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It is known that potential difference on metal/electrolyte or any kind of interphase can't be measured since voltmeter needed to measure it is made of metal which would in contact with metal and solution develop its own potential difference at interphase and as such affect the measurement. To solve this problem, potential is measured with respect to SHE. What I don't understand is that if you want to measure the electrode potential with respect to SHE, voltmeter needs to come in contact with two metal electrodes (one is electrode which potential you want to measure and the other is SHE) which will again create potential difference between the electrodes and voltmeter since two different metals in contact create potential difference between them. Can you explain?

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  • $\begingroup$ When two metals are in contact, they are at the same potential $\endgroup$
    – Maurice
    Mar 8, 2021 at 19:48
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    $\begingroup$ Seems well explained here: en.wikipedia.org/wiki/Galvani_potential. $\endgroup$
    – Ed V
    Mar 8, 2021 at 20:27
  • $\begingroup$ @Maurice Thermoelectric Seebeck effect is based on changes of this non-zero potential difference with temperature. $\endgroup$
    – Poutnik
    Aug 11, 2022 at 12:18
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    $\begingroup$ Generally, potential difference measurement and its errors and biases belong to domain of metrology, in spite of being essential to many domains of physics, chemistry and electronics. $\endgroup$
    – Poutnik
    Aug 11, 2022 at 12:34

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It is the same as measurement of voltage difference at any electronic circuit. The fact the metallic measuring points are attached to electrochemical electrodes is not relevant here.

Yes, there is metal contact potential difference, but it very low and very probably mutually canceling.

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  • $\begingroup$ Yes, maybe potential differences developed between different metals isn't too big so when comparing two redox systems these cancel each other. Another solution to this problem may be using voltmeter with probes made of same metals as electrodes, so that no potential difference develops. $\endgroup$ Mar 9, 2021 at 15:54
  • $\begingroup$ Even then, it is not related to electrochemistry, but rather to electronics or metrology. $\endgroup$
    – Poutnik
    Mar 9, 2021 at 18:41
  • $\begingroup$ I wouldn't agree since measurements of electrode potentials are very important in electrochemistry $\endgroup$ Mar 9, 2021 at 19:23
  • $\begingroup$ It is important, indeed. But mentioned issues have nothing to do with electrochemistry and are very minor. The measured voltage offset is much less than the measured voltage. The same metal would not help, as different metal contacts would just move elsewhere withing the measuring circuit. $\endgroup$
    – Poutnik
    Mar 9, 2021 at 23:22
  • $\begingroup$ Yes, I don't agree with what you said in the beggining for two reasons: 1) Contact potential differences of metals are actually electrochemical in nature, 2) Measurement and determination of potential differences on electrode/electrolyte interface is one the most important problems in electrochemistry and as such it is important to have good understanding of this problem. I agree with you that this problem is not something crucial since as you said these potentials are small compared to what you measure. $\endgroup$ Mar 10, 2021 at 16:39
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It is measured with the help of a reference electrode known as the standard hydrogen electrode (abbreviated to SHE). The electrode potential of SHE is 0 Volts. The standard electrode potential of an electrode can be measured by pairing it with the SHE and measuring the cell potential of the resulting galvanic cell. enter image description here

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