NOVELTY - A reversible system comprises a first electrode comprising liquid silver metal and a second electrode, where the first and second electrodes are separated by an oxygen ion-conducting solid electrolyte. The cell is capable of steam electrolysis when the polarity of the electrodes is selected such that the liquid silver is an anode. It is capable of electrical energy generation when the polarity of the electrodes is selected such that the liquid silver is a cathode.    USE - For steam electrolysis and energy generation, preferably for providing pure hydrogen to power fuel cells for transportation, defense and consumer electronic applications and for generating syngas for use in e.g. stationary and distributed power generation.    ADVANTAGE - The system employs an oxygen ion-conducting solid electrolyte at elevated temperatures with a system of electrodes to efficiently reduce steam at the cathode to form hydrogen gas-rich steam and oxidize a carbon feed containing hydrocarbons at the anode or convert hydrogen and oxygen into electrical energy. The use of liquid silver allows oxygen to dissolve in the liquid metal without oxidizing the metal. The system can be operated at zero to near zero pollution emission and within environmental hazard reduction goals.    DETAILED DESCRIPTION - A reversible system comprises a first electrode comprising liquid silver metal and a second electrode, where the first and second electrodes are separated by an oxygen ion-conducting solid electrolyte; a conduit for directing a first reactive material across the second electrode; and a conduit for contacting second reactive material with the first liquid silver electrode. The cell is capable of steam electrolysis when the polarity of the electrodes is selected such that the liquid silver is an anode. It is capable of electrical energy generation when the polarity of the electrodes is selected such that the liquid silver is a cathode. INDEPENDENT CLAIMS are also included for:    (1) a steam electrolysis system comprising an oxidizing compartment including a liquid metal anode and a reducing compartment comprising a cathode, where the oxidizing and reducing compartments are separated by an oxygen ion-conducting solid electrolyte; a conduit for directing steam across the cathode in the reducing compartment; and a conduit for contacting a carbon feed with the liquid metal anode in the oxidizing compartment;    (2) a solid oxide fuel cell comprising a reducing compartment comprising a liquid silver cathode and an oxidizing compartment comprising an anode; a conduit for directing an oxygen source across the cathode in the reducing compartment; a conduit for directing a hydrogen source across the anode in the oxidizing compartment; and an energy storage device for storing energy generated during operation of the fuel cell;    (3) a method of producing hydrogen comprising providing an electrolysis system; directing steam across the cathode in the reducing compartment; and contacting a carbon feed with the liquid metal anode in the oxidizing compartment, where the steam is reduced at the cathode to hydrogen and the carbon feed is oxidized at the anode; and    (4) a method of reversible operation of a cell comprising providing a cell comprising a first electrode including liquid silver metal and a second electrode; selecting the polarity of the electrodes such that the liquid silver is an anode, directing steam across the second electrode and contacting a carbon material with the first liquid silver electrode; and selecting the polarity of the electrodes such that the liquid silver is a cathode, directing hydrogen across the second electrode and contacting oxygen with the first liquid silver electrode.