A fundamental study on electrochemical hydrogen generation from borohydrides

Borohydrides (LiBH4, NaBH4, KBH4, etc.) are the most attractive materials for hydrogen storage due to their high-volumetric and -gravinnetric hydrogen density as well as safety issues. Although H-2 for fuel cells is generated by the hydrolysis of borohydrides, it is very difficult to control the rate of H-2 generation due to the nature of the catalytic reaction. In addition, the change in enthalpy (Delta H) of the reaction is directly wasted as heat generation. We propose a method for the electrochemical generation of hydrogen, in which a borohydride in an alkaline solution is oxidized at the anode while water is reduced at the cathode to generate H-2 gas. The cell has a cation exchange polymer electrolyte membrane between a precious metal anode and a Pt cathode to inhibit the crossover of BH4- anion. The open circuit voltage of the cell is positive, which raises the possibility of spontaneous operation with electrical generation as an alternative to the heat generation in hydrolysis. At the cathode, the rate of H-2 generation coincides well with the current density, indicating that H-2 generation from borohydrides can be electrochemically controlled by means of this hydrogen generator. (c) 2008 Elsevier B.V. All rights reserved.