Study of hydrogen storage and compression

The goal of this rapport is to present an overview of the different hydrogen storage technologies, currently available for industrial application or at earlier stages of development. In order to identify the water and mechanical work requirements for compression of hydrogen, flow sheets of several compression process are realized. In order to decrease the work needed for hydrogen compression, realizing part of the compression with a metal-hydride compressor and integrating the compression process with a solar hydrogen production plant was study. It shows that metal-hydride pre-compression of hydrogen using waste heat before mechanical compression has the potential to lower the mechanical work consumption by about 15%compared to multi-stage mechanical compression alone.

A multifaceted approach to hydrogen storage

Bengt Kasemo

The widespread adoption of hydrogen as an energy carrier could bring significant benefits, but only if a number of currently intractable problems can be overcome. Not the least of these is the problem of storage, particularly when aimed at use onboard light-vehicles. The aim of this overview is to look in depth at a number of areas linked by the recently concluded HYDROGEN research network, representing an intentionally multi-faceted selection with the goal of advancing the field on a number of fronts simultaneously. For the general reader we provide a concise outline of the main approaches to storing hydrogen before moving on to detailed reviews of recent research in the solid chemical storage of hydrogen, and so provide an entry point for the interested reader on these diverse topics. The subjects covered include: the mechanisms of Ti catalysis in alanates; the kinetics of the borohydrides and the resulting limitations; novel transition metal catalysts for use with complex hydrides; less common borohydrides; protic-hydridic stores; metal ammines and novel approaches to nano-confined metal hydrides. © 2011 the Owner Societies.

2011

Kinetics and Mechanism of Formic Acid Decomposition in Aqueous Solution using Ruthenium Pre-catalysts with Hydrophilic Phosphine Ligands

Weijia Gan

Hydrogen holds the potential to be an alternative to replace fossil fuels in the future. The tremendous research effort dedicated to the issue of hydrogen storage has led to considerable advancements in the development of both adsorption materials and chemical storage. Still, for many of these systems the gap between current state of research and industrial application is considerable. When it comes to systems for the reversible storage of hydrogen, the HCOOH/CO2 cycle currently shows the most promises. Its physical-chemical properties make formic acid an ideal system for hydrogen storage. Herein, a series of homogeneous catalytic systems have been developed for hydrogen generation from formic acid in aqueous solution. These catalysts are formed from commercially available RuCl3 with a variety of water-soluble phosphine ligands. These ligands vary in the type, number and position of their hydrophilic substituents. Most of them allow the efficient decomposition of formic acid under mild conditions for a large number of catalytic cycles. Especially a new series of cationic phosphine ligands provide the catalytic systems with high activity. Due to the observed high initial reaction rate of many catalytic systems, mechanistic studies have also been undertaken with important intermediates and a catalytic cycle being proposed. Accordingly, the heterogeneous catalysts have also been developed based on the immobilization of homogeneous ruthenium complexes. The immobilized catalysts also afford hydrogen with high purity and allow easy catalyst separation, overcoming the previous limitations in the use of homogeneous catalysts, particularly for mobile/portable applications. The research undertaken in this thesis is presented in three main parts: (i) the development and optimization of homogeneous catalytic systems; (ii) the development and optimization of heterogeneous/immobilized catalytic systems; (iii) the mechanistic studies on the initial fast catalytic cycle of homogeneous catalysts.

EPFL2012

Decreasing the Stability of Borohydride with Ionic Liquids for Hydrogen Storage and Carbon Dioxide Conversion

Loris Giovanni Lombardo

The world needs to move from a fossil fuel to a renewable energy based society. With the increasing electricity production from wind and PV, short and long term energy storage are becoming one of challenge of the 21st century. While batteries are the preferred method for short term storage, another technology is required for seasonal storage. Hydrogen is a valuable energy carrier owning its high energy density (122 kJ/g). However, compact and safe storage of H2 is challenging. The current solution is to compress hydrogen up to 700 bar for mobile application (fuel cell cars), and metal hydrides for stationary application. Material-based H2 storage avoids using high-pressure cylinder. Complex hydrides are especially attractive for solid-state H2 storage due to their high gravimetric and volumetric hydrogen density. Sodium borohydride (NaBH4) contains 10.6 mass% of H2, but high temperatures are needed to release H2 (505 Â°C) and the reaction is not reversible under moderate conditions. To apply complex hydrides in real applications, they must be modified to improve the kinetics and thermodynamics of H2 desorption. Several possibilities exist such as confinement into scaffolds, catalyst addition, or combination of several hydrides to modify the dehydrogenation pathway. The stability of complex hydrides is determined by the localization of the charge on the central atom of the complex. Therefore, in this thesis the interaction of highly polar or ionic compounds with complex hydrides were investigated. We combine NaBH4 with a special class of organic salts: ionic liquids (IL). Considering their chemical and thermal stability, IL are attractive additive. Using organic additives instead of expensive metal catalysts is another advantage. Two different techniques were employed to combine the IL and NaBH4. The first one consists of mechanochemically milling them to create an interaction between BH4- and IL. The second one is to directly synthesized IL borohydrides ([IL][BH4]) by metathesis reaction. Different ILs, such as vinylbenzyltrimethylammonium chloride ([VBTMA][Cl]), 1-butyl-3-methylimidazolium chloride ([bmim][Cl]), and 1-ethyl-1-methylpyrrolidinium bromide ([EMPY][Br]) were tested. [bmim][BH4] was able to release H2 below 100 Â°C. The hydrogen content ranges between 2.4 mass% and 2.9 mass%. The second challenge of this century is the CO2 problematic. Atmospheric CO2 concentration linearly increases, leading to greenhouse effect. Carbon capture and sequestration (CCS) and utilization (CCU) are primordial research topic to stabilize the CO2 emission. Hydrides are primary reducing agents, thus reduction of CO2 can be accomplished with them. Direct CO2 reduction at ambient conditions is challenging for classical borohydrides. With our [IL][BH4], gaseous CO2 can be captured and reduced under ambient conditions (1 bar, RT). Three CO2 bounds with boron to give triformatoborohydride ([HB(OCHO)3]â. Dilute CO2 (6 vol%) can be used as well. The reaction was followed in real time with a magnetic suspended balance (MSB). Further, CO2 reduction happened when air is used as a carbon dioxide source. Formic acid can be obtained by adding HCl. Thus, ionic liquid borohydrides have great potential as a CO2 absorber and reducer to alternative fuels. In short, we applied ionic liquid to destabilized borohydrides. The resulting materials exhibited potential for solid-state hydrogen storage, as well as CO2 capture and transformation.