Katalytische Wasserstofffreisetzung aus chemischen Wasserstoffspeichern : Chemische und technologische Herausforderungen für eine Kopplung mit Brennstoffzellensystemen
- Catalytic hydrogen release from chemical hydrogen storage : chemical and technology challenges for coupling with fuel cell systems
Klindtworth, Elisabeth; Palkovits, Regina (Thesis advisor); Eichel, Rüdiger-A. (Thesis advisor); Liauw, Marcel (Thesis advisor)
Aachen (2020, 2021)
Dissertation / PhD Thesis
Dissertation, RWTH Aachen University, 2020
In this dissertation the potential of catalytic hydrogen release from different chemical hydrogen storage systems for a sustainable hydrogen cycle was investigated. For this purpose, borohydride and formic acid were selected as favorable hydrogen storage media. For the dehydrogenation of these hydrogen storage media, different catalysts were tailor-made, and their activity and selectivity were evaluated in both batch and continuous operation. In the first part of the work borohydride was coupled with various ionic liquids. 1-propyl-3-methylimidazolium BH4- and 1-ethyl-3-methylimidazolium BH4- were identified as particularly promising due to low melting points and high hydrogen capacities. Subsequently, the hydrogen release was optimized for a micro fuel cell by catalyzed hydrolysis with metal catalysts and acid initiators, first in batch operation and later in a semi-continuous process. Hydrogen was completely released by the continuous addition of 1 M HCl to 1-propyl-3-methylimidazolium BH4- and the hydrogen release rate could be adjusted by the acid addition rate. The relationship between hydrolysis and acid addition was followed by 11B-NMR spectroscopy. Based on these results, a mechanism for the hydrolysis of 1-propyl-3-methylimidazolium BH4- with acids was proposed. In the second part formic acid was used as a liquid hydrogen storage material and the catalyzed dehydrogenation was investigated. For this purpose, supported catalysts known from literature were compared with immobilized catalysts in terms of activity and selectivity in batch operation. Immobilized Ru and Ir species on tailor-made polymers and covalent triazine networks were identified as preferential catalysts and used in continuous operation in liquid and gas phase in various catalyst test plants. In gas phase dehydrogenation of formic acid, the polymer-based Ru catalyst and Ir catalyst stabilized by a triazine network were most active and the Ir catalyst showed stable activity over 72 h. In proof of concept studies, the potential of 1-propyl-3-methylimidazolium BH4- and formic acid vapor by coupling the catalytic hydrogen release with a micro fuel cell was evaluated. Based on the demonstration of electricity production from the catalytically released hydrogen from 1-propyl-3-methylimidazolium BH4- and formic acid steam, the feasibility of the two chemical hydrogen storage systems was confirmed.