Addition Of Polytetrafluoroethylene Research Articles

Comprehensive Analysis of Wettability in Waterproofed Gas Diffusion Layers for Polymer Electrolyte Fuel Cells.

In polymer electrolyte fuel cells (PEFCs), the gas diffusion layer (GDL) is crucial for managing the flooding tolerance, which is the ability to remove the water produced during power generation from the assembled cell. However, an improved understanding of the properties of GDLs is required to develop effective waterproofing strategies. This study investigated the influence of the polytetrafluoroethylene (PTFE) content on the pore diameter, porosity, wettability, water saturation, and flooding tolerance of waterproofed carbon papers as cathode GDLs in PEFCs. The addition of minimal PTFE (∼6 wt %) to carbon paper provided external waterproofing, whereas internal waterproofing was achieved at a higher PTFE content (∼13 wt %). However, excessive PTFE (∼37 wt %) led to macropore collapse within the carbon paper, reducing fuel cell performance. Although PTFE addition was expected to improve the flooding tolerance, operando synchrotron X-ray radiography revealed that the water saturation level in carbon paper increased with increasing PTFE content. These findings provide a benchmark for assessing whether GDLs meet the flooding tolerance requirements of PEFCs and may be applicable to waterproofed GDLs in electrochemical devices for water and CO2 electrolysis.

Determination of “tribological performance working fields” for pure PEEK and PEEK composites under dry sliding conditions

Poly-ether-ether-ketone (PEEK) and PEEK composites are widely used polymers in many engineering applications where dry sliding is required. In this study, the influence of sliding velocity and applied load values on the friction and wear behavior of pure PEEK, 30 wt% glass fiber reinforced PEEK (PEEK-30GF), 30 wt% carbon fiber reinforced PEEK (PEEK-30CF) and 10 wt% carbon fiber+10 wt%graphite +10 wt%poly-tetra-fluoro-ethylene (PTFE) filled PEEK (ie. High (H) pressure (P) and velocity (V) resistant PEEK (PEEK-HPV)) composites rubbing against AISI 304 stainless steel disc was investigated. The experiments were carried out at room temperature under dry sliding conditions in a pin-on-disc wear rig. The applied loads ranged from 30 to 250 N, while the sliding velocities ranged from 1.0 to 4.0 m/s. At these load and velocity ranges, the friction coefficient-wear rate relationship of pure PEEK and composites was established and evaluated. In addition, the operating load-velocity limits of each material were determined and stated. The lowest coefficient of friction and wear rate were obtained in PEEK-HPV, PEEK-30CF, PEEK-30GF composites and pure PEEK polymer, respectively. In addition, it was observed that the coefficient of friction (CoF) decreased and the specific wear rate (SWR) increased with the increase in sliding velocity and applied load in all PEEK materials. The wear rate values of PEEK-HPV and PEEK-30%CF composites are in the range of 10−7 - 10−6 (mm3/Nm), while the wear rate values of pure PEEK and PEEK-30%GF are in the range of 10−6 - 10−5 (mm3/Nm). It was determined that carbon fiber, graphite and PTFE additives added to PEEK polymer as hybrid were very effective in reducing the wear rate of PEEK composite (PEEK-HPV). An adhesive wear mechanism was observed in PEEK-HPV and PEEK-30CF composites both at low load and velocity values and at high load and velocity values.

Unveiling the Role of PTFE Surface Coverage on Controlling Gas Diffusion Layer Water Content.

Gas diffusion layers (GDLs) are usually coated with a hydrophobic agent to achieve a delicate balance between liquid and gas phases to maximize mass transport. Yet, most GDL numerical models to date have assumed an average contact angle for all materials, thereby eliminating the possibility of studying the role of the polytetrafluoroethylene (PTFE) content. This study introduces two mixed wettability algorithms to predict the mixed wetting behavior of GDLs composed of multiple materials. The algorithms employ contact angle and distance to solid materials to determine the critical capillary pressure for each pore voxel. The application of the algorithms to the estimation of capillary pressure vs saturation curves for two GDLs, namely, a micro-computed tomography (μ-CT) reconstructed SGL 39BA GDL and a stochastically reconstructed Toray 120C GDL, showed that, in agreement with experimental data, the addition of PTFE resulted in a decrease in saturation at a given capillary pressure. For Toray-120C, the mixed wettability model was capable of reproducing experimentally observed features in the intrusion curve at low saturation that could not be reproduced with a single wettability model, providing a clear link between PTFE coverage and intrusion at low saturation. Numerical results also predicted an increased breakthrough pressure and a decrease in saturation with increasing PTFE, in agreement with experimental observations. The decreased saturation at breakthrough improves gas transport through the layer while maintaining the layer's ability to remove water. Diffusivity simulations confirm the increase in diffusivity at breakthrough with increasing PTFE, thereby providing a rationale for the addition of PTFE, as well as for the optimal amount. This study emphasizes the importance of multimaterial wetting models and calls for more detailed investigations into PTFE and ionomer distributions in GDLs and catalyst layers, respectively.

Cold-Sintered ZnO Ceramic Composites Co-Doped with Polytetrafluoroethylene and Oxides.

Grain boundaries play a significant role in determining the performance of ceramic-based materials. The modulation of interfacial structures provides a promising approach to improve the physicochemical and electrical properties of ceramic materials. In this work, the grain boundary structures of ZnO-based ceramics were manipulated by incorporating polytetrafluoroethylene (PTFE) and metal oxides through the cold sintering process (CSP). It was found that the grain size of ZnO-based ceramics can be effectively reduced from 525.93 nm to 338.08 nm with an addition of PTFE and metal oxides of CoO and Mn2O3. Microstructural results show that most of the PTFE phase and metal oxides were distributed along the grain boundaries, which may lead to the increased grain boundary resistance from 1.59 × 106 ohm of pure ZnO to 6.21 × 1010 ohm of ZnO-based ceramics doped with PTFE and metal oxides, and enhanced Schottky barrier height from 0.32 eV to 0.59 eV. As a result, the breakdown field and nonlinear coefficient of the ZnO-based ceramics were improved to 3555.56 V/mm and 13.55, respectively. Therefore, this work indicates that CSP presents a feasible approach to design functional ceramic composites through the integration of polymer and metal oxides.

Comparative study on the tribological properties of poly(arylene ether nitrile)/polytetrafluoroethylene composites: The influence of filler size and testing conditions

AbstractIn this work, the influence of polytetrafluoroethylene (PTFE) filler size and testing conditions (i.e., air, water, and lubricating oil) on the tribological properties of poly(arylene ether nitrile) (PEN) was systematically investigated. The results showed that the addition of PTFE was beneficial to improve the tribological properties of PEN‐based composites which was related to the easier formation of transfer film on the surface of friction pair. Samples which were tested in water demonstrated a relatively higher friction coefficient (μ) and wear loss when compared with those tested in dry air and lubricating oil scenarios, which was attributed to the fact that friction induced heat and wear debris could be timely removed by water. In addition, the infiltration of water further reduced the interaction between PTFE filler and PEN, which aggravated the wear loss of sample blocks. When tested in lubricating oil, pure PEN showed the lowest wear loss when compared with that of PEN/PTFE composites. At a given content (20 wt%) of PTFE fillers, PEN/PTFE1.5μm exhibited the lowest μ in lubricating oil whereas PEN/PTFE5μm demonstrated the lowest specific wear loss in air condition (1.18 × 10−6 mm3/N·m). This work provided some useful information for the design and application of PTFE‐containing polymer composites that can be targeted in different lubrication scenarios in industrial fields.

Characterisation of flame retarded recycled PET foams produced by batch foaming

CO2-assisted batch foaming was used to manufacture low-density (ρ = 200–350 kg/m3) microcellular foams from bottle-grade recycled poly(ethylene terephthalate) (rPET) in flame retarded form. The foamability of the PET regrind was enhanced using a reactive chain extender while the flame retardant properties of the rPET foams were improved by incorporating 6% aluminium-tris-(diethylphosphinate) flame retardant (FR). The effects of adding 1% natural montmorillonite (MMT) and polytetrafluoroethylene (PTFE) powder as potential cell nucleating agent and flame retardant synergist were also investigated. As a result of FR addition, the foam structure became less uniform, but the presence of MMT was found to improve uniformity of cellular size and distribution. The applied FR mainly acts in the gas phase as flame inhibitor, but also promotes charring of the foams, as revealed by thermogravimetric analysis (TGA) and pyrolysis combustion flow calorimetry (PCFC). The fine microcellular structure and high cell density allow homogeneous distribution of FR additives, and thus only moderate increase in flammability was observed for the high-porosity (>75%) foams compared to the corresponding bulk materials, as characterized by similar limited oxygen index (LOI) values. In cone calorimeter tests, for the flame retarded foams a 50% reduction in peak heat release rate (PHRR) and a 30% reduction in total heat release (THR) values were measured compared to the FR-free reference. The PTFE addition to the FR formulation was found to increase the time-to-ignition (TTI), reduce PHRR and effective heat of combustion (EHC) while increase charring. The mechanical performance of the flame retarded rPET foams was found to be primarily determined by the apparent density and less affected by the presence of FR additives. Due to strain-induced crystallization occurring during cell growth, the rPET foams are highly crystalline (χ > 25%) which leads to increased thermomechanical resistance compared to unfoamed references.

Effect of current density and polytetrafluoroethylene on the properties of micro‐arc oxide coating of pure aluminum

AbstractMicro‐arc oxidation (MAO) is a surface treatment technology that enhances the surface properties of valves by creating a ceramic oxide layer on the metal surface. The goal of this study is to investigate the influence of current density on the properties of aluminum coatings during preparation and to improve the tribological properties of MAO/PTFE self‐lubricating films on the coating surface. The characterization of the coating was performed using X‐ray photoelectron spectroscopy, X‐ray diffraction, Raman spectra, and energy dispersive spectroscopy. The roughness, hardness, and elastic modulus of the coatings were tested using atomic force microscopy and nanoindentation. Tribological experiments were conducted to evaluate the tribological properties of the coatings. The experimental results show that the friction coefficient (COF), roughness, hardness, and elastic modulus of the MAO coating increase with the increase of current density. Additionally, the friction coefficient of the MAO composite coating significantly decreases after the addition of polytetrafluoroethylene (PTFE), improving the service life and application range of the metal coating. These findings are expected to promote the development of valve metal in various application fields.

Freezing characteristics of supercooled water in gas diffusion layer of proton exchange membrane fuel cells

The freezing characteristics of supercooled water in a gas diffusion layer (GDL), which are the bases for the cold start-up of proton exchange membrane fuel cells (PEMFCs), were investigated. An experimental apparatus for noncontact temperature measurement and observation systems was developed. GDL and GDL with a microporous layer (MPL) were prepared, and freezing experiments using a water-containing GDL under various cooling rates were performed with variations in polytetrafluoroethylene (PTFE) content and water saturation. Furthermore, based on the experimental results, the freezing initiation probability was theoretically investigated to elucidate the freezing characteristics. Results showed that, with increasing supercooling of water in GDL, the freezing probability of water increased abruptly. The effect of saturation showed a different trend depending on PTFE addition. For the GDL without PTFE, the freezing initiations occurred at approximately 6 °C of supercooling degree, and the probability approached 1.0 at approximately 9.5–11.5 °C, with saturation dependency. In contrast, for both GDL and GDL + MPL containing PTFE, the initiation temperature characteristics were relatively similar, which were approximately 8–12 °C, regardless of the saturation and PTFE content. In these cases, the ice-nucleating activity of water in the GDL was possibly stronger than that in the MPL.

Preparation, Characterization, and Kinetic Analysis of Fluorine- containing Aluminum Thermite

The addition of polytetrafluoroethylene as a binder in aluminum thermite allows the application of aluminum thermite from the traditional high temperature and high heat to the chemical corrosion direction. The stability of the samples was tested by theoretical calculations of the critical thermal explosion and mechanical sensitivity experiments. The microscopic morphology of the aluminum thermite was characterized by scanning electron microscopy, and the thermodynamic properties of the samples at different heating rates were investigated by the TG-DSC method.

Solid-state cross-coupling reactions of insoluble aryl halides under polymer-assisted grinding conditions.

In this study, polymer-assisted grinding (POLAG), a ball-milling technique based on the use of polymer additives, was applied to mechanochemical solid-state Suzuki-Miyaura cross-coupling reactions of insoluble aryl halides. We found that the efficiency of this challenging solid-state cross-coupling was improved by the addition of polytetrafluoroethylene (PTFE) as a POLAG additive under high-temperature ball-milling conditions. Our results suggest that POLAG is a promising approach for controlling the reactivity of insoluble substrates that are barely reactive under conventional solution-based conditions.

Synthesis of Hybrid PVDF–PTFE Membrane Using Nonhazardous Solvent for Ethanol–Water Separation through Membrane Distillation

This work was focussed on synthesizing a polyvinylidene fluoride (PVDF)–polytetrafluoroethylene (PTFE) hybrid flat sheet membrane using a nonhazardous solvent dimethyl sulfoxide (DMSO) for ethanol–water separation via vacuum membrane distillation (VMD). The base polymer (PVDF) concentrations were varied from 12 wt% to 16 wt% and the copolymer (PTFE) loading were ranged from 1 wt% to 2 wt% (e.g., 1.0 wt%, 1.5 wt%, and 2.0 wt%). The morphological characteristics, porosity, and contact angle (CA) were examined for the synthesized membranes. An increased CA was observed when PTFE loading was increased in the dope solution. The addition of PTFE to the dope solution efficiently diminished the formation of micro voids and increased the hydrophobicity of the membrane with improved characteristics. Membrane pore size, porosity, and thickness increased significantly from 0.17 µm to 0.21 µm, 48.37% to 67.79%, and 79.31 µm to 107.62 µm, respectively, within the studied range. A pure PVDF membrane CA of 88° was increased to 117.3° for 2 wt% loaded PTFE in PVDF. The synthesis of PVDF–PTFE hybrid membranes that used DMSO as a solvent and distilled water as a nonsolvent in a coagulation bath appears to be viable for membrane preparation via phase inversion to provide a reliable and sustainable separation process with a safer environment. The performance of the synthesized membrane was studied for flux and the separation factor. The maximum ethanol flux and separation factor obtained were 11 kg/m2/h and 7.0, respectively. This work suggests that the PVDF–PTFE hybrid flat sheet membranes could be used for ethanol separation in VMD.

Preparation and characterization of cross-linked waterborne acrylic /PTFE composite coating with good hydrophobicity and anticorrosion properties

The use of waterborne acrylic coatings in anticorrosion applications is challenging owing to the existence of numerous hydrophilic carboxyl groups. Hence, the objective of this study was to develop a facile method of preparing waterborne acrylic anticorrosive coating. Specifically, a waterborne hydrophobic acrylic resin (PFSA) with 3-(methacryloyloxy)propyltris(trimethylsilyloxy) silane (M3T) and 2-(perfluorooctyl)ethyl methacrylate (FMA) as hydrophobic monomers was synthesised via semi-continuous seed emulsion polymerisation. Owing to the substantial influence of the acrylic acid (AA) content on the polymerisation stability, the effect of the AA amount on the emulsion polymerisation process and surface properties of the PFSA film were assessed, where the M3T/FMA mass ratio was set to 4.47. The latex particles were proven to have a core-shell structure using transmission electron microscopy. When the AA content was 2.75 wt%, the water contact angle of the obtained PFSA-2 film reached 103.2°, and the emulsion coagulum was only 0.66%. Thereafter, CPFSA coatings (namely, CPFSA-1, CPFSA-2, and CPFSA-3) were obtained by mixing PFSA-2 with different proportions of trimethylolpropane-tris-(β-N-aziridinyl) propionate (XR-100; 2, 4, and 6 wt%). Similarly, CPFSA@PTFE coatings (namely, CPFSA-1 @PTFE, CPFSA-2 @PTFE and CPFSA-3 @PTFE) were prepared by mixing CPFSA with 2 wt% polytetrafluoroethylene (PTFE). The cross-linking between PFSA and XR-100 reduced the water absorption rate and strengthened the coating hardness, adhesion, and compactness, despite a slight decrease in thermal stability. The addition of PTFE to the CPFSA further improved the film hydrophobicity, smoothness and they all exhibited excellent mechanical durability. Most importantly, electrochemical impedance spectroscopy indicated that the corrosion resistances of the investigated coatings used as the topcoats in 3.5 wt% NaCl solution followed the order CPFSA@PTFE > CPFSA > PFSA-2 > Bare epoxy. Especially for the CPFSA-2 @PTFE coating, |Z| 0.01 Hz was 2.182 × 1010 Ω cm−2 even after 15 days of immersion.

Energy Performance of HMX‐Based Aluminized Explosives Containing Polytetrafluoroethylene (PTFE)

AbstractInvestigation of the energy performance of HMX‐based aluminized explosives added with polytetrafluoroethylene (PTFE) oxidizer was undertaken and compared with the PTFE‐free aluminized explosive of similar formulation. Firstly, the heat of explosion was measured in a calorimetric bomb, next the underwater explosion was conducted, then the cylinder expansion test was performed, and finally, the detonation reaction zone parameters were determined by the interface particle velocity experiment. Compared with the PTFE‐free aluminized explosive, the addition of PTFE into aluminized explosives increases the heat of explosion significantly from the calorimetric data. The PTFE‐containing aluminized explosive also yields the longer first bubble oscillation time in the underwater explosion than the PTFE‐free and ammonium perchlorate‐containing counterparts. From the cylinder test data, the wall velocity and Gurney energy were determined. The aluminized HMX containing PTFE shows an inferior acceleration ability to PTFE‐free aluminized HMX, but exhibits a stronger afterburning potential. The addition of PTFE to aluminized HMX decreases detonation velocity and CJ pressure and increases the detonation reaction zone time and length. It has reasons to believe that the PTFE partially decomposes in detonation reaction zone. Conclusions on the potential use and suggestion for future research of PTFE as an oxidizer in aluminized explosives are drawn.

Influence of Li2MoO4 and polytetrafluoroethylene addition on the cold sintering process and dielectric properties of BaBiLiTeO6 ceramics

Composites of BaBiLiTeO6 (BBLTO) - Li2MoO4 (LMO) and BaBiLiTeO6 - polytetrafluoroethylene (PTFE) were fabricated using cold sintering process and their microwave dielectric properties were investigated for the first time. Phase purity and reactivity of the composites were studied using XRD and vibrational spectroscopy. Influence of filler content, sintering duration and temperature on the density and dielectric properties of the composites were studied. Both BBLTO-LMO and BBLTO-PTFE composites exhibit dense microstructures at optimized sintering conditions. Broadband (10 MHz–1 GHz) dielectric response shows that relative permittivity (εr) and dielectric loss (tanδ) of composites are in the range of 9–16 and 0.02–0.11 respectively and the experimental relative permittivity is compared with theoretical models. A microstrip patch antenna based on BBLTO - PTFE composite was designed using High Frequency Structure Simulator (HFSS) software and the fabricated antenna radiates at 2.88 GHz with a return loss of −26.8 dB and impedance bandwidth of 90 MHz.

Statistical characterization of non-linear microscopic mechanical deformation through randomly oriented fibrous porous transport layers for advanced electrochemical energy systems

A robust compression model based on the unit-cell beam bending theory is presented to predict the mechanical behavior of stochastically generated fibrous porous transport layers (PTLs) at various clamping pressures. For this purpose, three-dimensional PTLs were constructed by piling random paper-type carbon-fiber structures. A representative elementary volume was determined based on the relative porosity gradient errors with a 95% confidence level for statistical analyses. Subsequently, a mechanical compression model based on the beam bending theory was developed to determine the microscale deformation characteristics of the PTLs for electrochemical energy systems. Based on the beam bending theory, carbon fibers are modeled as beams, and the bending of fibers is considered to be the main contributor to deformation of the PTLs. The numerical model shows good agreement with published experimental data in literature, i.e., a nonlinear stress–strain relationship. Next, the model was applied to feature bulk and local mechanical variations of the PTLs as functions of the number of carbon-fiber layers, porosity, polytetrafluoroethylene (PTFE) loading, and external clamping pressure. It was found that the addition of binder/PTFE into fibrous substrates results in the decreased porosity and increased mechanical strength of the PTLs. The detailed three-dimensional microscale deformation simulations revealed that the statistical mean strain of the PTLs was exponentially proportional to the porosity in the range 0.7–0.9 and decreased on addition of PTFE in the fibrous carbon substrate at a stack clamping pressure of 1 MPa. Moreover, the statistically estimated local strain distribution along the in- and through-planes of the PTLs indicated that the microscopic local deformation was approximately uniform through the PTLs. This modeling study can be utilized to understand the mechanical behavior of heterogeneous PTLs during external compression for advanced electrochemical systems.

Measurement of Contact Angles at Carbon Fiber-Water-Air Triple Phase Boundaries inside Gas Diffusion Media of Polymer Electrolyte Membrane Fuel Cells from Xray Computed Tomography

Gas diffusion layers (GDLs) are porous fiber layers that are used for various electrochemical applications, including fuel cells, electrolyzers, CO2 reduction reaction electrolyzers, and redox flow batteries. Depending on its application, a GDL’s wettability is controlled by the addition of polytetrafluoroethylene (PTFE). The PTFE addition is highly stochastic, resulting in inhomogeneous distribution. Furthermore, the fibers, carbonaceous binder, and PTFE all have different surface roughness and surface properties that dictate GDL wettability. To determine the contact angle of the GDL, goniometer measurements of external contact angle are used, where a droplet of water is placed on the top of the GDL and a contact angle is projected onto a detector. However, this form of measurement has limitations that need to be accounted for as the GDL is highly porous and its surface and internal contact angles might be different due to inhomogeneous binder and PTFE distribution. For the first time, we have applied a method to calculate the internal contact angle distribution of water inside various commercial GDLs. Lattice Boltzmann water transport simulations using these contact angle distributions yielded results much closer to experimental values than simulations that used goniometer-measured constant contact angles. XPS was used to correlate surface oxide groups to measured internal contact angles.AlRatrout et al. developed an open-source C++ code to compute local contact angles at triple phase boundary points (comprised of a solid and two fluids) from micro Xray computed tomography (XCT) images of porous media [1]. We applied it to segmented micro XCT images of water filled commercial GDL samples and computed local contact angles at air-GDL-water triple phase contacts points (Figure 1A). We obtained a state of mixed wettability inside all GDL samples, with contact angles ranging from 0° to 180° inside the pores (Figure 1B). Several works have calculated average contact angles similar to our results using other methods [2, 3]. Hydrophilicity is due to the presence of surface oxide groups on GDL fibers while hydrophobicity is due to the chemical nature of carbon and the roughness of the GDL fibers. Lattice Boltzmann water transport simulations were performed with the spatially distributed, mapped contact angles and constant contact angles measured with a goniometer (Figure 1C-F) [4]. When our mapped, mixed-wettability contact angle distributions were used, the simulation revealed several regions of high liquid saturation that the constant contact angle simulations did not capture. These results agreed with experimental observations. Thus, for robust water transport simulations, we suggest that distributed contact angles should be used instead of goniometer-measured constant contact angles.

In situ micro-fibrillization and post annealing to significantly improve the tribological properties of polyphenylene sulfide/polyamide 66/polytetrafluoroethylene composites

Self-lubricating polyphenylene sulfide (PPS)-based composites were achieved by in-situ construction of ordered polyamide 66 (PA) microfibrillar structure coupling with the addition of polytetrafluoroethylene (PTFE) powders as solid lubricants, using high shear injection moulding technique. The influence of annealing temperature on the in-situ formed PA microstructure and properties such as crystalline structure, mechanical as well as tribological performance of corresponding composites was studied in detail. Results suggested that PPS (56 wt%)/PA (24 wt%)/PTFE (20 wt%) composites exhibited the best tribological properties after annealing at 150 °C for 1h. The lowest friction coefficient and specific wear rate are as low as 0.139 and 4.372 × 10−6 mm3/Nm which are nearly 80% and 1.83 × 103 times lower than pure PPS, respectively. This work provides a facile method to reduce both friction and wear properties of self-lubricating thermoplastic polymers which are critical for weight reduction and energy saving in industrial fields.

Preparation of hierarchical core-shell Al-PTFE@TA and Al-PTFE@TA-Fe architecture for improving the combustion and ignition properties of aluminum

Due to the dense oxide film on the surface of aluminum powder, the combustion efficiency of aluminum powder is reduced and the ignition temperature is increased. The addition of polytetrafluoroethylene (PTFE) and the use of ball milling can effectively improve the ignition and combustion properties of aluminum powder. However, the Al-PTFE composite prepared by ball milling usually limits the combustion efficiency of aluminum due to its low PTFE content. In addition, the presence of the F element on the surface of the Al-PTFE particles makes Al-PTFE and HTPB adhesives produce interface effects, making it difficult for Al-PTFE composites to be used in composite propellants. Herein, through simple tannic acid (TA) self-aggregation and the self-assembly reaction of TA with iron ions, the [email protected] and [email protected] composites with hierarchical core-shell structure are prepared. Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and thermogravimetry and differential scanning calorimetry (TG-DSC) are uesd to characterize these composites. The experimental results show that the establishment of TA and TA-Fe interface layer can effectively decrease the ignition temperature of Al-PTFE composite in the oxygen. In addition, [email protected] and [email protected] can effectively inhibit aluminum agglomeration compared with Al-PTFE during the combustion process.

Flexible graphite bipolar plates for vanadium redox flow batteries

The effects of polytetrafluoroethylene (PTFE) additives on expanded graphite bipolar plates (BPs) for vanadium redox flow batteries (VRFB) are investigated. Pure expanded graphite plates have immense potential for use in low-cost, rapid, and continuous fabrication of high performance VRFBs. However, pure expanded graphite BPs suffer from severe swelling in vanadium electrolytes over short periods of time, exhibiting decreased efficiency of 2.3% within 35 charge/discharge cycles. In contrast, expanded graphite BPs containing 6 and 10 wt% PTFE do not experience swelling or efficiency loss during cycle tests. The prevention of swelling is a key factor contributing to the use of expanded graphite plates for VRFB stacks. Microstructural analysis reveals that our fabrication method provides uniform PTFE distribution. PTFE polymers suppress swelling by providing coverage of surface cracks, repelling aqueous solutions due to their hydrophobicity, and more importantly, providing binding forces between expanded graphite layers. PTFE additives increase electrical resistivity, but improve flexibility, allowing for the fabrication of very thin plates. Thin flexible BPs exhibit low areal electrical resistance and thus the ohmic voltage loss of the BPs with 6 wt% PTFE is less than 1.2 mV (<0.1% of the VRFB nominal voltage of 1.25 V) even at a high current density of 0.2 A cm−2, which is negligible compared with other factors.

Optimizing the structural design of cathode catalyst layer for PEM fuel cells for improving mass-specific power density

The design of cathode catalyst layers (CCLs) is essential for enhanced charge transfer and mass transport of proton exchange membrane fuel cells (PEMFCs). In this work, CCLs are designed to constitute the three sub-layers with different polytetrafluoroethylene (PTFE) loadings for each sub-layer. The improper addition of PTFE in the different CCL positions can increase the gas-liquid phase’s mass transfer resistance through the triple-phase boundary. Low PTFE content leads to an inefficient hydrophobic nanoparticle distribution. However, excessive PTFE causes active site losses. The high voltage loss is a common result of unsuitable PTFE content, especially within the high current density operation condition. The membrane electrode assembly (MEA) contains 10 wt% PTFE loading in the out layer (faced to the gas diffusion layer), shows the best performance. At potentials of 700 mV and 600 mV, the output current densities approach 710 and 1120 mA/cm2, respectively. Furthermore, using Electrochemical impedance spectroscopy (EIS), the effect of PTFE sub-layers position on the charging transfer impedance and the mass transfer impedance has also been analyzed in this study. It is confirmed that the performance of MEA with an appropriate PTFE gradient design is improved significantly.