High Temperature Steam Electrolysis for Efficient Hydrogen Production

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Solid oxide electrolysis cells (SOECs) are expected, in principle, to provide the highest efficiency of electrolytic hydrogen production, because the applied voltage can be reduced due to favorable thermodynamic and kinetic conditions. It is desirable, however, to operate SOECs at a reduced temperature for a wide choice of the component materials as well as a utilization of various waste heat sources. The aim of this research project is to develop high performance electrodes for the SOECs operating at medium temperatures. We have obtained the following results.1. Mixed conducting samaria-doped ceria (SDC) cathode with highly dispersed Ni catalysts exhibited very high performance. At 700-900℃, the Ni-dispersed SDC cathode exhibited the highest performance at 17 vol.%-Ni loading, due to the effective enhancement of the reaction rate by increasing the active reaction sites and lowering the electronic resistance.2. The cathode activity was found to increase with an increase in the ionic co … More nductivity of zirconia electrolyte, similar to the case of SOFC electrodes. An SOEC comprised of Ni-dispersed SDC cathode, ScSZ electrolyte, La(Sr)Co03 anode (with SDC interlayer) exhibited high performance for the short term test; 12R-free cell voltage = 1.13 V at 0.5 A/cm2 and 900℃ under the atmosphere of H2O + H2 (P[H20] = 0.6 atm) and 02 (1 atm).3. We have developed double layer-type (catalyst layer/current collecting layer) electrodes. As the H2 catalyst layer (anode for SOFC and cathode for SOEC) interfaced with YSZ solid electrolyte, SDC particles were employed in combination with Ni metal electrocatalysts (10 to 20 vol.% of nanometer-size Ni) highly dispersed on their surfaces. The current collecting porous layer of Ni-SDC cermet (60 vol.% of micrometer-size Ni) was formed on the catalyst layer. The H2-electrode with 10 vol.% Ni in the catalyst layer exhibited high performance, due to the effective enhancement of the reaction rate by increasing both the active reaction sites and the electronic conductance. Lao.6Sr0.4Co0.2Fe0.8O3 (LSCF)/(LSCF+SDC) double layer-type electrode worked well to evolve 02 in an SOEC. It was found that the addition of 40 vol.% SDC in the catalyst layer enhanced the performance effectively. Less