Helmholtz-Zentrum Geesthacht, 2018-02-22

Scientific work of the project

Storage of electrical energy by converting it to hydrogen

High volume related storage density and high energy efficiency

Windmills (courtesy SIEMENS AG) Windmills (courtesy SIEMENS AG)

The transition towards a sustainable, carbon-free and reliable energy supply system capable of meeting the increasing energy demand is considered one of the greatest challenges of the 21st century, as expressed e.g. by the 20/20/20 initiative of the European Commission [1]. In order to integrate renewable energy sources (e.g. from sun, wind, and wave energy), being unevenly distributed in location and time, advanced energy storage systems have to be developed.

These storage systems have to fulfil the requirements of a high volume related storage density, and preferably low weight for portable applications. A high energy efficiency is required to keep operating cost as low as possible, and especially not to decrease the overall efficiency of the energy conversion chain from limited resources (e.g. sun in Northern Europe) to the end user.

[1] “The EU climate and energy package“

Requirements for hydrogen storage

Novel zeolite type Magnesium Boronhydride structure synthesized at Aarhus University (Filinchuk, Richter, Jensen, Dmitriev, Chernyshov, Hagemann, Angew. Chem. Int. Ed. 2011, 50, 11162.) Novel zeolite type Magnesium Boronhydride structure synthesized at Aarhus University (Filinchuk, Richter, Jensen, Dmitriev, Chernyshov, Hagemann, Angew. Chem. Int. Ed. 2011, 50, 11162.)

Taking into account, that in solid state hydrogen storage ca. 50% of weight and volume is needed for balance of plant (BoP, e.g. hull, heat exchanger etc.), for achieving the call targets on weight and volume related system capacities, hydrogen storage materials have to possess theoretical storage capacities of more than 80 kg H2/m3 of material volume and more than 8 weight% at least.

Though metal hydrides have been investigated since the early 1970’s and again with high effort since the beginning of this century worldwide, still no hydrogen storage material exists today, additionally to capacity, also fulfilling all of the following requirements at the same time:

  • Kinetics and temperatures of the hydrogen loading and discharge reactions suitable for the application, for which the storage material is used, e.g. PEM-, HT PEM- or SO-FCs.
  • High cycling stability of the storage material, being especially important for stationary hydrogen storage, where several thousands and more of hydrogen loading / discharge cycles are required.
  • Cost of the storage materials at an acceptable level of <50 €/kg, allowing for a storage system cost level at or below 500 €/kg of stored H2.
  • Practical proof of the advantage of a solid state hydrogen storage system with respect to cost and energy in a working prototype of a combined fuel cell – solid state hydrogen storage system.

The aim of BOR4STORE

A new generation of boron hydride based storage materials

Solid state hydrogen storage tank constructed at HZG. The tank contains 8kg of Sodium Alanate and stores up to 4500 Nl of hydrogen. Solid state hydrogen storage tank constructed at HZG. The tank contains 8kg of Sodium Alanate and stores up to 4500 Nl of hydrogen.

BOR4STORE will tackle these challenges by a new generation of boron hydride based storage materials. Only boron hydride based hydrogen storage materials exhibit the necessary high hydrogen storage capacities (more than 120 kg H2/m3 and up to 18 wt %) [2] among all known hydrogen storage materials suitable for gas phase loading and discharge. They have been investigated in EU projects by members of the BOR4STORE consortium with respect to synthesising them directly from the elements (NESSHY: Empa, IFE, HZG, FLYHY: AU, IFE, HZG), understanding reaction mechanisms (NESSHY:: Empa, IFE, HZG, COSY: Empa, HZG, UNITO, FLYHY: AU, IFE, HZG, UNITO), modifying them by anion substitution (FLYHY: AU, IFE, HZG) or introducing them in nanosized scaffolds (NANOHY: IFE, NCSRD). Important steps forward towards fully reversible hydrogen loading have been made by mixing them with other hydrides in the so called Reactive Hydride Composites (RHC) (COSY: Empa, HZG, UNITO). Furthermore, the potential for decreasing dehydrogenation temperatures by partial fluorine substitution and enhancing reaction kinetics by nanoconfinement of the hydrides in nanosized scaffolds was demonstrated (FLYHY and NANOHY), Significant progress has also been made in the US (e.g. DOE Metal Hydride Center of Excellence) and in Japan (e.g. HYDROSTAR project). But the following deficits still remain unsolved:

Temperatures for decomposition at reasonable reaction speeds were too high (> 350°C) or too low (RT or below RT in the case of "unstable” boron hydrides like Al(BH4)3 or Zr(BH4)4), reversibility of hydrogen loading was only very limited or impractical in the case of pure boron hydrides, cycling stability was either not tested at all or tested to less than 100 cycles only.

  • Boron based materials cost of several thousand €/kg are too high for large scale application.
  • Use of boron hydride based storage materials in a practical application (e.g. to supply a fuel cell), especially with a heat recovery system in order to improve the global efficiency of the tank – application - system, has not been demonstrated yet.

To overcome these deficits, BOR4STORE will

  • Synthesise novel boron hydride based materials (e. g. bi- and tri-metal boron hydrides, which can be anion substituted) and composites (e.g. Eutectically Melting Composites (EMC)) with high hydrogen storage capacities >8 wt.% and >80 kg H2/m3, and evaluate their suitability for practical application in a careful materials downselection process,
  • accelerate reaction kinetics and adjust reaction temperatures appropriately to supply a SOFC with sufficient hydrogen pressure and flow at acceptable rehydrogenation times of 1 hour or below by systematically investigating additives to understand their effects on rate limiting reaction steps,
  • enhance the cycling stability of the materials to several 1000 cycles also by suitable additives as well as by scaffolding the storage material in pore size optimised porous materials to tailor reaction pathways, prevent phase separation and retain a high storage density,
  • decrease materials cost to reach the long term target of < 50 €/kg in large scale production, by (a) developing cost effective materials synthesis routes, and (b) systematically investigating the effects of impurities on storage properties to enable the use of more cost effective raw materials with less stringent requirements on purity, and
  • demonstrate the suitability, high energy and cost efficiency of a boron hydride based laboratory prototype tank, containing ca. 100 – 1000 g of storage material, to correspondingly supply a 0.1 - 1 kW SOFC (exact power to be decided in the course of the project) as a model for a continuous power supply for specific applications like net independent telephone or weather stations, backup power for lighting and control, CHP, potentially being also a model for APU’s for trains or ships and other portable applications.
[2] L. H. Rude, T. K. Nielsen, D. B. Ravnsbæk, M. B. Ley, B. Richter, L. M. Arnbjerg, U. Bösenberg, M. Dornheim, Y. Filinchuk, F. Besenbacher, T. R. Jensen Physica Status Solidi, A 2011, 208(8) 1754–1773.


Integrated prototype of a stationary power supply

Deliverables of the project will be

  • a novel solid state hydrogen storage prototype system based on boron hydrides, with system capacity > 4 wt.%, and > 40 kg H2/m3, with materials reaction enthalpies and kinetics of hydrogen loading and discharge suitable for integrating it with a SOFC, with tested cycling stability >98% of retained capacity over at least 500 loading-unloading cycles,
  • cost effective production routes of the materials, with demonstrated potential for scale-up and for reaching a system cost of 500 €/kg of stored H2,
  • a laboratory prototype of a 0.1 - 1 kW SOFC integrated with a 0.1 - 1 Nm3 hydrogen storage system for continuous energy supply with significantly improved storage capacity and overall energy efficiency compared to compressed gas storage and other fuel cell technologies, respectively.
  • an indicator of allowable hydrogen purity for stable storage properties,
  • Techno – economical evaluation of the scaled prototype (in connection to the aforementioned applications), thereby demonstrating the techno-economical readiness of solid state hydrogen storage technology.

Telecom-station on Mountain. Telecom-station on Mountain.