Determination of state-of-discharge of zinc-silver oxide button cells. I. Galvanostatic measurements

Galvanostatic measurements have been performed on numerous types of Zn-Ag₂O button cells, including low and high drain versions of multiple sizes with various lot numbers from six manufacturers throughout the world. The aim was to find a fast, reliable, nondestructive state-of-discharge indicator. The passivation time constant,i ^1/2, was found to decrease with increasing state-of-discharge. A linear relationship was usually found between 40 and 100% state-of-discharge. The passivation time was not retained at the preferred state-of-discharge indicator due to the removal of excess charge during the measurement and the long recovery time necessary to return to the characteristics of the cell which prevailed before passivation. The initial passivation time constant increased linearly with increasing capacity or volume of the cell with a slope depending on the manufacturer. The slope or E/t value of the potential vs time curve was found to be the more reliable and practical state-of-discharge indicator. Applications are limited to a go/no go test with a selection at 50±10% state-of-discharge. Bell shape changes of the passivation time constant vs state-of-discharge in the 0–40% state-of-discharge range preclude the selection at low state-of-discharge values. The test current giving an appropriate slope between either 2 and 10 s or 10 and 30 s was found to follow the rough correlation:i _test (mA)0.5 C nominal (mA h). The charge withdrawn during the measurement was about 0.1% of the nominal capacity. A calibration was needed for each cell dimension, each manufacturer and possibly, each lot number to set the precise current level giving the appropriate E/t value at 50±10% state-of-discharge. Success ratios of the predictions were in the 90% range with a known calibration. The wrong predictions were mainly due to the large dispersion of the electrical characteristics of the cells and to the low state-of-discharge value which is needed for practical applications.This is the first of a series of papers dedicated to Professor Ernest Yeager on the occasion of his 60th birthday.     

Determination of state-of-discharge of zinc-silver oxide button cells. III. In situ impedance measurements of each electrode

The ac impedance of each electrode of Zn-Ag₂0 button cells (30–50 mA h) has been measured over an extended range of frequencies using a Hg/HgO reference electrode located in a small hole drilled through the positive case terminal. The high frequency impedance spectrum of the Ag₂O cathode is a straight line with a 22.5° slope typical for diffusion at a porous electrode. The low frequency end exhibits a 45° sloped straight line characteristic of diffusion processes at a planar electrode. The deposition process is fast and hence the change transfer resistance is usually not clearly evident in the complex plane impedance plot. The impedance response of the zinc anode shows a capacitive loop at high frequencies and some inductive effects characteristic of adsorption processes. At low frequency the complex plane impedance plot of the total cell is a straight line of slope close to 45° mainly ascribed to the Ag₂0 cathode. At high frequencies equally important contributions from the two electrodes are evident. The main change in impedance which results from discharge is the decrease of the characteristic relaxation frequency of the high frequency capacitive loop of the zinc anode. The determination of the state-of-discharge at a frequency higher than 1 Hz is best realized if (i) the characteristic relaxation frequency of the high frequency capacitive loop occurring at the zinc anode decreases with discharge and (ii) the response of the Ag₂O cathode is quasi-linear over the entire frequency range. Under these conditions the characteristic relaxation frequency at the zinc anode or some related parameters can be clearly seen on the spectrum measured at the two terminals and used as a state-of-discharge indicator.This is the final part of a series of papers dedicated to Professor Einest Yeager on the occasion of his 60th birthday.     

Electrochemical measurements on metal oxide electrodes—II. Impedance measurements on Nb-doped single crystal TiO2

Mott—Schottky plots were measured on single crystal Nb-doped TiO₂ in aqueous buffer solutions and KCl electrolytes of concentration between 1 M and 10^?4 M KCl. The influence of surface pretreatment, nature of the dopant and solution conductivity on the Mott—Schottky plots was examined. The surface pretreatment was found to affect the frequency dispersion of the Mott—Schottky plots. Analyses of published data and results from the present study suggest that the point of zero charge of differently doped TiO₂ samples influences the flatband potential. The impedance measurements in KCl electrolytes showed that the flatband potential of single crystal Nb-doped TiO₂ could be determined in low conductivity electrolytes such as 10^?3 M KCl.     

Determination of polyolefin film properties from refractive index measurements. II. Birefringence

The use of refractive index data for studying changes in oriented polyolefin films has been demonstrated. Application of this technique to oriented polypropylene and polyethylene films showed that the birefringence is a linear function of the refractive index in the direction of maximum orientation. By utilizing refractive index, density, and crystallinity data the crystalline refractive indices n_c and (n_a + n_b)/2 and polarizabilities α_∥ and α_⊥ could be estimated for polypropylene and polyethylene.     

Impedance parameters and the state-of-charge. II. Lead-acid battery

The determination of the state-of-charge of the lead-acid battery has been examined from the viewpoint of internal impedance. It is shown that the impedance is controlled by charge transfer and to a smaller extent by diffusion processes in the frequency range 15–100 Hz. The equivalent series/parallel capacitance as well as the a.c. phase-shift show a parabolic dependence upon the state-of-charge, with a maximum or minimum at 50% charge. These results are explained on the basis of a uniform transmission-line analog equivalent circuit for the battery electrodes.Nomenclature Battery This word is used synonymous with the word cell - R _p equivalent parallel resistance () - R _s equivalent series resistance () - ¦Z¦ modulus of impedance () - C _p equivalent parallel capacitance (F) - C _s equivalent series capacitance (F) - a.c. phase-shift (radians or degrees) - 2f - f a.c. frequency (Hz) - R resistance of electrolyte solution and separator () - ¯C double layer capacity (F) - W diffusional (Warburg) impedance () - R _t resistance due to polarization () - energy transfer coefficient - T absolute temperature (K) - R gas constant - F Faraday constant - C _O ⁰ bulk concentration of the oxidant - C _R ⁰ bulk concentration of the reductant - D _O diffusion coefficient of the oxidant - D _R diffusion coefficient of the reductant - Warburg coefficient - N number of pores/area - A active area of the electrode (cm²) - S state-of-charge - a anode - c cathode - L inductance - I _o exchange current     

Impedance analysis of nanostructured iridium oxide electrocatalysts

Impedance data were collected for nanostructured iridium oxide (NIROF) at potentials below those at which the oxygen evolution reaction commences. The measurements included thin oxide films covered by a protective Nafion™ layer and thicker composite Nafion™-oxide electrodes. The time constants for the low-frequency diffusion process were approximately the same for both types of electrodes, indicating diffusion in individual particles in the porous electrode rather than across the film. The diffusion process involves trapping of the diffusion species. The impedance data indicated that there were no significant variations in conductivity of the oxides with potential, as opposed to what appears to be the case for anodically formed iridium oxide films (AIROF). This is interpreted to reflect differences in electronic structure between NIROF and AIROF.     

Determination of the molecular weight between cross-links of elastomeric stocks by tensile retraction measurements. II. Polyurethanes

Tensile retraction measurements of M_c were made on a variety of polyurethanes or polyurethane-ureas. These samples were prepared using a number of prepolymer MW and functionalities. In addition, the stoichiometry of the cure was allowed to range widely. In all cases, excellent linear correlation coefficients were obtained between the M_c and the A_max of the test. The slope and M_r (the value of M_c extrapolated to A_max = 1) determined from this was used to characterize the polymer. These data allowed the determination of χ for each of the different systems such that comparable values of M_c could be measured by swelling. Identical formulations cured at different temperatures were shown to have measurable differences in M_c, slope, and percentage set. These variations appear to relate to the perfection of the network and morphology of the hard domains.     

Experimental optimization of alkaline zinc-silver oxide primary cell with respect to the zinc electrode preparation and composition

The optimization of parameters controlling the fabrication of zinc electrodes, by the slurry paste method, has been carried out. The parameters varied were active material composition, applied compression and electrode thickness. The optimum values obtained by a factorial experimental programme were: a zinc material that contains 2–4 wt% HgO, 0·5–2% PVA, and 94–97·5% ZnO; a compression of 500–1500 psi applied to the zinc electrode; and an electrode thickness of 0·265-0·35 mm.     

Impedance measurements during the cycling of a zinc electrode

Impedance spectra have been obtained during the cycling of a zinc electrode both in a Leclanché-cell-type electrolyte and in an alkaline zincate solution. Changes in impedance plots indicate an increase in the electrode area and a variation of the electrode kinetics with cycling. The kinetics of zinc deposition appear to be very sensitive to the contamination of electrolytes by dissolution products. The results confirm a correlation between the presence of an additive such as NBu₄ Br and the increase of the cycle life of the zinc electrode.     

Impedance measurements for the evaluation of protective nonmetallic coatings

Questions regarding the interpretation of impedance data obtained with metal—coating—electrolyte solution systems are discussed on the basis of theoretical considerations and experimental results. The analysis of plots in the form of Nyquist diagrams leads to the conclusion that the method provides valuable information about protective properties of coatings and enables identification of the mechanism of protection.     

Impedance and transient study of aluminium barrier-type oxide films

The effect of the passivation potential on the properties of the barrier films formed on high purity aluminium has been examined. The current-time responses were recorded, the charge used during formation of the barrier film was determined, and the steady-state currents were discussed. Impedance measurements provided an insight into the characteristic sizes of barrier films. Equivalent circuits which illustrate the examined aluminium/oxide film/electrolyte systems were proposed and individual circuit elements were defined. The resistance and thickness of the barrier film were shown to increase linearly with increase in the passivation potential, while increase in solution pH caused a marked decrease in the total system impedance. The paper also defines current efficiency in the formation of the barrier film. The value of 20% indicates that the formation of barrier films on aluminium is a process that takes place with considerable current losses. The mechanism of barrier film growth has been examined within the framework of two models suggested by different authors. Both agreements with and differences from the theories proposed have been indicated.     

Electrochemical behaviour of copper in neutral aerated chloride solution. II. Impedance investigation

A.c. and EHD impedance measurements were performed on a Cu rotating disc electrode immersed in neutral aerated NaCl and the results were compared with simulated curves according to the kinetic model developed in Part I. The agreement is good over the whole anodic range and at the corrosion potential. A slowing down of the mass transport rate is explained by diffusion through a surface layer (Cu₂O) at the corrosion potential and for the close anodic range. It is confirmed that, on the cathodic plateau, the interface may be considered as uniformly accessible for the cathodic partial reaction of oxygen reduction. However, at less cathodic potential a surface layer effect due to CuCl must also be taken into account. Diffusion coefficients for both O₂ and CuCl ₂ ^– were determined by EHD impedance.     

Design of dedicated instrumentation for temperature distribution measurements in solid oxide fuel cells

A thermocouple was designed for temperature distribution measurements in solid oxide fuel cells. A theoretical model, based on mixed convective–radiative heat transfer was used to predict the thermocouple response. The proposed flat type thermocouple was shown to be a high sensitive, low error temperature sensor, capable of satisfying the requirements for solid oxide fuel cell thermal behaviour research. Thereafter, a purpose-built, thin, flat-type thermocouple has been used for temperature distribution measurements at the cathode side of a planar solid oxide fuel cell. High temperature conditions of 1223K have been tested. Beside temperature mapping, local hot spots have been easily located.     

Impedance spectroscopy study of electrochromism in sputtered iridium oxide films

The a.c. impedance response of sputtered iridium oxide films (SIROFs) was studied at room temperature in 1M H₂SO₄ between 1mHz and 50mHz. The spectra were recorded as a function of applied potential in the range of electrochromic properties from 0.0 to 1.0V vs SCE and before and after an electrochemical treatment consisting of alternatively colouring and bleaching the electrode. The spectra were analysed with help of an equivalent circuit. Between 0.4 and 1.0V, the spectra can be interpreted as due to electrochemical proton insertion in a single phased compound. From the data, hydrogen chemical diffusion coefficients with values ranging from 2 × 10^–8 to 1.1 × 10^–7cm²s^–1 are found. It is shown that this parameter increases fourfold after the cycling treatment and significantly decreases with the amount of inserted hydrogen. Below 0.4V spectrum changes are observed over the intermediate frequency range studied, indicating some changes of the interfacial reactivity which remain to be clarified.     

Mixed potential measurements in the elucidation of corrosion mechanisms—II. Some measurements

The behaviour of the mixed potential as a function of oxidant concentration and agitation is examined for a variety of corrosion reactions. Using the theory developed in a previous paper, this information is used to elucidate the mechanism of each reaction.The dissolution of mercury, copper and silver in the presence of ferric ions was studied. For the Fe(III)-CuSO₄^2? system, it was shown that the anodic dissolution half-reaction was activation controlled and the cathodic half-reaction was diffusion controlled. Changing the anion to Cl^? made both half-reactions diffusion controlled. For the Fe(III)AgNO₃^? system, the anodic half-reaction is diffusion controlled the ferric reduction being activation controlled. In the attack of ferric ions on mercury in nitrate solution, both half-reactions are activation controlled.The metal oxidation reaction in which silver is oxidized to silver iodide by the triiodide ion was considered. It was shown that the ir drop in the AgI layers had a negligible effect on the corrosion potential.An examination of the behaviour of the corrosion potential in the Cu(II)Zn metal displacement reaction enabled estimates to be made of the anodic area at various times during the reaction. It was shown that in the first stage of the reaction the anodic area is fairly constant and equal to the geometric area of the zinc. As the second stage is entered, the anodic area suddenly drops to about 3 per cent of the geometric area, at which level it remains constant.     

Characterization of porous aluminium oxide films from a.c. impedance measurements

An equivalent circuit (EC) that reproduces the a.c. impedance of porous aluminium oxide films in a highly approximate manner is proposed. The results reveal that electrochemical impedance spectroscopy (EIS) is a powerful tool for obtaining detailed information on the electrochemical properties of both the porous and barrier layer on which the corrosion resistance of aluminium depends. The impedance at a given frequency can be used for accurate calculation of the electrochemical parameter for the oxide film represented by each element of the EC. In this way, the effects of any factor on sealing and ageing of anodized aluminium oxide films can be precisely analysed. The EIS technique provides an effective, advantageous alternative to existing seal quality control tests.     

Antimony in lead-acid cells. III. Transport measurements

The mechanism of transport of Sb(V) in H₂SO₄ through 12 commercial separators was investigated. This was carried out by comparing the diffusion coefficient of Sb(V) with the electrical ionic conductivity which should be simply related if diffusion is the rate-controlling transport process. Rates increased as convective flow became dominant. Separators with pore diameters below 2 m and above 20 m showed transport rate control by diffusion and convective flow, respectively. Between 2 and 20 m both processes contributed significantly.     

Electrochemical measurements on metal oxide electrodes—I. Zirconium dioxide

Electrochemical studies were conducted on ZrZrO₂ electrodes as part of the program in this laboratory on the development of pH probes for use in high temperature/high pressure aqueous systmes. The influence of various methods of preparation of the oxide electrode on the open circuit potential (V_oc) and flatband potential (V_fb) were investigated. Electrodes with low impedance had a V_oc that exhibited a Nernstian response to pH (?59 mV/pH) at 23°C, and oxide electrodes with high impedance had a V_oc tht was insensitive to pH. Because of the frequency dispersion in the Mott—Schottky plots and the exhaustion of the oxide, V_fb could not be determined for the ZrO₂ films. The electrochemical results indicate that the ZrZrO₂ electrodes as used in this study do not offer much prospect for monitoring the pH of aqueous solutions.     

Blends containing polymers of epichlorohydrin and ethylene oxide. II. Polyacrylates

The phase behavior of blends of various polyacrylate homopolymers and two commercial ethyl acrylate (EA) and n-butyl acrylate (nBA) copolymers with polyepichlorohydrin (PECH), poly(ethylene oxide) (PEO), and a copolymer of epichlorohydrin and ethylene oxide [P(ECH/EO)] was examined using differential scanning calorimetry and optical indications of phase separation on heating, i.e., lower critical solution temperature (LCST) behavior. Poly(methylacrylate) (PMA) was shown to be miscible with PECH, PEO, and P(ECH/EO) while only PECH was found to be miscible with the higher polyacrylates: poly(ethyl acrylate), EA copolymer, poly(n-propyl acrylate), and nBA copolymer. However, even PECH was found to be only partially miscible with poly(n-butyl acrylate). In general, glass transitions observed by DSC for blends were not as broad as those found in corresponding polymethacrylate blends. All mixtures showed LCST behavior, and, based on this and excess volume measurements, to the extent possible, qualitative conclusions were made concerning the relative strength of the interactions among the various blend pairs. For PECH it appears that the interaction with polyacrylates decreases with increasing size of the alkyl group. The commercial copolymers seem to interact more exothermically with PECH than the corresponding homopolymers. The interaction with PMA is apparently larger for PECH than for PEO or for P(ECH/EO). Interactions for the latter two are about the same. The apparently exothermic interactions between ECH and EO units are not sufficiently strong to preclude miscibility of P(ECH/EO) with PMA. As for the polymethacrylates, it is clear that the chlorine moeity of PECH is needed for miscibility with higher polyacrylates.     

Conduction in Bi2O3-based oxide ion conductor under low oxygen pressure. II. Determination of the partial electronic conductivity

In order to investigate the partial electronic conduction in the high oxide ion conductor of the system Bi₂O₃-Y₂O₃ under low oxygen pressure, e.m.f. and polarization methods were employed. Although the electrolyte was decomposed when the \(P_{{\text{O}}_{\text{2}} }\) was lower than the equilibrium \(P_{{\text{O}}_{\text{2}} }\) of Bi, Bi₂O₃ mixture at each temperature, the ionic transport number was found to be close to unity above that \(P_{{\text{O}}_{\text{2}} }\) . The hole conductivity (σ _p) and the electron conductivity (σ _p) could be expressed as follows, $$\begin{gathered} \sigma _p \Omega cm = 5 \cdot 0 \times 10^2 \left( {P_{O_2 } atm^{ - 1} } \right)^{{1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} \exp \left[ { - 106 kJ\left( {RT mol} \right)^{ - 1} } \right] \hfill \\ \sigma _p \Omega cm = 3 \cdot 4 \times 10^5 \left( {P_{O_2 } atm^{ - 1} } \right)^{ - {1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} \exp \left[ { - 213 kJ\left( {RT mol} \right)^{ - 1} } \right] \hfill \\ \end{gathered} $$ These values were much lower than the oxide ion conductivity under ordinary oxygen pressure.