Direct borohydride fuel cell
From Wikipedia, the free encyclopedia
Direct Borohydride Fuel Cell or DBFCs are a subcategory of Alkaline fuel cell where the fuel is a solution of Sodium borohydride. 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 CO2 in the air.
Sodium borohydride is used in experimental fuel cell systems as a means of storing hydrogen. As a fuel it is less flammable and less volatile than gasoline but much more corrosive. It is relatively environmentally friendly because it will quickly degrade into inert salts when released into the environment. The hydrogen can be regenerated for a fuel cell by catalytic decomposition of the aqueous borohydride solution:
- NaBH4 + 2H2O → NaBO2 + 4H2
Direct Borohydride Fuel Cells (DBFC) decompose and oxidize this fuel directly, side-stepping hydrogen production and even producing slightly higher energy yields:
- Fuel Cell's Cathode: 2O2 + 4H2O + 8e- => 8OH- E0=.4v
- Fuel Cell's Anode: NaBH4 + 8OH- => NaBO2 + 6H2O + 8e- E0=1.24v Total E0=1.64v
DBFCs could be produced more cheaply (because they do not need expensive platinum catalysts) and provide higher power output per mass than a traditional fuel cell. Unfortunately, DBFCs do produce some hydrogen from a side step reaction of NaBH4 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. Either fuel cell will produce water, and the water can be recycled to allow for higher concentrations of NaBH4.
After releasing its hydrogen and being oxidized, NaBO2 or Borax is produced. Borax is relatively inert and non-toxic; it is a common detergent and soap additive, though it is toxic to ants and is an ingredient of ant poisons. The borax waste can be pumped into a waste tank or bladder inside the fuel tank.
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.
Sodium borohydride costs US$50 per kg, but with borax recycling and mass production projected prices for the fuel are as low as US$1/kg.
[edit] References
The Direct Sodium Borohydride Fuel Cell for Unmanned Underwater Vehicle Application (pdf)
| Fuel Cells |
|---|
| Types: AFC | BE | DBFC | DEFC | DMFC | EGFC | FAFC | MCFC | MFC | MHFC | PAFC | PCFC | PEC | PEMFC | RFC | rfc | SOFC | ZFC |
| Other: Hydrogen Economy | Hydrogen storage | Hydrogen station | Hydrogen Vehicles |
 |
|
|||
