Hydrocarbon Fuel Cells with Fluoride Electrolytes

Cairns, Elton J.

doi:10.1149/1.2423782

Cited by 20 publications

(36 citation statements)

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“…An investigation of various fuels [6], concluded that the largest oxidation rates were obtained with propane. In sufficiently concentrated electrolytes, the small water content may cause the rate of water diffusion to be rate-limiting [3].…”

Section: Several Other Factors Influence the Performance Ofmentioning

confidence: 99%

“…The increase in operating temperature that is possible with H 3 PO 4 fuel cells increases kinetics and current densities. A binary CsF-HF electrolyte that operated at elevated temperatures was also promising but it had water management problems [6]. Therefore, H 3 PO 4 was considered to be the most practical electrolyte [1] and was chosen as the electrolyte for this study.…”

Section: Introductionmentioning

confidence: 99%

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Mathematical model for a direct propane phosphoric acid fuel cell

et al. 2005

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A mathematical model was developed and used to predict the performance of direct propane phosphoric acid (PPAFC) fuel cells, utilizing both Pt/C state-of the-art electrodes and older Pt black electrodes. It was found that the overpotential caused by surface processes on the platinum catalyst in the anode is much greater than the potential losses caused by either ohmic resistance or propane diffusion in gas-filled and liquid-filled pores. In one comparison, the anode overpotential (0.5 V) was larger than the cathode overpotential (0.3 V) at a current density of 0.4 A cm )2 for Pt loadings 4 mg Pt cm )2 . The need for sufficient water concentration at the anode, where water is a reactant, was indicated by the large effect of H 3 PO 4 concentration. In another comparison, the model predicted that at 0.2 A cm )2 , modern carbon supported Pt catalysts would produce 0.35 V compared to 0.1 V for unsupported Pt black catalysts that were used several decades ago, when the majority of the research on direct hydrocarbon fuel cells was performed. The propane anode and oxygen cathode catalyst layers were modeled as agglomerates of spherical catalyst particles having their interior spaces filled with liquid electrolyte and being surrounded by gasfilled pores. The Tafel equation was used to describe the electrochemical reactions. The model incorporated gas and liquid-phase diffusion equations for the reactants in the anode and cathode and ionic transport in the electrolyte. Experimental data were used for propane and oxygen diffusivities, and for their solubilities in the electrolyte. The accuracy of the predicted electrical potentials and polarization curves were normally within ±0.02 V of values reported in experimental investigations of temperature and electrolyte concentration. Polarization curves were predicted as a function of temperature, pressure, electrolyte concentration, and Pt loading. A performance of 0.45 V at 0.5 A cm )2 was predicted at some conditions.

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Section: Several Other Factors Influence the Performance Ofmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mathematical model for a direct propane phosphoric acid fuel cell

et al. 2005

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“…The relationship for the fraction of the surface covered by hydrocarbon species (and therefore not available to hydrogen) is expressed by O.Oo.3QsH --O.Oo.3Q H 0.00.3eric = [5] 0-00.3QsH…”

Section: ] To Calculate the Values Of The Bracketed Expression Desimentioning

confidence: 99%

“…For these reasons and because of the fact that fuel cells using hydrofluoric acid electrolyte oxidize saturated hydrocarbons at high current densities, it was decided that a study would be made of the adsorption of a saturated hydrocarbon on platinum in hydrofluoric acid. Propane was selected as the simplest typical saturated hydrocarbon because it is the smallest molecule containing both CH2 and CH3 groups, and it exhibits 1Present address: Argonne National Laboratory, Argonne, Illinois 60439. good reactivity on platinum in hydrofluoric acid (5,6).…”

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confidence: 99%

The Kinetics of Propane Adsorption on Platinum in Hydrofluoric Acid

Cairns

Breitenstein

1967

J. Electrochem. Soc.

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As a first stage in the investigation of the electrochemical oxidation of saturated hydrocarbons on platinum in acid electrolytes, the rate of adsorption of propane on a smooth platinum electrode was studied at 90~ in 37 mole % HF. Using an all-PTFE apparatus and single linear voltage sweep techniques, the surface coverage by hydrocarbon species was measured as a function of adsorption time and potential. The steady-state coverage resulting from propane adsorption shows a sharp maximum at 0.2v (vs. rhe). The amount of the most electrochemically active species is highest at 0.3v. The adsorption rate follows Langmuir kinetics with a third-order dependence on free surface. The rate constant has been measured for 0.2 and 0.3v at 90~During the last few years there has been an active interest in the direct anodic oxidation of saturated hydrocarbons in fuel cells (1-10). Exploratory fuel cell investigations pointed out the usefulness of strong acid electrolytes in this connection. The acidic electrolytes which have received the most attention in hydrocarbon fuel cells are ,sulfuric acid (1), phosphoric acid (2-4), hydrofluoric acid (5-8), and cesium fluoride-hydrofluoric acid mixtures (5,6,9,10). In order to understand better the kinetics and mechanisms involved in the over-all process of anodic oxidation of hydrocarbons, it is desirable to study the various individual steps in the process, starting with the adsorption of the hydrocarbon on a suitable electrode material in the presence of electrolyte.Some work on the adsorption of methane (11) and ethane (12, 13) on platinum in perchloric acid has been done at temperatures below those where significant reactivity is shown in fuel cells. The results of Gilman (12) on ethane adsorption on platinum in perchloric acid were interpreted in terms of the kinetics of the adsorption process, the adsorption being second order in free surface and first order in ethane concentration. Propane adsorption on platinum in phosphoric acid has been studied (14, 15), but since the adsorption process was diffusion-controlled, no rate expressions could be derived from those results. Butane adsorption on platinum in sulfuric acid has been measured at steady state by tracer methods (16), and under unsteady-state conditions by the use of flow-through porous electrodes (17); neither investigation yielded quantitative kinetic information.In order to study the kinetics of the adsorption process, it is necessary to perform the adsorption experiments under conditions where diffusion is not controlling. This requires that the product of the concentration of dissolved hydrocarbon and its diffusion coefficient be large enough (and therefore, diffusion fast enough) that the adsorption step is the slower process. It is known that hydrofluoric acid enhances the solubility of saturated hydrocarbons in water (18), and it is expected that the fluoride anion is not adsorbed on platinum electrodes (19,20). For these reasons and because of the fact that fuel cells using hydrofluoric acid electrolyte oxidize satu...

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“…In addition to inventing and developing the PEFC, this group of researchers examined the thermodynamics of fuel cells 22,23 and did a considerable amount of work on direct-hydrocarbon fuel cells, [24][25][26][27][28][29] as well as direct-ammonia fuel cells. 30,31 They also developed new electrode structures 32,33 and examined new electrocatalysts for use with reformate fuels.…”

Section: General Fuel Cell Topicsmentioning

confidence: 99%