Through-plane Electrical Conductivity Research Articles

Boosting through-plane electrical conductivity: chitosan composite films with carbon-sepiolite and multiwalled carbon nanotubes

Flexible and electrically conductive materials are gaining significant attention across various domains, notably in electronics, biomedicine and food industry. One promising strategy involves the integration of electrically conductive nanostructures into a polymeric matrix to fabricate composite materials. However, achieving uniform through-plane electrical conductivity remains a challenge due to the preferential alignment of carbon nanostructures in the in-plane direction. Herein, we report the development of electrically conductive chitosan (CS)-based biocomposite films incorporating a multicomponent filler system. By combining carbon supported on sepiolite clay (CARSEP) with multiwalled carbon nanotubes (MWCNT), it is aimed to facilitate an interconnected distribution in both in-plane and through-plane directions. The optimized film, featuring a CS/CARSEP/MWCNT mass ratio of 50/40/10, exhibited a maximum electrical conductivity of 55.5 S/m and 0.1 S/m in the in-plane and through-plane directions, respectively. Additionally, migration studies demonstrated the absence of harmful compounds upon heating the film up to 60 °C in air, ethanol, or hexane. These findings highlight the potential of these flexible and electrically conductive biocomposite films, primarily composed of biobased materials, for applications requiring through-plane electrical conductivity.

High corrosion resistance and through-plane electrical conductivity of C/Ti and C/Cr coated metal bipolar plates used in PEMFC

To improve the corrosion resistance and enhance the electrical conductivity in a simulated proton exchange membrane fuel cell, carbon bound SS316L stainless steel plates were modified with titanium (Ti) or chromium (Cr). The SS316L interfacial contact resistance of 312.38 mΩ·cm2 was reduced to 1.59 mΩ·cm2 when modified with Ti and to 1.32 mΩ·cm2 when modified with Cr. The increase in potential enhanced the shedding of C films and the oxidation and dissolution of Ti and Cr buffer layers. The corrosion current density in the C/Ti coating was lower than C/Cr coating under high voltage polarization. The oxidation of Ti and Cr buffer layers led to poor appetency between the C film and the SS316L and to degradation of the through-plane electrical conductivities in the C/Ti and C/Cr coated metal bipolar plates.

Optimization of Filler Compositions of Electrically Conductive Polypropylene Composites for the Manufacturing of Bipolar Plates.

In this research, polypropylene (PP)-graphite composites were prepared using the melt mixing technique in a twin-screw extruder. Graphite, multi-walled carbon nanotubes (MWCNT), carbon black (CB), and expanded graphite (EG) were added to the PP in binary, ternary, and quaternary formations. The graphite was used as a primary filler, and MWCNT, CB, and EG were added to the PP-graphite composites as secondary fillers at different compositions. The secondary filler compositions were considered the control input factors of the optimization study. A full factorial design of the L-27 Orthogonal Array (OA) was used as a Design of Experiment (DOE). The through-plane electrical conductivity and flexural strength were considered the output responses. The experimental data were interpreted via Analysis of Variance (ANOVA) to evaluate the significance of each secondary filler. Furthermore, statistical modeling was performed using response surface methodology (RSM) to predict the properties of the composites as a function of filler composition. The empirical model for the filler formulation demonstrated an average accuracy of 83.9% and 93.4% for predicting the values of electrical conductivity and flexural strength, respectively. This comprehensive experimental study offers potential guidelines for producing electrically conductive thermoplastic composites for the manufacturing of bipolar fuel cell plates.

Scalable production of polyamide-6/graphene composites with enhanced electromagnetic shielding and thermal conductivity

Composites with thermal management (TM) capability and electromagnetic interference (EMI) shielding effect are in high demand for miniaturization and modernization of electronics. However, achieving both of these properties simultaneously by constructing a dense conductive network within the polymer matrix is a very big challenge. Herein, a fully scalable and sustainable production process for polyamide-6/few layer graphene (PA-6/FLG) with vigorous dispersion of FLG in the PA-6 matrix was demonstrated by combining mechanochemistry with supercritical CO2 (scCO2) technology. By this process, the bulk graphite was rapidly cleaved into a FLG (≈10 layers), which was completely coated onto the spherical PA-6 particles. The composite films of this coated powder with only 3 wt% FLG loading amount attained wonderful in-plane electrical conductivity (IP-σc) and through-plane electrical conductivity (TP-σc) of 4.59 S·m−1 and 29.59 S·m−1, respectively, and outstanding EMI shielding effect of 41.8 dBs. In addition, the in-plane thermal conductivity (IP- kc) and the through-plane thermal conductivity (TP- kc) were 1.78 W m−1 K−1 and 2.14 W m−1 K−1 respectively. Therefore, the films rapidly dissipate heat from an electronic LED chip. Moreover, PA-6/FLG composite filaments showed a smooth appearance and an electrical resistivity of 7.12 GΩ. This work has strong potential to improve the performance of different polymer/graphene composites and expand their applications.

Pressure-independent through-plane electrical conductivity measurements of highly filled conductive polymer composites

Highly filled conductive polymer composites (CPCs) are widely used in applications such as bipolar plate materials for polymer electrolyte membrane fuel cells and redox flow batteries, electromagnetic interference shielding and sensors due to their useful electrical properties. A common method for determining through-plane electrical conductivities $\left(\sigma_{\rm tp} \right)$ of such highly filled CPCs applies a conductive carbon paper between electrodes and sample with application of external pressure to improve electrical contact. We show the pressure-dependence of the measured $\sigma_{\rm tp}$ can be eliminated by using a liquid metal such as the gallium-indium eutectic alloy (EGaIn) as contact material. Results indicate that EGaIn reduces contact resistances and cause three to five times larger $\sigma_{\rm tp}$ compared to measurements with carbon paper contacts and pressures up to 20 bar.

Development of Corrosion Resistant and Electrically Conductive Coatings on Metallic Bipolar Plates for Applications in PEMFC

Proton exchange membrane fuel cell (PEMFC) is considered as one of the most promising alternative energy devices due to its high efficiency, low pollutants emission and possible application in automobiles. However, the application of PEMFC is still hindered by the high cost of some of its components such as bipolar plates (BPP) which are a key component in PEMFC to facilitate electron transfer, gas flow, heat and water removal. To reduce the cost, increase conductivity and durability, metallic bipolar plates, typically made of stainless steel, are normally used but they could suffer from severe corrosion in the acidic environment of PEMFC; the formation of corrosion products on the metal surface could reduce the through-plane electrical conductivity and increase the interfacial contact resistance (ICR) between the bipolar plates and gas diffusion layer, eventually causing high power loss in the fuel cell stack. Therefore, developing corrosion resistant and electrically conductive bipolar plates is of vital importance for the practical applications of PEMFC.Transition nitride coated stainless steel, such as titanium nitride (TiN) coated 316L SS, is considered as a possible solution to improve the performance metallic bipolar plates. In this work, TiN coated 316L SSs with heat treatment at different temperatures were prepared. The corrosion behaviours of the prepared samples were investigated in the simulated working environments of fuel cell. The heat treated samples exhibit the improved corrosion resistance compared with the pristine TiN coated samples and with an increase of the heat treatment temperature, the corrosion resistance tends to increase due to the formation of oxide and oxynitride on the sample surface. The ICR test results indicate that high temperature (450 ℃) heat treatment has detrimental effect on the electrical conductivity of samples due to the formation of a thick oxide dominated layer, while the samples heat treated at 300 ℃ only form the graded layers with suitable oxide amount which endows the coated specimens with a very low ICR value both before and after the corrosion tests.Moreover, TiN coatings with different amounts of Ta addition were also prepared. After the corrosion tests in the H2SO4 solution with pH=3 at 70 ℃, the results reveal that Ti150Ta30N samples exhibit the highest corrosion resistance compared with the pristine TiN coated samples and the samples with different amount of Ta addition. The steady state current density of Ti150Ta30N samples after long term potentiostatic polarization at 0.6 V (vs Ag/AgCl) is 0.02 μA/cm2 which is much lower than that of TiN coated samples. The Ti150Ta30N samples also presents a good electrical conductivity with low ICR values before and after the corrosion tests. These studies suggest that a suitable amount of oxygen or Ta incorporation into TiN is a feasible strategy to improve the corrosion resistance while maintaining considerable electrical conductivity of TiN samples.

The effects of GDL anisotropic transport properties on the PEFC performance

PurposeThis paper aims to numerically investigate the impact of gas diffusion layer (GDL) anisotropic transport properties on the overall and local performance of polymer electrolyte fuel cells (PEFCs).Design/methodology/approachA three-dimensional numerical model of a polymer electrolyte fuel cell with a single straight channel has been developed to investigate the sensitivity of the fuel cell performance to the GDL anisotropic transport properties – gas permeability, diffusivity, thermal conductivity and electrical conductivity. Realistic experimentally estimated GDL transport properties were incorporated into the developed PEFC model, and a parametric study was performed to show the effect of these properties on fuel cell performance and the distribution of the key variables of current density and oxygen concentration within the cathode GDL.FindingsThe results showed that the anisotropy of the GDL must be captured to avoid overestimation/underestimation of the performance of the modelled fuel cell. The results also showed that the fuel cell performance and the distributions of current density and oxygen mass fraction within the cathode GDL are highly sensitive to the through-plane electrical conductivity of the GDL and, to a lesser extent, the through-plane diffusivity, and the thermal conductivity of the GDL. The fuel cell performance is almost insensitive to the gas permeability of the GDL.Practical implicationsThis study improves the understanding of the importance of the GDL anisotropy in the modelling of fuel cells and provides useful insights on improving the efficiency of the fuel cells.Originality/valueRealistic experimentally estimated GDL transport properties have been incorporated into the PEFC model for the first time, allowing for more accurate prediction of the PEFC performance.

Processing Effects on the Through-Plane Electrical Conductivities and Tensile Strengths of Microcellular-Injection-Molded Polypropylene Composites with Carbon Fibers.

Polymers reinforced with conducting fibers to achieve electrical conductivity have attracted remarkable attention in several engineering applications, and injection molding provides a cost-effective way for mass production. However, the electrical performance usually varies with the molding conditions. Moreover, high added content of conducting fibers usually results in molding difficulties. In this study, we propose using microcellular (MuCell) injection molding for polypropylene (PP)/carbon fiber (CF, 20, and 30 wt%) composites and hope that the MuCell injection molding process can improve both electrical and mechanical performance as compared with conventional injection molded (CIM) parts under the same CF content. Both molding techniques were also employed with and without gas counter pressure (GCP), and the overall fiber orientation, through-plane electrical conductivity (TPEC), and tensile strength (TS) of the composites were characterized. Based on the various processing technologies, the results can be described in four aspects: (1) Compared with CIM, microcellular foaming significantly influenced the fiber orientation, and the TPECs of the samples with 20 and 30 wt% CF were 18–78 and 5–8 times higher than those of the corresponding samples molded by CIM, respectively; (2) when GCP was employed in the CIM process, the TPEC of the samples with 20 and 30 wt% CF increased by 3 and 2 times, respectively. Similar results were obtained in the case of microcellular injection molding—the TPEC of the 20 and 30 wt% composites increased by 7–74 and 18–32 times, respectively; (3) although microcellular injection molding alone (i.e., without GCP) showed the greatest influence on the randomness of the fiber orientation and the TPEC, the TS of the samples was the lowest due to the uncontrollable foaming cell size and cell size uniformity; (4) in contrast, when GCP was employed in the microcellular foaming process, high TS was obtained, and the TPEC was significantly enhanced. The high foaming quality owing to the GCP implementation improved the randomness of fiber orientation, as well as the electrical and mechanical properties of the composites. Generally speaking, microcellular injection combined with gas counter pressure does provide a promising way to achieve high electrical and mechanical performance for carbon-fiber-added polypropylene composites.

Solution acidity and temperature induced anodic dissolution and degradation of through-plane electrical conductivity of Au/TiN coated metal bipolar plates used in PEMFC

A novel composite coating of gold/titanium nitride on stainless steel (Au/TiN/SS) was developed by introducing Au dots onto a TiN coating to improve the corrosion resistance and electrical conductivity of stainless steel bipolar plates for the polymer electrolyte membrane fuel cell (PEMFC). The effects of temperature and pH on conductivity and corrosion resistance of the Au/TiN/SS in a simulated PEMFC environment were investigated. The results showed that the interfacial contact resistance of TiN coating reduced from 5.48 mΩ cm2 to 1.72 mΩ cm2 after introducing the Au dots, indicating that Au dots can enhance the interfacial conductivity of the composite coating on stainless steel. The increases of solution temperature and acidity enhanced the dissolution of TiN as well as the delamination of Au dots from the composite coating, and the corrosion current density (icorr) of Au/TiN coating increased in high temperature and strong acidic environments. The thin layer of TiNxOy and TiO2 around the Au dots was preferentially dissolved to detach the Au from the composite coating, therefore induced the degradation of through-plane electrical conductivity of the Au/TiN coated metal bipolar plates.

Preparation and characterization of carbon fiber reinforced plastics (CFRPs) incorporating through-plane-stitched carbon fibers

In this study, novel methods are proposed for manufacturing carbon fiber-reinforced plastics (CFRPs) to enhance their thermal and electrical conductivities and mechanical properties. Polyacrylonitrile (PAN)- and pitch-based carbon fibers were used as the stitching materials, to provide conductive paths through the CFRP body in the through-plane direction. The through-plane thermal and electrical conductivities of the stitched CFRPs were drastically enhanced by a maximum of 2.23 times, and 54.7 times compared to non-stitched CFRP, respectively. The mechanical properties of the stitched CFRPs were also investigated using dynamic mechanical analysis. The results indicate that the pitch-based carbon fibers enhanced the storage modulus of CFRPs, while CFRPs stitched using PAN-based carbon fibers showed decreased value. A thin metal coating was applied to both sides of the CFRPs, and the through-plane thermal conductivity of the silver-coated, stitched CFRPs was slightly enhanced (maximum of 9%), while the through-plane electrical conductivity of the CFRPs was dramatically enhanced (maximum of 498 times). The results indicate that a synergistic effect between the stitched carbon fibers and metal coating can improve the through-plane thermal and electrical conductivities of the CFRPs. This implies that CFRPs manufactured using these simple and effective strategies can be used in the space industry.

Microporous Graphite Composites of Tailorable Porosity, Surface Wettability, and Water Permeability for Fuel Cell Bipolar Plates

To address the water management problem in proton-exchange membrane fuel cells, porous graphite composites were prepared by incorporating sacrificial pore-forming agents in the blend of graphite and a phenolic resin formed into a flat plate using compression molding. Sucrose was found to be an effective porogen in the porous plate production process. The effects of relative amounts of graphite, polymer, and porogen in the composite were studied. Bipolar plate properties such as the water uptake by wicking and vacuum infusion, gas-breakthrough pressure across the water-infused pores, electrical conductivity, and flexural strength of the plates were measured and correlated with the plate composition. The plate porosity was evaluated by determining the masses of dry and water-infused plates in air and under water. The porosity, ε, showed a linear increase with an increase in the porogen concentration in the range of 0–10%. The permeabilities, K, of water through the graphite plates with different porosity values were calculated by measuring the water flux over a range of pressures. The water permeability increased with oxidation and hydrophilization of the pore surface. Dynamic water contact angle measurements were used to characterize the effect of chemical and thermal treatments on the water wettability of the plates. The gas-breakthrough pressure of the water-infused plates was found to be linearly correlated with the parameter, γcos⁡θ/K/ε, proportional to the capillary pressure of the gas–water interface of surface tension, γ, and contact angle, θ. Porous plates capable of a total water uptake greater than 25 wt %, with the gas-breakthrough pressure higher than 10 psi, through-plane electrical conductivity exceeding 100 S cm–1, and flexural strength exceeding 25 MPa were obtained.

Patternable cellulose/MWCNT laminated nanocomposites with anisotropic thermal and electrical conductivity

To construct eco-friendly materials with anisotropic thermal/electrical conductivity and designable structure and shape not only is the goal of electrical materials, but also meets the requirement of sustainable society. In this work, patternable and laminated cellulose/MWCNT nanocomposites with excellent anisotropic thermal and electrical conductivity are prepared by a scalable and eco-friendly process, including a paper-making step, assembly step and in-situ welding step. In the obtained nanocomposites, the cellulose layer acts as the insulator, and the cellulose/MWCNT layer as the electrical and thermal conductor with a special segregated MWCNT network. As a result, the in-plane and through-plane electrical conductivity of the cellulose/MWCNT nanocomposite with 22.7 wt% MWCNT are 1458 and 1.48 × 10-10 S/m, respectively, and the in-plane and through-plane thermal conductivity are 1.98 and 0.34 W·m-1·K-1, respectively. Moreover, the cellulose/MWCNT nanocomposites have high electromagnetic shielding effectiveness of 31.1 dB when the thickness is 0.9 mm, good tensile strength of 156 MPa, and high shape stability at 240 °C. More interestingly, the laminated cellulose/MWCNT materials with patterned shape and sophisticated conductive circuit can be easily fabricated to work as a special and custom-tailor electronic element, thermal management device and electric-heating anti-counterfeiting pattern. Such novel cellulose/MWCNT nanocomposites prepared by a simple, effective and scalable process exhibit a huge potential in environmentally-friendly electrical and thermal management device, electromagnetic shielding element and advanced electronic anti-counterfeiting tag.

Tuning of anisotropic electrical conductivity and enhancement of EMI shielding of polymer composite foam via CO2-assisted delamination and orientation of MXene

Integration of a foam structure into a shielding material not only reduces its mass density but also enhances its electromagnetic interference (EMI) shielding performance. In this study, poly(vinylidene fluoride) (PVDF) composite films and foams consisting of carbon nanotubes (CNTs) and bulk Ti3C2Tx MXenes were fabricated. Prominent anisotropy with high in-plane electrical conductivity (σ∥) and low through-plane electrical conductivity (σ⊥) was achieved (e.g., σ∥ = 17.02 S/m and σ⊥ = 0.42 S/m with 1 wt% MXenes) in the composite films due to the aligned structure of the MXenes in the PVDF matrix. With CO2-assisted foaming, the intercalation of PVDF chains and cell-induced biaxial stretch facilitated reorganized orientation and delamination of the MXenes. Consequently, σ∥ decreased and σ⊥ increased, and exhibiting an isotropic feature. Furthermore, the integration of the foam structure resulted in an increased σ⊥, which improved the EMI shielding effectiveness (EMI SE) to 65.1 dB at a MXene content of 12 wt%, owing to enhanced multi-reflections, dielectric loss and conduction loss. Moreover, the shielding effectiveness coming from reflection was reduced to lower than 3 dB due to the decrease in σ∥ and destructive interference in the composite foam, thus leading to an absorption-dominated mechanism. Additionally, the prepared composite foams exhibited outstanding thermal conductivity and mechanical strength, enabling them to be used as lightweight and robust EMI shielding materials that could transform EM wave energy into Joule heat.

Material properties and structure of natural graphite sheet

Natural graphite sheet (NGS) is compressible, porous, electrically and thermally conductive material that shows a potential to be used in fuel cells, flow batteries, electronics cooling systems, supercapacitors, adsorption air conditioning, and heat exchangers. We report the results of an extensive material characterization study that focuses on thermal conductivity, thermal diffusivity, electrical conductivity, coefficient of thermal expansion (CTE), compression strain, and emissivity. All the properties are density-dependent and highly anisotropic. Increasing the compression from 100 to 1080 kPa causes the through-plane thermal and electrical conductivities to increase by up to 116% and 263%, respectively. The properties are independent of the sheet thickness. Thermal and electrical contact resistance between stacked NGS is negligible at pressures 100 to 1080 kPa. In the in-plane direction, NGS follows the Wiedemann-Franz law with Lorenz number 6.6 times 10^{-6} W Omega K^{-2}. The in-plane CTE is low and negative (shrinkage with increasing temperature), while the through-plane CTE is high, increases with density, and reaches 33 times 10^{-6} K^{-1}. Microscope images are used to study the structure and relate it to material properties. An easy-to-use graphical summary of the forming process and NGS properties are provided in Appendices A and B.

Mechanical, electrical and thermal properties of graphene oxide-carbon nanotube/ ABS hybrid polymer nanocomposites

Multiwalled carbon nanotubes (MWCNTs), functionalized carbon nanotubes (FCNTs) and graphene oxide-carbon nanotube (GCNTs) hybrid Bucky paper (BP) reinforced acrylonitrile-butadiene-styrene (ABS) composites are prepared via vacuum filtration followed by hot compression molding. The nanomechanical, electrical and thermal properties of these BP reinforced ABS composites are studied. The nanoindentation hardness and elastic modulus of GCNTs-ABS hybrid composites reached to 389.98±91.79 MPa and 7669.6±1179.12 MPa respectively. Other nanomechanical parameters such as plastic index parameter, elastic recovery, the ratio of residual displacement after load removal and displacement at maximum load are also investigated. The improved nanomechanical properties are correlated with Raman spectroscopy and scanning electron microscopy (SEM). It is found that GCNTs and their composites showed the higher value of defect density. The maximum value of defect density range for GCNTs and GCNTs-ABS is (297.4 to 159.6) and (16.0 to11.6), respectively. The higher defect density of GCNTs indicates that the interfacial interaction between the ABS, which was further correlated with electrical and thermal properties. Additionally, the through-plane electrical conductivities of MWCNTs, FCNTs and GCNTs based ABS composites were 6.5±0.6, 4.5±0.7 and 6.97±1.2 S/cm respectively and thermal conductivities of MWCNTs, FCNTs and GCNTs reinforced ABS composites; 1.80, 1.70 and 1.98 W/mK respectively. These GCNTs-ABS composites with this value of thermal conductivity can be used in various applications of efficient heat dissipative materials for electronic devices.

Enhancing through-plane electrical conductivity by introducing Au microdots onto TiN coated metal bipolar plates of PEMFCs

Developing a high electrically conductive and corrosion-resistant coating on metal bipolar plate is of prime importance for its application in polymer electrolyte membrane fuel cells. To achieve it and further improve its through-plane conductivity, we herein prepared a composite coating by introducing Au microdots onto TiN coated stainless steel (Au/TiN/SS). Au dots provide additional conduction paths and thus Au/TiN/SS exhibits a remarkably lower interfacial contact resistance than that of TiN/SS after 200 h of test, suggesting that incorporation of Au dots into TiN provides an effective approach to achieving dual merits of high conductivity and corrosion resistance.

Poly(phenylene sulfide) Graphite Composites with Graphite Nanoplatelets as a Secondary Filler for Bipolar Plates in Fuel Cell Applications

Graphite nanoplatelets (GNPs) have been used as a secondary filler to improve the electrical conductivity of poly(phenylene sulfide) (PPS)/graphite composites for use as bipolar plates in fuel cells, and the effects of adding small quantities of GNPs on the electrical, thermal, and mechanical properties of PPS/GNP/graphite composites have been extensively studied. The GNPs were compounded with PPS to produce master batch (MB) chips that were further ground to fine MB powder (MBg). PPS/MBg/graphite powders were compressed to fabricate 10-mm thick square samples. Composites containing a large quantity of graphite (~80 wt%) were then tested for use as a bipolar plate in phosphoric acid fuel cells. When 5 wt% GNP was added to the PPS/graphite composite, the in-plane electrical conductivity increased almost twofold from 643 to 1340 S·cm−1, the through-plane electrical conductivity increased from 19 to 54 S·cm−1, the through-plane thermal conductivity increased approximately two-fold from 60 to 129 W·(mK)−1, and the flexural strength decreased slightly from 32 to 26 MPa. The fractured surface of the compressed MBg sample revealed well-dispersed GNPs in the PPS matrix, which created electrical pathways and improved the electrical conductivity of the non-conducting PPS matrix material. Thus, the PPS/GNP/graphite composite is a promising system for bipolar plate applications because a higher amount of graphite (~93 wt%) is needed in PPS/graphite composites to reach the same level of electrical conductivity as the PPS/MBg(5 wt%)/graphite (75 wt%) composite, and such a large quantity of graphite is difficult to process and leads to weaker mechanical properties.

Balancing the corrosion resistance and through-plane electrical conductivity of Cr coating via oxygen plasma treatment

Developing an electrically conductive and corrosion-resistant coating is essential for metal bipolar plates of polymer electrolyte membrane fuel cells (PEMFCs). Although enhanced corrosion resistance was seen for Cr coated stainless steel (Cr/SS) bipolar plates, they experience a quick decrease of through-plane electrical conductivity due to the formation of a porous and low-conductive corrosion product layer at the plate surface, thus leading to an increase in interfacial contact resistance (ICR). To tackle this issue, the multilayer Cr coatings were deposited using the magnetron sputtering with a remote inductively coupled oxygen plasma (O-ICP) in the present study. After the O-ICP treatment, a Cr oxide layer (CrO*) is formed on the specimen surface. The CrO*/Cr/SS has a remarkably lower stable corrosion rate (iss) than that of the native Cr oxides (CrOn/Cr/SS). Compared with CrOn/Cr/SS, the excellent performance of CrO*/Cr/SS is attributed to a denser and thicker surface layer of CrO* with Cr being oxidized to its highest valence state, Cr (VI). More importantly, the through-plane electrical conductivity of the specimens treated by the optimized O-ICP decreases much slowly than CrOn/Cr/SS and thus, the increament of ICR of CrO*/Cr/SS after the potentiostatic polarization test is considerably smaller than that of CrOn/Cr/SS, which is benefited from the reduced iss that mitigates the deposition of corrosion products and hinders further oxidation of Cr coating. Therefore, CrO*/Cr/SS proves to be a well balanced trade-off between corrosion resistance and through-plane electrical conductivity. The results of this study demonstrate that O-ICP treatment on a conductive metal coating is an effective strategy to improve the corrosion resistance and suppress the increase of ICR over the long-term polarization. The technique reported herein exhibits its promising potential application in preparing corrosion resistant and electrically conductive coatings on metal bipolar plates to be used in PEMFCs.

Fabrication of multi-filler thermoset-based composite bipolar plates for PEMFCs applications: Molding defects and properties characterizations

The bipolar plate (BP) material should possess contradictory properties. They should also manufacture from low-cost methods and materials. In the current investigation, thermoset-based composite materials reinforced with conductive fillers, and the compression molding process is implemented. In addition to fabricating the bipolar plates (BPs) with and without the flowing channels, alleviating the defects during the molding process is performed. The channels are perfectly formed on the plates with the designed depth of 0.65 mm and 0.5 mm of width. In the meanwhile, we alleviate different molding defects, which spoil the surface appearance and part properties. Regarding the physical properties, the water contact angle is measured to be around 85°. The through-plane electrical conductivity of molded plates showed high values up to 38 S/cm, and the interfacial contact resistance measured to be 18–24 mΩ cm2. The mean value of the flexural strength of the produced samples was equal to 47 MPa, which is almost twice the DOE target (>25 MPa).

Poly(phenylene sulfide)-graphite composites for bipolar plates with preferred morphological orientation

Bipolar plates in phosphoric acid fuel cells require inertness to phosphoric acid as well as excellent electrical, thermal, and mechanical properties. For this application, we prepared poly(phenylene sulfide) (PPS)-graphite composites with random or ordered graphite orientations by compression and extrusion-compression processes, respectively. Due to current limitations of extruding graphite-filled polymers, only moderately high graphite concentrations were used (up to 40 wt%). The compressed composites contained graphite sheets in a planar orientation (parallel to the pressing direction) and exhibited highly anisotropic electrical and thermal conductivity, with much higher in-plane than through-plane components. In contrast, composites that were extruded prior to compression exhibited randomly oriented graphite due to shearing forces during extrusion and therefore displayed isotropic properties. Thus, their through-plane electrical and thermal conductivity was superior to those of the ordered composite, while the in-plane properties were inferior. Notably, the internal graphitic structure affected the electrical conductivity more than the thermal conductivity. The randomly oriented composite also exhibited superior flexural strength, although the thermal stability of the two composites was almost equal. This study offers insights into the structure-property relationship of PPS-graphite composites as well as the effect of the orientation of conductive two-dimensional fillers on anisotropic properties.