Relationship Between The Normal Hydrogen Electrode (NHE) and The Standard Hydrogen Electrode (SHE)
During the early development of electrochemistry, researchers used the normal hydrogen electrode as their standard for zero potential. This was convenient because it could actually be constructed by having " a platinum electrode into a solution of 1N strong acid and hydrogen gas through the solution at about 1 atm pressure". However, this electrode/solution interface was not entirely reproducible, so the standard for zero potential was later changed. What replaced it was a theoretical electrode/solution interface, where the concentration of H+ was 1m, but the H+ ions were assumed to have no interaction with other ions (a condition not physically attainable at those concentrations). To differentiate this new standard from the previous one it was given the name 'Standard Hydrogen Electrode'.
In summary,
NHE: potential of a platinum electrode in 1N acid solution (historical standard, no longer in use)
SHE: potential of a platinum electrode in a theoretical solution (the current standard for zero potential)
Read more about this topic: Standard Hydrogen Electrode
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