Multi-functional Materials for Hydrogen Technology

Cross-section of asymmetric Matrimid membrane obtained via the so-called "phase inversion"

In the field of materials for hydrogen technology (hydrogen production from regenerative sources or via separation from natural gas, storage, application in fuel cells) we have identified the following major challenges:

For a cost effective mass production of hydrogen from regenerative or fossile sources, effective separation and processing technologies with least energy cost have to be developed.

For hydrogen storage, light metal hydrides offer many advantages. Especially for mobile applications light tanks are necessary. Here high hydrogen desorption temperatures have to be lowered and sluggish reaction kinetics to be increased, to achieve higher efficiency and short refuelling times.

PEM fuel cells are favoured for automobiles and many stationary applications. To achieve high efficiencies and power densities, the low proton conductivity of the currently available membranes at temperatures of more than 100°C and at low humidity has to be increased.

Various hurdles must be overcome on the way to establish the hydrogen technology. Single components have to be developed further and in the end in a overall concept have to be adjusted to each other. Directly connected to these issues we have focused our activities on three main areas:

Membranes for Hydrogen Production, Separation and Related Processes

In this field we develop new and improved membranes for hydrogen separation, and CO₂ separation, based on polymeric materials (like Matrimid, etc.), new organic-inorganic composites and membranes with alternative transport mechanisms. New membranes are being developed e.g. as part of the Helmholtz Alliance MEM-BRAIN.

In the framework of the EU project "Solhydromics" proton- and electron-conducting membranes for the generation of hydrogen by means of artificial photosynthesis are investigated. The proton conductivity of composite membranes, which were developed in the framework of this project is in the range of about 10^-2 to 10^-1 S / cm, comfortably within the values that are needed for the future Solhydromics-device.

Membranes for Fuel Cells

We are developing novel membranes for Polymer Electrolyte Membrane Fuel Cells (PEM FC) to help the establishment of fuel cells as a competitive technology for energy conversion for automotive and portable applications.

Here we develop PEM FC membranes to work at temperatures higher than 100°C and at low humidity. Problems related to water transport and cathode flooding are key issues. Therefore we develop new proton conductive polymeric materials (e.g. new block copolymers) and organic-inorganic composites (sulfonated polymers with functionalised silica, phosphates, new organic-inorganic frameworks, etc.) and new structured layers for membrane-electrode-assemblies.

In this field the Helmholtz-Zentrum Geesthacht coordinated the Virtual Institute "Asymmetric Structures for Polymeric Electrolyte Fuel Cell" in collaboration with 3 German universities (Ulm, Kiel and Hamburg-Harburg), as well as the Helmholtz centres DESY and FZJ. Training activities we re supported by the Marie Curie program (Euromembranes). Novel membranes for fuel cells based on polyoxadiazoles and polytriazoles are developed also in cooperation with the National Research Council (NRC) of Canada in a Helmholtz-NRC funded project.

Hydrogen Storage Materials

Hydrogen storage tank based on 8 kg of sodium alanate as storage material, designed and built by the Helmholtz-Zentrum Geesthacht in the frame of the STORHY project

For hydrogen and fuel cell technology an effective and compact form of hydrogen storage is extremely important. Therefore we develop nanocrystalline light metal hydrides and reactive composites with highly reversible hydrogen storage capacity, allowing the fast release and recharging of hydrogen.

We use the technology of high energy ball milling to mix suitable powders and achieve an optimized nanocrystalline structure. In order to get a deeper scientific understanding of the mechanisms enhancing hydrogen dissociation, diffusion, uptake and release, we investigate e.g. the surface reactions of metal/metal hydrides with hydrogen by in-situ spectroscopic methods.

We characterise the hydrogen reaction of nanocrystalline light metal hydrides in dependence of defect density and surface area. We also evaluate novel hydrogen release reactions and their reversibility in view of technical application. Our aim is to design a prototype tank shell for metal hydrides.

These activities were and are supported by the European projects STORHY, NESSHY and FLYHY (Helmholtz-Zentrum Geesthachtcoordination), by the Marie Curie Research Training networks HYTRAIN and COSY (Helmholtz-Zentrum Geesthacht coordination), and especially by the Helmholtz Initiative "FUNCHY: Functional Materials for Mobile Hydrogen Storage". In this Helmholtz-Zentrum Geesthacht coordinated initiative the German Helmholtz Centres Helmholtz-Zentrum Geesthacht and Karlsruhe Institute of Technology, the Leibniz Institute for Solid State and Materials Research Dresden, Germany, the Vrije Universiteit Amsterdam, the Netherlands, and the Empa, Duebendorf, Switzerland, closely work together in improving various candidates for an optimized storage material with a capacity higher than 5 weight% and uptake and release kinetics at temperatures below 150°C and at ambient pressure which are suitable for mobile applications.