Direct Borohydride Fuel Cell DBFC

These cells used metal borohydrides such as sodium borohydride as a fuel as it contains up to 10.5% of hydrogen by weight. This cell also uses Nafion as the 

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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 ... 

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. 

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". 

The direct borohydride fuel cell (DBFCs) usually operates in one single alkaline environment since the BH4 ion is imstable in neutral and acidic media. The theoretical OCV of a conventional DBFC in a single alkaline solution is 1.64 V. An acid-alkaline hybrid DBFCs can have oxidation of BH4" in alkaline and reduction of O2 (or H2O2) in acid. The theoretical OCV of this acid-alkaline hybrid DBFCs can reach as high as 3.0 V. The reactions are... 

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). 

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