Maria G. Medeiros

Magnesium Solution Phase Catholyte Seawater Electrochemical System

In accordance with the present invention, an electrochemical system is provided which comprises a plurality of cells, the cells being formed by spaced apart bipolar electrodes. Each of the electrodes is formed by an anode portion formed from a magnesium containing material and an electrocatalytic material joined to a surface of the anode. The electrodes are spaced such that the anode portion of one electrode faces the electrocatalytic material of the adjacent electrode. The electrochemical system also comprises a manifold system for introducing a seawater-catholyte solution into the spaces between the electrodes. An electrical connection is provided across the cells so as to initiate the reduction of the seawater-catholyte solution at the electrodes and to create electrical power. In a preferred embodiment, the seawater-catholyte solution is a seawater-hydrogen peroxide or seawater-sodium hypochlorite solution. A process for generating electrical power using the electrochemical system of the present invention is also described.

Enhanced electrochemical performance in the development of the aluminum/hydrogen peroxide semi-fuel cell

Abstract Significant accomplishments from this research effort have defined and characterized the nature and rate of the chemical dynamics at the anode and cathode, thus allowing the development of the aluminum/hydrogen peroxide couple as an energy-dense semi-fuel cell system. This effort has included the investigation of new aluminum alloys, development of new electrocatalysts for the hydrogen peroxide, optimization of the operating parameters and modelling of the electrochemical performance of the couple. Furthermore, it has demonstrated a technique that will enhance the electrochemical properties of selected aluminum anodes, while controlling unwanted corrosion reactions at a tolerable level. The unique methodology described in this paper involves the use of additives to activate the surface of the aluminum anode-electrolyte, thus avoiding alloying, processing and heat treating. In addition to this anode development, we have identified a novel electrocatalyst that enhances effective and efficient electrochemical reduction of hydrogen peroxide, thus shifting the predilection of the peroxide from parasitic decomposition to desired high rate electrochemical reduction. The improved performance of this electrochemical couple has led to the attainment of current densities of 500 to 800 mA cm −2 , five to seven times that originally achievable at comparable cell voltages of 1.4 to 1.2. System-level modelling, based on the experimental evidence reported in this paper, indicates that the aluminum/hydrogen peroxide couple is a versatile and energetic electrochemical energy source.

Optimization of the magnesium-solution phase catholyte semi-fuel cell for long duration testing

A magnesium semi-fuel cell (Mg-SFC) was investigated as an energetic electrochemical system for low rate, long endurance undersea vehicle applications. This electrochemical system uses a Mg anode, a sea water electrolyte, a Nafion membrane, a carbon paper cathode catalyzed with Pd and Ir, and a catholyte of hydrogen peroxide in a sea water/acid electrolyte. Unique to the approach described here is the use of a magnesium anode together with the introduction of the catholyte in solution with the sea water, thus operating as a semi-fuel cell as opposed to a battery. Five critical operating parameters were optimized using a Taguchi matrix experimental design. Using these optimized conditions, high voltage and high efficiencies were obtained during long duration tests.

Application of an Anode Model to Investigate Physical Parameters in an Internal Reforming Solid-Oxide Fuel Cell

A one-dimensional model of chemical and mass transport phenomena in the porous anode of a solid-oxide fuel cell, in which there is internal reforming of methane, is presented. Macroscopically averaged porous electrode theory is used to model the mass transfer that occurs in the anode. Linear kinetics at a constant temperature are used to model the reforming and shift reactions. Correlations based on the Damkohler number are created to relate anode structural parameters and thickness to a nondimensional electrochemical conversion rate and cell voltage. It is shown how these can be applied in order to assist the design of an anode.

Recent Developments in Borohydride Fuel Cells

Developments in direct borohydride fuel cells (DBFC) are considered together with electrolyte stability and the choice of membrane and electrode materials. The cyclic voltammetry of borohydride oxidation was studied at three electrodes: a) gold on carbon, Au/C, b) gold on titanate nanotubes, Au/TiN and (c) gold foil. Similar currents were observed from the three electrodes. A DBFC in a single, 2- and 4-bipolar cell configuration with Au/C anode and Pt/C cathode produced 2.2, 3.2 and 9.6 W showed cell voltages of 1.06, 0.81 and 3 V, respectively. In another single cell, the reduction of peroxide on a Pd/Ir coated microfibrous carbon cathode was catalytically more active than a platinised-carbon one. The maximum power density achieved was 78 mW cm-2 at a cell voltage of 1.09 V. The need for further research is highlighted, particularly into new electrocatalyst materials

Modeling and Verification of Steady State Operational Changes on the Performance of a Solid Oxide Fuel Cell

Solid oxide fuel cells (SOFCs) offer many potential benefits as an energy conversion device. This paper addresses experimental validation of a numerical SOFC model that has been developed. Results are compared at steady state operation for temperatures ranging from 1073 K to 1173 K and for H 2 gas concentrations fuel supplies of 10-90% with a balance of N 2 . The results agree well with a maximum of 13.3% difference seen between the numerical and experimental results, which is within the limit of the experimental uncertainties and the material constants that are measured, with most comparisons well below this level. It is concluded that since the model is very sensitive to material properties and temperature that for the best results they should be as specific as possible to the experiment. These specific properties were demonstrated in this paper and a validation of a full fuel cell model, with a concentration on the anode, was presented.