High performance polymeric bipolar plate based on polypropylene/graphite/graphene/nano-carbon black composites for PEM fuel cells

In the present study, the effect of the addition of electrically conductive additives such as graphite, graphene, and high structure nano-carbon black on the manufacturing of polypropylene bipolar plates was studied. Furthermore, for achieving better dispersion of graphene in the matrix, maleic anhydride grafted polypropylene, as a compatibilizer, was utilized. An internal mixing device was used in order to mix additives with polypropylene matrix. Additionally, molding procedure was performed via the compression molding method. In-plane electrical conductivity as well as the flexural strength of various compositions were studied. The best composition of such composites possessed the electrical conductivity of 104.63 S/cm and flexural strength of 44.28 MPa. These values are higher than those designated by the United States Department of Energy for construction of bipolar plates.     

Highly conductive epoxy/graphite composites for bipolar plates in proton exchange membrane fuel cells

Carbon-filled epoxy composites are developed for potential application as bipolar plates in proton exchange membrane (PEM) fuel cells. These composites are prepared by solution intercalation mixing, followed by compression molding and curing. Electrical conductivity, thermal and mechanical properties, and hygrothermal characteristics are determined as function of carbon-filler content. Expanded graphite and carbon black are used as synergistic combination to obtain desired in-plane and through-plane conductivities. These composites show high glass transition temperatures (T_g ∼ 180 °C), high thermal degradation temperatures (T₂ ∼ 415 °C), in-plane conductivity of 200–500 S cm⁻¹ with 50 wt% carbon fillers, in addition to offering high values of flexural modulus, flexural strength, and impact strength, respectively 2 × 10⁴ MPa, 72 MPa, and 173 J m⁻¹. The presence of carbon fillers helps reduce water uptake from 4 to 5 wt% for unfilled epoxy resins to 1–2 wt%. In addition, morphology, electrical, mechanical, and thermal properties remain unchanged on exposure to boiling water and acid reflux. This data indicate that the composites developed in this work meet many attributes of bipolar plates for use in PEM fuel cells.     

Study on carbon nanotube reinforced phenol formaldehyde resin/graphite composite for bipolar plate

Using carbon nanotubes (CNTs) after different Fenton treatments as a reinforcement and a phenol formaldehyde resin/graphite (PF/G) composite as matrix, a new composite for bipolar plate was formed by hot-pressing. The effects of Fenton, Fenton/ultrasonic and Fenton/ultraviolet treatments on the surface of the CNTs, and the bend strength and conductivity of bipolar plate composite produced using them were investigated. It was found that Fenton/UV treatment was an effective and advanced oxidation process, which could generate a large quantity of hydroxyl groups and few carboxyl groups on the sidewalls of the CNTs, but without severe damage. The functional groups on CNTs after Fenton/ultraviolet treatment can improve the interfacial adhesion between CNTs and matrix, which can improve the bend strength, but does not play an important role in the improvement of the conductivity. The bend strength and conductivity of the composite with 3% CNTs after Fenton/ultraviolet treatment are 68.6 MPa and 145.2 s cm⁻¹, respectively, when pressed at 240 °C for 60 min.     

High performance polyvinylidene fluoride/graphite/multi-walled carbon nanotubes composite bipolar plate for PEMFC with segregated conductive networks

Composite bipolar plates (BPs) are preferred to graphite BPs and metal BPs, in proton exchange membrane fuel cells (PEMFC), due to their pronounced advantages. However, facile and high-efficiency fabrication of high performance composite BPs, remains a challenge. In this study, high performance polyvinylidene fluoride (PVDF)/graphite/multi-walled carbon nanotubes (MWCNTs) composite BPs with segregated conductive network are prepared by structural design and compression molding. Due to the “brick-mud” structure formed in composite BPs by structural manipulation, its conductivity of low filler content is greatly improved. In addition, segregated synergistic conductive networks are observed in composite BPs after adding MWCNTs. The composite BP (5 wt% MWCNTs and 35 wt% graphite) exhibited electrical conductivity of 161.57 S/cm and area specific resistances of 7.5 mΩ cm². Moreover, the composite BPs have good flexural strength, excellent hydrophobicity and corrosion resistance. In summary, our work provides a simple and feasible strategy for manufacturing high performance composite BPs with low fillers.     

Aluminate cement/graphite conductive composite bipolar plate for proton exchange membrane fuel cells

Aluminate cement/graphite conductive composite bipolar plate for proton exchange membrane fuel cells (PEMFC) was prepared by mold pressing at room temperature. The effect of size of graphite particles on the conductivity and the flexural strength of composite bipolar plate were discussed. Resistance to acid corrosion, thermal property and pore size distribution of this composite bipolar plate were also investigated in this paper. The experiment results show that the conductivity and the flexural strength of this composite bipolar plate can be improved by choosing uniform size graphite as conductive fillers. The corrosion current is about 10^−4.5 A cm⁻² from polarization curves of this composite bipolar plate, which shows that this composite bipolar plate is acid corrosion-resistant. Al and Ca ions may leach from this composite bipolar plate after 1 M H₂SO₄ acid corrosion. But Al and Ca ions leaching from this composite bipolar plate are only a little percentage of the total Al and Ca ions content in the composite bipolar plate after acid corrosion at 30 °C. This composite bipolar plate is also thermally stable from room temperature to 400 °C. The large amount of pore in this composite bipolar plate is gel capillary pores because of the hydration and solidification of aluminate cement, which make it possess humidifying function during the PEMFC operating.     

Study on the preparation and properties of novolac epoxy/graphite composite bipolar plate for PEMFC

In this study, the graphite/polymer composite bipolar plate was manufactured by a bulk-molding compound process. Low-cost novolac epoxy was chosen to compound with natural graphite and black carbon. The electrical properties and mechanical properties of composite bipolar plate were studied. The aging behavior was characterized according to the changes in property before and after the immersion test. The results show that the composite bipolar plates have good corrosion resistibility in the simulated solution of 0.005 mol L⁻¹ H₂SO₄ + 2 × 10⁻⁶ mol L⁻¹ HF. TGA result shows that the novolac epoxy/NG composite has excellent thermal stability. The optimum processing conditions for preparing composite bipolar plate are: resin content about 15 wt.%; molding pressure 200 MPa; curing temperature 180 °C; graphite particle size −200 mesh. Under the optimum conditions, the composite bipolar plates have been produced, the electrical conductivity can attain to 120 S/cm and flexural strength is higher than 38 MPa.     

Study on the electrical and mechanical properties of phenol formaldehyde resin/graphite composite for bipolar plate

With phenol formaldehyde resin (PF) powder and graphite powder as raw materials, a kind of conductive composite for bipolar plate is obtained by hot-pressure molding. The effects of PF resin content, molding temperature and time on conductivity and bending strength of the composite were investigated in this paper; and the optimum PF resin content, molding temperature and time were obtained. The results show that: the conductivity decreases and bending strength increases with the increasing of PF resin content; the conductivity varies wave-like and bending strength increases firstly and then decreases with the increasing of molding temperature; the effects of molding time on properties of the composite are similar to that of molding temperature; and the best conductivity and bending strength of the composite are 142 s cm⁻¹ and 61.6 MPa, respectively, when its PF resin content is 15% molded at 240 °C for 60 min.     

High-temperature,polymer–graphite hybrid composites for bipolar plates: Effect of processing conditions on electrical properties

High-temperature thermoplastic–graphite composites are prepared using polyphenylene sulfide (PPS) and polyether sulfone (PES) containing natural graphite powder. All samples are prepared by high pressure compaction and heating to high temperatures. The effect of a third additional conducting component on the electrical resistance of these composites is studied. A low resistance of the order of 0.1 Ω can be obtained even for a graphite concentration of 50% by addition of the third component. The effect of a mixing/blending technique on the anisotropy of conductivity is investigated. Solution blending of PES with graphite leads to lower anisotropy values than powder mixing and compression moulding. The samples when exposed continuously to a working temperature of 100 °C give a small but significant reduction in electrical resistance. X-ray diffraction studies on composites prepared by different techniques indicate that there is restructuring and crystallite re-orientation of the graphite phase in the samples. A large reduction in the crystallite size is observed for samples prepared by solution blending while re-orientation occurs after heat treatment. The changes in electrical properties can be correlated with these structural transformations in the composites.     

Effects of resin content and preparing conditions on the properties of polyphenylene sulfide resin/graphite composite for bipolar plate

In the paper, a kind of polyphenylene sulfide (PPS) resin/graphite (G) composite for bipolar plate was prepared by using the PPS resin as adhesive and simple hot pressing. The influences of the resin content, the molding temperature and holding time on the conductivity and the bending strength of the PPS/G composite bipolar plate were investigated firstly and then the optimum content and the preparing conditions of the composite were obtained. The experimental results show that the electrical conductivity decreases and the bending strength reveals a serrated variation with increase in PPS resin content; when the holding time is certain, the conductivity decreases and the bending strength increases with the molding temperature increasing. The experimental results further show that the effect of the holding time on the properties of the composite is different at different molding temperatures. The PPS/G composite with 20% PPS resin content has electrical conductivity of 118.9 S cm⁻¹ and bending strength of 52.4 MPa when it molded at 380 °C for 30 min, and has electrical conductivity of 105 S cm⁻¹, bending strength of 55.7 MPa when it molded at 390 °C for 30 min. The properties of the composites can meet the requirements of United States Department of Energy (DOE).     

Hygrothermal effects on properties of highly conductive epoxy/graphite composites for applications as bipolar plates

The hygrothermal effects on mechanical, thermal, and electrical properties of highly conductive graphite-based epoxy composites were investigated. The highly conductive graphite-based epoxy composites were found to be suitable for applications as bipolar plates in proton exchange membrane (PEM) fuel cells. The hygrothermal aging experiments were designed to simulate the service conditions in PEM fuel cells. Specifically, the composite specimens were immersed in boiling water, aqueous sulphuric acid solution, and aqueous solution of hydrogen peroxide. The water uptake, changes in surface appearance and dimensions, glass transition behavior and thermal stability, and electrical and mechanical properties were evaluated. The water uptake at short time increased linearly with the square root of time as in linear Fickian diffusion. The presence of graphite significantly reduced both the rate and extent of water uptake. No discernible changes in specimen dimensions, surface appearance, and morphology of the composites were observed. The electrical conductivity and mechanical properties remained almost unchanged. The wet specimens showed slight reduction of glass transition temperature (T_g) due to plasticization of epoxy networks by absorbed water, while the re-dried specimens showed small increase of T_g. The composites maintained high electrical conductivity of about 300–500 S cm⁻¹ and good mechanical properties and showed thermal stability up to 350 °C.     

Preparation and properties of carbon nanotube/polypropylene nanocomposite bipolar plates for polymer electrolyte membrane fuel cells

This study aims at the fabrication of lightweight and high performance nanocomposite bipolar plates for the application in polymer electrode membrane fuel cells (PEMFCs). The thin nanocomposite bipolar plates (the thickness <1.2 mm) consisting of multiwalled carbon nanotubes (MWCNTs), graphite powder and PP were fabricated by means of compression molding. Three types of polypropylene (PP) with different crystallinities including high crystallinity PP (HC-PP), medium crystallinity PP (MC-PP), low crystallinity PP (LC-PP) were prepared to investigate the influence of crystallinity on the dispersion of MWCNTs in PP matrix. The optimum composition of original composite bipolar plates was determined at 80 wt.% graphite content and 20 wt.% PP content based on the measurements of electrical and mechanical properties with various graphite contents. Results also indicate that MWCNTs was dispersed better in LC-PP than other PP owing to enough dispersed regions in nanocomposite bipolar plates. This good MWCNT dispersion of LC-PP would cause better bulk electrical conductivity, mechanical properties and thermal stability of MWCNTs/PP nanocomposite bipolar plates. In the MWCNTs/LC-PP system, the bulk electrical conductivities with various MWCNT contents all exceed 100 S cm⁻¹. The flexural strength of the MWCNTs/LC-PP nanocomposite bipolar plate with 8 phr of MWCNTs was approximately 37% higher than that of the original nanocomposite bipolar plate and the unnotched Izod impact strength of MWCNTs/LC-PP nanocomposite bipolar plates was also increased from 68.32 J m⁻¹ (0 phr) to 81.40 J m⁻¹ (8 phr), increasing 19%. In addition, the coefficient of thermal expansion of MWCNTs/LC-PP nanocomposite bipolar plate was decreased from 32.91 μm m⁻¹ °C⁻¹ (0 phr) to 25.79 μm m⁻¹ °C⁻¹ (8 phr) with the increasing of MWCNT content. The polarization curve of MWCNTs/LC-PP nanocomposite bipolar plate compared with graphite bipolar plate was also evaluated. These results confirm that the addition of MWCNTs in LC-PP leads to a significant improvement on the cell performance of the nanocomposite bipolar plate.     

Electrodeposition of graphene nano-thick coating for highly enhanced performance of titanium bipolar plates in fuel cells

We report in this paper a simple method of coating very thin graphene film on titanium substrate, affording it markedly enhanced resistance to corrosion and much decreased electrical contact resistance under the environment of proton exchange membrane fuel cells (PEMFC). The graphene film is formed by electrodepositing graphene oxide (GO) on Ti sheet via normal pulse voltammetry, followed by reducing the deposited GO at 500 °C in hydrogen atmosphere. The resultant graphene film, with a thickness of only around 50 nm, evenly covers and covalently bonds to the Ti sheet, as revealed by SEM, Raman and XPS. Both potentiodynamic and potentiostatic tests of the graphene coated Ti (G/Ti) sample are conducted under simulated chemical environment and electrode potentials of PEMFC. Under all the circumstances, the corrosion currents of G/Ti sheet are in the order of 10⁻⁷ A/cm², significantly less than that of bare Ti sheet. Moreover, the coated graphene film on Ti sheet leads to a much lower and more stable interfacial contact resistance (ICR) of around 4 mΩ cm². These results mean that the G/Ti sheet meets the U.S. DOE target of 2020 for PEMFC bipolar plates (BP) in terms of both the corrosion and electrical resistance. Therefore, the G/Ti sheet appears to be a very promising BP material in PEMFC.     

Self-assembled graphene film to enable highly conductive and corrosion resistant aluminum bipolar plates in fuel cells

We report in this paper a novel method to form protective graphene film on aluminum substrate, which is particularly applicable to bipolar plates in proton exchange membrane (PEM) fuel cells. By simply immersing an aluminum sheet in an aqueous solution of graphene oxide (GO), a layer of cross-linked GO gel forms on the aluminum sheet, taking advantage of dissociated aluminum ions as a cross-linker. Then the cross-linked GO is converted to graphene at 400 °C in hydrogen atmosphere. The chemistry of the self-assembled GO layer and its conversion to graphene film is revealed by FTIR and XPS. Under simulated fuel cell environment the graphene coated aluminum sheet shows a corrosion current density of <1 × 10^?6 A/cm², which is around four orders of magnitude lower than a bare aluminum sheet. Meanwhile, the graphene film on aluminum results in a much lower and more stable interfacial contact resistance (ICR) of <5 mΩ cm². These enable the graphene coated aluminum sheet to meet the U.S. DOE targets of 2020 for bipolar plates in terms of both the corrosion and electrical resistance. Thus the proposed method is very promising for protecting aluminum bipolar plates in PEM fuel cells.     

Development of bipolar plates for fuel cells from graphite filled wet-lay material and a thermoplastic laminate skin layer

In this paper, a method with the potential to rapidly produce thermoplastic polymer composite bipolar plates with improved formability and through-plane conductivity is described. In our earlier work, it was reported that composite bipolar plates made with graphite filled wet-lay materials exhibited excellent mechanical properties and in-plane electrical conductivity. However, the through-plane conductivity and formability of the materials needed improvement. In this work, laminate polymer composite plates consisting of a wet-lay based core and a fluoropolymer/graphite skin layer are manufactured in an effort to improve formability and through-plane conductivity. These plates are characterized by their through-plane and in-plane conductivity, half-cell resistance, and mechanical properties at ambient and elevated temperatures. The laminate plates with PPS based wet-lay core exhibited bulk conductivities of above 300 S cm⁻¹, tensile strength of up to 34 MPa, and flexural strength of up to 54 MPa. Compared to the bipolar plates consisting of wet-lay material only, the bipolar plates with laminate structure exhibited an increase in through-plane conductivity of 25–35%, as well as a decrease in half-cell resistance by a factor of up to 5. The laminate bipolar plates can be manufactured in several ways with two of them being discussed in detail in the paper.     

Development of bipolar plates for fuel cells from graphite filled wet-lay material and a compatible thermoplastic laminate skin layer

In this paper a method with the potential to lead to the rapid production of thermoplastic polymer composite bipolar plates with improved mechanical properties, formability, and half-cell resistance is described. In our previous work it was reported that laminate structure composite bipolar plates made with a polyphenylene sulfide (PPS) based wet-lay material as the core and a polyvinylidene fluoride (PVDF)/graphite mixture as the laminate exhibited improved formability, through-plane conductivity, and half-cell resistance over that of wet-lay based bipolar plates. However, the mechanical strength of the laminate plates needed improvement. In this work laminate polymer composite plates consisting of a PPS/graphite-based laminate mixture and a PPS based wet-lay core are manufactured in an effort to improve mechanical strength. Additionally, our existing channel design has been altered to reduce the channel depth from 0.8 to 0.5 mm in an effort to improve the half-cell resistance by reducing the total plate thickness. The plates are characterized by their half-cell resistance and mechanical properties at ambient and elevated temperatures. The PPS based laminate plates exhibited half-cell resistances as low as 0.018 Ω cm², tensile strength of up to 37 MPa, and flexural strength of up to 60 MPa at ambient temperature. The laminate bipolar plates can be manufactured in several ways with two of them being discussed in detail in the paper.     

Electrical properties of carbon-based polypropylene composites for bipolar plates in polymer electrolyte membrane fuel cell (PEMFC)

An investigation is made of the electrical properties of polypropylene/graphite (PP/G) composites as prospective replacements for the traditional graphite bipolar plate in proton-exchange membrane fuel cells. The composites have relatively low electrical conductivities, i.e., up to 28 S cm⁻¹ at 90 wt.% G. Combination of G with carbon black (CB) is an effective way to develop higher conductivity composites. The conductivity reaches 35 S cm⁻¹ by combination of 25 wt.% CB and 55 wt.% G to 20 wt.% PP. This is five times the value at 80 wt.% G and 20 wt.% PP (7 S cm⁻¹). Two methods are mainly adopted for the preparation of composites, namely, melt compounding and solution blending. Solution blending of PP with conductive fillers followed by moulding of the dried powder leads to higher conductivities compared with those of melt-compounded composites. The combination of conjugated conducting polymers such as polyaniline (PANi) with the PP, G, and CB is also investigated. It is found that composites containing PANi have lower conductivities than those of the neat composites. This decrease in conductivity is attributed to the poor thermal stability of PANi.     

Development of ultralight and thin bipolar plates using epoxy-carbon fiber prepregs and graphite composites

Using the excellent mechanical strength and in-plane electrical conductivity of epoxy-carbon fiber prepregs, we design and fabricate ultrathin composite bipolar plates (BPs) for fuel cells. For the successful fabrication of prepreg-based BPs, it is essential to increase the through-plane electrical conductivity of pristine prepregs and reduce the electrical contact resistance due to excessive surface resin extruded during compression molding. In addition, the moldability of prepreg layers should be greatly improved for the proper construction of a serpentine flow field on the prepreg surface. To resolve all these technical issues, we suggest a multilayer BP structure in which prepreg layers, pure graphite layers, and graphite-resin composite layers are combined and compression-molded. The multilayered prepreg BP is approximately 0.6 mm thick and exhibits good electrical behavior (in-plane conductivity of 172 S cm^?1 and through-plane conductivity of 38 S cm^?1), with a high-quality serpentine flow channel configuration. The test results clearly demonstrate that the low through-plane electrical conductivity and poor moldability of pristine prepregs are greatly improved by our proposed BP design and fabrication.     

Hydrogen storage performance in palladium-doped graphene/carbon composites

In this study a two-dimensional graphene sheet (GS) doped with palladium (Pd) nanoparticles was physically mixed with a superactivated carbon (AC) receptor and used as a hydrogen adsorbent. The hydrogen adsorption/desorption isotherm of the Pd-doped GS catalyst/AC composite (Pd-GS/AC) is determined using a static volumetric measurement at room temperature (RT) and pressure up to 8 MPa. The experiments show that the H₂ uptake capacity of 0.82wt.% for Pd-GS/AC is obviously enhanced, measuring 49% more than the 0.55wt.% for Pd-free GS/AC at RT and 8 MPa. Highly reversible behavior of Pd-GS/AC is also observed. Moreover, the isosteric heat of adsorption for Pd-GS/AC (−14 to −10 kJ/mol) is higher than that for pristine AC (−8 kJ/mol). An increase in H₂ uptake in the Pd-GS/AC suggests the occurrence of a relatively strong interaction between the spilt-over H and the receptor sites due to the spillover effect.     

A single-type aluminum/composite hybrid bipolar plate with surface modification for high efficiency PEMFC

An aluminum/composite hybrid bipolar plate with a bypass aluminum channel has been developed. The mechanical abrading technique and electromagnetic-carbon technique are employed for surface modification of aluminum and composite, respectively. The optimum processes of surface modification techniques for aluminum and composite are investigated to promote intimate contact between aluminum and carbon fibers of composite for low electrical resistance. After the surfaces of the aluminum and carbon fiber prepregs are treated with the surface modification techniques, they are co-cured with the single-type of bipolar plate to lower the electrical contact resistance. In this study, it has been found that the hybrid bipolar plate has only 3% of the electrical resistance of the conventional composite bipolar plates.     

Coating of stainless steel and titanium bipolar plates for anticorrosion in PEMFC: A review

Anticorrosion coating for stainless steel (SS) and titanium bipolar plates were evaluated to improve the corrosion resistance and electrical conductivity in PEMFC. The PEMFC offers clean and environmentally friendly usage in electrical power systems. The bipolar plates contribute 60%–80% of the total components of PEMFC stack with electrical conductivity >100 S cm^?1. Therefore, high conductivity and corrosion resistance are observed for long-term operations in PEMFC. Recent works has developed the cost-effective and feasible alternative materials to replace graphite bipolar plates. Metallic materials, such as SS and titanium, possess good electrical conductivity but poor corrosion resistance. Coating of SS and titanium bipolar plates can improve the corrosion resistance of metallic bipolar plates. Excellent performance of bipolar plates was recorded by using NbC coating for stainless steel materials. The ICR value using plasma surface alloying method was 8.47 mΩ cm² with a low current density (I_corr) between 0.051 and 0.058 μA cm^?2. The criteria for both current densities (<1 μA cm^?2) and electrical conductivity (<10 mΩ cm²) met the DOE's 2020 technical targets. In addition, conventional air brush method can be used for fabricating multilayer coatings onto substrates because it is self-cleaning, low cost and offers high volume and large area production. Vapor deposition method, a highly advanced coating technology using PVD, suitable for coating bipolar plates because it is environmentally friendly and can be used in high temperatures, producing materials with good impact strength and excellent abrasion resistance. PEMFC cost is still too high for large scale commercialization, which is the cost of raw material and processing to allow fabrication of thinner plates contributes substantially to the total PEMFC cost. Some future works on fuel cell anticorrosion research with reasonable coating method is suggested to reduce the cost in order to facilitate the move toward commercialization especially for SS and titanium bipolar plates.