有益偏析自组装纳米结构中温固体氧化物燃料电池/电解池复合氧电极

For large-scale application，intermediate temperature solid oxide cells (including fuel cells and electrolysis cells) (IT-SOC) have to face a big challenge of high cost and insufficient durability of the system due to lack of highly performing and sufficiently stable oxygen electrodes, as well as simple and economic fabrication process. Significant improvement of activity and stability for oxygen reactions (ORR and OER) is strongly dependent on exploring tailorable nanostructured novel materials and economic synthesis process to prevent harmful segregation and improve tolerance to high oxygen partial pressure under anodic polarization. In this project, we will focus on conventional perovskite oxygen electrode Ln1-xSrxFe1-y(Cu/Co)yO3-δ (Ln=La,Pr,Ba), and we firstly propose a strategy to synthesis nanostructured perovskite (SP)-layered perovskite (RP) dual-phase composites as oxygen electrode for IT-SOC by one step self-assembly process through promoting "beneficial segregation" of Sr. We will investigate the composition and structure transition between "beneficial" and "harmful" function of the as-prepared oxygen electrodes to elucidate their structure-activity relationship. Finally, we will study the variation of SP:RP ratio and nano-structure of the optimum composite with the change of electrode working conditions (temperature, polarization) based on series of advanced characterization, as well as the dynamic self balancing process of the composites, we will then try to reveal the promoting mechanism of the composites on performance and durability of the electrodes, and thus providing significant information for designing and developing next-generation highly performing and highly durable IT-SOC composite oxygen electrodes.

寻求高性能、高稳定性的氧电极催化剂及其简便、经济的制备方法，是规模化应用中温固体氧化物燃料电池/电解池（ITSOC）技术的最大挑战之一。而显著提高氧反应（氧还原ORR和氧析出OER）活性和稳定性的难点是开发具有特定纳米结构的新材料和可控制备方法避免有害偏析和提高电解条件下的高氧分压耐受能力。本项目拟以传统钙钛矿氧电极Ln1-xSrxFe1-y(Cu/Co)yO3-δ(Ln=La,Pr,Ba)为研究对象，首次提出通过促进Sr的“有益偏析”自组装一步合成不同纳米结构的钙钛矿（SP）-层状钙钛矿（RP）两相复合氧电极。研究该氧电极组分、结构和性能“有益”与“有害”的转化，阐明其构效关系。并结合先进表征技术，探索SP、RP两相组分和结构随电极工作条件(温度, 极化)改变存在的动态自平衡，确定其对复合氧电极性能和稳定性影响的作用机理，为开发新一代高性能、高稳定性SOC复合氧电极奠定理论和实验基础。

寻求高性能、高稳定性的氧电极催化剂及其简便、经济的制备方法，是规模化应用中温固体氧化物燃料电池/电解池（ITSOC）技术的最大挑战之一。本项目首次成功用一步法自组装制备了SP-RP两相多孔复合氧电极。研究了RP相原位生成的影响因素，发现A位Sr比La对两相形成的影响更为显著；B位高价离子掺杂可以稳定钙钛矿相，从而调控RP第二相形成的动力学，并有利于两相复合电极在更宽的RP相存在范围内表现出性能改善，而通常RP相在一个比较窄的含量范围表现出异质界面对电极性能的显著促进作用。RP/SP异质结构对材料性能的影响与RP第二相的尺寸密切相关，存在临界尺度，临近临界尺度，提高电极性能，反之，则显著降低电极性能。RP/SP异质结构也表现出电子效应，可以提高阴极材料的电子电导率。RP-SP异质界面对SOFC阴极电催化性能的作用受电极结构、电极材料制备方法和电极材料掺杂情况影响。通过直接混合不同方法单独合成的两相，研究了各种氧电极的结构和性能在高温下（800℃）随时间变化，发现RP相的存在抑制了钙钛矿电极中普遍存在的“有害”偏析，揭示了抑制机理为改变和重新建构钙钛矿电极的表面微结构。对通过原位析出制备的SP-RP两相复合氧化物进行不同程度的还原，探索了自主装可控制备多级纳米结构电极的途径，得到了具有不同微观结构和形貌的复合电极如核壳结构、纳米网络结构等。虽然这些纳米结构仅在还原气氛中稳定，因此意外获得具有多级纳米结构的燃料电极的创新制备方法。 阐明了RP/SP异质结构在多孔阴极中的形成机理为：由组分粒径和表面元素分布两种因素决定组分相之间是否能有效形成异质结构和显著提高阴极性能。通过设计和制备具有互补端基的两相，驱动两相之间有效形成异质结构，并且该结构在高温条件下随时间演变形成RP/SP核壳结构，显著提高氧电极性能。通过异质界面形成前后组分的带隙计算和价带偏移计算揭示了异质界面处高活性的起源为带隙能量变窄，导电性提高，从而加快电子转移和容纳更多氧气空位，进而加速ORR过程。