The aim of this work was to develop and characterise electrically conductive materials for proton exchange membrane fuel cells and bipolar plates (BPPs). These BPPs were made from highly conductive blends of polyethylene terephthalate (PET) and polyvinylidene fluoride (PVDF), as matrix phase. The conductive materials were developed from carefully formulated blends composed of conductive carbon black (CB) powder and, in some cases, graphite synthetic flakes mixed with pure PET, PVDF or with PVDF/PET systems. They were first developed by twin‐screw extrusion process then compression‐molded to give BPP final shape. As the developed blends have to meet properties suitable for BPP applications, they were characterised for their rheological properties, electrical through‐plane resistivity (the inverse of conductivity), oxygen permeability, flexural and impact properties. Results showed that lower resistivity was obtained with PVDF/CB blends due to the higher interfacial energy between the PVDF matrix and CB and also the higher density and crystallinity of PVDF, compared to those of PET. It was also observed that the lowest resistivity values were obtained with mixing PVDF and PET at controlled compositions to ensure PVDF/PET co‐continuous morphology. Also, slow cooling rates helped to attain the lowest values of through‐plane resistivity for all studied blends. This behaviour was related to the higher crystallinity obtained with low cooling rates leading to smaller amorphous regions in which carbon particles are much more concentrated.

S urfi-Sculpt® is a power beam process, invented at and patented by TWI, which enables controlled surface features to be developed on a range of substrates, including but not limited to metals, polymers and ceramics. Such surface features were first demonstrated using electron beams, employing electromagnetic coils to first focus the beam and then deflect this focused beam over the material surface in a rapid and controlled manner. This article will describe more recent work, which has involved the use of focused laser beams to develop similar features. The processFibre delivered laser beams and galvanometer driven scanning mirrors were used in this work to produce the rapidly moving spot of laser energy required for the process. After generation of a molten pool in the substrate material, the beam is then rapidly moved relative to the workpiece. As a result of vapour pressure and surface tension effects, the laser beam movement results in material being moved from within the pool to regions at the extreme end of the beam movement. By repeating this process, it is possible to build up protrusions of several millimeters in height above the surface of the material. By combining and sequencing these protrusions together, a variety of shapes or features can be formed.The laser experiments have been performed in air and in various gaseous environments and, for comparison purposes, with electron beam work, in vacuum. The technique is not limited to the production of protruding surface features; it can also be used to modify the structure deeper within the work-piece, so as to effect modification in the bulk substrate, for example, by the creation of deep holes in the material.The types of surfaces produced are being investigated for many applications, including orthopaedic implants, with improved fixation due to promotion of bone in-growth, preparations for metals to be joined to composite, and for making surface features that enhance thermal transfer for high performance heat exchangers. InvestigationsIn the results reported here, both disc and fibre lasers have been used at relatively modest laser powers of less than 2kW, in conjunction with two different laser beam scanning systems, both developed primarily with laser welding applications for the automotive industry in mind. The disc laser was manufactured by Trumpf and the fibre laser by IPG Photonics. The scanning systems were manufactured by Trumpf and Arges.Trials were conducted on both metal alloys (Ti-6Al-4V) and plastics (polypropylene and polyethylene). For all materials, initial work consisted of producing simple linear shapes, using a repeated 'swipe' of the focused beam across the surface of the material. The main process variables were laser power, swipe speed, swipe length and the dwell time between swipes. Subsequently, more complex shapes were attempted, by combining several single swipes together to form a pre-determined pattern. For both the Trumpf and IPG laser systems, the minimum focused spot size was estimated to be between 0.3 and 0.34 mm in di...

Some 1-alkyl-3-methylimidazolium-based ionic liquids were synthesized, characterized, and immobilized on membranes to form supported ionic liquid membranes. The supported ionic liquid membranes were characterized by SEM. The initial transmembrane pressures were investigated for each type of impregnated membrane. The CO 2 /CH 4 single gas and mixed gas permeability (CO 2 and CH 4) have been investigated. The results showed that the CO 2 /CH 4 ideal selectivities and mixed gas selectivities reached 15.45-23.9 and 13.91-22.82, respectively (equivalent to separation yields of 93.3-95.98 %). The 1-alkyl-3-methylimidazolium acetate impregnated membrane leads to a slightly lower CO 2 /CH 4 selectivity, however, this ionic liquid is stable, free of halogen and has a low price. The impregnated membranes prepared from polyvinylidene fluoride are more stable than those from polyethersulfone support, and have a higher affinity for CO 2 compared to other gas. The obtained high CO 2 /CH 4 selectivities indicate that immobilized membranes can be used for CO 2 separation processes.

This research work aimed at developing, by twinscrew extrusion process, electrically conductive sheets for proton exchange membrane fuel cell (PEMFC) bipolar plates. For this, a series of highly conductive blends were carefully formulated from a co-continuous mixture of polythylene terephthalate (PET)/polyvinylidene fluoride (PVDF) and high specific surface area carbon black (CB) and graphite (GR) conductive additives. Several major factors, such as CB/GR content, PVDF/PET composition and morphology, and also PET crystallinity were shown to have remarkable effects on these three main properties.

The aim of this work was to develop and characterize electrically conductive bipolar plates (BPPs) used in proton exchange membrane fuel cells (PEMFCs). These BPPs were made from highly conductive blends of polyethylene terephthalate (PET) and polyvinylidene fluoride (PVDF), as matrix phase. The conductive materials were developed from carefully formulated blends composed of conductive carbon black powder (CB) mixed with pure PET, PVDF, or with PVDF/PET systems. They were first developed by twin screw extrusion (TSE) process then compression molded to give BPP final shape. Focus was made on the effect of crystallization of PVDF and PET polymers on the electrical through-plane resistivity of BPPs. It was observed that lower resistivity was obtained with PVDF/CB blends due to the higher interfacial energy between the PVDF matrix and CB and also the higher density and crystallinity of PVDF, compared to those of PET. For the different systems studied, slow cooling rates helped to attain the lowest values of through-plane resistivity since higher PET crystallinity led to smaller amorphous region in which CB was more concentrated. In addition, BPPs made from (PVDF/PET)/CB blends led to lower through-plane resistivity when the PVDF/PET phase had a co-continuous morphology. This is mainly due to the selective localization of the CB in the PET phase leading to a denser conductive carbon network. The lowest through-plane resistivity was around 0.3 Ohm.cm obtained with a (50/50 PVDF/PET)/CB filled with 30 wt% CB.