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It's well known that if you mix $\ce{H2}$ and $\ce{O2}$ in ambient conditions, the $\ce{H2}$ will be stable indefinitely, and will only react with $\ce{O2}$ to form water when ignited by a flame. The reason being that for the reaction

$$\ce{2H2 + O2 -> 2H2O} \label{rxn:1}\tag{1}$$

to occur, first the bonds must be broken in $\ce{H2}$ and in $\ce{O2},$ which is an insurmountable activation energy at room temperature.

So I am confused why a hydrogen fuel cell works at room temperature without ignition, as it is powered by the same chemical reaction \eqref{rxn:1}.

In particular, why can the strong double bond in $\ce{O2}$ suddenly be broken in this context without a flame?

My best guess is that somehow the electron sea in the copper wire acts as a catalyst. If this is true, what are the details of this mechanism that allows the $\ce{O2}$ bond to break at room temperature?

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  • $\begingroup$ My guess would be that the reaction you've stated isn't the actual reactions occurring but the overall reaction of the two half equations that take place in an alkaline hydrogen-oxygen fuel cell. $$\ce{H2 + 2OH- ->2H2O + 2e- }$$ $$\ce{O2 + 2H2O + 4e- ->4OH-}$$ $\endgroup$
    – H.Linkhorn
    Jun 9, 2019 at 16:58

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You guessed it right that hydrogen and oxygen mixtures will remain stable. Someone in Harvard waited for >30 years and found very little water if any. As you said, there is a energy barrier. What type of materials can lower this barrier? Catalysts.

The electrode materials require some catalysts such as platinum or nickel. Of course, making cheaper and sustainable catalysts is an extensive area of research. If a person discovers a better catalyst which is far more common than Pt, then that person certainly deserves a big award. Copper does not act as a catalyst here.

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  • $\begingroup$ Thanks! I was missing the connection to Platinum. After reading more about this, I feel like I am still missing the magic of how metals are able to break the O2 bond on their surface. Posting in a new question here: chemistry.stackexchange.com/questions/116602/… $\endgroup$
    – rampatowl
    Jun 9, 2019 at 18:07
  • $\begingroup$ Search the key word adsorption of hydrogen on platinum. People must be studying this phenomenon for ages. $\endgroup$
    – AChem
    Jun 9, 2019 at 19:09

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