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

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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?