Structure / reactivity relationships in N-containing Liquid Organic Hydrogen Carrier (LOHC) systems

在旨在将氢储存在富含氢的固体或液体中的化学储能技术中，液体有机氢载体(LOHC)特别吸引人，因为它们允许在当今燃料的基础设施中处理氢。LOHC体系是一种储氢介质，它由一对贫氢的、典型的芳香族或杂芳烃液体(H0-LOHC)和一对富氢的、典型的脂环或杂脂环液体(HX-LOHC)组成。H0-LOHC通过放热催化加氢反应储存氢，而HX-LOHC通过吸热催化脱氢反应释放氢。到目前为止，选择分子作为LOHC系统的使用在很大程度上是出于实际和工程上的考虑。诸如“它能大量供应吗？”、“它足够坚固吗？”、“它足够便宜吗？”、“生态毒性呢？”在很大程度上主导了遴选过程。因此，到目前为止，已经对数量相对较少的不同分子进行了更详细的研究。在纯粹的基础科学基础上，对“理想的LOHC对”的探索显然非常相关，到目前为止还没有发生过。特别是，现代计算化学与最先进的分析、表面科学和“真正的”催化研究相结合的潜力，到目前为止还没有被应用于在可逆氢化/脱氢循环中寻找更好的LOHC分子来存储氢。在这个项目中，我们的目标是基于对多相脱氢反应中结构/反应活性关系的基本了解，使用模型表面和模型底物来开发和评估含氮LOHC系统。新分子的选择将基于对其特定功能以及最有利的热力学和动力学进行计算的预筛选。这些特性将与化学稳定性相结合，以允许重复充电和释放循环。例如，靶向HX-LOHC分子将实现极低的脱氢温度、在加氢/脱氢循环中的高耐久性以及极低的熔点。这将通过对所选分子的官能团和几何结构的适当选择来实现。因此，基于知识的性能增强的储氢化合物的开发是有针对性的。

Among the chemical energy storage technologies aiming for storing hydrogen in hydrogen-rich solids or liquids, Liquid Organic Hydrogen Carriers (LOHC) are particular appealing as they allow for hydrogen handling in the infrastructure of today’s fuels. LOHC systems are hydrogen storage media, that consist of pairs of hydrogen-lean, typically aromatic or heteroaromatic liquids (H0-LOHC) and hydrogen-rich, typically alicyclic or heteroalicyclic liquids (Hx-LOHC). H0-LOHC stores hydrogen by an exothermic catalytic hydrogenation reaction while Hx-LOHC releases hydrogen by an endothermic catalytic dehydrogenation reaction. So far, the selection of molecules considered for the use as LOHC systems was very much driven by practical and engineering considerations. Questions like “is it available in large quantities?”, “is it robust enough?”, “is it cheap enough?”, “what about ecotoxicity?” have largely dominated the selection process. Consequently, a relatively small number of different molecules have been investigated so far in greater detail. The obviously very relevant quest for “the ideal LOHC pair” on purely fundamental scientific grounds has not been taken place so far. In particular, the potential of modern, computational chemistry in combination with state of the art analytics, surface science and “real” catalytic studies has so far not been applied to find better LOHC molecules for hydrogen storage in reversible hydrogenation/dehydrogenation cycles. In this project, we aim to develop and evaluate nitrogen-containing LOHC systems based on the fundamental understanding of the structure / reactivity relationship in the heterogeneous dehydrogenation reaction using model surfaces and model substrates. The new molecules will be selected based on a pre-screening by computations for their specific functionality and the most favorable thermodynamics and kinetics. These properties will be combined with chemical robustness to allow for repeated charging and release cycles. Target Hx-LOHC molecules will enable, for example, extremely low dehydrogenation temperatures, high durability in hydrogenation / dehydrogenation cycles combined with very low melting points. This will be realized by a proper choice of functionality and geometry of the selected molecules. Thus, a knowledge-based development of hydrogen storage compounds with enhanced performance is targeted.