Voltage Components at Gas Evolving Electrodes

A general statement of voltage components at gas evolving electrodes, including ohmic losses, surface overpotential, gas concentration, and ionic concentration overvoltages, is presented. Discussed and illustrated are the means for estimating the value and measurability of each component. A subcomponent of the surface overpotential, termed hyperpolarization, a result of masking of the electrode by bubbles, is quantified. In hydrogen or oxygen evolution from sulfuric acid, the largest of the bubble‐related components is the concentration overpotential, due to supersaturation of the electrolyte with dissolved gas. In carbon dioxide evolution from aluminum oxide dissolved in cryolite, ohmic effects are the most important. Hyperpolarization of the electrodes is estimated to be 2, 5 and 25 mV in hydrogen, oxygen, and carbon dioxide evolution, respectively.