Reference electrode potentials (25 °C)
Potentials of common reference electrodes against the standard hydrogen electrode. A reported potential must name its reference; converting between scales only means adding or subtracting these values.
| Standard hydrogen electrode | SHE | Pt | H2(g, 1 bar) | H+(aq, a = 1) | 0.000 | — |
|---|---|---|---|---|
| Silver–silver chloride (saturated KCl) | Ag/AgCl (sat. KCl) | Ag | AgCl(s) | KCl(aq, sat.) | 0.197 | 0.196 |
| Silver–silver chloride (3 M KCl) | Ag/AgCl (3 M KCl) | Ag | AgCl(s) | KCl(aq, 3 M) | 0.210 | — |
| Silver–silver chloride (1 M KCl) | Ag/AgCl (1 M KCl) | Ag | AgCl(s) | KCl(aq, 1 M) | 0.235 | 0.235 |
| Silver–silver chloride (0.1 M KCl) | Ag/AgCl (0.1 M KCl) | Ag | AgCl(s) | KCl(aq, 0.1 M) | 0.288 | 0.288 |
| Saturated calomel electrode | SCE | Hg(l) | Hg2Cl2(s) | KCl(aq, sat.) | 0.241 | 0.242 |
| Calomel electrode (1 M KCl) | NCE (1 M KCl) | Hg(l) | Hg2Cl2(s) | KCl(aq, 1 M) | 0.280 | 0.280 |
| Calomel electrode (0.1 M KCl) | Calomel (0.1 M KCl) | Hg(l) | Hg2Cl2(s) | KCl(aq, 0.1 M) | 0.334 | 0.334 |
The “computed” column uses E°(AgCl/Ag) = 0.22233 V, E°(Hg₂Cl₂/Hg) = 0.26808 V and the KCl mean activity m·γ± in the Nernst equation, and agrees with the tabulated values within 2 mV; the 3 M KCl Ag/AgCl value is the one quoted by electrode makers (±3 mV). Compilations differ by a few millivolts, mostly because of junction potentials.