Storage of Renewable Energy by Reduction of CO2 with Hydrogen

The main difference between the past energy economy during the industrialization period which was mainly based on mining of fossil fuels, e.g. coal, oil and methane and the future energy economy based on renewable energy is the requirement for storage of the energy fluxes. Renewable energy, except biomass, appears in time- and location-dependent energy fluxes as heat or electricity upon conversion. Storage and transport of energy requires a high energy density and has to be realized in a closed materials cycle. 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. However, the hydrogen density in a storage system is limited to 20 mass% and 150 kg/m3 which limits the energy density to about half of the energy density in fossil fuels. Introducing CO2 into the cycle and storing hydrogen by the reduction of CO2 to hydrocarbons allows renewable energy to be converted into synthetic fuels with the same energy density as fossil fuels. The resulting cycle is a closed cycle (CO2 neutral) if CO2 is extracted from the atmosphere. Today's technology allows CO2 to be reduced either by the Sabatier reaction to methane, by the reversed water gas shift reaction to CO and further reduction of CO by the Fischer–Tropsch synthesis (FTS) to hydrocarbons or over methanol to gasoline. The overall process can only be realized on a very large scale, because the large number of by-products of FTS requires the use of a refinery. Therefore, a well-controlled reaction to a specific product is required for the efficient conversion of renewable energy (electricity) into an easy to store liquid hydrocarbon (fuel). In order to realize a closed hydrocarbon cycle the two major challenges are to extract CO2 from the atmosphere close to the thermodynamic limit and to reduce CO2 with hydrogen in a controlled reaction to a specific hydrocarbon. Nanomaterials with nanopores and the unique surface structures of metallic clusters offer new opportunities for the production of synthetic fuels

Mg for hydrogen storage: synthesis, nanostructure and thermodynamics properties

Nowadays alternative energies are an extremely important topic and the possibility of using hydrogen as an energy carrier must be explored. Many problems infer the technological application of this abundant and powerful resource, one of them the possibility of storage. In the framework of suitable materials for hydrogen storage, magnesium has been the center of this study because it is cheap and the amount of stored hydrogen that it achieves (7.6 wt%) is extremely appealing. Nanostructure helps to overcome the slow hydrogen diffusion and the functionalization of surfaces with transition metals or oxides favors the hydrogen molecule dissociation/recombination. The aim of this research is the investigation of the metal-hydride transformation in magnesium nanoparticles synthesized by inert-gas condensation, exploiting the fact that they are a simple model system. The so produced nanostructured powder has been analyzed in response to nanoparticles surface functionalization by transition metal clusters, specifically palladium, nickel and titanium, chosen on the basis of their completely different Mg-related phase diagrams. The role of the intermetallic phases formed upon heating and hydrogenation treatments will be presented to provide a comprehensive picture of hydrogen sorption in this class of nanostructured storage materials

Surface Reactions are Crucial for Energy Storage

Reactions between gas molecules, e.g. H-2 and CO2 and solids take place at the surface. The electronic states and the local geometry of the atomic arrangement determine the energy of the adsorbate, i.e. the initial molecule and the transition state. Here we review our research to identify the surface species, their chemical state and orientation, the interaction with the neighbouring molecules and the mobility of the adsorbed species and complement the experimental results with thermodynamic modelling. The role of the Ti was found to be a bridge between the charged species preventing the individual movement of the ions including charge separation. The Ti has no catalytic effect on the hydrogen sorption reaction in borohydrides. The physisorption of molecular hydrogen is too weak at ambient temperature to reach a significant hydrogen storage density. The addition of a hydrogen dissociation catalyst to a nanoporous material with a large specific surface area may potentially enable the spillover of hydrogen atoms from the metal catalyst to the surface of the porous material and chemisorb on specific sites with a much higher binding energy compared to physisorption. The intercalation of alkali metals in C-60 fullerenes increases the interaction energy of hydrogen with the so-called metal fullerides significantly. Sterical diffusion barriers by partial oxidation of the surface of borohydrides turned out to redirect the reaction path towards pure hydrogen desorption and suppress the formation of diborane, a by-product of the hydrogen evolution reaction from borohydrides previously undetected. The combination of a newly developed gas controlling system with microreactors allows us to investigate complex reactions with small quantities of nano designed new catalytic materials. Furthermore, tip-enhanced Raman spectroscopy (TERS) will allow the investigation of the reactions locally on the surface of the catalyst and the near ambient pressure photoelectron spectroscopy enables analysis of the surfaces in ultra-high vacuum and in situ interaction with the adsorbates i.e. while the reaction takes place. This brings us in a unique position for the investigation of the heterogeneous reactive systems. The mechanism of the Ti catalysed hydrogen sorption reactions in alanates was recently established based on spectroscopic investigations combined with thermodynamic analysis of the transition states

Storing Renewable Energy in the Hydrogen Cycle

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/m3 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

Storage of Renewable Energy by Reduction of CO2 with Hydrogen

The main difference between the past energy economy during the industrialization period which was mainly based on mining of fossil fuels, e.g. coal, oil and methane and the future energy economy based on renewable energy is the requirement for storage of the energy fluxes. Renewable energy, except biomass, appears in time- and location-dependent energy fluxes as heat or electricity upon conversion. Storage and transport of energy requires a high energy density and has to be realized in a closed materials cycle. 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. However, the hydrogen density in a storage system is limited to 20 mass% and 150 kg/m(3) which limits the energy density to about half of the energy density in fossil fuels. Introducing CO, into the cycle and storing hydrogen by the reduction of CO, to hydrocarbons allows renewable energy to be converted into synthetic fuels with the same energy density as fossil fuels. The resulting cycle is a closed cycle (CO2 neutral) if CO, is extracted from the atmosphere. Today's technology allows CO, to be reduced either by the Sabatier reaction to methane, by the reversed water gas shift reaction to CO and further reduction of CO by the Fischer Tropsch synthesis (FTS) to hydrocarbons or over methanol to gasoline. The overall process can only be realized on a very large scale, because the large number of by-products of FTS requires the use of a refinery. Therefore, a well-controlled reaction to a specific product is required for the efficient conversion of renewable energy (electricity) into an easy to store liquid hydrocarbon (fuel). In order to realize a closed hydrocarbon cycle the two major challenges are to extract CO, from the atmosphere close to the thermodynamic limit and to reduce CO2 with hydrogen in a controlled reaction to a specific hydrocarbon. Nanomaterials with nanopores and the unique surface structures of metallic clusters offer new opportunities for the production of synthetic fuels.LME

Storing Renewable Energy in the Hydrogen Cycle

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

MgH₂ by Gas Phase Condensation: Nanostructure Morphology and Hydrogen Sorption Behaviour

AbstractInert gas condensation was employed to prepare nanoparticles of Mg and MgH2 which morphology, clustering degree and structural stability have been investigated by X-ray diffraction and electron microscopy. Thermodynamic functional properties of the Mg and MgH2 nanostructured samples were investigated by high pressure differential scanning calorimetry. Some specific features of the morphology of the samples prepared by inert gas condensation are compared with powders obtained by ball milling through desorption kinetics behavior.</jats:p

Insight into the decomposition pathway of the complex hydride Al3Li4(BH4)(13)

The decomposition pathway of the complex hydride Al3Li 4(BH4)13 is in the focus of this study. Initially the compound attracted great interest due to its high H2 capacity (17.2 wt.%) and desorption at moderate temperatures (&lt;100 °C). This work sheds light on its decomposition reaction by a unique experimental setup of thermogravimetry combined with spectroscopic gas phase analysis (FT-IR and MS) at ambient conditions. It is observed that the compound itself is metastable and decomposes immediately into its components, solid LiBH 4 and Al(BH4)3 which is monitored in the gas phase. Carbon addition decreases the observed mass loss and the spectroscopic gas phase analysis is used to learn about the impact of carbon addition. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved