Hydrogen overpotentials on metal cathodes
Potentials and overpotentials of 11 cathodes measured by Tafel in 1905 in 2 N sulfuric acid at about 12 °C and 0.1 A/cm², with the extra energy the overpotential costs per mole of H₂.
| — | 1.974 | 1.30 | 251 | — | |
| polished | 1.970 | 1.30 | 251 | — | |
| rough | 1.900 | 1.23 | 237 | — | |
| — | 1.890 | 1.22 | 235 | — | |
| — | 1.820 | 1.15 | 222 | — | |
| — | 1.670 | 1.00 | 193 | — | |
| — | 1.620 | 0.95 | 183 | — | |
| — | 1.600 | 0.93 | 179 | queried in the original | |
| — | 1.460 | 0.79 | 152 | — | |
| — | 1.410 | 0.74 | 143 | — | |
| platinised | 0.745 | 0.07 | 14 | — |
η = ε − 0.674 V (the reversible hydrogen electrode against mercury–mercurous sulfate in 2 N sulfuric acid). Values are time-maximum readings at constant current; on copper, nickel and gold the potential drifted for hours and is less reliable. Overpotentials change with current density, temperature and surface condition.