Two mechanisms behind the appearance of ions in the vapor-gas sheath around a hot electrode immersed in an electrolyte, electrolyte surface instability against the surface charge and field evaporation, are considered. It is shown that the concept of the thermally activated field evaporation of ions provides a better approximation to experimental conditions. A dispersion relation for capillary-barogravity waves at the electrolyte-saturated vapor charged interface is derived. Critical conditions for the instability of these waves are found.