Activation of nitrogen modified carbons by KOH: Investigation of pore formation processes and, respectively, the release of nitrogen

近二十年来，氮改性多孔炭分别被用作超级电容器、蓄电池、氧化还原液流电池等电化学储能材料，受到越来越多的关注。同时，KOH的活化作用对孔隙率的产生起着主导作用。与模板辅助路线不同，该方法需要较低工作量，且允许制备具有极大内表面积(高达3000m2/gBET)和高度微孔率的材料。目前的大量出版物突显了这一专题的相关性；例如，在过去两年期间，科学网列出了大约200篇文章。对文献的评价表明，KOH对氮改性碳的活化与两种情况有关。首先，激活伴随着氮的大量释放。结果表明，氮素总量减少，不同形态氮素的质量比发生变化。关于这一点的报道部分是相互矛盾的，但大部分报道的是吡啶类物种的降解有利于吡咯类物种的形成。然而，尽管许多文献已经描述了氮的释放，但对这一现象以及如何通过合成条件来控制氮的释放仍然缺乏系统的研究。其次，必须考虑氮物种对活化过程本身的影响。氧化还原反应在KOH活化的反应网络中起着重要作用。如果碳的电子性质因氮修饰而改变，那么对活化过程的影响是可以预料的。然而，这种相关性在文献中很少被提及。对这一现象的讨论仅限于假设，这也是由于缺乏对合适的参照系的系统研究造成的。因此，本项目的目的是系统地研究氮改性碳的活化过程，涉及以下问题：1.哪些过程导致氮从碳基质中释放？2.氮改性以什么方式影响气孔的形成？

Nitrogen modified porous carbons have been investigated as materials for electrochemical energy storage systems such as super capacitors, accumulators or redox flow batteries, respectively, with steady growing interest since the last two decades. In the meantime, the activation using KOH plays a dominating role to produce porosity. In difference to template assisted routes that method requires low effort and allows to produce materials with extreme inner surface areas (up to > 3000 m2/g BET) and high degree of microporosity. The relevance of the topic is underlined by the current large number of publications; e.g. about 200 articles are listed in web of science for the period of the last two years. The evaluation of the literature yielded that the activation of nitrogen modified carbons by KOH is connected with two circumstances. First, the activation is accompanied by the substantial release of nitrogen. As the result the total quantity of nitrogen is decreased and the quantity ratios of different nitrogen species are changed. The reports on that are partially contradictory to each other but the degradation of pyridinic species in favor of the formation of pyrrolic species has been mostly reported. However, although the release of nitrogen has been described in numerous publications, there is still a lack of systematic investigations of that phenomenon and, respectively, of how to control it by the synthesis conditions. Second, the impact of nitrogen species on the activation process itself has to be considered. Redox reactions play an important role in the reaction network of the KOH activation. If electronic properties of the carbon are changed by nitrogen modification an impact on the activation process has to be expected. However, such correlations are mentioned in the literature only rarely. The discussion of that phenomenon is restricted to assumptions which is again caused by the lack of systematic investigations on suitable reference systems.It is therefore the aim of the project to investigate the process of the activation of nitrogen modified carbons systematically regarding the following questions: 1. Which processes cause the release of nitrogen from the carbon matrix?2. In what way is the pore formation impacted by the nitrogen modification?