Electrochemical hydrogen Storage Systems

Abstract

As the global need for energy increases, scientists and engineers have found a possible solution by using hydrogen to power our world. Although hydrogen can be combusted as a fuel, it is considered an energy carrier for use in fuel cells wherein it is consumed (oxidized) without the production of greenhouse gases and produces electrical energy with high efficiency.Chemical storage of hydrogen involves release of hydrogen in a controlled manner from materials in which the hydrogen is covalently bound. Sodium borohydride and aminoborane are two materials given consideration as chemical hydrogen storage materials by the US Department of Energy. A very significant barrier to adoption of these materials as hydrogen carriers is their regeneration from "spent fuel," i.e., the material remaining after discharge of hydrogen.The U.S. Department of Energy (DOE) formed a Center of Excellence for Chemical Hydrogen Storage, and this work stems from that project. The DOE has identified boron hydrides as being the main compounds of interest as hydrogen storage materials. The various boron hydrides are then oxidized to release their hydrogen, thereby forming a "spent fuel" in the form of a lower boron hydride or even a boron oxide. The ultimate goal of this project is to take the oxidized boron hydrides as the spent fuel and hydrogenate them back to their original form so they can be used again as a fuel. Thus this research is essentially a boron hydride recycling project.In this report, research directed at regeneration of sodium borohydride and aminoborane is described. For sodium borohydride, electrochemical reduction of boric acid and sodium metaborate (representing spent fuel) in alkaline, aqueous solution has been investigated. Similarly to literature reports (primarily patents), a variety of cathode materials were tried in these experiments. Additionally, approaches directed at overcoming electrostatic repulsion of borate anion from the cathode, not described in the previous literature for electrochemical reduction of spent fuels, have been attempted. A quantitative analytical method for measuring the concentration of sodium borohydride in alkaline aqueous solution has been developed as part of this work and is described herein. Finally, findings from stability tests for sodium borohydride in aqueous solutions of several different compositions are reported.For aminoborane, other research institutes have developed regeneration schemes involving tributyltin hydride. In this report, electrochemical reduction experiments attempting to regenerate tributyltin hydride from tributyltin chloride (a representative by-product of the regeneration scheme) are described. These experiments were performed in the non-aqueous solvents acetonitrile and 1,2-dimethoxyethane.A non-aqueous reference electrode for electrolysis experiments in acetonitrile was developed and is described.iii One class of boron hydrides, called polyhedral boranes, became of interest to the DOE due to their ability to contain a sufficient amount of hydrogen t...

Clinical Applications of Magnesium Hydride

“…The system of producing hydrogen-water, as shown in Figure 3, includes a reactor, reverse osmosis unit, valve, pump, control unit, digital display, water input, hydrogen-water output, hydrogen-water for therapeutic use, magnesium hydride block, and tap water input. Figure 4 shows the porous structure of magnesium hydride of 35 × 35 × 17 in millimeters which was manufactured by direct hydrogenation processes using a low-cost combustion synthesis [24,25].…”

Reaction of Magnesium Hydride with Water to Produce Hydrogen

“…Magnesium hydride is a light gray crystalline power that evolves into hydrogen at high temperatures above 320℃ under normal pressure [6]. On contact with water, it decomposes slowly to form hydrogen gas and magnesium hydroxide.…”

Maximized On-Demand Hydrogen Generator Design

“…NaBH 4 , a promising hydrogen storage medium that has attracted the interest of the environmentally-friendly research community, was recently proven to be unviable for on-board vehicular hydrogen power consumption; even with the most optimistic results, sodium borohydride could barely meet the 2007 targets designated by the Department of Energy [6]. Although those results do not necessarily mean that sodium borohydride is completely unusable, they do prove that NaBH 4 cannot solve one of the biggest problems troubling the science community -clean gasoline replacement.…”