基于嵌段共轭聚合物功能化纳米碳电催化剂的设计及氧还原特性

Increasing attention has been paid to developing a suitable strategy to effectively afford abundant catalytic active sites on pristine nanocarbons while retaining their high surface area and conductivity for fast electron and mass transport for producing advanced and inexpensive non-metal oxygen reduction catalyst to replace noble catalysts for large-scale applications in clean energy systems such as fuel cells. This project starts from the viewpoint of structure design and proposes to surface-functionalize nanocarbons with judiciously-designed water-soluble block conjugated polymer to greatly improve the electrocatalytic oxygen reduction performance, by reasonably regulating the intra-molecular charge-transfer interaction between the conjugated block and the carbon to induce a larger fraction of active sites on the carbon surface and by grafting the flexible coil block to impart good hydrophilicity and accelerate the mass transfer during oxygen reduction reaction. The research will help to establish a simple but effective method to mass produce high-performance carbon-based oxygen reduction electrocatalysts, which can be used in clean energy systems such as fuel cells. By combining the simulation and experimental study, this project will unravel the origin of the catalytic active sites of the conjugated polymer modified carbon-based electrocatalysts as well as the related molecular regulation mechanism, and cast light on new methods and principles to significantly improve the oxygen reduction performance of pristine carbon materials, which will provide a theoretic direction and universal principle for the design of new carbon-based oxygen reduction electrocatalysts.

如何有效地赋予原始碳材料丰富的催化活性位,且保持其高的比表面和导电性来确保催化反应中快速的电荷和质量传输，进而开发高效低成本的碳基氧还原催化剂来取代商业的贵金属催化剂并大规模应用于燃料电池等清洁能源器件，成为国际上的热门研究课题。本课题从结构设计角度出发，拟设计水溶性刚柔嵌段共轭聚合物来修饰纳米碳，通过简单的表面功能化来实现纳米碳的氧还原性能的显著提升；通过调控刚性共轭嵌段与纳米碳分子间的电荷转移相互作用来诱导丰富的催化活性位；接枝柔性嵌段为复合材料提供良好的亲水性，降低纳米碳的团聚，加速催化反应中的质量传递，从而确立一种简单有效的新方法用于宏量制备高性能的碳基非金属氧还原催化剂。结合理论计算和实验研究，揭示共轭聚合物修饰的纳米碳催化剂的催化活性位的来源和调控机制，阐明实现纳米碳材料的氧还原性能显著升级的新方法和原理，为新型高性能的碳基非金属氧还原催化剂的设计和合成提供理论指导和普适原则。

电催化氧还原和氧析出反应是燃料电池和可充电锌空气电池中的两个重要的能量转化过程。而发展高效，低成本且稳定的电催化剂是当前亟需解决的瓶颈。本项目发展了几种简单有效且普适的分子设计策略，充分挖掘聚合物和纳米碳各自的优势，构建了一系列聚合物/纳米碳的催化界面,实现了电催化氧还原和氧析出催化性能的显著提升，从而获得了一系列基于聚合物修饰的无金属和杂原子碳纳米管的高效稳定的单/双功能电催化剂。代表性的工作包括：1）提出利用原始纳米管的本征拓扑缺陷作为活性位点，利用聚合物（比如聚马来酸酐）特定的含氧官能团诱导的氢键作用建立有效的表/界面微环境，调控中间产物的吸附能, 降低反应过电位；所制备的聚马来酸酐/纯纳米管复合柔性膜可用作氧析出催化剂，在1M KOH中显示了较低的过电位（298mV@10 mA cm-2），这一性能与商用的贵金属二氧化钌相媲美。我们提出的氢键调控策略具有普适性，能够被拓展到其他具有含氧官能团的聚合物。2）通过聚电解质（聚二烯丙基二甲基氯化铵）修饰纯纳米管，利用聚电解质特有的拉电子基团调制界面电荷转移相互作用，诱导碳表面电荷重新分布，从而创造丰富的电催化析氧活性位点；同时通过静电作用吸附反应物氢氧根离子从而创造局部离子缓冲层，促进反应动力学；因此，聚电解质修饰的纯碳纳米管在0.1 M和1M KOH（370 mV@10 mA cm-2）电解质中均表现出良好的电催化析氧催化性能。3）设计了一种共轭嵌段聚合物（聚(3,4-乙烯二氧噻吩)-b-聚乙烯醇）用来修饰纯的碳纳米管，可创造有效的界面微环境并诱导界面电荷转移相互作用，最终实现反应吸附能和反应活性位点的双重调控。获得的复合膜催化剂显示了良好了电催化氧还原和氧析出双功能催化性能。并可作为一体化空气电极，用于实际的可充电锌空气电池，显示良好的器件性能。通过实验和理论研究，揭示了原始纳米碳中本征Stone-Wales缺陷的催化效应以及聚合物独特的助催化效应，为探索新的无金属聚合物/碳基高效电催化剂提供了一些通用的设计策略和理论指导。