Fuel direct borohydride

B. H. Liu, S. Suda, Hydrogen storage alloys as the anode materials of the direct borohydride fuel ceU , J. Alloys Compd. 454 (2008) 280-285. 

Methanol is the most electro-reactive organic fuel, and, when it is electro-oxidized directly at the fuel anode (instead of to be transformed by steam reforming in a hydrogen-rich gas), the fuel cell is called a DMFC. More generally if the direct oxidation of a given fuel (alcohols, borohydrides, etc.)... 

The application of gold as an electrocatalytic component within the fuel cell itself has to date been limited primarily to the historical use of a gold-platinum electrocatalyst for oxygen reduction in the Space Shuttle/Orbiter alkaline fuel cells (AFC)88 and the recent use of gold for borohydride oxidation in the direct borohydride alkaline fuel cell (DBAFC).89,90 Electrocatalysts with lower cost, improved carbon monoxide tolerance and higher... 

Figure 14.1 QinetiQ s tubular direct borohydride alkaline fuel cell (DBAFC), reproduced courtesy of QinetiQ Ltd.

The product of the decomposition is, like in the Millennium Cell system, sodium metaborate. The system shows the same problems for the regeneration of NaBH4 from an aqueous solution of metaborate as described below. One advantage of the direct borohydride fuel cell systems is that platinum as catalyst is not needed. Unfortunately, depending on the temperature of the solution, some hydrogen gas is produced in a side reaction. However, this hydrogen can be piped out or can be used as additional fuel in a subsequent PEM fuel cell. 

The protide transition to proton has also been successfully applied to the development of a new type of fuel cell, the Direct Borohydride Fuel Cell (DBFC). The principle of the DBFC is briefly summarized by the following equation ... 

Compact hydrogen storage devices have been developed for use with small PEMFC in the past few years. The cost effectiveness will be improved significantly by applying BHJ solutions as the hydrogen fuel source to handy or mobile electronic devices such as portable computers, PDA, CD-cameras and UPS. The fuel cost even now is estimated to be very reasonable for such compact devices with capacity ranges from a few tens to a few hundred watts. The borohydride fuel costs, estimated from today s market price are shown in Fig. 6.47 for the PEMFC and in Fig. 6.48 for the DBFC (direct borohydride fuel cell). 

Wee J-H (2006) Which type of fuel cell is more competitive for portable application direct methanol fuel cells or direct borohydride fuel cells J Power Sources 161 1-10... 

Fuel cells are usually open systems, and their energy density and specific energy is largely based on the storage of fuel (and oxidant in the case of air-independent systems). Of the fuel cell types considered here, hydrogen PEMs, PAFCs and hydrogen AFCs use hydrogen as fuel, direct methanol fuel cells (DMFC) use aqueous methanol solution or pure methanol, and (alkaline) direct borohydride fuel cells (DBFC) use sodium borohydride solution as the liquid fuel. 

Ponce-de-Leon C, Kulak A, Williams S, Jimenez IM, Walsh FC (2011) Improvements in direct borohydride fuel cells using three-dimensional electrodes. Catal Today 170 148-154... 

Yi L, Hu B, Song Y, Wang X, Zou G, Yi W (2011) Smdies of electrochemical performance of carbon supported Pt-Cu nanoparticles as anode catalysts for direct borohydride-hydrogen peroxide fuel cell. J Power Sources 196 9924-9930... 

The price of sodium borohydride is currently too high by far for a practical application. Compared with hydrogen production from natural gas its price is 130 times higher. However, the idea of applying sodium borohydride as a fuel has the prerequisite of recycling the sodium borate product, and this could lower the price on the basis of mass production [98]. An alternative to hydrogen generation from sodium borohydride is the direct borohydride fuel cell, which is not within the scope of this book, so will not be discussed. 

FUEL CELLS USING INORGANIC LIQUIDS AS FUELS 4.12.1 Direct Borohydride Fuel Cells... 

Liu B. H., Z. P. Li, Current status and progress in direct borohydride fuel cell technology development, J. Power Sources, 187, 291 (2009). 

Ponce de Le6n, C., F. C. Walsh, D. Pletcher, D. J. Browning, J. B. Lakeman, Direct borohydride fuel cells, J. Power Sources, 155, 172 (2006). 

This voltage is noticeably higher than that obtained from hydrogen, and at eight electrons per molecule it indicates a fuel of remarkable potency. Unfortunately, the voltages actually obtained are not so different from a hydrogen fuel cell, because the catalysts that promote the direct borohydride oxidation of equation 5.4 also promote the hydrolysis reaction ... 

Ma, J. Choudhury, N. A. Sahai, Y, A comprehensive review of direct borohydride fuel cells. Renewable... 

Ma J, Liu Y, Zhang P et al (2008) A simple direct borohydride fuel cell with a cobalt phthalocyanine catalyzed cathode. Electrochem Commun 10 100-102... 

The redox potential in Eq. (6.14) is -0.4 V versus a reversible hydrogen electrode (RHE). Although BH4 is more resistant to hydrolysis than other hydrides such as alanates, the hydrolysis of BHa" (Eq. (6.15)) readily occurs in the presence of some catalysts. In particular, platinum-based catalysts, which are common anodes in direct borohydride fuel cells (DBFCs), cause significant decomposition of BH4". 

Wee, J.H. (2006) A comparison of sodium borohydride as a fuel for proton exchange membrane fuel cells and for direct borohydride fuel cells. Journal of Power Sources, 155, 329-339. 

---