• Energy Research

This contribution proposes the usage of Liquid Organic Hydrogen Carriers (LOHC) for the establishment of a decentralised energy storage network. Due to the continually increasing amount of renewable energy within the power grid, in particular in countries of the European Union, a huge demand for storage capacities develops that can hardly be met by large-scale systems alone. Because of their high storage density and good manageability LOHC substances permit the local storage of excess energy in residential and commercial buildings. Following the approach of a CHP system (‘combined heat and power’ or more precisely a ‘combined heat and storage’ system), thermal losses from the storage processes can be used for heating (and cooling) purposes in order to increase the overall efficiency. An evaluation of the economic feasibility identifies possible approaches to generate income from storage operation. The usage of exhaust heat for heating proves to significantly support the business case by providing a considerable financial contribution that is usually not exploitable for centralised storage units.

2‐Propanol/acetone is a promising liquid organic hydrogen carrier system for fuel cell reactions. Herein, six different concepts for a 2‐propanol/acetone fuel cell system are evaluated in MATLAB simulation with respect to their thermodynamic integration and technical feasibility. Four of the concepts use a direct 2‐propanol fuel cell while the other two first release molecular hydrogen from 2‐propanol and subsequently use a hydrogen fuel cell. The presented liquid phase 2‐propanol fuel cell concept is thermodynamically feasible but cannot be realized technically using commercial Nafion membranes, due to membrane dissolution by the 2‐propanol/acetone/water fuel mixture. Gaseous 2‐propanol fuel cells imply a high heating requirement for the evaporation of the fuel. A direct high‐temperature fuel cell using 2‐propanol is thermodynamically feasible because there is less water in the overall system but is not technically feasible because of the esterification of phosphoric acid. A very interesting option is the conversion of gaseous 2‐propanol to pressurized hydrogen in an electrochemical pumping step followed by a hydrogen fuel cell, because here the waste heat of a sufficiently hot hydrogen fuel cell can drive the 2‐propanol evaporation.

The oxygen functionalized LOHC system benzophenone/dicyclohexylmethanol reveals new possibilities in the field of hydrogen transport and storage.

This study presents benzyltoluene/perhydro benzyltoluene as a very favourable liquid organic hydrogen carrier (LOHC) system for potential industrial applications.

Future energy systems will be determined by the increasing relevance of solar and wind energy. Crude oil and gas prices are expected to increase in the long run, and penalties for CO2 emissions will become a relevant economic factor. Solar- and wind-powered electricity will become significantly cheaper, such that hydrogen produced from electrolysis will be competitively priced against hydrogen manufactured from natural gas. However, to handle the unsteadiness of system input from fluctuating energy sources, energy storage technologies that cover the full scale of power (in megawatts) and energy storage amounts (in megawatt hours) are required. Hydrogen, in particular, is a promising secondary energy vector for storing, transporting, and distributing large and very large amounts of energy at the gigawatt-hour and terawatt-hour scales. However, we also discuss energy storage at the 120–200-kWh scale, for example, for onboard hydrogen storage in fuel cell vehicles using compressed hydrogen storage. This article focuses on the characteristics and development potential of hydrogen storage technologies in light of such a changing energy system and its related challenges. Technological factors that influence the dynamics, flexibility, and operating costs of unsteady operation are therefore highlighted in particular. Moreover, the potential for using renewable hydrogen in the mobility sector, industrial production, and the heat market is discussed, as this potential may determine to a significant extent the future economic value of hydrogen storage technology as it applies to other industries. This evaluation elucidates known and well-established options for hydrogen storage and may guide the development and direction of newer, less developed technologies.

The benzyltoluene‐based liquid organic hydrogen carrier (LOHC) system enables the safe transport and loss‐free storage of hydrogen. At least 26% of the lower heating value of the released hydrogen, however, has to be invested in form of heat to release the stored hydrogen. The low operation temperatures of catalytic distillation (CD) can facilitate waste heat integration to reduce external heat demand. Herein, the continuous hydrogen release from perhydro benzyltoluene via CD is demonstrated. It is revealed in the experimental results that this mode of operation leads to a high hydrogen release rate and very efficient noble metal catalyst usage at exceptionally mild conditions. The hydrogen‐based productivity of platinum of 0.35 gH2 gPt−1 min−1 (0.7 kWLHV_H2 gPt−1) at a dehydrogenation temperature of only 267 °C is found to be nearly four times higher than for the conventional continuous liquid‐phase dehydrogenation at the same temperature. Furthermore, simulation results of the CD process are described. The feasibility of a fully heat‐integrated process for electricity generation from the released hydrogen via CD using waste heat from the fuel cell for the CD reboiler is demonstrated. The technical potential of coupling the H12–BT dehydrogenation by CD with high‐temperature fuel cell operation is highlighted by the simulation.

Perhydro-N-ethyl carbazole is dehydrogenated in continuous flow using a reactor produced by rapid prototyping, releasing hydrogen equivalent to 4.32 kWel L−1.

A new concept for storage and superregional transport of solar energy from the earth's desert belt is proposed. The concept is based on solid alkaline earth metal compounds, showing an energy-rich and an energy-lean state which are used in an energy distribution cycle. The concept is evaluated with regard to overall solar-to-electricity efficiency and benchmarked by the overall efficiency of the DESERTEC concept. For a scenario assuming that the current share of electricity production from lignite coal in Germany is replaced by the here proposed concept, the CO2 mitigation potential is calculated. The assessment shows that the proposed concept can compete with the benchmark and even shows high potential for optimization.