Storing Renewable Energy in the Hydrogen Cycle

Abstract

An energy economy based on renewable energy requires massive energy storage, approx. half of the annual energy consumption. Therefore, the production of a synthetic energy carrier, e.g. hydrogen, is necessary. The hydrogen cycle, i.e. production of hydrogen from water by renewable energy, storage and use of hydrogen in fuel cells, combustion engines or turbines is a closed cycle. Electrolysis splits water into hydrogen and oxygen and represents a mature technology in the power range up to 100 kW. However, the major technological challenge is to build electrolyzers in the power range of several MW producing high purity hydrogen with a high efficiency. After the production of hydrogen, large scale and safe hydrogen storage is required. Hydrogen is stored either as a molecule or as an atom in the case of hydrides. The maximum volumetric hydrogen density of a molecular hydrogen storage is limited to the density of liquid hydrogen. In a complex hydride the hydrogen density is limited to 20 mass% and 150 kg/m(3) which corresponds to twice the density of liquid hydrogen. Current research focuses on the investigation of new storage materials based on combinations of complex hydrides with amides and the understanding of the hydrogen sorption mechanism in order to better control the reaction for the hydrogen storage applications.

From Enzymes to Functional Materials—Towards Activation of Small Molecules

“…Hence it is desirable to find suitable pathways to utilize carbon dioxide as aC 1 -C 3 feedstock and establish an artificial carbon cycle. [297] The main problem,h owever,a ssociated with such an artificial cycle is the high energy demand( À1.97 VinD MF [298] or À1.90 Vinw ater [299] vs. SHE) required to convert CO 2 into au seful product, such as carbon monoxide, formic acid, formaldehyde, or methanol ( Figure 23). [300] Furthermore, the formation of the high-energy carbon dioxide anion radicald uring the reduction processes resultsi nl ow selectivity towardss pecific reduction products.…”

Improved hydrogen storage properties of MgH2 by the addition of TiCN and its catalytic mechanism

“…Among various new energy carriers, hydrogen is one of the most promising candidates as it can be converted to electricity through fuel cell without emitting pollutants [2]. However, the realization of the "hydrogen economy" requires a high energy density and safe hydrogen storage technology [3]. So far, numerous efforts have been made by researchers worldwide to develop hydrogen storage materials to meet the requirements of effective capacity, safety, mild reaction temperature and operating pressure.…”