直接碳氢燃料固体氧化物燃料电池熔融金属锑基阳极过程及电池稳定性研究

Solid oxide fuel cells (SOFC) are based on ceramic electrolytes that are oxygen-ion conductors. Because the electrolytes conduct oxygen ions, it is at least theoretically possible to carry out the electrochemical conversion of any combustible fuel, including liquid hydrocarbons or even solid fuels like coal. The generation of electrical power by direct utilization of various fuels in an SOFC would also provide significant benefits if it could be practiced on a large scale. The efficiency of an SOFC can be very high, with negligible NOx emissions. Moreover, if CO2 sequestration is required, the exhaust gas from the anode is highly concentrated, allowing for easy CO2 capture. Finally, direct utilization of hydrocarbon fuels would greatly simplify the overall conversion process by eliminating the need for gasification and steam reforming steps. It is useful to consider what a practical cell might look like before starting work on such a system. Because both Sb and Sb2O3 are molten at the expected operating temperatures, we envision fabricating cells that have similarities to flow batteries, a design fundamentally different from that used in the work of CellTech Power. The design will allow the region of contact between the carbonaceous fuel and the Sb to be isolated from the region of contact between the Sb and the electrolyte. This is critical issue because most fuels will contain ash and other impurities that could otherwise fill the anode compartment. Herein we propose a two-year program aimed at demonstrating the feasibility of the concepts in this proposal for the generation of electrical power from hydrocarbon fuels. In this proposal, a working fuel cell with a molten-metal anode, capable of operating on various hydrocarbons, will be designed and tested. Cells will be operated in a manner similar to that found in flow batteries, utilizing natural convection to transport Sb and Sb2O3 to and from tubular cells. The work here will examine the operation of these cells on a range of hydrocarbon fuels to determine the effects of various impurities, including sulfur. This proposal of new molten Sb system is meant to show that practical anode with high anti-coke and sulfur tolerance can be built based on molten Sb electrodes. The fundamental principles that will be developed as part of this proposal will be useful for any fuel-cell anode designs based on molten-Sb anodes.

开发具有抗积碳耐硫毒化能力的阳极一直是SOFC的研究重点，然而到目前为止，积碳和硫毒化问题并没有得到根本解决。本项目深入分析了直接碳氢燃料SOFC阳极及直接碳燃料电池阳极材料发展，提出了一种新型的高温熔融锑基直接碳氢SOFC电极体系，利用锑电极特殊的电极过程解决SOFC阳极积碳和硫毒化问题。通过TPR、在线色谱和在线质谱法研究碳氢燃料还原氧化锑的动力学行为及电极行为；通过分析电池性能变化以及阳极成分变化得到锑阳极耐硫毒化行为；采用电化学法、合成新型电解质及铈基保护层等方法解决熔融锑阳极高极化条件下电解质腐蚀问题；利用锑和氧化锑密度差实现阳极的自然对流，最终阐明熔融锑阳极过程的控制步骤，得到具有高稳定性高电极活性的直接碳氢SOFC阳极。本项目提出了一种新型直接碳氢燃料SOFC阳极体系，有望得到具有高稳定性高催化活性的抗积碳耐硫毒化阳极，为解决直接碳氢SOFC阳极积碳硫毒化问题提供一条新途径。

目前直接碳氢燃料电池因其燃料来源广泛、发电效率高而受到人们广泛关注。然而其积碳硫毒化、电极反应复杂以及电池长期稳定运行等问题仍没有得到解决。为了解决以上问题，本项目提出了熔融锑-氧化锑（Sb-Sb2O3）阳极体系。在高温时金属锑被氧离子电化学氧化为氧化锑，因其密度小于锑而上浮到表面被碳氢燃料还原为金属锑，从而实现金属锑的循环，最终实现碳氢燃料的有效传质的目的。该体系不存在熔融碳酸盐腐蚀等问题，具有结构简单、易于传质及工业放大等优点。本项目的研究中确定了锑电化学氧化和氧化锑化学还原的控制步骤，得到了电池反应的动力学行为，为直接碳氢燃料电池稳定运行提供了理论基础。本项目的实施对碳氢燃料的高效利用提供了切实可行的方法，为解决困扰我们的环境问题提出了一种有效的新途径。本项目在研究中通过sol-gel法成功地制备了单相ScSZ粉体，粉体平均粒径为90 nm，表面积达到8.7 m2•g-1，适用于流延成型法制备ScSZ电解质。ScSZ素坯分别在1400 oC、1450 oC、1500 oC、1550 oC和1600 oC烧结。随着烧结温度的增加，气孔逐渐减少，晶粒逐渐长大。其中，1550 oC烧结的样品抗弯强度最高，达到708 MPa。1550 oC烧结的样品电导率最高，在800 oC电导率达到0.14 S•cm-1。1550 oC烧结的电解质的单电池展现了最佳的放电性能，在650 oC、700 oC、750 oC和800 oC的最大功率密度分别为0.18、0.36、0.51和0.72 W•cm-2。在此基础上进行了电池电解质腐蚀行为及机制方面的详细的研究。项目执行期间研究了不同电解质的腐蚀行为，以及阳极管中不同的传质方式对电解质腐蚀行为的影响，并且对腐蚀的微观机制进行了分析。研究发现不同阳离子掺杂的氧化锆基电解质会发生不同程度的腐蚀，且腐蚀过程可能与阳离子在晶格中不同的晶格结合能有关，借此结果可以得到性能稳定的电解质材料，实现电池的长期稳定运行。截止项目完成时共发表SCI论文4篇，影响因子4以上的文章2篇，授权专利2份，培养硕士研究生2名，本科生6名，顺利完成了项目的预期目标。