Ionic fluxes and membrane potentials are coupled by the Nernst–Planck equation. This equation is widely used to describe transport phenomena in biological and artificial membranes. In biological membranes, most often, the Goldman approximation is used, assuming constant electrical field in the membrane. Although the nature of transport processes of charged species is similar as for biological ... [Show full abstract] membranes, usually, a different method of description prevails in the literature, based on simplified empirical description of boundary potentials (Nicolsky–Eisenman equation), resulting from ion-exchange equilibria on the membrane/solution interface. Diffusion potential can be taken into account, described usually by considering the Henderson approximation. More advanced descriptions are also proposed as diffusion layer models (DLM) and recently the most advanced approach based on the Nernst–Planck–Poisson equations, without splitting the membrane potential into boundary and diffusion potentials.