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

氮改性多孔炭作为电化学储能系统的材料，如超级电容器、锂离子电池或氧化还原液流电池，在过去的二十年里受到了越来越多的关注。同时，KOH活化对孔隙的形成起主导作用。与模板辅助路线不同，该方法需要低努力并且允许生产具有极端内表面积（高达> 3000 m2/g BET）和高度微孔性的材料。目前大量的出版物突出了该主题的相关性;例如，在过去两年中，科学网列出了约200篇文章。对文献的评价得出，通过KOH活化氮改性的碳与两种情况有关。首先，活化伴随着氮的大量释放。其结果是，氮的总量减少，不同形态氮的数量比例发生变化。关于这方面的报道部分相互矛盾，但吡啶类物种的降解有利于吡咯类物种的形成的报道最多。然而，尽管在许多出版物中描述了氮的释放，但仍然缺乏对该现象的系统研究，以及分别缺乏如何通过合成条件来控制氮的释放。 其次，必须考虑氮物质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的作用。如果碳的电子性质通过氮改性而改变，则必须预期对活化过程的影响。然而，这种相关性在文献中很少提到。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考系统的系统研究所造成的，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.氮气改性以何种方式影响孔隙形成？

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?