PrFeO3基固体氧化物燃料电池阳极原位出溶金属纳米催化剂机理与应用

Perovskite oxide anodes for solid oxide fuel cell (SOFC) have the advantages of coking-tolerant, sulfur-tolerant and redox cycling stability, but their electrochemical performance and catalytic activity toward hydrocarbon fuels still need improving. Firstly, based on the PrFeO3 with perovskite structure, controlling their crystalline stability by doping alkaline earth elements and transition metal elements as well as adjusting the stoichiometry will be performed at the beginning of the project. Secondly, we will investigate the occurrence conditions and distribution of the metallic nanoparticles (Ni, Co, Pd, Ru) exsolved from stable perovskite oxides in reducing atmosphere. The influence of the exsolutions on the electrochemical performance and catalytic activity of the perovskite anodes will also be studied in detail. Thirdly, the stability of nano metal catalysts in-situ formed during the perovskite oxides decomposition or partial decomposition will be investigated. Forthly, combined with the theoretical calculation of co-segregation energy and oxygen vacancy formation energy using density functional theory, further clarifying the mechanism of exsolution. Finally, analyzing the influence of anode microstructure on the exsolution features by comparing the exsolution phenomenon of rare earth ferrite anodes with different microstructures prepared by the coating method and porous scaffold solution impregnation method, respectively. The implementation of the project is of great significance to in situ growth of metallic nano-catalyst on the artificially controllable conditions, preparation of novel high-performance perovskite anode materials for SOFC and the development of SOFC techniques.

固体氧化物燃料电池（SOFC）的钙钛矿氧化物阳极具有抗碳沉积、耐硫毒化和氧化还原循环稳定等优点，但其电化学性能及对烷烃燃料的催化活性仍有待提高。本项目以钙钛矿结构的PrFeO3为基础，首先通过掺杂碱土和过渡族金属及改变化学计量比调控晶格稳定性；其次研究在还原气氛中Ni、Co、Pd、Ru金属纳米颗粒从结构稳定的钙钛矿氧化物上出溶的条件、出溶物分布规律及其对阳极电化学性能和催化活性的影响；并对分解和部分分解体系原位分解形成金属催化剂的稳定条件进行研究；然后结合密度泛函理论计算所得共分离能和空位形成能，明确出溶机制；最后对涂覆法和多孔骨架溶液浸渍法制备的两种微结构的稀土铁酸盐电极上的出溶现象进行对比，分析阳极微结构对纳米金属催化剂出溶的影响规律。本项目的实施对人工可控条件下实现金属纳米颗粒原位生长、实现新型高性能SOFC钙钛矿阳极材料的制备以及SOFC技术的发展都具有重要意义。

本项目以发展能耐受氧化还原循环、具有抗碳沉积和硫中毒的固体氧化物燃料电池（SOFC）阳极新材料和阐明过渡族金属微纳米颗粒在稀土（La、Pr）铁酸盐上的出溶规律与机制为目的，开展了系统的实验和理论研究。研究发现：①未掺杂及较低价态易还原过渡族金属（Co、Ni）掺杂PrFeO3在SOFC阳极环境下会发生分解，而高价态过渡族元素（Ti、Nb、Ta、W、Mo）掺杂能保持其钙钛矿结构而只发生易还原金属出溶；A位缺位可促进B位过渡族金属纳米颗粒出溶。②类钙钛矿结构的PaBaFe1.75Nb0.25O5+δ在还原气氛中发生部分分解，导致电导率、对氢吸附能力和电化学性能持续提高，但长期运行过程中有明显团聚；从稳定钙钛矿结构中出溶的纳米颗粒具有坚固的金属-氧化物界面，而分解形成的纳米颗粒的界面强度较弱；相比于化学还原，电化学反应会加速部分分解生成阳极颗粒团聚。③Sr1.9Fe1.5Mo0.5-xCuxO6-δ阳极在还原气氛升温中先后出现Cu和Fe的出溶，并分解生成R-P相，其与母相形成有利于提高催化性能的异质结构，Cu的掺杂抑制了Fe纳米颗粒的团聚。④在YSZ多孔陶瓷骨架中浸渍法制备Pr0.8Sr0.2Fe0.9M0.1O3－δ（M=Fe, Co，Ni，Ti，Nb）的单相性不及溶胶-凝胶制粉方法；在纯氢800℃环境中，浸渍制备Ti和Nb掺杂体系会在保持钙钛矿母相结构的基础上有少量Fe纳米颗粒出溶，而Fe、Ni、Co掺杂体系会完全分解，其中过渡族金属会被还原成Fe或形成Ni-Fe及Co3Fe7合金。⑤基于密度泛函的理论计算发现，PrFeO3在A位掺Sr、B位掺Nb的稳定性最高；LaSrFeTaO系统稳定性和氧空位形成能随Ta掺杂量增加，其形成焓随氧空位浓度（δ）增加而降低；氢分子吸附在PrFeO3（001）面Fe原子上方，Nb掺杂吸附能最大。⑥PrFeO3和LaFeO3掺杂过渡族金属离子所制备的电极材料具有较高的电化学性能，可用于氢氧SOFC、直接碳SOFC的阳极和锌空气电池的氧电极。本项目取得的成果不但可以直接推动SOFC氧化物阳极材料的研究和开发，对于指导其它催化剂材料的研究也具有一定的借鉴作用。