HYDROGEN-PRODUCTION FROM HIGH-TEMPERATURE STEAM ELECTROLYSIS USING SOLAR-ENERGY

Fundamental studies of hydrogen production by high-temperature steam electrolysis were made using solar energy as a heat source. A sintered ZrO2 + 8 mol% Y2O3 ceramic is used as an electrolyte. Both sides of this electrolyte were coated with platinum porous electrodes on the one side acting as a cathode and on the other as an anode. The electrolytic cell was inserted into a porous zirconia ceramic tube placed at the focal point of a solar concentrator and heated up to 1000-degrees-C by concentrated solar radiation. Water vapor was introduced into a cathodic compartment using argon as a carrier gas. On supplying a direct current to this cell, the gas taken out from the cathodic compartment was analysed by gas chromatography and production of hydrogen was confirmed. The current efficiency in this high-temperature electrolysis was 98%. The electrochemical efficiency reached 71%. Combining our high-temperature electrolyser cell with a solar AMTEC or a solar thermoelectric conversion, hydrogen can be produced only using a solar energy as a primary energy. The overall energy efficiency was estimated as 20-28% for this hydrogen production system. This efficiency is twice that of photovoltaic electrolysis. From this fundamental research, it is concluded that high-temperature steam electrolysis using solar energy as a primary energy source is a promising technique to produce hydrogen cleanly.