It is demonstrated that detachment of electrons in the afterglow of an electronegative plasma can lead to a significant increase in negative wall potential with respect to the plasma potential. This effect can be used to modify the near-wall sheath electric field and thickness, which are important for plasma processing applications. Also in the afterglow, this effect can lead to an increase in electron density with time, and a reduction (up to total exclusion) in diffusion cooling of electrons and can thus be used to modify the electron temperature.