Velleman BATFUEL1 - Manual

Information sheet
Velleman

1/1 Last update: 4/12/2008
Direct borohydride fuel cell
Direct borohydride fuel cells (DBFCs) are a subcategory of alkaline fuel cells that use a
solution of sodium borohydride for fuel. The advantage of sodium borohydride over
conventional hydrogen in an alkaline fuel cell is that the highly alkaline fuel and waste
borax prevents poisoning of the fuel cell from carbon dioxide (CO2) in the air.
Borax
Borax (E285) is also known as sodium borate, sodium tetraborate or disodium
tetraborate. It is an important boron compound, a mineral, and a salt of boric acid. It is
usually a white powder consisting of soft colorless crystals that dissolve easily in water.
Borax has a wide variety of uses. It is a component of many detergents, cosmetics, and
enamel glazes. It is also used to make buffer solutions in biochemistry, as a fire retardant,
as an anti-fungal compound for fiberglass, as an insecticide, as a flux in metallurgy, and
as a precursor for other boron compounds.
The term borax is used for a number of closely related minerals or chemical compounds
that differ in their crystal water content, but usually refers to the decahydrate.
Commercially sold borax is usually partially dehydrated.
Chemistry
Sodium borohydride could potentially be used in more conventional hydrogen fuel cell
systems as a means of storing hydrogen. The hydrogen can be regenerated for a fuel cell
by catalytic decomposition of the borohydride:
NaBH
4
+ 2H
2
O → NaBO
2
+ 4H
2
Direct borohydride fuel cells decompose and oxidize the borohydride directly, side-
stepping hydrogen production and even producing slightly higher energy yields:
Cathode: 2O
2
+ 4H
2
O + 8e −
→ 8OH − E 0 = +0.4V
Anode: NaBH
4
+ 8OH −
→ NaBO
2
+ 6H
2
O + 8e − E 0 = +1.24V
Total E
0
=+1.64V
Advantages
DBFCs could be produced more cheaply than a traditional fuel cell because they do not
need expensive platinum catalysts. In addition, they have a higher power density.
Unfortunately, DBFCs do produce some hydrogen from a side step reaction of NaBH
4
with water heated by the fuel cell. This hydrogen can either be piped out to the exhaust or
piped to a conventional hydrogen fuel cell. Every fuel cell will produce water, and the
water can be recycled to allow for higher concentrations of NaBH
4
.
After releasing its hydrogen and being oxidized, NaBO
2
or borax is produced. Borax is a
common detergent and soap additive and is relatively non-toxic. Borax can be
hydrogenated back into borohydride fuel by several different techniques, some of which
require nothing more than water and electricity or heat. These techniques are still in
active development.