Decrease In Contact Resistance Research Articles

Improvements of Electrical and Electrochemical Activities at Nb-SnO2 Supports by Aggregation and Pt Loading as Fuel Cell Cathode Catalysts

Polymer electrolyte fuel cells (PEFCs) are highly attractive power generation systems for fuel cell vehicles and residential co-generation systems. Platinum-based catalysts supported on carbon are important cathode catalysts for PEFCs, but the degradation of the carbon support in the high potential range is a key issue to be solved. Tin oxide (SnO2) is one of the good candidates for alternative non-carbon support with high electrical conductivity and stability in the high potential range.1 We have succeeded the synthesis of a Nb-doped tin oxide (Nb-SnO2) support with an aggregated network structure, like carbon black (CB), by a flame oxide-forming method.2-4 In this research, we evaluate the electrical conductivity and electrochemical activity of the Pt supported Nb-SnO2 with such unique morphology (Pt/ Nb-SnO2) by rotating disk electrode (RDE) and membrane electrode assembly (MEA). The obtained particles (crystallite size, 10-20 nm; specific surface area, 40-100 m2/g) were partially sintered with nearest neighbors and constructed an aggregated network structure with primary pore (diameter < 30 nm) and secondary pore (diameter > 30 nm). We evaluated the level of necking between nanoparticles with “Necking Index” (NI=SBET/SXRD) defined by the fraction of a specific surface area of particles measured by BET method (SBET) to that of the particles estimated from the mean crystallite size determined by the XRD method (SXRD). The apparent electrical conductivity (σapp.) of the support increased with decreasing NI, (Fig. 1, bold line), which rely on both the decrease of contact resistance by development of the necking among the particles and the change of microstructure from a closed-packed aggregate type to a chain-like aggregate type. Some particles exhibited a deviation from the simple correlation curve to higher conduction values even though the NI was nearly the same (Fig. 1: dotted line). The electrical conductivities of corresponding Nb-SnO2 increased with increasing their primary pore volumes due to a development of ramification of the chain-like aggregated structure with improvement of the electron conducting paths (Fig. 2). Moreover, we found that σapp. of Pt/ Nb-SnO2 catalysts were more than two orders of magnitude higher than those of the corresponding supports.The kinetically controlled current density (j k,Pt) for the oxygen reduction reaction (ORR) at 0.80 V of Pt/Nb-SnO2 (17 wt%, Pt particle size, 3.0 nm) increased with increasing σapp. and exceeded that of commercial Pt supported on carbon black catalyst (Pt/CB) (Fig. 3). The single serpentine pattern cell (Japan Automobile Research Institute (JARI) standard cell) with Pt/Nb-SnO2 also showed superior performance to that with Pt/CB.This work was supported by funds for the “HiPer-FC Project” of NEDO, Japan.

Performance of 3D-Printed Fuel Cells and Stacks

3D-printing, a.k.a. additive manufacturing (AM), has become a popular topic in the general public and in industry [1]. There is recent interest in using AM to fabricate fuel cell components because of AMs ability to build metal parts with complex geometries with relatively short lead times [2]. Fuel cell bipolar plates (BPPs) require complex internal passageways for coolant flow fields making them a good candidate for AM. By building one piece BPPs the number of parts, the number of seals and the complexity of assembly can be decreased. We present the performance characteristics of a 400W fuel cell system made with BPPs made of Ti-alloy (Ti-6Al-4V) and built by 3D-printing. The BPPs are made by direct metal laser sintering (DMLS) and are coated by Treadstone Inc. with Au-microdots and a TiO2layer to decrease contact resistance and protect against corrosion. Titanium alloy is examined because of its high strength-to-weight ratio which makes it an ideal material for aerospace applications. This work extends our previous work regarding the contact resistance of 3D-printed metal BPPs to include functional fuel cell stacks [3]. The performance characteristics of single cells and stacks will be discussed in the context of surface finish, flatness, feature tolerance, weight, cell-to-cell variability, scaling and contact resistance. Overall DMLS is an exciting new technique with great promise for future rapid prototyping of BPP designs and many other fuel cell components. However, greater advances in surface finish, feature thinness and flatness are needed before BPPs built by 3D-printing will compete with the traditional machined or formed BPPs.

Enhanced performance of graphene by using gold film for transfer and masking process

In this study, we tried to reduce the organic contamination of graphene. This organic contamination most likely occurs during the graphene transfer and lithography steps, which in turn degrades the quality of the graphene. Inorganic Au film was applied for Au-assisted transfer instead of the conventional thin poly(methyl methacrylate), and a new fabrication process using the Au-film for the transfer and masking layer was designed in order to minimize the contamination of graphene from organic residues. As a result, we demonstrated that the overall qualities of the transferred graphene film and graphene transistors have been highly improved. These improvements include an enhancement of mobility, and a decrease of defects, unintentional doping, contact resistance, and sheet resistance.

Temperature effect on the conductivity of knitted fabrics embedded with conducting yarns

The electrical resistance of knitted fabrics embedded with conducting yarns at different temperatures was studied in this paper. Two types of resistance, linear resistance and contact resistance have been considered and discussed by experimental studies and theoretical modeling. Two silver-coated conductive yarns, yarn A and B, with linear resistance of 68.6 Ω/cm and 1 Ω/cm respectively, were embedded into normal knitted woolen fabrics. The temperature effect on the resistance of these two conductive knitted fabrics as a function of applied voltages was extensively explored. The results have shown that the resistance of either conductive knitted fabric decreases significantly (maximum 30%) when its temperature is rising. It can be explained by two main factors: the electrical resistance of the silver-coated conductive yarns decreases as temperature rises; the physical contact of the overlapped conductive yarns extends due to heating on woolen fabrics, which causes a decrease in contact resistance. This research has shown that the temperature effect on the conductivity of the knitted fabrics embedded with conductive yarns should be carefully considered in future industrial applications.

Ohmic Contact Properties Depending on AlGaN Layer Thickness for AlGaN/GaN High Electron Mobility Transistor Structures

Mo/Al/Ti or TiN/TiSi2ohmic contacts were fabricated on AlGaN/GaN HEMT structures having various thicknesses of AlGaN layers. Optimum thicknesses depending on annealing temperature were found, which should be correlated with the contact formation mechanism. AlGaN/GaN HEMTs (high electron mobility transistors) have drawn lots of attention for high frequency and power applications owing to high mobility of 2DEG. One of the important issues of the devices is formation of ohmic contacts with low contact resistance. Since contact metal layers are usually placed on the AlGaN layer under which two-dimensional electron gas (2DEG) is induced, current passes through the AlGaN layer, a barrier layer for electrons, should be formed. Various models of the contact formation mechanism, such as the intrusion of metal into 2DEG [1] and formation of n-type region due to N vacancies [2], have been discussed. However, comprehensive understanding for the mechanism is still insufficient so far. We expect that optimum AlGaN thickness is present to obtain low contact resistance because of a trade-off between increase in the resistance by increasing the thickness due to thicker barrier and that by decreasing the thickness due to depletion of 2DEG. In this work, we revealed the prospect experimentally, and discussed mechanism based on the phenomenon. The wafers used in this study consist of 30-nm-thick undoped AlGaN with GaN layer epitaxially grown on Si (111) substrates. The top AlGaN layers were thinned by the cyclic etching in which oxidation in O3 ambient and removal by hydrofluoric acid were carried out, so that samples with various AlGaN thicknesses were prepared. Contact electrodes, Mo/Al/Ti (35/60/15nm) or TiN/TiSi2 (45/20nm) [3], were formed by sputtering followed by subsequent annealing (400-1100 oC for 1min. in N2) on the samples, as shown in Fig. 1. Contact resistances were evaluated by the TLM method. A typical characteristic of the contact resistance vs. AlGaN thickness for the case of relatively low annealing temperature (650oC) is shown in Fig.2. The optimum AlGaN thickness to get the lowest resistance, 11.6 nm in this case, was clearly observed. On the other hand, in the case of higher annealing temperature (950oC or 1100oC), the monotonous decrease in contact resistance with the thickness was observed as shown in Fig.3. The increase in contact resistance in the region thinner than 11.6 nm is speculated to be due to depletion of 2DEG, which is common to the both low and high temperature cases. While, the increase in contact resistance for thicker layers at low temperature annealing, as shown in Fig.2, is probably attributed to high resistivity in the AlGaN layer. However, in the case of high temperature annealing, as shown in Fig.3, some mechanism of the metal intrusion and/or the conversion to n-type to overcome the thick barrier layer should work effectively. In conclusion, dependences of contact resistance on thickness of the AlGaN layer were observed, and they indicated existence of the optimum thickness. Discussion of these properties correlated with mechanism of ohmic contact formation will be useful for further understanding of the contact technology for AlGaN/GaN HEMTs.

Analysis of electrical parameters of organic thin film transistors based on thickness variation in semi‐conducting and dielectric layers

This research study analyses the impact of semi-conductor (t osc) and dielectric (t ox) thicknesses on top contact (TC) and bottom contact (BC) organic thin film transistors (OTFTs) using Atlas 2-D numerical device simulation. Thickness of each layer is varied from 20 to 150 nm. The parameters such as electric field, charge carrier distribution and trap density are analysed from device physics point of view with variations in organic semi-conductor layer and dielectric thicknesses. A decrease of 22% in TC to BC current ratio is observed for maximum increase in t osc, whereas, it remains almost constant at unity with variations in t ox. Furthermore, the maximum mobility for TC is achieved at t osc of 20 nm and reduces monotonically with further increase in thickness because of lowering of average charge. However, its highest value is obtained at 60 nm for BC structure that declines with positive or negative change in t osc. Besides this, the threshold voltage (V t) shows a reduction of 50% for both the structures on scaling down t ox from 150 to 20 nm. Furthermore, the ON to OFF current ratio is found to be more dependent on t osc as compared with t ox. This is because of a dominant impact of t osc reduction on OFF current as compared with impact of t ox reduction on the ON current. Additionally, a decrease in contact resistance (R C) is observed in TC structure for thicker active layer while operating at lower Vgs . However, at high gate voltage, t osc maps to the access resistance that results in higher R C values.

Application Examples for the Different Measurement Modes of Electrical Properties of the Solar Cells

Abstract The aim of the paper was to apply the newly developed instruments ‘Corescan’ and ‘Sherescan’ in order to measure the essential parameters of producing solar cells in comparison with the standard techniques. The standard technique named the Transmission Line Method (TLM) is one way to monitor contacting process to measure contact resistance locally between the substrate and metallization. Nowadays, contact resistance is measured over the whole photovoltaic cell using Corescanner instrument. The Sherescan device in comparison with standard devices gives a possibility to measure the sheet resistance of the emitter of silicon wafers and determine of both P/N recognition and metal resistance. The Screen Printing (SP) method is the most widely used contact formation technique for commercial silicon solar cells. The contact resistance of manufactured front metallization depends of both the paste composition and co-firing conditions. Screen printed front side metallization and next to co-fired in the infrared conveyor furnace was carried out at various temperature from 770°C to 920°C. The silver paste used in the present paper is commercial. The investigations were carried out on monocrystalline silicon wafers. The topography of co-fired in the infrared belt furnace front metallization was investigated using the atomic force microscope and scanning electron microscope (SEM). There were researched also cross sections of front contacts using SEM microscope. Front contacts of the solar cells were formed on non-textured silicon surface with coated antireflection layer. On one hand, based on electrical properties investigations using Sherescan instrument it was obtained the knowledge of the emitter sheet resistance across the surface of a wafer, what is essential in optimizing the emitter diffusion process. On the other hand, it was found using Corescan instrument that the higher temperature apparently results in a strongly decreased contact resistance.

Enhanced Performance of GaN-Based Green Light-Emitting Diodes with Gallium-Doped ZnO Transparent Conducting Oxide

Ga-doped ZnO (GZO) transparent conducting oxide was grown by oxygen plasma-enhanced pulsed laser deposition. GZO grown in the presence of oxygen radicals had resistivity of 1 × 10−3 Ω cm and average visible (500–700 nm) transmittance of 92.5%. A low specific contact resistance of 6.5 × 10−4 Ω cm2 of GZO on p-GaN was achieved by excimer laser annealing (ELA) treatment of p-GaN before GZO electrode deposition. The ELA-treated light emitting diode (LED) fabricated with the GZO electrode as a current-spreading layer resulted in light-output power enhanced by 56.2% at 100 mA compared with that fabricated with a conventional Ni/Au metal electrode. The high-light output and low degradation of light-output power were attributed to the decrease in contact resistance between the p-GaN layer and the GZO electrode and uniform current spreading over the p-GaN layer. In addition, low contact resistance results in a decrease of self-heat generation during current drive.

Ag–graphene hybrid conductive ink for writing electronics

With the aim of preparing a method for the writing of electronics on paper by the use of common commercial rollerball pens loaded with conductive ink, hybrid conductive ink composed of Ag nanoparticles (15 wt%) and graphene–Ag composite nanosheets (0.15 wt%) formed by depositing Ag nanoparticles (∼10 nm) onto graphene sheets was prepared for the first time. Owing to the electrical pathway effect of graphene and the decreased contact resistance of graphene junctions by depositing Ag nanoparticles (NPs) onto graphene sheets, the concentration of Ag NPs was significantly reduced while maintaining high conductivity at a curing temperature of 100 ° C. A typical resistivity value measured was 1.9 × 10−7 Ω m, which is 12 times the value for bulk silver. Even over thousands of bending cycles or rolling, the resistance values of writing tracks only increase slightly. The stability and flexibility of the writing circuits are good, demonstrating the promising future of this hybrid ink and direct writing method.

Increased Power Density of Solid Oxide Fuel Cells Using LaGaO3 Film Prepared by Screen Printing Method with (Ba,La)CoO3-δ and Pr1.9(Ni,Cu,Ga)O4+δ Composite Oxide Cathode

Effects of microstructure and phase compatibility in a composite of Ba0.5La0.5CoO3–δ (BLC) and Pr1.9(Ni,Cu,Ga)O4+δ (PNCG) with a mass ratio of 5:1 (BP51) on electrochemical properties were investigated with varying firing temperature of the composite as cathode (973–1373 K). Grain growth was observed with increasing firing temperature while single phase was maintained below 1173 K in the composite. Area specific resistance (ASR) of BP51 cathode fired at 1073 K was decreased due to fine particles, intimate contact, and phase purity, leading to enhancement of reactivity on oxygen exchange and diffusion of oxygen species. Moreover, BP51 cathode with small grains revealed improved electrochemical performance compared with that of coarse particles. Accordingly, increased maximum power density of ca. 1.3 and 0.2 Wcm−2 at 973 and 773 K was achieved in an anode supported single cell of Sr- and Mg-doped LaGaO3 (LSGM) electrolyte film with fine BP51 cathode owing to decrease in both electrode polarization and interfacial contact resistance. Furthermore, cell performance was stable under an applied current density of 1.7 Acm−2 at 973 K. This study reveals that fine BP51 composite is a promising cathode for high performance intermediate temperature SOFCs.

The effect of boron nitride on electrical conductivity of nanocarbon-polymer composites

The electrical conductivity concentration and temperature dependences of polymer composite materials (CMs) with nanocarbon fillers [graphite nanoplatelets and multi-walled carbon nanotubes (MWCNTs)] were investigated. Epoxy resin modified with organosilicon compound was used as polymer matrix. The content of nanocarbon filler in varied from 1 to 10 wt%. To study of the synergetic properties the additional dispersed dielectric filler—boron nitride (BN) was added to given systems in content of 27 wt%. The electrical resistivity of CMs was investigated in the temperature range of 77–300 K. In the studied CMs the percolation transition at sufficient low filler content (0.01–0.022 vol. fr.) was observed. The values of critical index varied from 3.0 to 5.2. The electrical conductivity of investigated CMs was analyzed in the framework of proposed model that takes into consideration the morphology of filler particles. It was shown that the increase of electrical conductivity of GNP-polymer CM in the presence of BN is attributed to the decrease of contact resistance between filler particles, while for MWCNT-polymer CM is due to the increase of the number of conductive chains in this particular system.

Impact of excess phosphorus doping and Si crystalline defects on Ag crystallite nucleation and growth in silver screen‐printed Si solar cells

AbstractGood quality contacts between metal and silicon emitter are crucial for high crystalline solar cell efficiencies. We investigate the impact of defects originating from electrically inactive phosphorus on contact formation within silver thick film metallized silicon solar cells. For this purpose, emitters with varying sheet resistance, depth, and dead layer were metallized with silver pastes from different generations. Macroscopic contact resistivity measurements were compared with the microscopic contact configurations studied by scanning electron microscopy. The density of direct contacts between Ag crystallites grown into Si and the Ag finger bulk is essential for low contact resistivity. The presence of glass‐free regions needed for such direct contacts depends on the paste composition and on the surface texture, and does not vary with the Si emitter properties. Indeed, the decrease in contact resistivity correlates with increasing density of Ag crystallites embedded in the Si surface. Furthermore, the density of Si surface‐embedded Ag crystallites scales proportional to the electrically inactive P and is independent of the sheet resistance. Using the newest silver paste, the Ag crystallite density is independent of the emitter doping, but the Ag crystallite size increases as a function of the thickness of the dead layer. Transmission electron microscopy characterization of the excess P‐doped Si crystal lattice shows that significant strain and Si bond weakening may play a major role for both Ag crystallite nucleation and growth. Finally, we studied Si crystal defects by metallizing nanocracks, dislocations, and grain boundaries and found that Ag crystallite nucleation is defect‐property dependent. Copyright © 2013 John Wiley &amp; Sons, Ltd.

In-plane conduction characterisation and charge transport model of DMSO co-doped, inkjet printed Poly(3,4-ethylenedioxythiophene): Polystyrene sulfonate (PEDOT:PSS)

The technologically important inkjet printed poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) films, at different extents of co-doping with dimethyl sulfoxide DMSO, have been studied in terms of in-plane charge transport and electric field force microscopy (EFM). Similarly to past studies of spin coated PEDOT:PSS films, room temperature conductivity is enhanced by a factor of 103 to 130Scm−1 on the addition of 5% DMSO, Hall probe analysis demonstrated a decrease in contact resistance from 106Ω to 104Ω whilst variable-temperature conductivity analysis shows an increase in the VRH exponent from 0.25 to 0.5 signifying a charge transport evolution from Mott Variable Range Hopping in 3-dimensions to a pseudo 1-dimensional Variable Range Hopping. In addition, electric field force microscopy (EFM) showed a corresponding threefold increase in PEDOT grain size. Further analysis was conducted to determine the hopping length and the ratio of the hopping length versus localization length in the electron transport model.

Analysis of the temperature dependence of the forward voltage characteristics of GaInN light-emitting diodes

The forward voltage characteristics of GaInN light-emitting diodes are studied in the temperature range of 80 K to 450 K. The forward-voltage-vs.-temperature curve has a “two-slope” characteristic with a slope of dVf/dT = −1.7 mV/K and −8.0 mV/K at room temperature and cryogenic temperatures, respectively. To investigate the two-slope characteristic, we perform transmission-line-model measurements on p-type GaN and show that both p-type contact and sheet resistance decrease drastically with increasing temperature. We conclude that dVf/dT in the high-slope region is limited by p-type sheet and contact resistance, and in the low-slope region by the GaN pn junction properties.

Modeling electrical conductivity of nanocomposites by considering carbon nanotube deformation at nanotube junctions

This paper investigates the effect of carbon nanotube (CNT) deformation on the electrical conductivity of CNT polymer composites at crossed nanotube junctions using a revised 3-dimensional CNT percolating network model. Two aspects of the work are considered. The first is concerned with the effect of CNT deformation on its intrinsic and contact resistances at CNT-CNT junctions. An analytical model based on electron ballistic tunneling theory and Landauer-Büttiker formula is proposed to describe the variation of CNT-CNT contact resistance at the CNT-CNT junction in terms of local deformation of CNT walls and CNT-CNT distance. In addition, a model exclusively based on experimental data to describe the change of CNT intrinsic resistance in terms of its cross-section deformation is adopted. The second is concerned with the relationship among the CNT-CNT distance, the angle between two adjacent CNTs, and the dimensions of local deformation of CNT walls and its impact on the corresponding intrinsic and contact resistance of CNTs near and at a CNT-CNT junction. Finally, Monte Carlo simulations are conducted to evaluate these effects on the electrical conductivity of nanocomposites for different CNT weight fractions. Our results reveal that the local deformation of CNT walls plays a significant role in the evaluation of electrical conductivity of CNT polymer composites. The intrinsic resistance in the deformed part of CNTs near a CNT-CNT junction increases much faster than the decrease of CNT-CNT contact resistance at the same junction when two CNTs are getting closer, resulting in a net increase of resistance at the junction. Numerical results show that the current model agrees with existing experimental data better than existing models without considering the effect of CNT deformation, which tends to overestimate the electrical conductivity of CNT polymer composites containing homogeneously dispersed percolating CNT network.

Effect of Cu interfacial layer thickness on spin-injection efficiency in NiFe/Cu/graphene spin valves

The spin injection efficiency in NiFe/Cu/graphene spin-valves has been investigated systematically with emphasis on the Cu thickness effect. An optimum Cu thickness is found to be around 2.5 nm for which spin injection efficiency up to 8.4% has been measured. With a further increase of Cu thickness, the efficiency decreases to 3.6%−3.8% at 3.5 nm and is hardly measureable at 5 nm and beyond. The decrease is discussed in the context of enhanced spin-flip scattering at the NiFe/Cu interface and grain boundaries in the polycrystalline Cu as well as current shunting induced lengthening of travelling distance of electrons inside Cu. On the other hand, a further reduction of Cu thickness below 2.5 nm results in pinholes which also lowers the spin-injection efficiency. In addition to the Cu thickness, another factor which affects the spin signal is the DC bias voltage. The non-local magnetoresistance is highest when measured under zero-bias condition and becomes smaller when a DC bias is applied. The reduction of efficiency correlates well with the decrease in Cu-graphene contact resistance, which is consistent with the non-ohmic nature of Cu-graphene interface. Hanle spin precession curves were measured at different back gate biases from which the spin relaxation length was determined to be 1.6 μm−2.7 μm.

Vapor Phase Polymerization Deposition of Conducting Polymer/Graphene Nanocomposites as High Performance Electrode Materials

In this paper, we report chemical vapor phase polymerization (VPP) deposition of novel poly(3,4-ethylenedioxythiophene) (PEDOT)/graphene nanocomposites as solid tantalum electrolyte capacitor cathode films. The PEDOT/graphene films were successfully prepared on porous tantalum pentoxide surface as cathode films through the VPP procedure. The results indicated that the high conductivity nature of PEDOT/graphene leads to the decrease of cathode films resistance and contact resistance between PEDOT/graphene and carbon paste. This nanocomposite cathode film based capacitor showed ultralow equivalent series resistance (ESR) ca. 12 mΩ and exhibited better capacitance-frequency performance than the PEDOT based capacitor. The leakage current investigation revealed that the device encapsulation process does not influence capacitor leakage current, indicating the excellent mechanical strength of PEDOT-graphene films. The graphene showed a distinct protection effect on the dielectric layer from possible mechanical damage. This high conductivity and mechanical strength graphene based conducting polymer nanocomposites indicated a promising application future for organic electrode materials.

The effect of thermal annealing of graphene under ammonia atmosphere on its electrical properties and contact to p-GaN

We investigated the effects of thermal annealing of graphene on its electrical properties with the aim of improving the electrical contacts between graphene and the p-GaN layer. Compared with pristine graphene which shows ambipolar characteristics, graphene thermally annealed under NH3 atmosphere exhibited obvious p-type characteristics and increased conductance, representing the hole doping effect in the graphene. This result is contrary to the expectation for substitutional doping of nitrogen in graphene, and can be attributed to the physisorption of gas molecules on the graphene surface. Due to the lowering of the Fermi level and the enhancement in the conductivity of annealed graphene, electrical contact to the p-type GaN has been improved, with the specific contact resistance decrease from 1.02Ω∙cm2 to 0.49Ω∙cm2.

Vapor Phase Polymerization Deposition Conducting Polymer Nanocomposites on Porous Dielectric Surface as High Performance Electrode Materials

Abstract We report chemical vapor phase polymerization (VPP) deposition of poly(3,4-ethylenedioxythiophene) (PEDOT) and PEDOT/graphene on porous dielectric tantalum pentoxide (Ta2O5) surface as cathode films for solid tantalum electrolyte capacitors. The modified oxidant/oxidant-graphene films were first deposited on Ta2O5 by dip-coating, and VPP process was subsequently utilized to transfer oxidant/oxidant-graphene into PEDOT/PEDOT-graphene films. The SEM images showed PEDOT/PEDOT-graphene films was successfully constructed on porous Ta2O5 surface through VPP deposition, and a solid tantalum electrolyte capacitor with conducting polymer-graphene nano-composites as cathode films was constructed. The high conductivity nature of PEDOT-graphene leads to resistance decrease of cathode films and lower contact resistance between PEDOT/graphene and carbon paste. This nano-composite cathode films based capacitor showed ultralow equivalent series resistance (ESR) ca. 12Ω and exhibited excellent capacitance-frequency performance, which can keep 82% of initial capacitance at 500 KHz. The investigation on leakage current revealed that the device encapsulation process has no influence on capacitor leakage current, indicating the excellent mechanical strength of PEDOT/PEDOT-gaphene films. This high conductivity and mechanical strength of graphene-based polymer films shows promising future for electrode materials such as capacitors, organic solar cells and electrochemical energy storage devices.

Anticorrosion Coating of Carbon Nanotube/Polytetrafluoroethylene Composite Film on the Stainless Steel Bipolar Plate for Proton Exchange Membrane Fuel Cells

Composite film of carbon nanotube (CNT) and polytetrafluoroethylene (PTFE) was formed from dispersion fluids of CNT and PTFE. The composite film showed high electrical conductivity in the range of 0.1–13 S/cm and hydrophobic nature. This composite film was applied to stainless steel (SS) bipolar plates of the proton exchange membrane fuel cell (PEMFC) as anticorrosion film. This coating decreased the contact resistance between the surface of the bipolar plate and the membrane electrode assembly (MEA) of the PEMFC. The output power of the fuel cell is increased by 1.6 times because the decrease in the contact resistance decreases the series resistance of the PEMFC. Moreover, the coating of this composite film protects the bipolar plate from the surface corrosion.