There is a kind of battery, the total change in the battery when discharge is not a chemical reaction but a physical diffusion process of substances from a high concentration to a low concentration. This kind of battery is called concentration difference battery. The scale hydrogen atom was taken as a comparison, that is, the potential value of the scale electrode of hydrogen was set as 0. Compared with the hydrogen scale electrode, the higher potential was positive, and the lower potential was negative. An electrode used as a reference for measuring the potential of various electrodes.