Lasse Bay

Simultaneous anion and cation mobility in polypyrrole

Polypyrrole (PPy) polymer films permanently doped with large, immobile anion dodecyl benzene sulfonate (DBS) have been characterized by cyclic voltammetry in order to clarify the roles of cations and anions in the aqueous electrolyte as mobile ions in the film. Aqueous solutions of 0.05–0.1 M alkali metal chlorides as well as BaCl2, NaBr and (CH3CH2CH2)4NBr were used to investigate the effects of both the ionic charge, size and shape. In 1:1 electrolytes using small ions only three peaks are present: a sharp cathodic peak at ca. −0.6 V vs. SCE representing both the insertion of cations and the expulsion of anions; a broad anodic peak centered at ca. −0.5 V representing the expulsion of cations; and a second broad peak at +0.2 to +0.5 V corresponding to anions being inserted. Although the motion of cations is the most important, as expected, there is a significant anion contribution, thereby complicating reproducibility when employing PPy(DBS) polymers as actuators. When the cation is doubly charged, it enters the film less readily, and anions dominate the mobility. Using a large and bulky cation switches the mechanism to apparently total anion motion. The changes in area of the three peaks in slow cyclic voltammograms enable the shifts in mechanism to be followed in detail. The charge and the size/shape dependence point to future possibilities for improving the control and reproducibility of electroactive polymer actuators.

Dynamics of the YSZ-Pt interface

Abstract Yttria stabilized zirconia (YSZ)-Pt point electrodes were examined by linear potential sweep, potential step and impedance measurements at 1000 °C in air. Inductive loops and hysteresis phenomena with long relaxation times were found. Atomic force microscopy showed changes of the interface between Pt and YSZ induced by the current passage. These changes involve transport of solid and are slow enough to explain the large time constants. The low frequency capacitance and inductive loop forming an entire circle indicate the presence of gas reservoirs at the YSZ-Pt interface.

Hydrogen solubility in Pr-doped and un-doped YSZ for a one chamber fuel cell

Yttria-stabilised zirconia electrolytes (YSZ and Pr-doped YSZ) and yttria-doped strontium cerate (SYC) were tested in a one chamber fuel cell fed with a mixture of methane and air at 1223 K. The obtained performances were 4 mW cm -2 , 3 mW cm 2 , 2.5 mW cm -2 , and 0.15 mW cm -2 for SYC, 1.8 mol.% Pr-doped YSZ, 17 mol.% Pr-doped YSZ, and un-doped YSZ, respectively. These values are lower than those reported by Asano et al., due to poisoning of the gold electrode. The solubility of hydrogen in the electrolytes was compared by means of tracer exchange using a H 2 + D 2 O mixture and subsequent SIMS analysis. Doping of Pr in the YSZ resulted in a higher intensity of the D ion, which indicated that hydrogen solubility was raised by the doping. The solubility of hydrogen in the electrolyte may affect the performance of one chamber fuel cells.

Surface intermediates on metal electrodes at high temperature

Abstract The mechanisms widely conceived for the O2-reduction or H2-oxidation reactions in SOFCs involve intermediate O/H species adsorbed on the electrode surface. The presence of these intermediates is investigated by linear sweep voltammetry. In air at moderate temperatures (500°C) Pt in contact with YSZ is covered with adsorbed oxygen which vanishes at high temperature (1000°C). On Ni (YSZ) a specific layer of NiO is observed above the equilibrium potential while no surface species involving hydrogen can be identified at SOFC anode conditions.

Properties of polypyrrole doped with alkylbenzene sulfonates

Conducting polymers such as polypyrrole (PPy) doped with large anionic detergents have high stability in aqueous systems. PPy can be reversibly oxidised and reduced electrochemically. The redox change of PPy is accompanied by a change in volume of the polymer. This is partly ascribed to take-up of ions and solvent molecules. This volume change can be used as a polymer actuator (artificial muscle) working in a narrow voltage range (less than 1 V). The properties of the PPy polymer are largely determined by the dopant ions and also by the deposition conditions and the substrate. A free-standing 10 micrometers thick film is prepared electrochemically at a constant current from an aqueous solution of pyrrole and sodium alkylbenzene sulfonate. The mechanical properties of the film (tensile strength and Youngs modulus) and the reversible linear elongation between the oxidised and reduced states are measured. Alkylbenzene sulfonates with alkyl chain lengths between 1 and 22 carbon atoms are used as dopant anion. The films made with the different anions have highly different properties and are here compared to outline the influence of the size of the anion. A maximum in linear elongation is found for p-(n-octyl)benzene sulfonate and in conductivity for p-(n-butyl)benzene sulfonate.