What is potential verses Standard Hydrogen Electrode (SHE)?


Dokument-ID TE8351


Veröffentlichungsdatum 03.08.2021
What is potential verses Standard Hydrogen Electrode (SHE)?
Definition of potential vs. SHE and table for different reference systems.
Most electrochemical measurements (measurements taken with probes like pH, Oxidation/Reduction Potential (ORP), Ion Selective Electrodes (ISE), and Electrolytic Conductance (EC)) are potentiometric.

Potentiometric measurements are where the probe measures a potential in millivolts (mV) which is then either reported as the result (like with ORP), or is then used to calculate the result using a calibration (like with pH and ISE).

There are multiple factors that impact a mV reading. The one that is relevant to this question is the reference system. The purpose of reporting a potential vs. SHE is to address any differences in mV measurement caused by differences in reference systems. This means that an identical sample would give different mV readings on different probes that have different reference systems, even if they are reading identical to theoretical and all other variables are constant. A Standard Hydrogen Electrode (SHE) is the standard that all other reference systems are compared to. If the potential vs. SHE for two probes with different reference systems is known, the mV results can be compared to each other on the same relative scale. Also, if you know what a standard should read with SHE and know what the potential vs. SHE is for a probe, it can easily be calculated what that probe should read on that same standard.

Below is a table of potential vs. SHE for several different reference systems. The User Manual for most electrodes will give either a potential vs. SHE, or it will provide what reference system is used for that electrode.
Reference System Potential vs. SHE (mV)
Ag/AgCl - 3 M KCl +208
Red Rod- Saturated KCl +199
Ag/AgCl - 1 M KCl +235
Ag/AgCl - 0.6 M KCl (sea water) +250
Ag/AgCl - Saturated KCl +199
Hg/Hg2Cl2 - Saturated KCl (SCE: Standard Calomel Electrode) +244
Hg/Hg2Cl2 - 1 M LiCl +280
Hg/Hg2SO4 - Saturated K2SO4 +651
Hg/Hg2SO4 - 1 M H2SO4 +616
Hg/HgO - 0.1 M KOH +174
The Complete Reference Manual is attached. 

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