Introduction of Hydrogen Energy

Transcription

1 Introduction of Hydrogen Energy Bing Hung CHEN ( 陳炳宏 ) Department of Chemical Engineering National Cheng Kung University Tainan 70101, TAIWAN E mail: bkchen@mail.ncku.edu.tw Outline Introduction - hydrogen energy Hydrogen production Application of hydrogen energy Hydrogen storage High pressure tanks Liquefied hydrogen Metal hydrides Chemical hydrides NaBH 4 NH 3 BH 3 1

2 Introduction Energy and Environment 3 Ref. Ref. Züttel et al., 010 Introduction Renewable Energy 1. Wind Energy. Solar Energy 3. Geothermal Energy 4. Hydroelectricity / Hydropower 5. Biomass Energy 6. Biofuels: Ethanol & Biodiesel 7. Hydrogen Energy Ref. detail/zh_cn/993/ Ref. Ref. Ref. green living.prositeslab.com/zh tw/1/types ofalternative energy/ Ref. energy/biomassenergy/biomass energy.html Ref. innovation en US/renewableenergy en US/ 4

3 Introduction Renewable Energy 5 Ref. The US Energy Information Administration under the US Department of Energy Introduction Hydrogen Energy Secondary Energy Sources: (US DoE s definition) Secondary energy sources are also referred to as energy carriers, because they move energy in a useable form from one place to another. The two most well known energy carriers are: Electricity Hydrogen We get electricity and hydrogen from the conversion of other sources of energy, such as coal, nuclear, or solar energy. These are called primary sources. 6 Ref. The US Energy Information Administration 3

4 Introduction Hydrogen 1. Hydrogen gas was first artificially produced in the early 16th century, via the mixing of metals with strong acids.. In , Henry Cavendish was the first to recognize that hydrogen gas was a discrete substance. 3. Hydrogen is a concern in metallurgy as it can embrittle many metals complicating the design of pipelines and storage tanks. 4. Hydrogen is highly flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume. 5. Hydrogen is the lightest element ( au). 6. Hydrogen melts at K ( C) 7. Hydrogen condenses to a liquid at temperatures of 0.8K (-5.87 C) 7 Ref. Wikipedia on Hydrogen Application of Hydrogen Energy Ref. Kirubakaran et al., 009 Ref. U.S. Energy Information Administration 4

5 Application of Hydrogen Energy Anode: H H + + e E o = 0V vs SHE Cathode: ½ O + H + +e H O E o = 1.9 V vs SHE Overall reaction: H + ½ O H O E o = 1.9 V vs SHE In real applications: Commonly the PEMFC deliver a voltage in between 0.6 & 0.7 V; while the best performed one could give it around 0.8V. Ref. Kirubakaran et al., 009 Ref. U.S. Energy Information Administration Application of Hydrogen Energy 5

6 Application of Hydrogen Energy Application of Hydrogen Energy 6

7 Introduction Hydrogen Production Thermochemical methods CH H O CO 3H Steam Reforming of Methane CO HO CO H Partial Oxidation of Hydrocarbons (POX) Gasification of Biomass, Coal, or Wastes Sulfur-Iodine (S-I) Cycle Electrolysis of Water Biological Process Other processes 4 13 Ref. Züttel et al., 010 Ref. Ogden., 1999 Introduction Hydrogen Production 14 Ref. [Florida Solar Energy Center (FSEC)] 7

8 Introduction Hydrogen Production Sulfur-Iodine (S-I) Cycle: Recover heat to produce H Net reactions: H O H + O ( ~ 50%) The three reactions that produce hydrogen are as follows: (1) I + SO + H O HI + H SO 4 (393K) ~ Bunsen reaction. () H SO 4 SO + H O + O (1100K ~ 1400K) (3) HI I + H (70K) This S I process is a chemical heat engine. Heat enters the cycle in high temperature endothermic chemical reactions and 3, and heat exits the cycle in the low temperature exothermic reaction 1. The difference between the heat entering the cycle and the heat leaving the cycle exits the cycle in the form of the heat of combustion of the hydrogen produced. 15 Ref. Wikipedia on Sulfur iodine cycle Introduction Hydrogen Energy Property of liquid and gaseous hydrogen: 16 Ref. Midilli et al., 005 8

9 On-Board Hydrogen Storage - USA Targets were set by the FreedomCAR Partnership in January 00 between the United States Council for Automotive Research (USCAR) and U.S. DOE (Targets assume a 5 kg H storage system). The 005 targets were not reached in 005. The targets were revised in 009 to reflect new data on system efficiencies obtained from fleets of test cars. The ultimate goal for volumetric storage is still above the theoretical density of liquid hydrogen. Ref. Hydrogen Storage High-pressure tanks Compressed hydrogen tanks at 5,000 psi (~35 MPa) and 10,000 psi (~70 MPa) have been certified worldwide. Liquefied hydrogen The energy density of hydrogen can be improved by storing hydrogen in a liquid state. Metal hydrides Conventional high-capacity metal hydrides require high temperatures (300 to 350 C) to liberate hydrogen, but sufficient heat is not generally available in fuel cell transportation applications. Chemical hydrides Commonly reactions involve chemical hydrides with water or alcohols, called hydrolysis reactions, to produce hydrogen. Ref. 9

10 Hydrogen Storage 19 Hydrogen Storage 0 Ref. 10

11 High pressure tanks Carbon fiber-reinforced 5,000 psi and 10,000 psi compressed hydrogen gas tanks are under development by Quantum Technologies and others. The inner liner: high molecular weight polymer The intermediate shell: carbon fiber-epoxy resin composite The outer shell: carbon fiber reinforced plastic composite 1 Ref. Quantum Pressurized Storage Tank High pressure tanks For a vehicle running for 500 km, around 5~6 kg of hydrogen has to be stored in the car; that is, the working pressure will be raised at 35~70 MPa inevitably because of the size limitation for the space. Notably, the deviation between ideal and real gases becomes larger with the increase of working pressure. Ref. Eberle et al.,

12 High pressure tanks The disadvantages: 1. High weight of high pressure tanks decreases volumetric capacity (or energy density). The cost of high pressure tanks increases by using high molecular weight polymer than metals. 3. Energy consumption, refueling times and heat management need to be considered. 3 Ref. Ref. The 70MPa high-pressure hydrogen tank Liquefied hydrogen Hydrogen is liquefied and stored at 0.1 MPa and -53 C so that the insulating issue of the system has to be well considered. Currently, under utilization of insulated pressure vessels, around ~3 vol% of hydrogen is observed to evaporate per day, and the first run off of hydrogen is found after 3~4 days in parked cars. Ref. Zhou., 005 Ref. Cumalioglu et al., 008 The pipeline between the vessel and station has to be cool down to around -53 C for ensuring minimizes the loss of hydrogen. 4 1

13 Liquefied hydrogen Concerns: 1. Hydrogen boils-off. Hydrogen liquefaction 3. Volume 4. Weight 5. Tank cost 6. Safety 5 Ref. Ref. Metal hydrides Metal hydrides have the potential for reversible on-board hydrogen storage and release at low temperatures and pressures. The optimum "operating P-T window" for polymer electrolyte membrane (PEM) fuel cell vehicular applications is in the range of 1-10 atm and 5-10ºC. Gravimetric density: CoNi 5 H 6 : 1.1% LaNi 5 H 6 :0.9% low MgH : 7.6% Decomposition temperature too high 6 Ref. Annemieke et al., 008 Ref. 13

14 Metal hydrides Advantages of metal hydride: 1. No high-pressure gas or liquid involved. Safety concern over most existing hydrogen vehicles 3. Ideal for ships, with the extra weight providing to keep the ship stable. 7 Ref. Metal hydrides Metal hydrides could be directly dissociated by chemisorption and electrochemical reactions, as follows: x M + H MH x M + x HO + x e MH x x OH M: metal - - Metal and hydrogen usually form two different kinds of hydrides: α-phase only some hydrogen is absorbed β-phase hydride is fully formed Metal hydrides depends on different parameters and consists of several mechanistic steps. Metals have different ability in hydrogen dissociation, and the abilities depend on surface structure, morphology and purity. 8 Ref. Sakintuna et al.,

15 Metal hydrides Metal hydrides Hydrogen content (wt %) Decompose temperature ( o C) LiH MgH CuH TiH MgNiH TiCr H TiFeH TiMn 1.5 H TiCoH LaNi 5 H Chemical hydrides MH xh O M( OH) xh x x MXH 4H O 4H MOH H XO Chemical hydrides can directly react with water at ambient condition, leading to the generation of high purity of hydrogen with no CO, which can be directly fed into the fuel cell system without any purification. The reaction of NaH and LiH with water is too vigorous that is difficult to control so that is not a good choice to apply for portable device. 30 Ref. Liu and Li., 009; Fakioğlu et al., 004 Ref. Niemann et al., 008 Ref. Çakanyildirim and Gürü.,

16 Chemical hydrides 31 Chemical Hydrides for Hydrogen Storage The advantages of chemical hydrides: Higher purity of produced hydrogen Less energy-loss Lower operation pressure Gravimetric density (wt %) NaBH 4 NH 3 BH H can be released from hydrolysis of NaBH 4 and NH 3 BH 3 could proceed at room temperature. Both hydrolysis reactions can be catalyzed by acids (liquid or solid) or metal catalysts. Ref. Ref. C.H. Liu et al., Novel fabrication of solid-state NaBH 4/Ru-based catalyst composites for hydrogen evolution using a high-energy ball-milling process, Journal of Power Sources 195, (010) Ref. Catalysis 3 in hydrolysis of sodium borohydride and ammonia borane, and electrocatalysis in oxidation of sodium borohydride, Catalysis Today 170, 1- (011) 16

17 Chemical hydrides - NaBH 4 BOH ( ) 3 CHOH BOCH ( ) 3HO NaH B( OCH ) NaBH 3NaOCH Brown-Schlesinger process Na B O 16Na 8H 7SiO 4NaBH 7Na SiO Bayer process MgH NaB4O7 NaCO3 4NaBH4 8MgO CO Modified Bayer process NaBH 4 HO catalyst 4 H NaBO heat(17 kj ) log t1/ ph (0.034T 1.9) 33 Ref. Demirci and Miele., 009 Ref. Kojima and Haga., 00, 003 Ref. Haga and Kojima., 00 Ref. Broja and Schabacher., 1959 Chemical hydrides - NaBH 4 NaBH 4 solutions are nonflammable and can be stable in air for months. Hydrogen production only occurs in the presence of catalysts, even at 0 C, which is beneficial for some rigid regions worldwide. Hydrogen evolution rates are quite easily controlled. The reaction products are safe for the environment owingtotheonlygaseous product is water vapor. The gravimetric as well as volumetric H densities are relatively high. The product is able to be recycled. 34 Ref. Schubert et al., 1957 Ref. Wee., 006 Ref. Kreevoy and Jacobson., 1979 Ref. Marrero-Alfonso et al.,

18 Chemical hydrides - NaBH 4 NaBH 4 > Metal hydrides Liquid > Compressed Volume of 4 kg of hydrogen compacted in different ways, with size relative to the size of a car. NaBH 4 LaNi 5 H 6 Mg NiH 4 Liquefied H Compressed H (00bar) 35 Chemical hydrides Ammonia borane (NH 3 BH 3 or AB) The advantages of NH 3 BH 3 : The inherent hydrogen storage capacity of NH 3 BH 3 is 19.6 wt%. NH 3 BH 3 and its spent product after hydrolysis reaction are rarely toxic and stable. Long-term storage stability. More than 80 days stable in aqueous solution under an argon atmosphere. The smallest volume occupied for hydrogen supply ml for NH 3 BH 3 relative to 7.5 ml for NaBH 4 and 36 ml for liquefied hydrogen at 34 MPa to supply the same amount of hydrogen. Ref. C.H. Liu et al., Hydrogen generated from hydrolysis of ammonia borane using cobalt and ruthenium based catalysts, International Journal of Hydrogen Energy 37, (011) 18

19 Chemical hydrides Ammonia borane (NH 3 BH 3 or AB) Methods of produce hydrogen from NH 3 BH 3 Solid-state thermolysis: ~110 C nnh 3BH 3 NH BH n ~150 C NH BH HNBH n n 500 C n HNBH BN nh nh nh Transient-metal catalyzed dehydrogenation Ionic liquid catalyzed dehydrogenation Hydrothermolysis (thermolysis in solution phase) n Hydrolysis: NH BH H O catalyst 3H NH BO Chemical hydrides Ammonia borane (NH 3 BH 3 or AB) Hydrogen production from NH 3 BH 3 hydrolysis: Proposed hydrolysis reaction of ammonia borane: NH BH H O 3H NH BO catalyst Our previous work (in excess water): NH catalyst 3BH 3 H O 3 3 H NH H BO Our previous work (in limited water): NH BH x H O 3 H m H BO n HBO hydrate NH catalyst Ref. Liu et al., 01 Ref. Chou et al., 01 19

20 Chemical hydrides - NH 3 BH 3 and NaBH 4 Proposed total life cycle of ammonia borane for hydrogen generation. 39 Ref. Liu et al.,