Serguei D. Mikhailenko

Properties of SPEEK based PEMs for fuel cell application

Comparative studies of membranes prepared using different solvents, have shown that the casting solvent plays a significant role, affecting their proton conductivity and mechanical strength. It has been found that using DMF strongly decreases the membrane conductivity in comparison with other solvents studied. The 1 H NMR results yield an insight into the mechanism of this effect, evidencing the formation of the strong hydrogen bonding of sulfonic acid groups with DMF. This can explain the large discordances of more than an order of magnitude existing between the conductivity results for sulfonated polyetheretherketone (PEEK) in some previous studies and in this work. It is also found that residual sulphuric acid, which is very difficult to eliminate from highly sulfonated polyetheretherketone (SPEEK), also affects its conductivity and under high temperature treatment, enters into reaction with both DMF and N,N-dimethylacetamide (DMAc), causing their degradation. As discussed in the present contribution, the conductivity measurement technique may also be a reason for discrepancy in the reported conductivity characteristics of SPEEK.

Sulfonated polyether ether ketone based composite polymer electrolyte membranes

Electrochemical properties of a series of composite membranes prepared by incorporation of boron phosphate into polymeric matrix of sulfonated PEEK were studied. The conductivity of the composites was found to exceed largely that of pure SPEEK polymer. It was however lower than predicted by the effective medium theory for these mixtures. This is associated to the formation of a capillary pore system in the membranes. Despite the developed porosity the composite membranes proved to be mechanically strong and not affected by long term storage in water.

PEM fuel cells as membrane reactors: kinetic analysis by impedance spectroscopy

Proton exchange membrane fuel cells (PEMFC) are considered as electrochemical reactors, performances of which are regarded in the context of the various effects influencing FC output, such as mass transports, kinetic of electrode reactions and charge transfer in polymer electrolyte membrane (PEM). An experimental approach, involving the employment of impedance spectroscopy (IS), which allows a deep insight into the nature of these effects, is discussed and its applications to the different aspects of PEMFC functioning are reported. As examples of the use of IS in PEMFC studies, the investigations of the membrane conductivity and in situ studies of the anode and the cathode processes during FC operation are presented.

Electrical properties of sulfonated polyether ether ketone/polyetherimide blend membranes doped with inorganic acids.

The influence of blending with Ultem poly(ether imide) (PEI) and doping with HCl and H3PO4 on the properties of sulfonated poly(ether ether ketone) (SPEEK) was studied. Blending with PEI first results in an increase and then in a decrease in membrane swelling at PEI concns. greater than 5%. The elec. cond. of blend membranes follows the same trend. Doping with the acids enhances the cond. several-fold, and the effect of doping with HCl is more significant. PEI forms spherical particles dispersed in the SPEEK matrix and, at the same time, partially dissolves in SPEEK, which reduces the swelling of the matrix at higher PEI concns. The increase in the membrane capacity to absorb water at small PEI contents is due to the formation of new water adsorption sites along the interface between the particles and the matrix. A modified effective medium model yielded calcd. results in good agreement with the measured cond. values, when the exptl. absorption data were used in the simulation.

Electrical conductivity of boron orthophosphate in presence of water

The electrical conductivity (σ) of boron phosphate was measured using impedance spectroscopy. It was found to be dependent on the B/P ratio, calcination temperature and is strongly affected by the presence of water. High temperature calcined BPO4 exhibited water assisted conductivity, surpassing 10−3 S cm−1, which increased up to σ > 10−2 S cm−1 with decrease of calcination temperature. 1H, 31P and 11B MAS NMR evidenced that in the latter case this is due to hydrolytic formation of substantial amounts of phosphoric acid, while in the former case only partial hydrolysis occurs. When calcined at high temperature, boron phosphate proved to be reasonably stable in water.

Electrical impedance studies of the ammonium salt of 12-tungstophosphoric acid in the presence of liquid water

Abstract The ionic conductivity of the ammonium salt of 12-tungstophosphoric acid has been determined in dry Ar, at 100% RH and in presence of liquid water using impedance techniques. The conductivity increases from σ = 10 −5 –10 −4 S cm −1 for the material, stored in dry Ar to σ = 1.1–1.9 × 10 −2 S cm −1 at 100% RH. Mixed with 10% water the material gains a very high electrical conductivity in the range 3.3–8.0 × 10 −2 S cm −1 when the temperature varies from ambient to 60 °C. The dominant mobile charge carrier in this system seems to be hydrated H + . Water plays a decisive role in conductance, providing both charge carriers and a vehicle for their motion.

Impedance Analysis of Polyaniline in Comparison with Some Conventional Solid Electrolytes

Doped polyaniline (PANI) is well-known as an electronic (polaronic) conductor and mostly is used as semiconductor in various applications. However, in the literature there are examples of employment of the acid doped form of PANI as electrolytic filler in proton exchange membranes. In order to distinguish between two types of conduction, in the present study powdered samples of polyaniline, either in the form of emeraldine base (PANI-EB) or in the form doped with camphorsulfonic acid (PANI-CSA), were investigated using impedance spectroscopy both in the dry state and in contact with liquid water. The obtained spectra were compared with the spectra of such conventional solid electrolytes, as zeolites X and ZSM5 and a strong electrolyte boron orthophosphate, acquired in identical conditions. The most important dissimilarity between conventional electrolytes and PANI was that ion diffusion dominates in the impedance response of the formers, whereas the behavior of PANI is under control of electron/hole displacement and the diffusion part is quite inessential. This corroborates the results of analysis of temperature dependence of PANI conductivity, which revealed values of activation energy twice as large as typical solid electrolytes. Equivalent circuits, simulating the impedance responses of all materials, were built up and used to estimate a possible diffusion coefficient of cations in the comparable solids. It was found that the diffusion in a strong electrolyte such as BPO4 is ∼2 orders of magnitude faster than evaluated for zeolites and ∼4 orders higher than what was PANI estimation. A conclusion was made that the slow cation diffusion both in protonated and in base form of PANI makes them less efficient solid electrolytes than conventional materials.