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I searched from the internet but i got confused. I was not sure about my answer.

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    $\begingroup$ What exactly do you find confusing? $\endgroup$
    – andselisk
    May 20 '20 at 20:10
  • $\begingroup$ What exactly bubble hydrogen does in a hydrogen electorde $\endgroup$
    – Sinem
    May 20 '20 at 20:15
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    $\begingroup$ Ehhm, assures its functionality? Look, you probably want to give Wikipedia article a good read and refine your question. $\endgroup$
    – andselisk
    May 20 '20 at 20:20
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    $\begingroup$ Since it has not been mentioned yet, you appear to be referring to the Standard Hydrogen Electrode, called, for short, SHE. So your internet search was not so effective. $\endgroup$
    – Ed V
    May 20 '20 at 20:56
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The presence of $\ce{H_2}$ on the electrode is necessary, in order to satisfy Nernst' law. The potential of the $\ce{H_2}$ electrode is defined by the following expression : $$\ce{E = E° + (0.0592/2)·log{[H^+]^2/p(H_2)]}}$$ In this equation, $\ce{E°}$ is equal to Zero by definition. If we want the measured $\ce{E}$ value of the Hydrogen electrode to be also equal to Zero, the platinum electrode must be in contact with $\ce{H^+}$ in a solution where the activity is equal to $1$ (nearly $1$ M). But the platinum electrode must also be in contact with $\ce{H_2}$. The trouble is that $\ce{H_2}$ is not a metal. It is a gas, and it is not easy to have a gas in contact with a platinum electrode. Furthermore, the gas should be at $1$ atmosphere pressure. The simplest way of carrying out this contact is to have some pure $\ce{H_2}$ bubbles crossing the solution, with the hope that at least one or two droplets gets attached or adsorbed at the surface of the platinum. The yield is not remarkable, as nearly all bubbles are simply crossing the liquid to be lost at the surface of the liquid. But the small amount which stays fixed on the platinum electrode is sufficient to get the whole electrode at Zero potential.

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    $\begingroup$ Not an expert in electrochemisty, but I would think the gas doesn't have to be in contact with the electrode. Rather the solution has to be saturated with the gas. This is why you bubble the gas. Contact between bubbles adhering and releasing from the electrode would probably generate unwanted noise. $\endgroup$
    – Buck Thorn
    May 21 '20 at 8:25

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