The Diversity and Causes of Current-Potential Behaviour at Gas-Evolving Electrodes

As distinct from electrodes without gas evolution, the current dependence on the potential at gas-evolving electrodes exhibits a substantial variety of behaviour patterns. In potential-controlled cells, the current may smoothly increase up to a limiting value induced by mass transfer of the reactant. Alternatively, the current may attain a maximum followed by a usually substantial decrease to low values. This decrease may proceed smoothly or abruptly. The diversity of the shapes of the current/potential curves was found to depend mainly on the cell design and the operating conditions by a joint action of overpotential and ohmic potential drop. Elementary electrochemical relationships together with a few empirical auxiliary functions suffice to verify the distinct shapes of the current-potential curves and to explain the causes.