Russell R. Bessette

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.

A study of cathode catalysis for the aluminium/hydrogen peroxide semi-fuel cell

Abstract The characterization and use of a Pd and Ir catalyst combination on a C substrate in an Al/H2O2 semi-fuel cell is described. The Pd–Ir combination outperforms Pd alone or Ir alone on the same substrate. Scanning electron microscopy (SEM) and energy dispersive spectrophotometry (EDS) were used to establish the location of Pd, Ir and O in clusters on the cathode substrate surface. X-ray photoelectron spectroscopy (XPS) binding energy measurements indicate that Pd is in the metallic state and the Ir is in the +3 state. A configuration consisting of an Ir(III) oxide (Ir2O3) core and a Pd shell is proposed. The electrochemical, corrosion, direct and decomposition reactions which take place during cell discharge were evaluated. Improved initial and long term performance, at low current densities, of the Al/H2O2 semi-fuel cell incorporating a Pd–Ir on C cathode relative to a similarly catalyzed Ni substrate and a baseline silver foil catalyst is demonstrated.

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.

Fabrication and Rate Performance of a Microfiber Cathode in a Mg-H2O2 Flowing Electrolyte Semi-Fuel Cell

Three-dimensional electrodes based on an array of carbon microfibers were prepared by a process called direct-charging electrostatic flocking. The cathodes comprised carbon fibers 11 μm in diameter and 500 μm long that protruded from a titanium foil support like blades of grass. The fiber density was 125,000 fibers per cm 2 of geometric area. The fibers were coated with an alloy of Pd and Ir to catalyze hydrogen peroxide reduction. The electrochemical performance of catalyst-coated carbon microfiber arrays (CMAs) was investigated in a flowing electrolyte Mg-H 2 O 2 semi-fuel cell. In these studies, CMA-based cathodes showed higher voltages at high current densities, better power densities, and equivalent H 2 O 2 utilization compared to planar cathodes with the same loading of catalyst.

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

The development of a magnesium-hydrogen peroxide semi-fuel cell

The Naval Undersea Warfare Center (NUWC) Division Newport, Rhode Island is presently developing a magnesium-solution phase catholyte semi-fuel cell (Mg-SFC) as an energetic electrochemical system for low rate, long endurance unmanned undersea vehicle (UUV) applications. This novel electrochemical couple consists of a magnesium anode and a solution phase catholyte of hydrogen peroxide together with a seawater electrolyte. Critical to this effort was the successful development of a unique catalytic compound consisting of palladium and iridium together with a carbon based substrate, greatly enhancing the electrochemical reduction of hydrogen peroxide. An overall cell potential increase of +0.9 V (1.25 V to 2.12 V) was observed with this catalyst in place of the prior silver based catalyst; representing a 69.6% increase in cell voltage. To further enhance the reduction potential at the positive electrode and the subsequent increased specific energy of this system, NUWC has collaborated with The University of Massachusetts to develop and synthesize a novel high surface area per unit volume microfiber carbon electrode (MCE) using a textile science flocking technique. Use of the flocking technique, which involves the alignment and placement of highly conductive and high surface charge carbon microfibers via a high potential electric field (40 kV to 70 kV), has not been reported upon in the scientific literature. Volumetric surface area of 182 cm/sup 2//cm/sup 3/ has been achieved, and the resulting electrochemical payoffs are discussed.