石墨烯与钛酸铋钠异质结构中的热-电能量转换

This proposal aims at developing novel pyroelectricity based energy conversion materials that directly generate electricity from heat. The basic structure of the device is graphene/modified graphene/ferroelectrics/graphene (G-mG-F-G) heterostructures, where mG is one side modified graphene with pizoelectric effect. The graphene layers of these heterostructures are multilayer graphene sheets and act as transparent electrodes with extraordinary electrical and thermal conductivities. The modified graphene layer in the heterostructure is monolayer graphene sheet with un-symmetric coverage of Bi, Ba, Na, H, F adatoms or TiOx molecules. The effect of remnant polarization of the ferroelectric films on the density and mobility of the carriers of graphene electrodes will be investigated by first-principles calculation and Hall-effect measurements. Piezoelectricity of the modified graphene sheet in the G-mG-F-G heterostructure will be investigated by ab initio molecular dynamics simulation and scanning probe microscopy. The combination of computational and experimental investigations facilitates the designs of graphene-ferroelectrics heterostructures that could be used as practical pyroelectric generators with high current density and power density.In G-mG-F-G , the synergy of piezoelectric effect of the modified graphene layer and pyroelectric effect of the ferroelectric layers could result in the significantly enhanced thermal-to-electrical energy conversion.Through the optimization of graphene and ferroelectric layers, the output power density of the pyroelectric device can reach 1W/cm2. This research will provide an in-depth understanding on the effects of the interface between graphene and ferroelectrics on the piezoelectric and electrical properties of graphene sheets. This pioneering research in developing graphene-ferroelectric heterostructure could result in the practical applications of pyroelectric generators which are versatile, efficient and environmentally friendly in thermal-to-electrical energy conversion.

本项目旨在构建一种基于石墨烯(G)/钛酸铋钠(BNT)基铁电薄膜异质结构的热电能量转换器件，将环境中废弃热能收集并转换为电能。器件基本结构为（G电极/BNT薄膜/改性石墨烯(m G)/G电极），其中mG为具有压电效应的单面修饰石墨烯，G为高导热、高导电、透明石墨烯电极。通过BNT薄膜成分、结构及热释电性质的优化、G电极电导/热导性质的优化及BNT薄膜与m G之间的协同作用综合提高器件热电转换效率。拟通过实验研究与模拟计算结合重点解决石墨烯的非对称掺杂及压电性质表征、BNT薄膜极化状态对石墨烯电子输运性质、压电性质的影响规律、BNT热释电效应与m G压电效应协同作用等关键问题。最终获得电能输出功率密度大于1 W /cm2的热释电发电器件，明晰相关物理机制，获得廉价、高效的器件制备方案，获得高效率、环保、适用范围广的热释电发电器件。

本项目设计了一种基于无铅热释电材料钛酸铋钠(BNT)薄膜/氧化石墨烯(GO)异质结构的热释电发电器件，以BNT-GO异质结构为热电转换基元，得到了热-电能量转换密度大于1J/cm3的热电转换器件，当BNT-GO薄膜在电场强度为142.86～1 142.86 kV·cm-1的变化间，30～90 ℃时1圈的热电能量转换密度为1.352.66 J·cm-3。通过溶胶凝胶法制备了位于准同型相界的BNT(BNT0.94BT0.06)薄膜，得到了d33压电系数为73.30pm V-1的致密膜结构；通过搅拌水热法，创造性的在传统水热过程中加入机械搅拌，改变水热重结晶的结晶力场，得到了具有单晶结构的超长BNT纳米线；通过离子束沉积将单根BNT纳米线的两端固定，使用压电力显微镜研究了纳米线在不同电场下的畴结构变化，并得到了单根纳米线压电系数与直径的变化规律，得到当BNT纳米线的直径为16nm时，其d33压电系数为172pm V-1；分别通过抽滤法和LB法制备得到了不同厚度的GO薄膜，并研究了不同膜结构GO薄膜的铁电性质，使用压电力显微镜，首次从实验角度研究了GO本身的铁电性质，并提出GO薄膜的铁电效应是由GO片层内部和层间的氢键的电偶极矩的变化引起的，改变外加电场会造成氢键的伸长或压缩进而影响到GO内部偶极矩的改变；并在此基础上，构建了GO-P(VDF-TrFE)-GO层状薄膜异质结构，利用极性更强的P(VDF-TrFE)与GO官能团形成氢键来调控铁电性质，得到了具有高热释电性质的GO-P(VDF-TrFE)-GO薄膜。在明晰BNT与GO铁电性质的基础上，组装了组装了BNT-GO异质结构并研究其热-电转换能量密度，根据Olsen热-电能量循环计算得到其热-电能量转换可达1.352 J/cm3，热释电材料和发电器件的制备科学发展具有一定的推动作用。