The spatial distribution is discussed of the electrochemical potential of electrons and of the electrostatic potential in solid electrolyte cells without and with ion spillover on the gas-exposed electrode surfaces. In the latter case, where, over a wide temperature range, the spillover ions form an effective double layer at the electrode-gas interface, it is shown, both via an electrochemical and a surface science approach, that solid electrolyte cells are work function probes and work function controllers for their. gas-exposed electrode surfaces, in agreement with experiment. Under these conditions the work function of the working electrode is fixed by the applied potential and not by the gas phase at the working electrode. This is related to the effect of electrochemical promotion (non-Faradaic electrochemical modification of catalytic activity, NEMCA) and allows for further clarification of the concept of absolute electrode potential in solid state electrochemistry. (C) 2003 Elsevier Science B.V. All rights reserved.