Suppose I have an electrochemical hydrogen pump (Wikipedia), whereby I have an anode and cathode, each with supported catalyst, separated by a proton exchange membrane. When I apply an appropriate potential, H$_2$ is effectively transported across the membrane. Now assume I do not have platinum catalysts on both electrodes, but have different catalysts on anode and cathode. What I want is that the anode catalyst strongly favours the hydrogen oxidation reaction and the cathode catalyst strongly favours the hydrogen evolution reaction. Such that if I reverse bias the cell, so that the electrode that is normally the anode becomes the cathode and vice versa, I will have a much reduced flow of hydrogen through the membrane with respect to regular polarity.

Do such catalysts allowing for such an asymmetrical cell exist? Is such a thing possible?


  • 3
    $\begingroup$ catalysts can't favor one reaction direction over the other $\endgroup$
    – Andrew
    Jan 6, 2023 at 21:11
  • 1
    $\begingroup$ .. as if they could, you could create catalyst perpetuum mobile by inserting the catalyst in step 1 and removing it in the step 2.. $\endgroup$
    – Poutnik
    Jan 6, 2023 at 21:46
  • 1
    $\begingroup$ Note that there is a good habit to explain in text less usual acronyms to avoid guessing or searching. $\endgroup$
    – Poutnik
    Jan 7, 2023 at 7:11

1 Answer 1


Yes such a thing is possible.

One way to achieve this, to allow oxidation to preferably happen compared to reduction (or vice versa) one could look at semiconductor electrodes. What happens at a semiconductor electrolyte interface with an applied potential? It depends on the nature of your semiconductor (if the current is carried by holes or free electrons, the location of the band edges, the band gap etc.), typically a p-type semiconductor allows for a significant anodic current but a reduced cathodic current (and vice versa for the n-type). The electrode-electrolyte interface effectively behaves like a diode.

For more information (given I am unsure what your background is on this subject) I refer you to


or any general text describing electrochemistry with semiconductors would suffice.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.