I was trying to understand how the proton-exchange membrane fuel cell works. Online I read that in such a cell hydrogen is oxidized at an anode catalyst, mostly platinum, and a detached electron ends up going through the circuit.

My doubt is where is the energy coming from?

That the catalyst can split hydrogen molecules for ever, isn't this a violation of the Laws of Thermodynamics? If the platinum is oxidizing the hydrogen, it must get depleted some time later?

ps: im in high school

  • $\begingroup$ You should look for a reaction that depletes the platinum. Is there one? $\endgroup$
    – Buck Thorn
    Feb 3, 2022 at 17:04

1 Answer 1


If you want to understand the thermodynamics of a redox reaction, you have to look at both half-reactions. You are discussing the half-reaction that provides the electrons (and the protons):

$$\ce{H2 -> 2H+ + 2 e-}$$

There has to be a second half-reaction that consumes the electrons, e.g.

$$\ce{O2 + 4H+ + 4e- -> 2 H2O}$$

In combination, this is a redox reaction where the equilibrium lies on the side of the products.

$$\ce{O2 + 2H2 -> 2 H2O}$$

Those types of reactions can be used to generate electricity.

Like if this catalyst can split the hydrogen molecules for ever , then isn't this a violation of the Laws of Thermodynamics? If the Platinum is oxidizing the hydrogen , it must get depleted some time later?

The platinum is a catalyst. It affects the speed of the reaction (the kinetics), but not on which side the equilibrium lies (thermodynamics). The other half-reaction is oxidizing the hydrogen, and platinum is just a catalyst.


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