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 l Source of energy l Transport and storage of energy (around 20 Mio. t of oil in strategic energy reserve) l 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 l With renewable hydrogen clean electrical energy l In principle zero emission l High efficiency for energy conversion l But still to solve… l Reduce or replace platinum based catalyst l Better stability / higher temperature membranes Bild der Wissenschaft 2004

5. Why Hydrogen l Very high mass based energy density (120 MJ/kg) l Combustion exclusively to water (with oxygen) l Easily generated by electrolysis or from biomass Advantages Biomasse Vergasung Roh-H 2 EisenoxidEisen Wasser- dampf Rein-H 2

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

7. Explosion danger

8. Why Hydrogen Storage for Mobile Applications? l Fuel cell technology envisaged as future replacement of internal combustion engine l Well-to-wheel studies indicate that hydrogen in combination with fuel cells can reduce greenhouse gas emissions substantially (close to zero for renewable hydrogen) l System decision for hydrogen as energy carrier in Germany has been taken l 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“ Source: U. Eberle, GM FCA

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

10. Available technology: Liquid storage

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

12. Available technology: High pressure storage

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

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

15. Main cost drivers Chemical storage systems

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

17. Reforming of liquid fuels l Methanol or hydrocarbons have a high storage capacity l Methanol reforming possible at 200-300°C l Hydrocarbon reforming above 500°C l Partial oxidation more attractive CH 3 OH + H 2 O  CO 2 + 3 H 2 CH 3 OH + ½ O 2  CO 2 + 2 H 2

18. The fuel processor system Fuel Water-Gas Shift Steam Reformer RecuperatorRecuperator VaporizerVaporizer COCleanupCOCleanup CombustorCombustor FuelCellFuelCellPowerAir Exhaust Water

19. Decrease CO-formation in reforming H2OH2O n-heptane + surfactant Zr(OC 4 H 9 ) 4 Cu(NO 3 ) 2 Zr(OH) 4 (+ n-butanol Cu(OH) 2 (+ n-butanol CuO/ZrO 2 Cu(NO 3 ) 2 in H 2 O Cu(NO 3 ) 2 in H 2 O anionic surfactant aliphatic solvent sol-gel synthesis in reverse microemulsion metal-alkoxide precursor solution I. Ritzkopf et al., Appl.Catal.A-Gen. 2006 Cu/ZrO 2 0 10 20 30 40 50 60 70 80 90 100 240250260270280290300310 conversion Temperature/°C Commercial Cu/ZnO/Al 2 O 3 Microemuslion 0.59% CO 0. 12% CO MeOH steam reforming: Same activity Much less CO

20. NH 3 as storage material? l Production well established l Efficient with respect to energy consumption l Decomposition without trace to N 2 and H 2 l Easy liquifaction l High hydrogen content

21. CatalystCorporationLoading(%)T( o C)SV(h -1 ) X NH3 From Ni-Pt/Al 2 O 3 United Catalyst 5%Ni,1%Pt 600 5,000 78% Appl.Catal.A 227(2002)231 Raney Ni Grace Davison 93.8% 700 5,000 82% Appl.Catal.A 227(2002)231 Ni/MgO Tianjin Univ. 10% 650 800 98% Acta Petrolei Sinica (2002) 8 43 Ni/MO x Airox Nigen Equip. — 800 2,000 90% www.indiandata.com Ni-Ru/Al 2 O 3 Apollo Energy Sys. — 700 1,000 97% www.electricauto.com Ru/Al 2 O 3 Johnson Matt. 0.5% 700 5,000 84% Appl.Catal.A 227(2002)231 Unfavorable activity of commercial catalysts Summary 1)Typical operation temperature is as high as 700 o C 2)H 2 productivity is low, NH 3 space velocity is always < 5000 h -1

22. Pure NH 3, SV= 5,000 cm 3 /g cat h, 100 mgPure NH 3, 700 o C, 100 mg ~100% conversion could be achieved at 700 o C and 20000 h -1 Effect of space velocityEffect of Temperature Bayer MWCNTs (Co as the impurity)

23. Alternative: Metal hydrides Volume of the tank for 4 kg H 2 Schlapbach and Züttel, Nature 414, 353 (2001)

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

25. Hydrogen on demand™ NaBH 4 + 2 H 2 O 4 H 2 + NaBO 2 10.8 % 25wt.% NaBH 4 in H 2 O, 2 % NaOH Kat. H2H2 NaBO 2 in H 2 O Advantages: Liquid fuel as conventional harmless without catalyst

26. Hydrogen on demand in practice

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

28. Consequently:

29. Reversible Hydrides: Requirements As low as possible (ball park figure: 100 €/kg H 2 ) Cost Ideally absentMemoryeffect > 500Cycle stability As high as possible, i.e. no ignition with air or moisture Safety As low as possible (but related to equilirium pressure) Heat effects Around 1 bar at room temperatrueEquilibrium pressure < 50 barRehydrogenations pressure Dehydrogenation < 3 h Rehydrogenation < 5 min De-/rehydrogenationrate > 6.5 %Volumetric storage density > 6.5 %Gravimetric storage density TargetProperty

30. A reversible hydride in technical applications U 212 HDW

31. The „materials landscape“ 0 160 80 120 40 0 5 10 15 20 25 Mg 2 FeH 6 BaReH 6 LaNi 5 H 6 FeTiH 1.7 MgH 2 NaAlH 4 KBH 4 NaBH 4 LiAlH 4 LiBH 4 C8C8 C3C3 C1C1 H 2,l H on C Mass storage density [wt.%] Volumetric storage density [kg H 2 m -3 ] 5 g cm -3 2 g cm -3 1 g cm -3 0.7 g cm -3 3 NaAlH 4 Na 3 AlH 6 + 2 Al + 3 H 2 Ti Na 3 AlH 6 3 NaH + Al + 1.5 H 2 Ti Adapted from Schlapach and Züttel, Nature 414, 353 (2001)

32. The alternative: reversible hydrides 1.5 2.0 2.5 3.0 3.5 4.0 1/T [10 -3 K -1 ] 300 200 100 50 25 0 -20 100 10 1 0.1 Dissociation pressure [atm] MgH 2 Mg 2 NiH 4 Na 3 AlH 6 NaAlH 4 HT MT LT FeTiH LaNi 5 H 6 CoNi 5 H 4 MNi 5 H 6 TiCr 1.8 H 1.7 B. Bogdanovic et al. J.Alloy Compd. 302, 36 (2000)

33. The doping procedure l From solution l By ball-milling NaAlH 4 in Toluene Ti-compound

34. Most advanced system: ScCl 3 in situ doped 0 2 4 6 8 Time / min 108 116 114 112 110 120 160 180 140 Temperature / °C Pressure / bar System heated to 120°C, then pressurized. Capacity: 3.2 %

35. Other Alanates Unsuitable thermodynamics CaAlH 5 possibly useful

36. A Nitride-based system: Li 3 N/LiNH 2 Li 3 N + H 2  Li 2 NH + LiH 5.4 wt.% Li 2 NH + H 2  LiNH 2 + LiH6.5 wt.% at 250°C P. Chen et al., Nature 420, 302 (2004) Problems: Ammonia release Temperature too high

37. Summary and Outlook l Chemical storage systems promising as long term solution l Methanol reforming largely developed, but complex l NaAlH 4 presently most advanced system, but too low capacity l 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? l Probably strong tendency towards increased use of electricity directly, with smart grid technology providing some buffer l Materials based storage and transportation form of energy probably needed nevertheless l Hydrogen has many advantages, at present serious alternatives are methanol and synthetic hydrocarbons l Develop all systems further, until final decision can be made

40. Adam Opel AG Powerfluid FCI DFG 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 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 Further reading: F. Schüth et al., Chem.Commun. 2249 (2004) M. Felderhoff, B. Bogdanovic