Basic requirements for reference electrode
(1) the reversibility of the electrode is better, not easy to polarization. This requires that the reference electrode is reversible and the exchange current density is large (10-5A/cm2). When the current flowing through the electrode is less than 10 − 7A/cm2, the electrode is not polarized. Even if a slightly larger current flows for a short time, the potential can quickly return to the original value after the power is turned off.
(2) the electrode potential is relatively stable, and closer to zero potential, not easy to polarization or passivation. After the reference electrode is prepared, its potential should be stable after standing for several days.
(3) the potential reproducibility is good. The same reference electrode made by different persons or at different times shall have the same potential. The potential of each reference electrode made each time shall be the same after stabilization, and the difference shall be less than lmV.
(4) The temperature coefficient is small, that is, the potential changes with temperature. And when the temperature returns to the original temperature, the potential should quickly return to the original potential value.
(5) The preparation, actual use and maintenance are more convenient and durable. The reference electrodes that can meet the above requirements include hydrogen electrode, calomel electrode, mercurous sulfate electrode, mercuric oxide electrode, silver chloride electrode, etc. Most of these electrodes are of the second type.