Solid electrolytes may be used where the electrode reactants are gaseous as in a rechargeable oxide fuel cell or are liquids as in a cell of a rechargeable Na-S battery; porous polymer/oxide composites may be used as a separator where one electrode is a flow-through liquid containing a soluble redox molecule. Where two solid electrodes interact reversibly across an electrolyte, a solid-electrolyte may be used (i) as a separator in a dual liquid-electrolyte cell, (ii) in an all-solid-state battery, or (iii) in contact with an alkali-metal anode on one side and a liquid electrolyte on the other side. A solid-electrolyte interface with the anode would also block from reaching the anode soluble intermediate species of a solid-sulfur cathode reaction in a liquid catholyte. We discuss strategies for realizing the different strategies and introduce the concept of water-solvated glass/amorphous solid cation electrolytes/dielectrics. (C) The Author(s) 2015. Published by ECS. All rights reserved.