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Name: Brian
Status: student
Grade: 9-12
Location: SC
Country: USA
Date: Winter 2011-2012


Question:
Hello, I am a student in 10th grade and I was wondering if I could get some information about what happens when hydrogen peroxide decomposes by the use of a catalyst. Is there any transfer or release of electrons or ions during the decomposition? And if there is a release of ions and electrons could one hypothetically use this to power a fuel cell?



Replies:
Hi Brian,

The decomposition of hydrogen peroxide simply results in water, oxygen, and energy. A simple decomposition reaction. A fuel cell requires two components, a "fuel" and an "oxidizer" that are introduced separately at the anode and cathode (respectively) of the fuel cell, and combine (not decompose) in a controlled reaction, generating an external flow of electrons.

Hydrogen peroxide by itself would be of no use in a fuel cell because all it can do is decompose. It is an oxidizing agent, to be sure, but you will still need a separate "fuel". Further, uncontrolled decomposition of H2O2 by exposure to a catalyst, is counterproductive, since the decomposition will proceed within a few seconds, and the resulting oxygen will escape, and the resulting energy will be wasted heating the fuel cell.

Regards, Bob Wilson


Hydrogen peroxide decomposes by the reaction: 2 H2O2 (aq) -----> O2 (gas) + 2 H2O (liq) In the absence of a catalyst, this reaction is negligibly slow; HOWEVER, it is catalyzed by many substances: substances in/on the skin, MnO2 to mention just a couple.

No ions or electron transfers are required, but there are so many pathways, some mechanisms may well involve those pathways. The problem using H2O2 to power a fuel cell is controlling the speed of the reaction -- there would be some "engineering" design issues. If you do a search on the term(s) "decomposition of hydrogen peroxide", you will find a lot of information. The motivation for all the detailed information is that 100% H2O2 is a rocket fuel. Hydrogen peroxide comes in three concentrations that can be stabilized -- 3% (pharmacy grade), 30% (chemical reagent grade) and 70% (be very careful grade!!). Rocket grade (rocket fuel grade) requires special handling and is not commonly available -- very touchy!

Vince Calder



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