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This is a chemistry/technology kind of question. Some PEM fuel cells work with a rated hydrogen purity of 99.99%.

What would happen if the fuel cell stack is supplied with a hydrogen purity/concentration below the rated value?

Would the lack of hydrogen damage some cells?

I guess that the fuel cell stack would have a lower efficiency and that would depend on the stack design and technology, but most important, would that low purity hydrogen accelerate the degradation of the stack? I am assuming that the hydrogen concentration is not monitored by a microcontroller that can shut down the fuel cell.

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    $\begingroup$ AFAIK hydrogen full cells require efficient catalysis which can be severely and irreversibly affected by impurities blocking active catalyst centers. The required purity is kind of trade-off decision between operational and lifetime cost. $\endgroup$
    – Poutnik
    Jan 12, 2022 at 10:05
  • $\begingroup$ Look up "catalyst poisoning". The difference inquantity between 99.90% and 99.99% is irrelevant. You might also see how a catalytic lighter works. en.wikipedia.org/wiki/Lighter#Catalytic_lighter $\endgroup$ Jan 12, 2022 at 21:12
  • $\begingroup$ Thank you for the comments and answers. $\endgroup$ Jan 17, 2022 at 10:48

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It isn't only the concentration (and eventually, the amount) of impurity which has to be considered, but the chemical nature of the impurity. Read the certificate of analysis by your supplier.

  • If you use transition metal electrodes which are sensitive to sulfides, and this is the main impurity of the gas used, you may alter the the electrodes locally (chemisorption), and eventually irreversibly (by reaction).

  • If on the other hand the hydrogen gas contains traces of e.g., argon not participating in the electrochemical reactions, then the efficiency of your fuel cell will alter only as long as the impurity is present.

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