Question

What is the difference between the Normal Hydrogen Electrode (NHE) and the Reversible Hydrogen Electrode (RHE)?

- Also, if a redox happens at the NHE of 0.2 V, please calculate the potential for the RHE at pH = 1.

Answer 1

During the early development of electrochemistry, researchers used the normal hydrogen electrode as their standard for zero potential. This was convenient because it couldactually be constructed by having "[immersing] a platinum electrode into a solution of 1N strong acid and [bubbling] 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'. ^[2]

In summary,

NHE: potential of a platinum electrode in 1N acid solution

SHE: potential of a platinum electrode in a theoretical solution (the current standard for zero potential)