NOVELTY - A fuel cell/electrolyzer system (10) consists of a source of fuel (18), a source of electricity, an optional reformer (13), a feed stream of water or steam (17), an energy storage subunit (14), a thermal energy source (16), a fuel cell power generator/electrolyzer (20), and a separate storage media subunit (35). The optional reformer receives the source of fuel, and outputs a feed stream of water or steam. The energy storage subunit contains a metal-based material. The fuel cell/electrolyzer system is capable of charging and discharging using an energy storage function.    USE - Fuel cell/electrolyzer system is used for storing and releasing electrical energy.    ADVANTAGE - The fuel cell/electrolyzer system has high power density, and enables the efficient storing and releasing of electrical energy, by simple process, and is economical.    DETAILED DESCRIPTION - A fuel cell/electrolyzer system consists of a source of fuel, a source of electricity, an optional reformer, a feed stream of water or steam, an energy storage subunit, a thermal energy source, a fuel cell power generator/electrolyzer, an oxidant source, and a separate additional storage media subunit. The optional reformer receives the source of fuel, and outputs a feed stream of water or steam. The energy storage subunit receives the feed stream. The thermal energy source heats the discharged hydrogen rich hydrogen and steam, and provides a hydrogen rich hydrogen and steam fuel entry stream maintained at a temperature of 750 degrees C. The energy storage subunit contains a metal-based material for providing metal oxide and hydrogen at the discharge. The metal oxide is retained in the energy storage subunit for providing hydrogen rich fuel of hydrogen and steam. The volume ratio of hydrogen with respect to steam is 60-75:25-40. The fuel cell power generator/electrolyzer is separated completely from all other components in the system, and receives the heated hydrogen rich hydrogen and steam fuel entry stream and provides the energy out, depleted oxidant (22) out, and depleted hydrogen fuel (26) of water and steam. The electrolyzer splits the water into hydrogen and oxygen during charging, when the electricity source is fed into the system. The oxidant source is passed to the fuel cell power generator/electrolyzer. The separate additional storage media subunit contains a metal-based material to be fed with the depleted fuel out. The metal-based material chemically charges the depleted hydrogen fuel of water and steam exiting the fuel cell power generator/electrolyzer, and provides re-circulated fuel of higher hydrogen content and steam passed to the energy storage subunit. The source of fuel and optional reformer are eliminated, or their output is reduced during the steady state operation. The fuel cell/electrolyzer system is capable of charging and discharging using an energy storage function.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic flow diagram of the basic system of fuel cell/electrolyzer system having the fuel cell power generator.    System (10)    Optional reformer (13)    Energy storage subunit (14)    Thermal energy source (16)    Water or steam (17)    Fuel (18)    Fuel cell power generator/electrolyzer (20)    Depleted oxidant (22)    Separate storage media subunit (35)