Effect of Anode Gas Diffussion Layer Thickness and Porosity on the Performance of Passive Direct Methanol Fuel Cell

Fuel cells are finding wide range of applications from small capacity cells used for portable electronic devices to large capacity stacks for automobile applications. Among the different types of fuel cells, passive Direct methanol fuel cell (DMFC) has many advantages because of its simplicity. This paper presents the effect of Anode Diffusion Layer (ADL) thickness and its porosity on the performance of a passive DMFC. A one-dimensional, non-isothermal model is developed in MATLAB environment for exploring the complex physicochemical phenomena taking place inside the passive DMFC, by considering both heat and mass transfer effects. Modeling studies have been carried out by varying the ADL thickness from 0.1 mm to 0.6 mm, and the ADL porosity from 0.3 to 0.8. The concentration distribution of methanol, water and oxygen inside the cell have been predicted and, the crossover of methanol and water across the membrane have also been estimated. It is observed that increase in thickness of the ADL decreases the methanol corss over. Further, the effect of ADL thickness and porosity on the anodic overpotential and cathodic overpotential have been estimated. It was observed that increase in ADL thickness as well as its porosity increase the overpotentials.

Electrochemical Study of Potassium Fluoride in a Cryolite-Aluminum Oxide Molten Salt

Selective and efficient electrochemical methods to characterize aluminum are necessary. Current methods are based on potentiodynamic polarization, recurrent potential double pulses, chronopotentiometry, open-circuit chronopotentiometry, and potentiostatic electrolysis, but have not been used to characterize the deposition of aluminum in Na3AlF6-Al2O3-KF molten salts. The control processes of the formation of aluminum-tungsten inter-metallic compounds, and the deposition of aluminum have been investigated by using steady-state potentiodynamic cathodic polarization curves. The dissolution loss rate of aluminum was determined with an increase in KF concentration by the analysis of recurrent potential double pulses. Using chronopotentiometry, it was confirmed that the deposition potential of aluminum shifted more negative as the KF concentration increased, and a higher KF concentrations induced a higher cathodic overpotential. From open-circuit potential measurements and scanning electron micrographs, it was concluded that aluminum(III) ions react with tungsten substrates to form an aluminum-tungsten compound, and the reaction mechanism of aluminum was determined. These electrochemical methods applied with aluminum electrolysis were accurate, efficient, and reliable.

Determination of Activation Overpotential during the Nucleation of Hcp-Cobalt Nanowires Synthesized by Potentio-Static Electrochemical Reduction

The crystal growth process and ferromagnetic properties of electrodeposited cobalt nanowires were investigated by controlling the bath temperature and cathodic overpotential. The cathodic overpotential during electrodeposition of cobalt nanowire arrays, ΔEcath, was theoretically estimated by the difference between the cathode potential, Ecath, and the equilibrium potential, Eeq, calculated by the Nernst equation. On the other hand, the activation overpotential, ΔEact, was experimentally determined by the Arrhenius plot on the growth rate of cobalt nanowire arrays, Rg, versus (vs.) reciprocal temperature, 1/T. The ferromagnetic cobalt nanowire arrays with a diameter of circa (ca.) 25 nm had the preferred crystal orientation of (100) and the aspect ratio reached up to ca. 1800. The average crystal grain size, Ds, of (100) peaks was estimated by X-ray diffraction patterns and was increased by decreasing the cathodic overpotential for cobalt electrodeposition by shifting the cathode potential in the noble direction. Axial magnetization performance was observed in the cobalt nanowire arrays. With increasing Ds, coercivity of the film increased and reached up to ca. 1.88 kOe.

Hydrogen evolution reaction at Ru-modified nickel-coated carbon fibre in 0.1 M NaOH

The electrochemical activity towards hydrogen evolution reaction (HER) was studied on commercially available (Toho-Tenax) and Ru-modified nickel-coated carbon fibre (NiCCF) materials. Quality and extent of Ru electrodeposition on NiCCF tows were examined by means of scanning electron microscopy (SEM). Kinetics of the hydrogen evolution reaction were investigated at room temperature, as well as over the temperature range: 20-50°C in 0.1 M NaOH solution for the cathodic overpotential range: -100 to -300 mV vs. RHE. Corresponding values of charge-transfer resistance, exchange current-density for the HER and other electrochemical parameters for the examined fibre tow composites were recorded.

Effect of Ce0.8Sm0.2O1.9 Interlayer on the Electrochemical Performance of LaBaCo2O5+δ Cathode for IT-SOFCs

The Ce0.8Sm0.2O1.9(SDC) interlayer was prepared by screen-printing method between LaBaCo2O5+δ(LBCO) cathode and 8YSZ electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The effect of SDC interlayer on the electrochemical performance of LBCO cathode was investigated. Experimental results showed that the LBCO cathode with SDC interlayer showed much lower area-specific resistance (ASR) and polarization overpotential than that of LBCO cathode without SDC interlayer at the same test condition, exhibiting the better electrochemical performance. For LBCO cathode with SDC interlayer, the ASR was 0.457 Ωcm2at 800 °C in air, about 36.2 % lower than that of the LBCO cathode without SDC interlayer, and the cathodic overpotential was reduced by 38.0 % at a current density of 0.02 Acm-2at 700 °C in air. The application of a thin-layer SDC interlayer between cathode and dense 8YSZ electrolyte showed great potential in improving the cathode performance for IT-SOFCs.