Hydrogen as Energy Carrier F. Schüth MPI für Kohlenforschung, Mülheim

1. Hydrogen as Energy Carrier F. Schüth MPI für Kohlenforschung, Mülheim

2. Why do we need a new energy infrastructure? Oil discoveries are decreasing Reason for constant reserves/production is enhanced recovery „Peak oil“ is not too far away, may have already been reached

3. Roles of hydrocarbons in our economy • Source of energy • Transport and storage of energy(around 20 Mio. t of oil in strategic energy reserve) • Alternative storage • Reservoirs (Pumpspeicherkraftwerke), but the total installed capacity in germany only covers some minutes of the primary energy demand • Pressured gas storage, one system operating in Germany, but storage capactiy limited as well • Electrochemical: would need gigantic batteries

4. Hydrogen as future energy storage and transportation form Bild der Wissenschaft 2004 • With renewable hydrogen clean electrical energy • In principle zero emission • High efficiency for energy conversion • But still to solve… • Reduce or replace platinum based catalyst • Better stability / higher temperature membranes

5. Why Hydrogen Advantages • Very high mass based energy density (120 MJ/kg) • Combustion exclusively to water (with oxygen) • Easily generated by electrolysis or from biomass Roh-H2 Wasser- dampf Biomasse Vergasung Rein-H2 Eisenoxid Eisen

6. Why Hydrogen Advantages • Very high mass based energy density (120 MJ/kg) • Combustion exclusively to water (with oxygen) • Easily generated by electrolysis or from biomass • Efficient conversion to electricity in fuel cells • Non-toxic, odorless • Explosive within wide limits • Electricity-to-hydrogen-to-electricity substantial losses • Storage problem unsolved Disadvantages

7. Explosion danger

8. Source: U. Eberle, GM FCA Why Hydrogen Storage for Mobile Applications? • Fuel cell technology envisaged as future replacement of internal combustion engine • Well-to-wheel studies indicate that hydrogen in combination with fuel cells can reduce greenhouse gas emissions substantially (close to zero for renewable hydrogen) • System decision for hydrogen as energy carrier in Germany has been taken • Available technologies for hydrogen storage not fully satisfactory „If you want to name a single obstacle for the introduction of fuel cell technology in cars, it is the hydrogen storage“

9. The markets • 50 Million cars/years worldwide • Costs for storage 500 €/car • Total market volume 25 Billion €/year • Also other markets, such as laptops, mobile phones, houses

10. Available technology: Liquid storage

11. Source: U. Eberle, GM FCA Characteristics of liquid storage • Liquid hydrogen in superinsulated containers at -254 °C • Liquifaction/transport in principle managed technology • Boil-Off problems • Liquifaction highly energy intensive • Volumetric storage density unsatisfactory

12. Available technology: High pressure storage

13. Source: U. Eberle, GM FCA Characteristics high pressure storage • Compression of hydrogen up to 700 bar • In principle managable technology • Tanks presently much too expensive • Compression very energy intensive • Volumetric storage density unsatisfactory • Cylinders cause packaging problems

14. Storage Capacity: Comparison for 400 km range Source: U. Eberle, GM FCA

15. Chemical storage systems Main cost drivers

16. Panella et al., Carbon 43, 2209 (2005) Sorptive storage in high surface area materials • Exceedingly high capacities reported for storage in carbon nanotubes • Results could not be reproduced, reason clarified • All different high surface area materials fall on common line capacity vs. surface area • MOFs reported to deviate from this line, but not confirmed • If to be used, only in combination with 77 K cryosystems

17. Reforming of liquid fuels • Methanol or hydrocarbons have a high storage capacity • Methanol reforming possible at 200-300°C • Hydrocarbon reforming above 500°C • Partial oxidation more attractive CH3OH + H2O  CO2 + 3 H2 CH3OH + ½ O2 CO2 + 2 H2

18. Power Water-Gas Shift CO Cleanup Fuel Cell Steam Reformer Combustor Air Recuperator Vaporizer Exhaust Fuel Water The fuel processor system

19. n-heptane + surfactant Zr(OC4H9)4 Zr(OH)4(+ n-butanol CuO/ZrO2 Cu(OH)2 (+ n-butanol H2O Cu(NO3)2 0.59% CO 100 90 0. 12% CO 80 70 60 conversion 50 Commercial Cu/ZnO/Al2O3 40 Microemuslion 30 20 10 0 240 250 260 270 280 290 300 310 Temperature/°C Decrease CO-formation in reforming metal-alkoxideprecursor solution sol-gel synthesis in reverse microemulsion Cu/ZrO2 Cu(NO3)2 in H2O anionicsurfactant aliphaticsolvent MeOH steam reforming: Same activity Much less CO I. Ritzkopf et al., Appl.Catal.A-Gen. 2006

20. NH3 as storage material? • Production well established • Efficient with respect to energy consumption • Decomposition without trace to N2 and H2 • Easy liquifaction • High hydrogen content

21. Unfavorable activity of commercial catalysts • Summary • Typical operation temperature is as high as 700oC • H2 productivity is low, NH3 space velocity is always < 5000 h-1

22. Bayer MWCNTs (Co as the impurity) Effect of space velocity Effect of Temperature Pure NH3, 700 oC, 100 mg Pure NH3, SV= 5,000 cm3/gcat h, 100 mg ~100% conversion could be achieved at 700oC and 20000 h-1

23. Alternative: Metal hydrides Volume of the tank for 4 kg H2 Schlapbach and Züttel, Nature 414, 353 (2001)

24. Two alternatives for hydrides • Hydrolytic processes • Reversible Hydrides

25. H2 NaBO2 in H2O 25wt.% NaBH4 in H2O, 2 % NaOH Kat. Hydrogen on demand™ NaBH4 + 2 H2O 4 H2 + NaBO2 10.8 % Advantages: Liquid fuel as conventional harmless without catalyst

26. Hydrogen on demand in practice

27. Problems with Hydrolytic Storage • Modules have to be exchanged (solid) • Quite difficult control problems (solid) • Not very energy efficient • production of alkali metals • or production of metal hydrides • Expensive, even if prices would drop • Probably applications only in high-end niches

28. Consequently:

29. Reversible Hydrides: Requirements Property Target Gravimetric storage density > 6.5 % Volumetric storage density > 6.5 % De-/rehydrogenationrate Dehydrogenation < 3 h Rehydrogenation < 5 min Rehydrogenations pressure < 50 bar Equilibrium pressure Around 1 bar at room temperatrue Heat effects As low as possible (but related to equilirium pressure) Safety As high as possible, i.e. no ignition with air or moisture Cycle stability > 500 Memoryeffect Ideally absent Cost As low as possible (ball park figure: 100 €/kg H2)

30. A reversible hydride in technical applications U 212 HDW

31. Ti 3 NaAlH4 Na3AlH6 + 2 Al + 3 H2 Ti Na3AlH6 3 NaH + Al + 1.5 H2 The „materials landscape“ 5 g cm-3 2 g cm-3 1 g cm-3 0.7 g cm-3 160 Mg2FeH6 BaReH6 MgH2 LiBH4 120 NaBH4 LaNi5H6 KBH4 C8 FeTiH1.7 C1 LiAlH4 H2,l C3 80 Volumetric storage density [kg H2 m-3 ] NaAlH4 H on C 40 0 0 5 10 15 20 25 Mass storage density [wt.%] Adapted from Schlapach and Züttel, Nature 414, 353 (2001)

32. The alternative: reversible hydrides 300 200 100 50 25 0 -20 100 10 1 0.1 TiCr1.8H1.7 NaAlH4 MNi5H6 CoNi5H4 FeTiH Mg2NiH4 Dissociation pressure [atm] LaNi5H6 Na3AlH6 MgH2 HT MT LT 1.5 2.0 2.5 3.0 3.5 4.0 1/T [10-3 K-1] B. Bogdanovic et al. J.Alloy Compd. 302, 36 (2000)

33. The doping procedure Ti-compound • From solution • By ball-milling NaAlH4 in Toluene

34. 116 180 114 160 Pressure / bar 112 Temperature / °C 110 140 108 120 0 2 4 6 8 Time / min Most advanced system: ScCl3 in situ doped System heated to 120°C, then pressurized. Capacity: 3.2 %

35. Unsuitable thermodynamics CaAlH5 possibly useful Other Alanates

36. A Nitride-based system: Li3N/LiNH2 Li3N + H2Li2NH + LiH 5.4 wt.% Li2NH + H2 LiNH2+ LiH 6.5 wt.% at 250°C Problems: Ammonia release Temperature too high P. Chen et al., Nature 420, 302 (2004)

37. Summary and Outlook • Chemical storage systems promising as long term solution • Methanol reforming largely developed, but complex • NaAlH4 presently most advanced system, but too low capacity • Innovation potential in improved catalysts, hydrides with higher storage capacity ? ! ! ! ? ! ! ! ? ? !

38. Many problems solved with purpose-built vehicles

39. But will we have a hydrogen-based economy? • Probably strong tendency towards increased use of electricity directly, with smart grid technology providing some buffer • Materials based storage and transportation form of energy probably needed nevertheless • Hydrogen has many advantages, at present serious alternatives are methanol and synthetic hydrocarbons • Develop all systems further, until final decision can be made

40. M. Felderhoff, B. Bogdanovic M. German M. Härtel T. Kratzke M. Mamatha R. Pawelke A. Pommerin K. Schlichte W. Schmidt M. Schwickardi N. Spielkamp B. Spliethoff G. Streukens A. Taguchi J. von Colbe de Bellosta C. Weidenthaler B. Zibrowius H. Bönnemann, Mülheim S. Kaskel, Mülheim W. Grünert, Bochum K. Klementiev, Bochum U. Eberle, Adam Opel AG F. Mertens, Adam Opel AG G. Arnold, Adam Opel AG Further reading: F. Schüth et al., Chem.Commun. 2249 (2004) Adam Opel AG Powerfluid FCI DFG