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.     

Highly filled graphite/graphene/carbon nanotube in polybenzoxazine composites for bipolar plate in PEMFC

This research aims to develop polybenzoxazine (PBA) based composites suitable for bipolar plates in proton exchange membrane fuel cells (PEMFCs). PBA composites filled with carbon derivatives i.e. graphite, graphene, and multiwall carbon nanotubes (CNTs) were prepared. The effects of CNT contents from 0–2 wt% at an expense of graphite with constant content of graphene and benzoxazine on properties of the obtained composites were investigated. It was found that the composite with 2 wt% of CNTs exhibited through-plane thermal conductivity as high as 21.3 W/mK which is 44 times higher than that of the composite without CNTs. Also, this composite showed electrical conductivity of 364 S/cm, Flexural Strength of 41.5 MPa and Modulus 49.7 GPa, respectively. These values meet the requirements suggested by the Department of Energy, USA and confirm that these composites are great candidates as bipolar plates for PEMFCs.     

Fibre orientation effect on polypropylene/milled carbon fiber composites in the presence of carbon nanotubes or graphene as a secondary filler: Application on PEM fuel cell bipolar plate

Conductive polymer composite (CPC) materials are extensively used for the bipolar plate in Polymer Electrolyte Membrane Fuel Cells (PEMFCs). The produced CPC materials through the extrusion process strongly relate to electrical conductivity and mechanical properties. In this study, milled carbon fibre (MCF) reinforced polypropylene (PP) incorporating carbon nanotube (CNT), or graphene nanoplatelets (xGNP) are pre-mixed using the extrusion process to orientate the fibres before undergoing the compression moulding at 13.8 MPa and 200 °C for 15 min. The CNT composites exhibited the higher through-plane conductivity of 14.8 S/cm as compared to xGnP composites with 4.9 S/cm at 70 wt% of MCF. The flexural strength improved after being compressed to 99.6 MPa and 172.5 MPa for 70 wt% of CNT and xGNP, respectively. This reveals that the oriented fibres can boost the CPC performance.     

Improved hydrogen storage performance of Mg(NH2)2/LiH mixture by addition of carbon nanostructured materials

The effect of different carbon nanostructures specifically carbon nanotubes (CNTs) and carbon nanofibers (CNFs) on the improvement of the de/re-hydrogenation characteristics of a Mg(NH₂)₂/LiH mixture have been studied. Amongst CNTs and CNFs, the improvement in the hydrogenation properties for the Mg(NH₂)₂/LiH mixture is higher when CNFs are used as a catalyst. Investigations are also focused on the deployment of two different types of CNF (a) CNF1 (synthesized using a ZrFe₂ catalyst) and (b) CNF2 (synthesized using a LaNi₅ catalyst). The results show that CNF2 is better. The maximum decomposition temperature for the pristine Mg(NH₂)₂/LiH mixture is found to be ∼250 °C, which is reduced to ∼180 and ∼150 °C for the sample mixed with 4 wt% of multi-walled carbon nanotubes (MWCNTs) and CNF2 respectively. The activation energy for the dehydrogenation reaction is found to be 74 and 68 kJ mol⁻¹ for the samples mixed with MWCNT and CNF2 respectively, whereas the activation energy for the dehydrogenation reaction of the pristine Mg(NH₂)₂/LiH mixture is 97 kJ mol⁻¹. The catalytic activity and the de/re-hydrogenation characteristics of the Mg(NH₂)₂/LiH mixture mixed with different carbon nanostructures are described and discussed.     

Electrochemical performance of carbon-supported Pt(Cu) electrocatalysts for low-temperature fuel cells

Pt(Cu) nanoparticles supported on carbon nanofibers (CNFs), multi-walled carbon nanotubes (MWCNTs) and Vulcan carbon XC72, have been synthesized by electroless deposition and galvanic exchange. The structural analyses show contracted Pt fcc lattices due to the formation of a PtCu alloy core covered by a Pt-rich shell, mean crystallite sizes of about 3 nm, as well as good dispersion and carbon attachment. The electrochemical surface areas (ECSAs) of Pt(Cu)/CNF and Pt(Cu)/XC72 are comparable to those of commercial Pt/C and PtCu/C. The Pt(Cu) electrocatalysts show more negative onset potentials for CO oxidation than Pt/C and PtCu/C, thus indicating their greater CO tolerance. Pt(Cu)/CNF and Pt(Cu)/MWCNT present the highest mass activity and specific activity for the O₂ reduction, respectively, both with better relative stability than Pt(Cu)/XC72. Pt(Cu)/CNF and Pt(Cu)/MWCNT are then considered good cathode catalysts, yielding estimated savings of about 50 wt% Pt, when applied to low-temperature fuel cells.     

Impact of pressure on carbon films by PECVD toward high deposition rates and high stability as metallic bipolar plate for PEMFCs

Stainless-steel bipolar plates (BPPs) are widely used in place of graphite bipolar plates in proton exchange membrane fuel cells (PEMFCs). Amorphous hydrogenated carbon (a-C:H) coatings are widely used to improve the conductivity and corrosion resistance of metal bipolar plates. However, a-C:H coatings prepared by the sputtering method cannot be applied to quantity production on account of its low deposition rate. Our paper focuses on a-C:H coatings applied at metallic BPPs for PEMFCs produced by direct-current plasma-enhanced chemical vapor deposition (DC-PECVD) with high deposition rates. The effects of adjusting deposition pressures on the structure and properties of coatings have been investigated. The results show that the a-C:H coating deposited at 8 Pa deposition pressure have high stability, with a high deposition rate of 37.5 nm/min. As the deposition pressure increased, sp²-hybridized carbon atoms increased, the larger microcrystalline carbon clusters are found, and the structure will undergo different structural transformations in a-C:H coatings. Overall, the a-C:H coatings deposited at 8 Pa are attractive to be applied in metallic bipolar plate with have high deposition rates, dense coating structure, and proper carbon structure.     

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

Multiwalled carbon nanotubes (MWCNTs) are covalently modified with different molecular weights 400 and 2000 poly(oxyalkylene)-amine bearing the diglycidyl ether of bisphenol A (DGEBA) epoxy (POA400-DGEBA and POA2000-DGEBA) oligomers. The oxidized MWCNTs (MWCNTs-COOH) are converted to the acid chloride-functionalized MWCNTs, followed by the reaction with POA-DGEBAs to prepare the MWCNTs/POA400-DGEBA and MWCNTs/POA2000-DGEBA. FTIR, thermogravimetric analysis (TGA) and high resolution X-ray photoelectron spectra (XPS) reveal that the POA-DGEBAs are covalently attached to the surface of MWCNTs. The morphology of MWCNTs/POA-DGEBA is observed by TEM. The POA400-DGEBA coated on the MWCNTs is thicker and more uniform. However, the coating of POA2000-DGEBA on the MWCNTs shows a worm-like bulk substance and the MWCNT surface is bare. In addition, the flexural strength and the bulk electrical conductivity of the MWCNTs/polypropylene nanocomposite bipolar plates are measured 59% and 505% higher than those of the original composite bipolar plates by adding 8 phr of MWCNTs/POA400-DGEBA. The maximum current density and power density of the single cell test for the nanocomposite bipolar plate with 4 phr MWCNTs/POA400-DGEBA are 1.32 A cm⁻² and 0.533 W cm⁻², respectively. The overall performance confirms the functionalized MWCNTs/polypropylene nanocomposite bipolar plates prepared in this study are suitable for PEMFC application.     

Preparation and properties on the graphite/polypropylene composite bipolar plates with a 304 stainless steel by compression molding for PEM fuel cell

Graphite/polymer composites have high corrosion resistance, low contact resistance and low fabrication cost but low cell efficiency and mechanical strength. This study examined the electrical and mechanical properties of graphite/polypropylene composite bipolar plates. Carbon nanotubes (CNTs) were used to improve the electrical properties of the graphite/PP composites. Although the electrical properties increased when excess conducting filler was added to the composite, the mechanical strength decreased significantly. 304 stainless steel (304 SS) plates with different thicknesses were used as the support material of a graphite/PP composite bipolar plate. The 304 SS-supported graphite/PP composite bipolar plate had an optimum CNTs/graphite/PP composite composition of 1.2, 83 and 17 wt.%, respectively. The flexural strength of the 304 SS-supported graphite/PP composites increased from 35 to 58 MPa with increasing 304 SS thickness from 0.5 to 1 mm. The power density of the graphite bipolar plate and 304 SS-supported graphite/PP composite bipolar plate were 968 and 877 mW cm⁻², respectively. The 304 SS complemented the mechanical strength of the graphite/PP composite bipolar plate as well as the cell efficiency.     

A nanocomposite photoelectrode made of 2.2 eV band gap copper tungstate (CuWO4) and multi-wall carbon nanotubes for solar-assisted water splitting

We report on the photoelectrochemical performances of a nanocomposite photoactive material made of copper tungstate (CuWO₄) and multi-wall carbon nanotubes (MWCNT). The purpose of this work was to create a light absorber/charge collector composite material with tunable electronic transport properties to minimize the bulk resistance of CuWO₄ material class. Nanocomposite thin films (typically 2.0 ± 0.1 μm) were fabricated by means of spray pyrolysis using solutions containing copper acetate, ammonium metatungstate and MWCNT. Spray-deposited polycrystalline CuWO₄ films were found to be porous, though crack-free, and made of CuWO₄ nanoparticles with dimensions in the 10–50 nm range. Tauc plots derived from UV–visible and photocurrent spectroscopy techniques led to a consistent band gap value of 2.20 (±0.05) eV. Electrochemical impedance spectroscopy performed in pH10 buffer solution under Air Mass 1.5 global (AM1.5_G) at 0.8 V vs. saturated calomel electrode (1.63V vs. reversible hydrogen electrode) pointed out a bulk resistance reduction by 30% on nanocomposites photoanodes when compared to un-modified CuWO₄ control samples. It is worth mentioning that the reduction in bulk resistance was achieved with an extremely low MWCNT:CuWO₄ weight ratio (1:10,000), in which MWCNT absorbed less than 2% of incoming light. Subsequent linear scan voltammetry (LSV) performed in the same conditions revealed a photocurrent density increase of 26% at 0.8 V_SCE (1.63 V_RHE) compared to control samples. Additional LSV and incident photon-to-current efficiency measurements demonstrated that MWCNT served as effective electron collectors distributed throughout the entire CuWO₄ bulk.     

Hexagonal boron nitride (h-BN) nanoparticles decorated multi-walled carbon nanotubes (MWCNT) for hydrogen storage

Hydrogen is considered as the most promising clean energy carrier because of its abundance, environmental friendliness and high conversion efficiency. However, developing safe, compact, light weight and cost-effective hydrogen storage materials is one of the most technically challenging barriers to the widespread use of hydrogen as fuel. The present work reports the hydrogen storage performance of multi-walled carbon nanotubes (MWCNT)/hexagonal boron nitride (h-BN) nanocomposites (MWCNT/h-BN), where ultrasonication method is adopted for the synthesis of the MWCNT/h-BN nanocomposites. Hydrogenation process was carried out using Seiverts-like hydrogenation setup. Characterization techniques such as X-ray Diffraction (XRD), Micro-Raman Spectroscopy, Fourier Transform Infrared (FTIR) Spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDX), Nitrogen adsorption–desorption isothermal studies (BET), CHN-elemental analysis and Thermogravimetric Analysis (TGA) were used to analyze the samples at various stages of the experiment. A maximum of 2.3 wt% hydrogen storage is achieved in the case of acid treated MWCNTs (A-MWCNT) with 5 wt% of h-BN nanoparticles compared to pure MWCNTs that could store 0.15 wt% only. Moreover the calculated binding energy (0.42 eV) of stored hydrogen of A-MWCNT with 5 wt% of h-BN nanocomposite lies in the recommended range of binding energy (0.2–0.6 eV) for fuel cell applications. The TG study shows that 100% desorption is achieved at the temperature range of 120–410 °C and confirms that the prepared hydrogen storage medium will serve effectively in the realm of hydrogen fuel economy in near future.     

Preparation and properties of high performance nanocomposite bipolar plate for fuel cell

This study aims at developing lightweight and high performance composite bipolar plates for use in polymer electrolyte membrane fuel cells (PEMFCs). The thin polymer composite bipolar plates (the thickness <1.5 mm) containing of vinyl ester resin, graphite powder, organoclay have been fabricated by bulk molding compound (BMC) process. Organoclay was prepared by ionic exchange of montmorillonite (MMT) with three different molecular weight (M_w) of poly(oxypropylene)-backboned diamine intercalating agents. Results indicate that the basal spacing and content of MMT varied with M_w of POP-diamines are critical in determining the resultant mechanical properties for bipolar plates. Flexural strength of MMT composite plates was increased from 30.21 to 45.66 MPa by adding 2 phr of MMT. The flexural strength of the plate was also ca. 38% higher than the pristine graphite plate as the basal spacing of MMT was increased from 1.71 to 5.43 nm. Meanwhile, the unnotched impact strength of the composite plates was increased from 58.11 to 80.21 J m⁻¹. The unnotched impact strength of the plate was ca. 30% higher than that of the original graphite plates as the basal spacing of MMT was increased from 1.71 to 5.43 nm. The limiting oxygen index (LOI) and the UL-94 test revealed that the bipolar plate possesses excellent flame retardant with LOI >50 and UL-94-V0. The thermal decomposition temperature of each MMT composite plate is also higher than 250 °C. In addition, the bulk electrical conductivity of the bipolar plate with different MMT contents and basal spacing of MMT is higher than 100 S cm⁻¹. The corrosion current is less than 10⁻⁷ A cm⁻². Results confirm that the addition of MMT leads to a significant improvement on the performance of the composite bipolar plate.     

Incorporating carbon nanotube in a low-temperature fabrication process for dye-sensitized TiO2 solar cells

Dye-sensitized solar cells (DSSCs) incorporating TiO₂ porous films, prepared at a low temperature (150 °C), along with multi-wall carbon nanotubes (MWCNTs) were studied using two different electrolytes, namely LiI and THI. Electrochemical impedance spectroscopy (EIS) was employed to quantify the charge transport resistance and electron lifetime (τ_e) under different levels (wt%) of MWCNTs and electrolytes. The charge transport resistance at the TiO₂/dye/electrolyte interface (R_ct2) increased as a function of the MWCNT concentration, which ranged 0.1-0.5 wt%, due to a decrease in the surface area and decreased dye adsorption. The characteristic peak shifted to a lower frequency at 0.1 wt% of MWCNT, indicating a longer electron lifetime. The DSSC with the TiO₂ electrode containing 0.1 wt% of MWCNT resulted in a higher short-circuited current density (J_SC) of 9.08 mA/cm², an open-circuit voltage (V_OC) of 0.781 V, and a cell conversion efficiency of 5.02%. EIS was also conducted under dark conditions. The large value at a middle frequency represented electron transport at the TiO₂/dye/electrolyte interface (R_rec). The R_rec for 0.1 wt% MWCNT/TiO₂ was found to be 114 Ω, and for those with 0.3 and 0.5 wt% were 35 and 30 Ω, respectively. The significantly higher value of R_rec suggested that the charge recombination between injected electrons and electron acceptors in the redox electrolyte, I₃⁻, was remarkably retarded. Finally, electrolytes with LiI and THI were used to compare the cell conversion performance under the same conditions. It was found that more electrons were injected in the TiO₂ electrode and the electron recombination reaction was faster in the DSSC with THI than that with LiI.     

Platinum/carbon nanofiber nanocomposite synthesized by electrophoretic deposition as electrocatalyst for oxygen reduction

A platinum/carbon nanofiber (Pt/CNF) nanocomposite with a platinum loading of 15 wt% is prepared by a modified electrophoretic deposition (EPD) method, and the as-grown nanocomposite is used as the electrocatalyst for oxygen reduction reaction (ORR). For comparison, a Pt/CNF composite with 40 wt% platinum loading is prepared by chemical reduction. High resolution transmission electron microscope (HRTEM) images show that the size of platinum nanoparticles formed by EPD is about 1 nm, much smaller than those by chemical reduction (about 3–5 nm). Cyclic voltammetric analysis in a nitrogen saturated electrolyte shows that the electrochemical surface area of electrocatalyst by EPD is larger than that by chemical reduction. Moreover, although the electrocatalyst prepared by chemical reduction has a higher electrochemical capacity, it is less active than that prepared by EPD. Analysis of the electrode kinetics using Tafel plot suggests that the electrocatalyst prepared by EPD provides a strong ORR activity. Cyclic voltammetric measurements at different scan rates confirm that the ORR on the nanocomposites prepared by EPD is a diffusion-controlled process. This work demonstrates that the Pt/CNF composites synthesized by EPD are effective for ORR.     

Electrosynthesis of hierarchical Cu2O–Cu(OH)2 nanodendrites supported on carbon nanofibers/poly(para-phenylenediamine) nanocomposite as high-efficiency catalysts for methanol electrooxidation

The development of highly efficient catalysts using inexpensive and earth-abundant metals is a crucial factor in a large-scale commercialization of direct methanol fuel cells (DMFCs). In this study, we explored a new catalyst based on copper nanodendrites (CuNDs) supported on carbon nanofibers/poly (para-phenylenediamine) (CNF/PpPD) nanocomposite for methanol oxidation reaction (MOR). The catalyst support was prepared on a carbon paste electrode by electropolymerization of para-phenylenediamine monomer on a drop-cast carbon nanofibers network. Afterwards, CuNDs were electrodeposited on the nanocomposite through a potentiostatic method. The morphology and the structure of the prepared nanomaterials were characterized by transmission electron microscope, scanning electron microscope, energy dispersive X-ray, X-ray diffraction, and X-ray photoelectron spectroscope. The results suggested that a three-dimensional nanodendritic structure consisting of Cu₂O and Cu(OH)₂ formed on the hybrid CNF/PpPD nanocomposite. The catalytic performance of CuNDs supported on CNF, PpPD and CNF/PpPD was evaluated for MOR under alkaline conditions. The CNF/PpPD/CuNDs exhibits a highest activity (50 mA cm^?2) and stability toward MOR over 6 h, with respect to CNF/CuNDs (40 mA cm^?2) and PpPD/CuNDs (36 mA cm^?2). This inexpensive catalyst with high catalytic activity and stability is a promising anode catalyst for alkaline DMFC applications.     

Synthesis of carbon nanofibers/poly(para-phenylenediamine)/nickel particles nanocomposite for enhanced methanol electrooxidation

Several studies have been conducted on direct methanol fuel cells (DMFCs) to resolve major issues such as the high cost of the catalyst and the poisoning of the electrode. Herein, a low-cost catalyst based on nickel particles (NiPs), carbon nanofibers (CNF) and poly(para-phenylenediamine) (PpPD) was carried out using a simple electrochemical method. The morphology and structure of the nanocomposite electrodes are characterized by field-emission gun scanning electron microscopy coupled with an energy dispersive X-ray detector, X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. The effects of various parameters such as the PpPD film thickness and the NiPs content on the electrocatalytic performance of CPE/CNF/PpPD/NiPs are evaluated which lead to the optimized composition. The results of the methanol electrooxidation reaction at room temperature showed that the optimized CPE/CNF/PpPD/NiPs nanocomposite exhibits a high catalytic activity (I_p = 38.11 mA cm⁻²), good stability and durability for more than 6 h in comparison with CPE/CNF/NiPs. These findings truly highlight the synergetic effect of CNF/PpPD in enhancing the electrochemical activity and stability and the vast potential of CPE/CNF/PpPD/NiPs as low-cost catalyst and electrodes for DMFCs.     

Electrical and thermal conductivities of novel metal mesh hybrid polymer composite bipolar plates for proton exchange membrane fuel cells

This study prepares novel metal mesh hybrid polymer composite bipolar plates for proton exchange membrane fuel cells (PEMFCs) via inserting a copper or aluminum mesh in polymer composites. The composition of polymer composites consists of 70 wt% graphite powder and 0-2 wt% modified multi-walled carbon nanotubes (m-MWCNTs). Results indicate that the in-plane electrical conductivity of m-MWCNTs/polymer composite bipolar plates increased from 156 S cm⁻¹ (0 wt% MWCNT) to 643 S cm⁻¹ (with 1 wt% MWCNT) (D.O.E. target >100 S cm⁻¹). The bulk thermal conductivities of the copper and aluminum mesh hybrid polymer composite bipolar plates (abbreviated to Cu-HPBP and Al-HPBP) increase from 27.2 W m⁻¹ K⁻¹ to 30.0 W m⁻¹ K⁻¹ and 30.4 W m⁻¹ K⁻¹, respectively. The through-plane conductivities decrease from 37.8 S cm⁻¹ to 36.7 S cm⁻¹ for Cu-HPBP and 22.9 S cm⁻¹ for Al-HPBP. Furthermore, the current and power densities of a single fuel cell using copper or aluminum mesh hybrid polymer composite bipolar plates are more stable than that of using neat polymer composite bipolar plates, especially in the ohmic overpotential region of the polarization curves of single fuel cell tests. The overall performance confirms that the metal mesh hybrid polymer composite bipolar plates prepared in this study are promising for PEMFC application.     

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.     

Durability enhancement of a Pt/C electrocatalyst using silica-coated carbon nanofiber as a corrosion-resistant support

Electrochemical oxidation of a carbon support is one of the major challenges to making proton exchange membrane fuel cells (PEMFCs) durable. The aim of this study was to develop a durable carbon-based electrocatalyst support for use in PEMFCs. Platelet-type carbon nanofiber (PCNF) was coated in a uniform and discrete manner with silica by successive hydrolysis of two kinds of silica precursors, APTES and TEOS. The shape and thickness of the silica coating on carbon was controlled by adjusting the amount of APTES and TEOS. The platinum was mainly deposited on silica rather than carbon because the zeta potential of silica is more favorable to binding platinum precursor ions than that of PCNF. Accelerated degradation testing of the silica-coated catalysts (Pt/PCNFSiO₂) and Pt/PCNF showed that Pt/PCNFSiO₂ possess higher durability than Pt/PCNF under potential cycling. After 30,000 potential cycles ranging from 1.0 V to 1.5 V, the electrochemical surface area losses were 21%, 16%, and 11% and the half-wave potential (E_1/2) degradation losses were 16 mV, 9 mV, and 8 mV for Pt/PCNF and Pt/PCNFSiO₂ with two different amounts of silica wt%. Silica-coated carbon nanofibers are expected to be a suitable electrocatalyst support for PEMFCs.     

Preparation of multiwalled carbon nanotubes/Cd0.8Zn0.2S nanocomposite and its photocatalytic hydrogen production under visible-light

Multiwalled carbon nanotubes (MWCNTs)/Cd_0.8Zn_0.2S nanocomposites were synthesized via the simple co-precipitation of pretreated MWCNTs, acetates and sodium sulfide. The photocatalytic activities for hydrogen production of the produced MWCNTs/Cd_0.8Zn_0.2S with different amount of MWCNTs were systematically investigated under visible-light (λ ≥ 420 nm) irradiation. Enhanced photoactivity of the nanocomposite was observed and can be attributed to the synergetic effect of its components’ intrinsic properties, such as excellent light absorption and charge separation on the interfaces between the modified MWCNTs and Cd_0.8Zn_0.2S. It is also found that the nanocomposite with 15 wt% MWCNTs shows a higher photocatalytic hydrogen production efficiency and photostability than the pristine CdS and Cd_0.8Zn_0.2S nanoparticles. The MWCNTs/Cd_0.8Zn_0.2S nanocomposite holds promise for hydrogen production by improving the visible-light-driven photoactivity and photostability of Cd_0.8Zn_0.2S.     

Study on the mesocarbon microbeads/polyphenylene sulfide composite bipolar plates applied for proton exchange membrane fuel cells

Thermoplastic/graphite composite bipolar plates based on polyphenylene sulfide (PPS) and mesocarbon microbeads (MCMB) were prepared by compression molding at a pressure of 40 MPa and 400 °C. Electrical conductivity, bulk density, flexural strength, water and ethanol absorption were determined as function of PPS content. The influences of molding time, actived carbon and carbon fiber on the properties of the composite bipolar plates were investigated, the cross section of the composite plates were analyzed by scanning electron microscope (SEM). We found that the optimized PPS content is 20 wt% and the required molding time is 30 min. In particular, the composite plates containing 20 wt% PPS demonstrated in-plane conductivity as high as 133.7 S cm⁻¹, through-plane conductivity 21.37 S cm⁻¹, in addition to showing the value of density, flexural strength, water and ethanol absorption as 1.98 g cm⁻³, 38.82 MPa, 0.0409 and 0.352 g cm⁻³. The addition of actived carbon degraded all the performance of the bipolar plate, while addition of carbon fiber improved almost all the performance of bipolar plate except bulk density and through-plane conductivity. The performances of fuel cell with this composite bipolar plate were tested, no distinct variation occurred after the composite plates operating in fuel cell. These data indicates the chemical and mechanical stability of the composite plates and their potential application in fuel cell.