and Li-ion battery.     

A review of thermoplastic composites for bipolar plate applications

Bipolar plates are responsible for functions of vital importance to the long‐term performance of fuel cells. They play crucial roles in water and gas management, mechanical strength and electrical conductivity. It also significantly contributes to the volume, weight and cost of fuel cell stacks. The properties of bipolar plates are affected by the materials and processes used in the manufacturing of the plates. The objective of this article is to review the use of thermoplastic materials as polymer matrices in bipolar plate applications. Conductive composites consisting of different types and blends of thermoplastic polymers are detailed discussed. The effects of filler types and processing conditions are given. Several thermoplastic blends consisting of carbon black, carbon nanotube and graphite are evaluated. The dispersion of conductive fillers, in particular, polymer composites and polymer blend composites is also given. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluation of Quaternized polyvinyl alcohol/graphene oxide-based membrane towards improving the performance of air-breathing passive direct methanol fuel cells

Graphene oxide (GO) nanosheets are introduced to a Quaternized polyvinyl alcohol (QPVA) polymer matrix to obtain an anion exchange membranes (AEMs) for application of fuel cells. QPVA/GO nanocomposite membranes provide desirable properties such as low fuel uptake and permeability, excellent ionic conductivity, and cell performance, all of which are favorable for AEMs based on our previous works. Passive direct methanol fuel cells (DMFCs) are recognized as suitable technologies for use in portable devices. Nevertheless, the commercialization of DMFCs remains restricted due to a number of issues related to the conventional membrane; one of these issues is high fuel crossover problems due to high fuel uptake and permeability of Nafion membrane. This study aimed to expand the potential applications of QPVA/GO nanocomposite membranes in air-breathing passive DMFCs. The ionic conductivity, methanol uptakes (MUs), and permeabilities of self-synthesis QPVA/GO nanocomposites are examined to evaluate the ability to operate in methanol atmosphere. At 30°C, the ionic conductivity of the membranes reached 1.74 × 10⁻² S cm⁻¹. The MUs and permeabilities were as low as 35% and 7.6 × 10⁻⁷ cm² s⁻¹, respectively. The performance of air-breathing passive DMFCs bearing QPVA/GO nanocomposite membrane is much higher compared to conventional membranes. The maximum power density of air-breathing passive DMFCs was achieved 27.2 mW cm⁻² under the optimum condition of 2 M methanol + 4 M KOH at 70°C. Single-cells could be sustained for 1000 hours. This article is the first to optimize and highlight the performance air-breathing passive DMFCs by using a QPVA-based membrane.     

Additives in proton exchange membranes for low- and high-temperature fuel cell applications: A review

Polymer electrolyte membranes, also known as proton exchange membranes (PEMs), are a type of semipermeable membrane that exhibits the property of conducting ions while impeding the mixing of reactant materials across the membrane. Due to the large potential and substantial number of applications of these materials, the development of proton exchange membranes (PEMs) has been in progress for the last few decades to successfully replace the commercial Nafion^® membranes. In the course of this research, an alternate perspective of PEMs has been initiated with a desire to attain successful operations at higher working temperatures (120–200 °C) while retaining the physical properties, stability and high proton conductivity. Both low- and high-temperature PEMs have been fabricated by various processes, such as grafting, cross-linking, or combining polymer electrolytes with nanoparticles, additives and acid-base complexes by electrostatic interactions, or by employing layer-by-layer technologies. The current review suggests that the incorporation of additives such as plasticisers and fillers has proven potential to modify the physical and chemical properties of pristine and/or composite membranes. In many studies, additives have demonstrated a substantial role in ameliorating both the mechanical and electrical properties of PEMs to make them effective for fuel cell applications. It is notable that plasticiser additives are less desirable for the development of high-temperature PEMs, as their inherent highly hydrophilic properties may stiffen the membrane. Conversely, filler additives form an inorganic-organic composite with increased surface area to retain more bound water within the polymer matrices to overcome the drawbacks of ohmic losses at high operating temperatures.     

Novel functionalized carbon nanotubes as cross-links reinforced vinyl ester/nanocomposite bipolar plates for polymer electrolyte membrane fuel cells

In this study, the novel functionalized multi-walled carbon nanotubes (MWCNTs) are used as cross-links between MWCNTs-vinyl ester interfaces to achieve homogeneous dispersion and strong interfacial bonding for developing fully integrated MWCNTs-vinyl ester nanocomposite bipolar plates. POAMA (i.e. poly(oxyalkylene)-amines (POA) bearing maleic anhydride (MA)) are grafted onto the MWCNTs by amidization reaction, forming MWCNTs-POAMA. In the MWCNTs-POAMA/vinyl ester nanocomposites, MWCNT-POAMAs react with vinyl ester and become part of the cross-linked structure, rather than just a separate component. It is found that the MWCNTs-POAMA exhibited better dispersion in the vinyl ester matrix than those of pristine MWCNTs. Moreover, the results demonstrate that the mechanical and electrical properties of the vinyl ester nanocomposite bipolar plate are improved dramatically. The ultimate flexural strength, unnotched impact strength, in-plane electrical conductivity and contact resistance of the MWCNTs-POAMA/vinyl ester nanocomposite bipolar plate are increased by 45%, 90%, 315% and 28%, respectively. In addition, the maximum current and power densities of the single fuel cell test using the MWCNTs-POAMA/vinyl ester nanocomposite bipolar plates is enhanced from 1.03 to 1.23 A cm⁻² and from 0.366 to 0.518 W cm⁻², respectively, which suggested that a higher electron transfer ability for polymer electrolyte membrane fuel cell applications can be achieved.     

Self-humidifying nanocomposite membranes based on sulfonated poly(ether ether ketone) and heteropolyacid supported Pt catalyst for fuel cells

In the present study, the self-humidifying nanocomposite membranes based on sPEEK and Cs_2.5H_0.5PW₁₂O₄₀ supported Pt catalyst (Pt-Cs_2.5H_0.5PW₁₂O₄₀ catalyst or Pt-Cs_2.5) and their performance in proton exchange membrane fuel cells with dry reactants has been investigated. The XRD, FTIR, SEM-EDXA and TEM analysis were conducted to characterize the catalyst and membrane structure. The ion exchange capacity (IEC), water uptake and proton conductivity measurements indicated that the sPEEK/Pt-Cs_2.5 self-humidifying nanocomposite membranes have higher water absorption, acid and proton-conductive properties compared to the plain sPEEK membrane and Nafion-117 membrane due to the highly hygroscopic and acidy properties of Pt-Cs_2.5 catalyst. The single cells employing the sPEEK/Pt-Cs_2.5 self-humidifying nanocomposite membranes exhibited higher cell OCV values and cell performances than those of plain sPEEK membrane and Nafion-117 membrane under dry or wet conditions. Furthermore, the sPEEK/Pt-Cs_2.5 self-humidifying nanocomposite membranes showed good water stability in aqueous medium. After investigation of several membranes such as sPEEK and sPEEK/Pt-Cs_2.5 membranes, the self-humidifying nanocomposite membrane with sulfonation degree of 65.12% for its sPEEK and 15 wt.% of catalyst with 1.25 wt.% Pt within catalyst was found to be the best proton exchange membrane for fuel cell applications. This self-humidifying nanocomposite membrane has a higher single cell performance than the Nafion-117 which was frequently used as a proton exchange membrane for fuel cell applications.     

Neoteric advancements in polybenzimidazole based polymer electrolytes for high-temperature proton exchange membrane fuel cells - A versatile review

The world's dependence on hydrocarbon fuel to generate power has proven to be the primary source of energy production. The emission of dangerous toxic and effluent gases during the process of hydrocarbon extraction and utilisation poses a massive threat to the environment and human life. This has driven the research into green energy technology; polymer electrolyte membrane fuel cells (PEMFCs) is one of the future century's bright green and clean energy producers. The most critical factor in the fuel cell is the polymer electrolyte membrane (PEM), which is the heart of the fuel cell assembly. Recently, polybenzimidazole (PBI)-based high-temperature polymer electrolytes have attracted researchers because they have high chemical and thermal stability combined with fillers that can control proton mobility. There are several limitations to the usage of PBI in high-temperature PEMFCs and this review summarizes the various structural modification: phase inversion, semi-interpenetrating IPNs, branched blocks and physical modification methods like crosslinking, blending, doping, progress done by various researchers to tackle the drawbacks in PBI-based polymer electrolyte membranes.     

A review of quaternized polyvinyl alcohol as an alternative polymeric membrane in DMFCs and DEFCs

Direct methanol fuel cells (DMFCs) and direct ethanol fuel cells (DEFCs) have emerged as alternative power generators for portable devices and household appliances because of their easy and fast production of electricity, as well as high energy conversion to provide high-power density. However, several critical factors limit the commercialization of DMFCs and DEFCs, particularly issues related to polymer electrolyte membranes, including the high-cost production of Nafion membranes and cell degradation caused by high fuel crossover and dehydration. This review paper provides an overview of the current status and challenges in quaternized polyvinyl alcohol (QPVA)-based membranes as an alternative polymer electrolyte membrane for DMFCs and DEFCs. The main advantages of using QPVA-based membranes in fuel cells are reduced cost production of membrane, fuel-crossover minimization, and competitive conductivity with Nafion membrane. The effects of modifying the QPVA-based membrane, especially on conductivity properties, fuel crossover, uptake condition, mechanical, thermal, and chemical properties, and single-cell performance are comprehensively discussed. The best performances of DMFCs and DEFCs with utilizing QPVA-based membrane are reported as 272 and 144 mW cm⁻², respectively. This paper is the first to highlight the current status and challenges of QPVA-based membranes for DMFCs and DEFCs applications.     

Insight into time-correlated structure and interfacial evolvement of nanocomposite and semiconductor heterostructure for advanced fuel cells

Super ionic channel or shuttle correlated with interfacial engineering of nanocomposite structure and semiconductor-based material electrolytes has shown great potential in electrochemical applications, such as photochemical water splitting or low temperature advanced fuel cell. By adjusting apriority composition between n and p components, the up-to-date semiconductor-ionic membrane fuel cells (SIMFCs) exhibit the improved performance, especially for high ionic conductivity and power outputs at lower temperature. Facing the commercialization of novel advanced ceramic cells, a combined literature survey and phenomenological analysis is proposed to interpret the difference between the current-voltage curve and stability performance of low temperature solid oxide fuel cell (LTSOFC). Meanwhile, it is experimentally determined that the time constant, which is closely related to the interfacial structure and heterostructure, has played a great role in the cell properties. Herein, steady state instead of transient characteristic is preferred, dedicating to provide much more reliable data. Among several prototype cells on semiconductor-based electrolyte, only the candidate that can resist the high current operation shows suppressing inside electronic leakage and survives in short-term test. The results illustrate that though semiconductor-based nanocomposite or heterostructure is an effective methodology in developing low temperature ceramic fuel cells, its durability and the risk of short-circuit should be taken with much care.     

Hollow fiber membranes with polyimide matrix for sulfur-free hydrogen source

Sulfur-free hydrogen production is significant for sustainable energy such as fuel cell to avoid poisoning catalysts. The hollow fiber membrane is proposed as sulfur trapper for the hydrocarbon fuels. Hollow fiber membranes with polyimide (PI) matrix and adsorptive zeolites fillers are fabricated by dry–wet spinning with subsequent imidization process. By detailed investigation of FT-IR, thermal degradation cures, morphology and sulfur trapping performance, the molecular structure, thermostability and adsorption channels of membranes have been analyzed. The hollow fiber membranes have abundant pores, and the zeolites particles are incorporated in the three-dimension polymer matrix. The inlet fuel can be desulfurized to below 0.1 mg L⁻¹, which means that the outlet fuel can be used as sulfur-free hydrogen source for fuel cell applications. Excellent sustainability of the system with hollow fiber configuration show attractive on-board application potential.     

Carbon materials in composite bipolar plates for polymer electrolyte membrane fuel cells: A review of the main challenges to improve electrical performance

The technology of polymer electrolyte membrane (PEM) fuel cells is dependent on the performance of bipolar plates. There is a strong relationship between the material used in the manufacturing of the bipolar plate and its final properties. Graphite-polymer composite bipolar plates are well-established commercial products. Several other carbon based fillers are tested. Carbon nanotubes, carbon fibers, carbon black, graphite nanoplatelets and expanded graphite are examples of such materials. Structural characteristics of these particles such as morphology and size have decisive influence on the final properties of bipolar plates. Furthermore, the volumetric fraction of the filler is of prime importance. There is plenty of information on individual aspects of specific composite bipolar plates in the literature. Notwithstanding, the analysis of structure-property relationship of these materials in a comprehensive source is not found. In this paper, relevant topics on the structural aspects of carbon based fillers and how they influence the final electrical performance of composite bipolar plates are discussed. It is intended that this document contribute to the development of new and maximized products to the PEM fuel cell industry.     

A review on methanol crossover in direct methanol fuel cells: challenges and achievements

Direct methanol fuel cells have the potential to power future microelectronic and portable electronic devices because of their high energy density. One of the major obstacles that currently prevent the widespread applications of direct methanol fuel cells is the methanol crossover through the polymer‐electrolyte membrane. Methanol crossover is closely related to several factors including membrane structure and morphology, membrane thickness, and fuel cell operating conditions such as temperature, pressure, and methanol feed concentration. This work presents a comprehensive overview of the state‐of‐the‐art technology for the most important factors, affecting methanol crossover in direct methanol fuel cells. In addition, the current and future directions of the research and development activities, aiming to reduce the methanol crossover are reviewed and discussed in order to improve the performance of direct methanol fuel cells. Copyright © 2011 John Wiley & Sons, Ltd.     

Allotrope carbon materials in thermal interface materials and fuel cell applications: A review

The performance of allotrope carbon materials has been explored because of their superior properties in energy system applications. This review provides an understanding of the current work focusing on the applications of selected carbon materials in important energy systems, focus on thermal interface materials (TIMs), and fuel cell applications. This article begins with the introduction of TIMs and fuel cell in general working principle and presents details on carbon materials. The discussion focuses on updates from the latest research work and addresses current challenges and opportunities for research toward TIMs and fuel cell applications. The optimum performance of TIMs was seen when thermal conductivity achieved at a maximum of 3000 W (m K)⁻¹ by using vertically aligned carbon nanotubes (CNTs) and a minimum internal thermal resistance of 0.3 mm² K W⁻¹. Meanwhile for fuel cell, the platinum/CNTs catalyst applied proton exchange membrane fuel cell achieved high power density of 661 mW cm⁻² in the presence of Nafion electrolyte membrane. This review provides insights for scientists about the use of carbon materials, especially in energy system applications.     

Detailed analysis of polymer electrolyte membrane fuel cell with enhanced cross‐flow split serpentine flow field design

Most generally used flow channel designs in polymer electrolyte membrane fuel cells (PEMFCs) are serpentine flow designs as single channels or as multiple channels due to their advantages over parallel flow field designs. But these flow fields have inherent problems of high pressure drop, improper reactant distribution, and poor water management, especially near the U‐bends. The problem of inadequate water evacuation and improper reactant distribution become more severe and these designs become worse at higher current loads (low voltages). In the current work, a detailed performance study of enhanced cross‐flow split serpentine flow field (ECSSFF) design for PEMFC has been conducted using a three‐dimensional (3‐D) multiphase computational fluid dynamic (CFD) model. ECSSFF design is used for cathode part of the cell and parallel flow field on anode part of the cell. The performance of PEMFC with ECSSFF has been compared with the performance of triple serpentine flow design on cathode side by keeping all other parameters and anode side flow field design similar. The performance is evaluated in terms of their polarization curves. A parametric study is carried out by varying operating conditions, viz, cell temperature and inlet humidity on air and fuel side. The ECSSFF has shown superior performance over the triple serpentine design under all these conditions.     

The optimization performance of cross‐linked sodium alginate polymer electrolyte bio‐membranes in passive direct methanol/ethanol fuel cells

Consumption of methanol and ethanol as a fuel in the passive direct fuel cells technologies is suitable and more useful for the portable application compared with hydrogen as a preliminary fuel due to the ease of management, including design of cell, transportation, and storage. However, the cost production of commercial membrane is still far from the acceptable commercialization stage. Based to our previous works, the low cost of cross‐linked sodium alginate (SA) polymer electrolyte bio‐membrane shown the virtuous chemical, mechanical, and thermal characterization as polymer electrolyte membrane in the direct methanol fuel cells (DMFCs). This study will further the investigation of cross‐linked SA polymer electrolyte bio‐membrane performance in the passive DMFCs and the passive direct ethanol fuel cells (DEFCs). The experimental study investigates the influence of the membrane thickness, loading of catalysts, temperature, type of fuel, and fuel concentration in order to achieve the optimal working operation performances. The passive DMFCs is improved from 1.45 up to 13.5 mW cm^?2 for the maximum peak of power density, which is obtained by using 0.16 mm as an optimum thick of SA bio‐membrane that shown the highest selectivity 6.31 10⁴ S s cm^?3, 4 mg cm^?2 of Pt‐Ru as an optimum of anode catalyst loading, 2 mg cm^?2 of Pt at the cathode, 2M of methanol as an optimum fuel concentration, and an optimum temperature at 90°C. Under the same conditions of cells, the passive DEFCs are shown to be 10.2 mW cm^?2 in the maximum peak of power density with 2M ethanol. Based on our knowledge, this is the first work that reports the optimization works of performance SA‐based membrane in the passive DMFCs via experimental studies of single cells and the primary performance of passive DEFCs using the SA‐based membrane as polymer electrolyte membrane.     

Quaternized poly(vinyl alcohol)/alumina composite polymer membranes for alkaline direct methanol fuel cells

The quaternized poly(vinyl alcohol)/alumina (designated as QPVA/Al₂O₃) nanocomposite polymer membrane was prepared by a solution casting method. The characteristic properties of the QPVA/Al₂O₃ nanocomposite polymer membranes were investigated using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), micro-Raman spectroscopy, and AC impedance method. Alkaline direct methanol fuel cell (ADMFC) comprised of the QPVA/Al₂O₃ nanocomposite polymer membrane were assembled and examined. Experimental results indicate that the DMFC employing a cheap non-perfluorinated (QPVA/Al₂O₃) nanocomposite polymer membrane shows excellent electrochemical performances. The peak power densities of the DMFC with 4 M KOH + 1 M CH₃OH, 2 M CH₃OH, and 4 M CH₃OH solutions are 28.33, 32.40, and 36.15 mW cm⁻², respectively, at room temperature and in ambient air. The QPVA/Al₂O₃ nanocomposite polymer membranes constitute a viable candidate for applications on alkaline DMFC.     

Enhanced transport properties of graphene‐based,thin Nafion® membrane for polymer electrolyte membrane fuel cells

A polymer electrolyte membrane fuel cell (PEMFC) is one of the promising renewable energy conversion systems; however, its performance is considerably limited by the sluggish transport properties and/or reaction kinetics of the catalyst layers, especially at a high current density. In this study, graphene‐based, thin Nafion® membranes are prepared using 0 to 4 wt% of graphene nanoflakes, and the effects of the graphene are examined for enhanced transport properties. The electrical conductivity and dielectric constant are drastically enhanced to 0.4 mS/cm and 26 at 4 wt% of graphene nanoflakes, respectively, while the thermal conductivity linearly increases to 3 W/m‐K. The proton conductivity also significantly increases with the aid of graphene nanoflakes at >2 wt% of graphene nanoflakes, and the enhancement doubles compared with those of the carbon‐black (CB)‐based and carbon nanotube (CNT)‐based, thin Nafion® membranes, perhaps due to unique graphene structures. Additionally, the quasi‐steady‐state water contact angle increases from 113° to ~130° with the addition of graphene nanoflakes, showing that a hydrophobic‐like water wetting change may be related to the significant proton conductivity enhancement. This work provides an optimal material design guideline for the transport‐enhanced cathode catalyst layer using graphene‐based materials for polymer electrolyte membrane fuel cell applications.