It has a good proton conductivity of 0.1 S/cm at 70-90 °C under humidified conditions. Under these conditions, protons can be released from sulfonic acid groups.

Benzenesulfonic acid is the simplest aromatic sulfonic acid. It is highly water-soluble and a strong acid with a pKa of –2.8. It has been known since at least the 1880s; its synthesis, which goes back ...