【作者】 毕磊；

【导师】 刘卫；

【作者基本信息】 中国科学技术大学 ， 材料学， 2009， 博士

【摘要】 能源和环保已成为世界各国可持续发展必须要面对的主要问题。燃料电池作为一种高效、环境友好的将化学能转化为电能的装置受到了人们广泛的关注,其中固体氧化物燃料电池（SOFC）又是领域研究的一个热点。传统的固体氧化物燃料电池由于需要较高的工作温度,会带来一系列的问题,如电极的烧结、界面的扩散以及难于封接等。因此降低操作温度已成为固体氧化物燃料电池主要研究发展方向。以质子导体为电解质的质子导体固体氧化物燃料电池是实现固体氧化物燃料电池低温化的一个重要途径。本论文针对传统BaCeO₃基质子导体固体氧化物燃料电池的化学稳定性、烧结活性、电化学性能及薄膜制备工艺进行研究。论文第一章简要介绍了质子导体固体氧化物燃料电池的应用前景、工作原理和研究进展,着重阐述了质子导体固体氧化物燃料电池的核心-电解质材料在化学稳定性和电导率方面存在的问题。第二章发展了一种原位反应的方法来制备高质量的电解质薄膜。通过直接将金属氧化物混合然后沉积到阳极基底表面,利用金属氧化物在高温烧结时发生反应,使质子陶瓷膜电解质层的成相与致密在一步烧结过程中完成。研究结果表明借助原位反应制备出的质子陶瓷膜具有膜厚度小、致密度高等特点,是制备电解质薄膜的一种简便有效的方法。第三章采用原位反应的方法成功地在阳极基底上制备出厚度仅为15μm的Ba₃Ca_1.18Nb_1.82O_9-δ（BCN18）电解质薄膜,首次实现BCN18电解质的薄膜化,并且通过反应烧结使得BCN18的烧结温度降低到1400℃。此外,研究表明BCN18在CO₂和H₂O环境中具有极好的化学稳定性,虽然以BCN18为电解质的燃料电池的输出功率不如传统的BaCeO₃基质子导体燃料电池高,但BCN18极好的化学稳定性使它适用于比较苛刻的工作条件中,使其成为质子导体固体氧化物燃料电池电解质材料一种适合的选择。第四章通过在BaCeO₃中引入10%摩尔的Ta,研究Ta的掺杂对于传统BaCeO₃基质子导体化学稳定性和电化学性能的影响。研究结果表明,Ta的掺杂在保持其电化学性能不过度损失的情况下极大地提高了材料的化学稳定性,BaCe_0.7Ta_0.1Y_0.2O_3-δ（BCTY10）电解质膜可以在纯CO₂环境中稳定存在,以BCTY10薄膜为电解质的单电池在700℃时的最高功率可以达到约200mW/cm²并且可以稳定工作100小时,而没有掺入Ta的BaCeO₃基电解质材料短短几个小时的运行就发生了电池性能的明显衰减。第五章提出一种全固相法制备质子导体固体氧化物燃料电池,同时研究了阳极造孔剂含量对于BaCe_0.7Ta_0.1Y_0.2O_3-δ薄膜致密度的影响。研究结果表明BCTY10薄膜的致密度随着阳极造孔剂加入量的增多而提高,当阳极含有质量比30%的造孔剂时,薄膜已经完全致密,符合作为燃料电池电解质的要求。此外我们还探讨比较了BCTY10薄膜与传统Zr掺杂的BaCe_0.7Zr_0.1Y_0.2O_3-δ薄膜的化学稳定性,研究结果表明Ta掺杂BaCeO₃的方法比传统的Zr掺杂BaCeO₃的方法更能提高材料的化学稳定性。而以全固相法制备的BCTY10单电池也表现出良好的电池输出功率,表明全固相法为制备质子导体燃料电池提供了一种切实可行的途径,而BCTY10良好的化学稳定性和较好的电池输出功率表明其是一种很有前途的电解质材料。第六章深入研究了In的掺杂对于传统BaCeO₃材料在化学稳定性、烧结活性和电化学性能上的影响。研究结果表明In的掺杂可以有效提高BaCeO₃的烧结活性,并且样品的烧结活性随着In掺杂量的增加而提高。BaCe_0.7In_0.3O_3-δ（BCI30）薄膜经过1150℃烧结即可致密,它比稀土掺杂的BaCeO₃的致密化温度要低200-300℃。在提高烧结活性的同时,In的掺杂还有助于BaCeO₃材料化学稳定性的提高。研究涉及的不同浓度（10%-30%）In掺杂的BaCeO₃材料都显示出比稀土Y掺杂BaCeO₃样品更好的化学稳定性,其化学稳定性也优于加入少量Zr的样品(BaCe_0.7Zr_0.1Y_0.2O_3-δ。电导测量表征反映BCI30薄膜的膜电导率与传统稀土掺杂的BaCeO₃样品相当。我们知道,用传统的Zr掺杂来稳定BaCeO₃的方法虽然提高了其化学稳定性,但却大大降低了离子电导和样品的烧结活性;而用In对BaCeO₃进行掺杂,不仅起到了提高化学稳定性的作用,也提高了样品的烧结活性,同时还没有降低样品的电导率,故In元素可称为BaCeO₃的一种理想掺杂剂。电池性能评价反映BCI30薄膜电解质燃料电池在700℃的最大功率密度为342mW/cm²,而单电池的开路电压保持100个小时没有衰减,显示该材料未来实际运用中的巨大潜力。第七章中通过一种单步共烧的方法制备质子导体SOFC,单步共烧法制备质子导体SOFC在文献中还未见报道。研究表明以BaCe_0.7In_0.3O_3-δ薄膜为电解质的燃料电池可以实现单步共烧法制备,并且共烧温度对于单电池的性能有着决定性的影响。较低的共烧温度（1150℃）制备的电池虽然极化电阻比较小,但较大的欧姆电阻却限制其发展;而较高的烧结温度（1350℃）虽然可以减小电解质的膜电阻,但较为剧烈的界面反应以及较大的极化电阻使其性能急剧下降。只有通过适中的共烧温度（1250℃）制备的单电池才能达到较高的电池输出性能,虽然在该温度下制备的单电池的膜电阻和极化电阻均不是最低的,但适中的共烧温度却在膜电阻和极化电阻之间找到一个平衡点,在保证在不过度增加极化电阻的情况下提高电解质膜的电导率,使得在1250℃共烧的单电池有着最小的电池内阻,从而使其单电池的性能与其它温度烧结的单电池相比有较大的提高。第八章对本论文的工作进行了总结,并对质子导体SOFC今后的研究工作进行了展望。更多还原

【Abstract】 Energy crisis and environmental pollutions are problems that all country is now facing for the sustainable development.Fuel cells,which have been seen as a keystone for the future energy economy,have received considerable attention for their high energy conversion efficiency and low impact to environment as a mean of generating electricity.Among the fuel cell community,the solid oxide fuel cell （SOFCs） is a currently hot topic.However,the traditional SOFCs work at high temperatures,leading to many problems,such as electrode sintering,diffusion at interface and difficulty in preparation of seals and interconnect.The current trend in SOFC developments is the reduction of their working temperatures.Ceramic proton conductors have received much attention from the SOFC community because proton-conducting SOFCs would permit a reduction of the working temperature, which meet the demand of current trend of reducing the working temperature of SOFCs.This thesis investigates the chemical stability,sinterability,electrochemical performance and the thin-film preparation techniques for the BaCeO₃ based proton-conducting SOFCs.Chapter 1 describes the potential applications of proton-conducting SOFCs as well as its working principle and research progress.The trade-off relation between chemical stability and conductivity of proton-conducting electrolyte materials is intensively discussed.In Chapter 2,an in-situ reaction method is presented for preparing the proton-conducting electrolyte membrane with high quality.The key part of this method is to directly spray well-mixed suspension of metal oxides instead of pre-synthesized ceramic powders on the anode substrate in order to make the membrane dense and form the pure ceramic phase at the same time.Further,the in-situ reaction method promotes the densification of the supported membrane,which is proven to be a facile method for preparing protonic ceramic membranes.In Chapter 3,a thin Ba₃Ca_1.18Nb_1.82O_9-δ（BCN18） membrane electrolyte is prepared by the in-situ reaction method.It is the first time to realize the preparation of a thin-film BCN18 membrane.The obtained BCN18 membrane,which is about 15μm in thickness and showes high chemical stability against H₂O and CO₂,reaches high density after sintering at 1400℃.Furthermore,we study the electrochemical properties of a BCN18-based fuel cell.Although the cell performance of the BCN18-based fuel cell is not as good as the traditional BaCeO₃ based fuel cell, considering its high chemical stability,it still makes this material interesting for SOFCs at elevated temperatures,especially in an aggressive condition.In Chapter 4,Ta is introduced into BaCeO₃ lattice to form a new composition of BaCe_0.7Ta_0.1Y_0.2O_3-δ（BCTY10） for increasing the chemical stability of BaCeO₃-based materials.The research result shows that partially replacement of Ce by Ta can increase the chemical stability of barium cerate with only a little loss of electrical performance.The BCTY10 membrane can remain stable in 100%CO₂ at high temperatures.The BCTY10-based fuel cell generates a maximum power density of about 200 mW/cm² at 700℃.The BCTY10-based fuel cell remains stable in fuel cell working environment for more that 100 h,whereas the Ta-free BaCeO₃ fuel cell decays in a few hours.Chapter 5 describes an all solid state reaction for preparing a proton-conducting SOFC and also investigates the influence of the amounts of the pore forming additives in the anode substrates on the densification of the BCTY10 membranes.The result indicates that the supported BCTY10 membrane becomes denser with the increasing amount of pore forming additive in the anode.The BCTY10 membrane on a NiO-BCTY10 anode containing 30 wt.%starch achieves a high density and meet the requirement for using as an electrolyte for SOFCs.Furthermore,we find that Ta-doping strategy shows even better stability than the traditional Zr-doping strategy for stabilizing BaCeO₃.The single cell shows desirable cell performance,implying the all solid state reaction is a novel and easy way to prepare single ceils.The high stability of BCTY10 and the good cell performance indicates that BCTY10 is a promising material for proton-conducting SOFCs.In Chapter 6,we intensively study the influence of the doping of In on the chemical stability,sinterability and electrical performance for BaCeO₃-based materials.The result shows that indium is quite beneficial to the improvement of the sinterability for BaCeO₃ materials and the sinterability increases with the increasing doping amount of In.The supported BaCe_0.7In_0.3O_3-δ（BCI30） membrane reaches dense after firing at 1150℃,about 200-300℃lower than other rare earth doped-BaCeO₃ materials.The element of In increases the chemical stability of the BaCeO₃ materials.All the different levels of In-doped samples（from 10%to 30%） show much better chemical stability than that of the traditional rare earth doped BaCeO₃.The chemical stability of the In-doped samples is even better than that of BaCe_0.7Zr_0.1Y_0.2O_3-δ.The BCI30 membrane conductivity can compare with that of the traditional rare earth doped-BaCeO₃.Unlike the traditional strategy for stabilizing BaCeO₃,which indeed increases the chemical stability but greatly lowers the sinterability and conductivity of the samples,the In-doping strategy is beneficial to the improvement of the chemical stability of BaCeO₃ samples and enhances their sinterability in the meantime with little loss of electrical performance.A BCI30-based fuel cell generates a maximum power density of about 342 mW/cm² at 700℃and the open circuit voltage of the cell keeps stable for more than 100 h,indicating the In-doped BaCeO₃ materials are quite promising for application.Chapter 7 describes a single step co-firing process to prepare proton-conducting SOFCs,which has not been achieved before.The result proves the proton-conducting SOFC with the BaCe_0.7In_0.3O_3-δ（BCI30） electrolyte can be prepared by a single step co-firing process.Furthermore,we find that the co-firing temperature has great influence on the single cell performance.Although the cell co-fired at 1150℃shows the lowest polarization resistance and the cell co-fired at 1350℃shows the highest membrane conductivity,the cell co-fired at 1250℃seems to reach a proper compromise between the polarization resistance and the membrane conductivity, which leads to the lowest total cell resistance and the best cell performance.In Chapter 8,the researches presented in this dissertation are evaluated and future work concerning the development of proton-conducting SOFCs is discussed.更多还原