Theoretical performance of hydrogen-bromine rechargeable SPE fuel cell

A mathematical model was formulated to describe the performance of a hydrogen-bromine fuel cell. Porous electrode theory was applied to the carbon felt flow-by electrode and was coupled to theory describing the solid polymer electrolyte (SPE) system. Parametric studies using the numerical solution to this model were performed to determine the effect of kinetic, mass transfer, and design parameters on the performance of the fuel cell. The results indicate that the cell performance is most sensitive to the transport properties of the SPE membrane. The model was also shown to be a useful tool for scale-up studies

Nano-crystalline porous tin oxide film for carbon monoxide sensing

A tin oxide sol is deposited on platinum electrodes (12) of a sensor (10). The sol is calcined at a temperature of 500 to 800.degree. C. to produce a thin film of tin oxide with a thickness of about 150 nm to 2 .mu. and having a nano-crystalline structure with good stability. The sensor rapidly detects reducing gases, such as carbon monoxide, or hydrocarbons and organic vapors. Sensors using films calcined at around 700.degree. C. have high carbon monoxide selectivity with a response time of around 4 minutes and a recovery time of 1 minute, and therefore provide good detection systems for detection of trace amounts of pollutants such as toxic and flammable gases in homes, industrial settings, and hospitals

Review-Electrode Kinetics and Electrolyte Stability in Vanadium Flow Batteries

Two aspects of vanadium flow batteries are reviewed: electrochemical kinetics on carbon electrodes and positive electrolyte stability. There is poor agreement between reported values of kinetic parameters; however, most authors report that kinetic rates are faster for VIV/VV than for VII/VIII. Cycling the electrode potential increases the rates of both reactions initially due to roughening but when no further roughening is observed, the VII/VIII and VIV/VV reactions are affected oppositely by the pretreatment potential. Anodic pretreatment activates the electrode for the VII/VIII reaction, and deactivates it for VIV/VV. Three states of the carbon surface are suggested: reduced and oxidized states R and O, respectively, both with low electrocatalytic activity, and an intermediate state M with higher activity. The role of surface functional groups and the mechanisms of electron transfer for the VII/VIII and VIV/VV reactions are still not well understood. The induction time for precipitation of V2O5 from positive electrolytes decreases with temperature, showing an Arrhenius-type dependence with an activation energy of 1.79 eV in agreement with DFT calculations based on a VO(OH)3 intermediate. It also decreases exponentially with increasing VV concentration and increases exponentially with increasing sulphate concentration. Both arsenate and phosphate are effective additives for improving thermal stability

Modeling calculations of an aluminum-air cell

A mathematical model of the performance of an aluminum-air single cell with caustic electrolyte has been developed along with an efficient solution algorithm. The model includes kinetic expressions for the cathode and anode along with the aluminum corrosion reaction. The effects of mass transfer, migration, gas evolution, the mass balances and their inter-dependencies have been included. Comparison of calculation predictions with experimental data show good agreement. Calculations demonstrate the sensitivity of cell performance to cell dimensions, electrolyte concentration and flowrate, temperature, and most importantly, to cathode and especially anode kinetics. The model and solution algorithm may be useful to describing the performance of other types of flow electrochemical reactors.link_to_subscribed_fulltex

Analysis of Primary and Secondary Current Distributions in a Wedge-type Aluminum-air Cell

The primary and secondary current distributions near the leading edges of the cathode and anode of a wedge-type aluminum-air cell design were analyzed. Numerical calculations were accomplished by using a finite difference method and introducing an overlapping two-grid system technique. The calculations indicate that the current distributions on the cathode and anode at distances from the edges greater than 2 times the cell gap are uniform. In the edge region, the wedge angle between 0 and 10° has a negligible effect on the current distribution. High current densities at the cathode edge, which are detrimental to cathode life, are reduced by kinetic effects and by oversizing the cathode itself. The latter also favors cell performance but adds to the cell costs. An effectiveness factor is introduced which demonstrates the effectiveness of cathode oversize and the sensitivity to kinetics as represented by the Wagner number. The calculations indicate that only marginal performance gains can be expected when the cathode extends beyond the anode a distance greater than that of 1.5 times the amode-cathode gap