High Temperature Steam Electrolysis for Efficient Hydrogen Production

理论上，固体氧化物电解槽(SOECs)有望提供最高的电解氢生产效率，因为有利的热力学和动力学条件可以降低施加电压。然而，希望SOEC在较低的温度下运行，以获得广泛的组件材料选择以及各种废热来源的利用。本研究项目的目的是为中温运行的SOECs开发高性能电极。我们取得了以下成果：1.采用高分散镍催化剂的混合导电掺杂氧化铈(SDC)阴极具有很高的性能。结果表明：1.在700-900℃温度范围内，当镍负载量为17vol.%时，由于增加了活性反应中心，降低了电子阻力，有效地提高了反应速率，从而使阴极的性能达到最高。发现阴极活性随离子Co…的增加而增加氧化锆电解液的导电率更高，类似于SOFC电极的情况。由镍分散的固体氧化物阴极、ScSZ电解液、La(Sr)Co03阳极(带有中间层)组成的SOEC在短期测试中表现出较高的性能，在H2O+H2(P[H20]=0.6atm)和02(1atm)的气氛下，在0.5A/cm~2和900atm的气氛下，12R电池电压=1.13V。我们研制了双层(催化层/集电层)电极。采用SDC颗粒与高度分散的镍金属电催化剂(纳米镍的体积分数为10%~20%)相结合作为氢催化层(SOFC的阳极和SOEC的阴极)与YSZ固体电解液的界面。在催化层上形成了Ni-SDC金属陶瓷集电层(含60%的微米级镍)。在催化层中镍含量为10%的氢电极，由于增加了活性反应中心和电子电导，有效地提高了反应速度，因而表现出较高的性能。La0.6Sr0.4Co0.2Fe0.803(LSCF)/(LSCF+SDC)双层电极在SOEC中能很好地析出O2。结果表明，在催化层中加入体积分数为40%的SDC能有效提高催化剂的性能。较少

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