Carina Lagergren

Synthesis and Performance of LiCoO2 Cathodes for the Molten Carbonate Fuel Cell

A method for fabricating LiCoO2 electrodes has been developed. LiCoO2 powder was synthesized from Li2CO3 and CoCO3 powder by calcining in air at 650-degrees-C. Electrodes were tape cast in a nona ...

Active Area Determination of Porous Pt Electrodes Used in Polymer Electrolyte Fuel Cells: Temperature and Humidity Effects

This paper discusses the proper measure of the electrochemically active area (ECA)of carbon supported Pt catalyst in PEM fuel cells employing in situ cyclic voltammetry. The charges of the hydrogen ...

Influence of gas phase mass transfer limitations on molten carbonate fuel cell cathodes

The purpose of this paper is to elucidate to what extent mass transfer limitations in the gas phase affect the performance of porous molten carbonate fuel cell cathodes. Experimental data from porous nickel oxide cathodes and calculated data are presented. One and two-dimensional models for the current collector and electrode region have been used. Shielding effects of the current collector are taken into account. The mass balance in the gas phase is taken into account by using the Stefan–Maxwell equation. For standard gas composition and normal operating current density, the effect of gas-phase diffusion is small. The diffusion in the gaseous phase must be considered at operation at higher current densities. For low oxygen partial pressures, the influence of mass transfer limitations is large, even at low current densities. To eliminate the influence of conversion on polarization curves recorded on laboratory cell units, measurements should always be performed with a five to tenfold stoichiometric excess of oxygen. Two-dimensional calculations show rather large concentration gradients in directions parallel to the current collector. However, the influence on electrode performance is still small, which is explained by the fact that most of the current is produced close to the electrolyte matrix.

Investigation of Porous Electrodes by Current Interruption Application to Molten Carbonate Fuel Cell Cathodes

A transient agglomerate model for simulation and analysis of experimental data, obtained by current interruption on porous molten carbonate fuel cell cathodes, is presented. The initial fast change ...

Mathematical modelling of the MCFC cathode

Abstract Different models for the NiO cathode have been compared with respect to their abilities to predict polarization curves and the influence of the amount of electrolyte on the electrode performance. It has been shown that the agglomerate model for the MCFC cathode gives more reasonable results when the exterior agglomerate surface area is specifically taken into account. In the cathode only the outermost layer of nickel oxide particles in the agglomerate is utilized for the electrochemical reaction. The pseudohomogeneous approach is questionable for these agglomerates since the individual particles constituting the agglomerate are of the same size as the reaction zone thickness. A thin-film model with a roughness factor for the electrode surface appears to be as good a model as the agglomerate model. A model based on a chain of spherical agglomerates and the partially drowned agglomerate model are physically more realistic models than the homogeneous agglomerate model for the prediction of the influence of electrolyte fill on the electrochemical performance.

LiFeO2 ­ LiCoO2 ­ NiO Cathodes for Molten Carbonate Fuel Cells

Dissolution of the state-of-the-art lithiated nickel oxide cathode is a major obstacle for the development of molten carbonate fuel cell (MCFC) technology. LiFeO2 and LiCoO2 were reported earlier as the most promising alternative materials; however, they do not satisfactorily substitute for the state-of-the-art cathode material. A solid solution consisting of LiFeO2, LiCoO2, and NiO is expected to posses some desirable properties of these three materials. Powder compositions in the LiFeO2-NiO binary system and a ternary subsystem with a constant 50:50 molar ratio of LiFeO2:NiO were prepared by the Pechini method. After preliminary powder characterizations, the feasibility of new materials for MCFC cathode application was studied. Electrical conductivity and microstructural characteristics were investigated, first in the form of bulk pellets and then in ex situ sintered porous gas diffusion cathodes. Finally, the electrochemical performance of selected cathodes was evaluated by short-time laboratory scale cell operations. The electrical conductivity of the ternary compositions with 50:50 molar ratio of LiFeO2:NiO increases significantly with increasing LiCoO2 content up to about 25 mol %. Further increase of LiCoO2 content decreases conductivity. The cell study indicates the possibility of preparing cathodes suitable for MCFC application with a considerably high LiFeO2 content.

Mathematical modelling of the MCFC cathode : On the linear polarisation of the NiO cathode

Experimental polarisation curves for the porous lithiated NiO cathode used in molten carbonate fuel cells very often exhibit a linear shape over a wide potential range. It is shown by means of mathematical modelling that this linear behaviour can be explained by the interplay of intrinsic electrode kinetics, diffusion of electroactive species through an electrolyte film and the effective ohmic resistance of the pore electrolyte, providing that the cathodic transfer coefficient has a value of about 1.5. In contrast, with the generally assumed value of 0.5 of this transfer coefficient and with reasonable values of the effective electrolyte conductivity, predicted polarisation curves will always bend downwards over the overvoltage region of interest. The evolution of the polarisation curves with increasing electrolyte fill can be simulated by a model according to which the electroactive surface area becomes gradually blocked with the increasing amount of electrolyte.

Methodology for measuring current distribution effects in electrochromic smart windows.

Electrochromic (EC) devices for use as smart windows have a large energy-saving potential when used in the construction and transport industries. When upscaling EC devices to window size, a well-known challenge is to design the EC device with a rapid and uniform switching between colored (charged) and bleached (discharged) states. A well-defined current distribution model, validated with experimental data, is a suitable tool for optimizing the electrical system design for rapid and uniform switching. This paper introduces a methodology, based on camera vision, for experimentally validating EC current distribution models. The key is the methodologys capability to both measure and simulate current distribution effects as transmittance distribution. This paper also includes simple models for coloring (charging) and bleaching (discharging), taking into account secondary current distribution with charge transfer resistance and ohmic effects. Some window-size model predictions are included to show the potential for using a validated EC current distribution model as a design tool.

The Effects of Oxidant Gas Composition on the Polarization of Porous LiCoO2 Electrodes for the Molten Carbonate Fuel Cell

Stationary polarization curves were obtained for porous lithium cobaltite cathodes under varying temperatures and oxidant compositions. The exchange current densities were determined from the slope at low overpotentials by means of numerical calculations, taking into account the current density distribution. Positive influences on the exchange current density were found both for the partial pressure of oxygen and carbon dioxide. The results are similar to earlier data obtained from measurements on NiO electrodes. The values are not consistent with either the peroxide mechanism or the superoxide mechanism, two mechanisms often proposed in the literature.

Experimental determination of effective conductivities in porous molten carbonate fuel cell electrodes

In this work an electrochemical impedance spectroscopy method fbr the determination of the effective conductivities of the pore electrolyte and electrode matrix in porous electrodes has been used. ...