Solid polymer electrolytes activated carbon electrodes

Ishikawa, M., Morita, M., lhara, M. and Matsuda, Y., Electric double layer capacitor composed of activated carbon fiber cloth electrodes and solid polymer electrolytes containing alkylammonium salt, J. Electrochem. Soc., 1994, 141(7), 1730 1734. 

PANI-NTs synthesized by a template method on commercial carbon cloth have been used as the catalyst support for Pt particles for the electro-oxidation of methanol [501]. The Pt-incorporated PANl-NT electrode exhibited excellent catalytic activity and stabUity compared to 20 wt% Pt supported on VulcanXC 72R carbon and Pt supported on a conventional PANI electrode. The electrode fabrication used in this investigation is particularly attractive to adopt in solid polymer electrolyte-based fuel cells, which arc usually operated under methanol or hydrogen. The higher thermal stabUity of y-Mn02 nanoparticles-coated PANI-NFs on carbon electrodes and their activity in formic acid oxidation pomits the realization of Pt-free anodes for formic acid fuel cells [260]. The exceUent electrocatalytic activity of Pd/ PANI-NFs film has recently been confirmed in the electro-oxidation reactions of formic acid in acidic media, and ethanol/methanol in alkaline medium, making it a potential candidate for direct fuel cells in both acidic and alkaline media [502]. 

As shown in Fig. 5 7(b) the solid polymer electrolyte cell comprises a membrane, fuel cell type, porous electrodes and three further components z carbon collector, a platinized titanium anode support and a cathode support made from carbon-fibre paper The collector is moulded in graphite with a fluorocarbon polymer binder A 25 pm thick platinized titanium foil is moulded to the anode side to prevent oxidation. The purpose of the collector is to bnsure even fluid distribution over the active electrode area, to act as the main structural component of the cell, to provide sealing of fluid ports and the reactor and to carry current from one cell to the next E>emineralized water is carried across the cell via a number of channels moulded into the collector These channels terminate in recessed manifold areas each of which is fed from six drilled ports. The anode support is a porous conducting sheet of platinized titanium having a thickness of approximately 250 pm. The purpose of the support is to distribute current and fluid uniformly over the active electrode area. It also prevents masking of those parts of the electrode area which would be covered by the... 

Most commonly, the battery will be configured with a stack of bipolar cells (10 -100 cells per stack) to give a useful output voltage and with parallel flows for the electrolytes to each of the cells in the stack. Hence, the electrodes will be bipolar with a solid core from carbon, graphite, or a carbon/polymer composite and the three-dimensional elements bonded or pressed onto either side of the solid core. The composites are a blend of a chemically stable polymer and a micron-scaled carbon powder, most commonly an activated carbon Radford et al. [127] have considered the influence of the source of the carbon and the chemical and thermal treatments on the properties of such activated carbons, especially the pore size and distribution [126]. Even though reticulated vitreous carbon has been used for the three-dimensional elements [117], the predominant materials are graphite cloths or felts with a thickness of up to 5 mm, and it is clear that such layers are essential to scale the current density and thereby achieve an acceptable power density. Details of electrode performance in the more developed flow batteries are not available but, for example, Skyllas-Kazacos et al. [124] have tabulated an overview of the development of the all vanadium redox flow battery that includes the electrode materials and the chemical and thermal treatments used to enhance activity and stability. 

Flexible supercapacitors were made from PEDOT nanolibers as electrodes and polyacrylonitrile (PAN) nanolibers as separator by Larfogue et al. [19]. The PEDOT nanolibers were produced by combination of electrospinning and vapor-phase polymerization to form a conductive mat, and were used as the active material (electrodes), separated by a sheet of PAN nanolibers. Carbon-based clothes were used as the current collectors. The material layers were stacked together and embedded in a solid electrolyte containing an ionic liquid and polyvinylidene lluoride-co-hexa-fluoro-propylene (PVDF-co-HFP) as the host polymer. 

The electrochemically active electrode materials in Li-ion batteries are a lithium metal oxide for the positive electrode and lithiated carbon for the negative electrode. These materials are adhered to a metal foil current collector with a binder, typically polyvinylidene fluoride (PVDF) or the copolymer polyvinylidene fluoride-hexafluroropropylene (PVDF-HFP), and a conductive diluent, typically a high-surface-area carbon black or graphite. The positive and negative electrodes are electrically isolated by a microporous polyethylene or polypropylene separator film in products that employ a liquid electrolyte, a layer of gel-polymer electrolyte in gel-polymer batteries, or a layer of solid electrolyte in solid-state batteries. 

A solid-state supercapadtor with alkaline polymer electrolyte was reported for the first time by Lewandowski et al The polymer electrolyte was based on PEO-KOH-H2O. It served as both separator and binder for the electrode material. The selection of PVA was based on the fact that polymers like PVA, PEO and co-poly(epichlorohydrin-ethylene oxide) showed conductivity in the range of 10" S/cm. The separator was made by film casting from an aqueous solution of PEO and KOH in which the concentration of KOH was fixed at 40 wt% in the PEO so that the optimum mechanical strength of the film and conductivity was maintained. To make the electrodes, the PEO/KOH solution was mixed with activated carbon and acetylene black. A capacitance of 90 F/g for the activated carbon was reported and the capadtance values were comparable to that of the KOH electrolyte. The absence of any peak indicated pure electrostatic attraction in the capacitor behavior. When the system was studied at sweep rates higher than 20 mV/s, an appreciable decrease in capacitive behavior was observed due to ohmic drop. From the impedance measurement, the resistance was found to be around 0.77 ohm. The approximately calculated RC time constant was around 1.4 s. 

A considerable decrease in platinum consumption without performance loss was attained when a certain amount (30 to 40% by mass) of the proton-conducting polymer was introduced into the catalytically active layer of the electrode. To this end a mixture of platinized carbon black and a solution of (low-equivalent-weight ionomeric ) Nafion is homogenized by ultrasonic treatment, applied to the diffusion layer, and freed of its solvent by exposure to a temperature of about 100°C. The part of the catalyst s surface area that is in contact with the electrolyte (which in the case of solid electrolytes is always quite small) increases considerably, due to the ionomer present in the active layer. 

Carbon powder mixed with polymeric binder (PVdF, PTFE) has been widely used as anode material for lithium ion batteries and as the electrode material for EDLC with liquid electrolyte solutions. When such composite electrodes composed of carbon powder and polymer binder were used in all-solid-state EDLC, the performance was not good enough because of poor electrical contact between the electrode s active mass and the electrolyte. By having the electrolyte inside the composite electrode, the contact between the active mass in the electrode and the electrolyte can be considerably improved and hence the capacitance can... 

---