Steam as sweep gas in SOE oxygen electrode

The interest in producing hydrogen as energy storage medium for renewable electricity brought to the development to high efficient electrolyzers such as Solid Oxide Electrolyzer (SOE). Recent studies on SOEs focus mainly on the effect of the Hydrogen Electrode composition into performances varying the concentration of steam and hydrogen. This study investigates the Oxygen Electrode side where normally air is used as a sweep gas to flow pure oxygen, produced by SOE operation, out of the system. Water, in the form of steam, is proposed as an innovative sweep gas in oxygen electrode. The use of a different gas, such as steam, has the effect both of reducing oxygen concentration and changing thermodynamic local conditions of the SOE. Both phenomena influence electrochemical reaction and, consequently, cell voltage. At system level, this operation strategy allows to easily produce an oxygen flow as SOE by-product because no nitrogen in present in the oxygen electrode off gas and steam can be easily separated by condensation. Experimental study performed on a SOE single cell demonstrated that steam can be used in the oxygen electrode with the production of 100% oxygen on dry base. Negligible reduction of performance was measured and can be hardly distinguish from normal aging due to the test campaign. Open circuit voltage of 0.804 V and Area Specific Resistance of 0.582 Ω cm−2 were obtained at 800 °C. The new concept was for the first time assessed on experimental base and opens new paths for system design and integration of SOE electrolyzer units.