中国科学院过程工程研究所机构知识库

当前，化石燃料的过度使用造成的能源和环境问题迫使人们将目光转向研究和开发绿色可持续能源。H2O作为地球上大量存在的物质，如果能将其进行利用和转化得到氢能源，势必会为解决能源问题提供新途径。而CO2作为温室气体的主要成分，如果能将其转换为可持续利用的碳形式，则既可以减少环境污染又解决了能源问题。因此，H2O和CO2转换逐渐成为人们研究的重点。而在这些转化中，借助于太阳能构筑人工光合系统进行的光电催化水分解和二氧化碳还原反应，可以直接将太阳能转化为可储存的化学能。在这一过程中，催化剂的性能直接影响了反应的选择性和效率。作为一种新型的催化剂，大多数的多酸分子具有良好的光敏性和电化学活性，同时在组成上又含有大量的过渡金属和非金属元素，因此有望成为新型的绿色光电催化材料。但是多酸本身存在一些诸如活性较低，导电性较差，比面积较小等缺点。因此从材料设计的角度入手来对多酸进行优化，可以提高其催化性能，充分发挥多酸的独特性质。从以上研究背景出发本论文制备了一系列多酸基纳米复合材料，并对它们的光电催化性能进行了研究，主要内容如下：(1) 首先通过层层自组装的方法，依靠各物质之间的静电相互作用成功合成了石墨烯-CdS-多酸复合薄膜。实验结果表明石墨烯-CdS-多酸复合薄膜的光电流响应性能和单一的CdS薄膜相比增加了5倍。这是因为在CdS和多酸之间由光诱导引发的电子转移促进了CdS量子点中电荷的分离效率，而石墨烯的引入进一步促进了电荷向外电路的转移从而提高了复合薄膜的光电催化性能。这一工作为设计具有高效的水分解和污染物降解性能的光阳极材料开辟了一条新的道路。(2) 成功合成了一种含有Co/Cu混合的多酸，记为Cu6Co7。将该多酸以滴涂的方式负载在碳布上作为工作电极，研究结果发现在中性条件下无论是对HER还是OER，Cu6Co7/CC都表现出了良好的催化活性。更重的是，Cu6Co7这种催化剂具有很好的生物相容性，当和细菌Ralstonia eutropha结合后，可以将CO2高效的转化为生物质。该体系的光-生物质转化效率可以达到10 %，几乎是自然界植物的光合作用效率的10倍之多。该工作对于发展以多金属氧酸盐为基础的高效率的人工光合作用系统有很好的借鉴意义。(3) 在工作二的基础上得到的多酸虽然具有很好的催化性能，但是在电催化水分解中需要较大的过电位，使得能源的利用效率较低。因此本论文进一步考虑从多酸出发，将多酸与一种具有永久孔隙度和高表面积的ZIF材料进行复合，可以充分发挥二者各自的优势，或是产生更大的协同作用，来制备一种双功能的催化剂。最后得到的催化剂Co-Mo2C@NC不仅在碱性条件下表现出优异的电催化水分解性能，在中性条件下的HER和OER性能和上一章中的多酸Cu6Co7相比过电位明显降低。这项工作的研究为人们开发和利用地球含量丰富的过渡金属元素作为中性条件下电解水产生氢能源的研究提供了新思路。;At present, the energy and environmental problems caused by the excessive use of fossil fuels have forced people to turn their attention to research and develop green and sustainable energy sources. H2O, as a rich substance on the earth, will certainly provide a new solution to the energy problem if it can be utilized and converted into hydrogen energy. And as a major component of greenhouse gases, CO2 can be converted into carbon forms that can be used sustainably to reduce environmental pollution and solve energy problems. Therefore, the conversion of H2O and CO2 gradually become the focus of research. In these conversion reactions, solar energy can be directly converted into storable chemical energy by means of photoelectrocatalytic water decomposition and carbon dioxide reduction with the help of solar artificial photosynthesis system. In this process, the performance of the catalyst directly affects the selectivity and efficiency of the reaction.As a new class of catalyst, most of the polyoxometalate molecules have good photosensitivity and electrochemical activity, and at the same time, they contain a large amount of transition metal and non-metal elements. Therefore, they are expected to be a new type of green photoelectrocatalytic materials. But the polyoxometalate also has some weaknesses, such as low activity, poor conductivity, small area and so on. Therefore, we can start from the material design point of view to optimize the polyoxometalates to improve their catalytic performances and give full play to their unique nature. Here we prepared a series of pom-based nanohybrids and studied their photoelectrocatalytic properties. The main research contents are as follows:(1) First of all, we have successfully synthesized graphene-CdS-pom composite films by layer-by-layer self-assembly method through the electrostatic interaction between the materials. The experimental results show that the photocurrent response of graphene-CdS-pom composite films increases five-fold in comparison with the single CdS films. This is because the electron transfer between the CdS and pom promotes the separation efficiency of charges in the CdS quantum dots, and the introduction of graphene further promotes the transfer of charges to the external circuit and thus improves the photocatalytic activity of the composite thin film. This work opens up a new path for the design of photoanode materials with efficient water decomposition and pollutant degradation properties.(2) Then we successfully synthesized a mixed Co/Cu containing polyoxometalate, denoted as Cu6Co7. The pom was dropped on a carbon cloth as a working electrode. We find that Cu6Co7/CC show good catalytic activity for both HER and OER under neutral conditions. More importantly, this Cu6Co7 catalyst has a very good biocompatibility. When combined with bacteria Ralstonia eutropha, Cu6Co7/CC can reduce CO2 into biomass efficiently. The overall photo-to-biomass efficiency can reach 10%, which is nearly 10 times higher than the natural plants performance. This work paves the way for the development of polyxoxmetalate-based artificial photosynthetic systems with high efficiencies.(3) Based on the work (2), we see that although the pom has good catalytic performance, it still needs a large overpotential in the electrocatalytic water splitting, which makes the energy utilization efficiency lower. Therefore, we consider starting from the pom and combining the pom with a ZIF material, which has a permanent porosity and a high surface area, to give full play to their respective advantages, or to produce greater synergy to prepare a bifunctional catalyst. The resulting catalyst, Co-Mo2C@NC, exhibits not only excellent electrocatalytic properties under alkaline conditions but also in neutral conditions. Compared with Cu6Co7, the overpotential of Co-Mo2C@NC significantly reduced. The research of this work provides a new idea for people to develop and utilize the Earth's rich transition metal elements as the research of producing hydrogen energy in neutral condition.