| 其他摘要 | 对电极在染料敏化太阳能电池(DSC)中除了负责收集外电路的电子外，还有一个主要功能就是催化加速I3-与对电极之间电子交换。所以，高性能对电极材料需要兼具良好的催化能力和快速传输电子的能力。本论文设计制备了以下几种价廉并且可替代Pt的催化材料，应用于构建高效低成本DSC。具体工作如下：1）基于过渡金属氮化物的对电极材料。鉴于纳米过渡金属氮化物催化活性高但颗粒间电子传递电阻大的问题，我们通过对材料结构进行优化设计，构建具备电子/离子混合传输网络的特殊微纳米结构或者纳米复合结构电极，来提高其性能。首先，设计合成了具有分级结构的TiN介孔微球对电极，考察不同纳米结构对电池性能的影响。与纳米颗粒和平板TiN电极相比，介孔球独特的多级（微米/纳米）孔道结构不仅可以提供更多的反应催化位点，而且能增强电极材料与电解液间的接触，使得介孔球TiN电极组成电池的短路电流、开路电压、填充因子等光电参数大大提高，最终其光电转换效率比传统Pt对电极组装电池的效率提高了30 %左右。其次，我们构筑了一种由不同结构TiN纳米材料和PEDOT:PSS组成的无机/有机复合物，将其作为DSC的对电极材料。结果表明，TiN纳米材料在由PEDOT:PSS提供的导电骨架网络之中均匀分布，使其兼具高催化性和高导电性，表现出了优于TiN或PEDOT:PSS材料的光电转化性能。再次，设计合成了金属氮化物（TiN、VN、MoN）/氮掺杂石墨烯（NG）纳米复合材料，该复合物中金属氮化物作为催化活性材料原位生长、均匀分布在NG的片层结构中。这样的结构设计不仅因为NG的存在而有效避免了纳米活性材料的团聚，提供了更多的活性位点，而且NG兼具较大的比表面积与较好的电子导电能力，加速了电子输运。这两方面协同作用的结果使得复合材料表现出可以与Pt修饰电极相媲美的性能。2）氮掺杂碳材料对电极。碳材料是电子的良导体，但碳材料本身的催化能力较差。因此，我们对碳材料进行氮掺杂改性以期提高其催化性能。通过高温氨气还原的方法得到了多种氮掺杂的碳材料，包括氮掺杂碳黑（N-BC）、氮掺杂中间相碳微球（N-MCMB）和氮掺杂中间碳微球/碳纳米管的复合物（N-MCMB-CNT），研究了氮掺杂对其催化性能的影响。之后，通过改变氮化温度得到了不同掺氮量的氮掺杂石墨烯。随着温度的升高，掺杂氮含量减少，其催化性能呈下降趋势。这些结果均表明氮掺杂是提高碳材料催化性能的有效途径。3）三元过渡金属氮化物对电极。设计合成了多种三元过渡金属氮化物，包括MWN2(M=Fe、Mn、Co、Ni)、Fe6Mo7N2和Ni3Mo3N，并首次将其用作染料敏化太阳能电池的对电极，可获得与Pt对电极组装电池相媲美的光电转化效率。该研究结果为高催化活性和低成本的对电极材料的研究探索了一个新的发展方向。; As an indispensable component of dye-sensitized solar cells (DSCs), the counter electrode (CE) is responsible for collecting electrons from the external circuit, transfering them back to the redox electrolyte and catalyzing the reduction of triiodide ions to iodide ions which makes the cell a complete circuit. Therefore, the CEs possessing excellent electrical conductivity and superior electrocatalytic performance are highly desired. In this work, several materials were designed and synthesized as CEs to replace Pt to fabricate low cost and high efficiency DSCs. The major contents are presented as following: 1) Nano-structure and nano-composites of transition metal nitrides as CEs for DSCs.Generally, nano-particulate transition metal nitrides possess high electrocatalytic activity owing to the large surface area, but they also lower electron transport efficiency owing to the abundant grain boundaries and defects. To combine both high electrical conductivity and superior electrocatalytic activity in one material, we propose an alternative design strategy by constructing nanostructured transition metal nitrides or their composites for fabricating mixed conducting materials for electron and ion. Firstly, the hierarchical micro/nano-structured TiN spheres (micro/nano-TiNs) CEs were successfully synthesized to evaluate the relation between the structure of CE and the cell performance. Compared with particulate TiN and TiN flat electrodes, the as-prepared micro/nano-TiN electrode based DSCs deliver significantly improved photovoltaic performances in terms of JSC, VOC and FF, which is attributed to the abundant catalytically active sites and the accessible electrode/electrolyte contact derived from the unique structure. Ultimately, the overall energy conversion efficiency is 30 % higher than that of Pt electrode. Secondly, an inorganic/organic nanocomposite comprised of various nanostructure TiN and PEDOT:PSS was explored as a promising candidate for the CE in DSCs. It is demonstrated that TiN was dispersed uniformly in the PEDOT:PSS matrix, which was beneficial to electronic conduction. Correspondingly, these composite electrodes exhibited better catalytic activity compared with pristine TiN or PEDOT:PSS electrode，endowed an effective combined network of both high electrical conductivity and superior electro-catalytic activity. Finally, transition-metal nitride TMN (MoN, TiN, VN) nanoparticles/N-doped reduced graphene oxide (NG) hybrid materials presented alternative low-cost Pt-free CEs, in which TMN nanoparticles were highly dispersed on the surface of NG. A high concentration of active catalytic sites and an efficient electronic/ionic mixed conducting network generated by the nanostructure afford promising synergistic effects on the electrocatalytic characteristics for triiodide reduction. On the basis of these advantages, these nanostructured hybrid based cells deliver significantly enhanced photovoltaic performances, which are comparable with that of Pt devices.2）N-doped carbonaceous materials as CEs for DSCs. Carbonaceous materials possess high electrical conductivity but poor electrocatalytic activity. N-doped carbon black, N-doped mesocarbon microbead (N-MCMB) and N-doped MCMB-CNT (N-MCMB-CNT) were synthesized by heat-treatment under an ammonia atmosphere at a high temperature and were expected to enhance their intrinsically catalytic activity. The effect of N-doping on the electrochemical and photoelectrochemical performance of carbonaceous materials is analyzed in details. Subsequently, the N-doped reduced graphene oxide nanosheets (N-GNSs) with controllable N-doping were explored as an efficient metal-free catalyst for the I3- reduction reaction, revealing evident correlations between the electrocatalytic activity and the N-doping content of graphene. It is demonstrated that the performance of DSCs is dependent on the N-doping and an increasing doped N content results in an increase of the material’s apparent catalytic activity. Thus, N-doping has been proved to be an effective strategy to improve the electrochemical properties of carbonaceous materials intrinsically.3) Ternary transition-metal nitride as CEs for DSCs.Various ternary transition-metal nitrides were successfully designed and fabricated as CEs for DSCs for the first time, including MWN2 (M=Fe, Mn, Co, Ni), Fe6Mo7N2 and Ni3Mo3N. The DSCs using the ternary transition-metal nitride CEs have a comparable photovoltaic performance with the one using the conventional Pt CEs. We believe that the current work paves the way for developing highly efficient and low-cost CEs for DSCs. |
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