Hydrogen The “ Groupless ” Element

1. Hydrogen The “Groupless” Element • Hydrogen has three isotopes: 1H, 99.985%,2D, 0.015% and 3T, ~10-15%. • D2O melts at 3.8 °C,boils at 101.4 °C and is ~10% denser than H2O – hence • the name “heavy water”. • The main use of D2O is to slow down neutrons in nuclear reactors. • Approximately 1000 tons of D2O is also being used as part of a neutrino • detector at the Sudbury Neutrino Observatory (SNO) in Ontario. • It slows down chemical reaction involving H+ • Useful in determining reaction mechanism in • Organic and biochemistry. • It can also be used to determine orientational • Dynamics of water.

2. Tritium • 3T is used as a radioactive tracer in medicine and • biochemistry as it emits low energy βradiation • which does relatively little tissue damage. • The commercial value of 3T, however, • is that it is the fuel for the “hydrogen • Bomb” and Fusion Reactors. • 3T decays to 3He, a rare but very useful isotope. It has a • Lower boiling point than the common 4He, and used in • extreme low-temperature apparati for cryogenic physics.

3. Fuel Cells PEM FUEL CELL

4. Polymer Electrolyte Membrane Fuel Cell Alcohols can be used as fuels in these system. The catalyst and membrane materials are currently being developed

5. Solid Oxide Fuel Cell

6. O2- e- e- Fuel Air Exhaust

7. Fuel Cells could replace • Internal combustion engines (ICE) • Gas Motor Combined Heat and Power (CHP) • Mobile generators • Batteries • Power Stations • On-board Electricity Generation (Auxiliary Power Units, APU)

8. Portable electronic devices Direct Methanol Fuel Cell PDA with methanol fuel capsule H2 – PEMFC for mobile phone with H2 recharging unit Prototype DMFC IBM laptop and DMFC unit

9. Generator Replacements 1 kW portable H2- PEMFC generator DMFC generator with methanol container

10. Fuel Cells for Motive Power in Vehicles Demonstrated • A conventional car has fuel efficiency ranging between 7 to 20 km/l (18 to 50 MPG), or 14 to 5 L/100km • This translates to 6 to 18 m for 1 g of fuel • This is a difference of 1400 to 4000 fold. • >3000 miles in 12 days - Range • 100 mph - Speed/power • -1 -> 35oC – Operating temperature range • World Record Fuel efficiency 25 km for 1 g H2. • Key Targets • Cost $120/kW • Lifetime, reliability

11. Domestic CHP Units CERES POWER SOFC System generates domestic electricity needs and provides heating – overall efficiency > 80%

12. Power Generation on the Mega Watt Scale Rolls Royce 1 MW SOFC system http://www.rolls-royce.com/energy/tech/fuelcells.jsp Fuel Cell Energy Molten Carbonate 0.3 MW system

13. Hydrogen Stands Alone! • Actually, hydrogen belongs to group 1, but it’s not an alkali metal. • It behaves like an alkali metal and like a halogen • Electronegativity of 2.1 which is between Boron at 2, and Carbon at 2.5. • i.e. more electronegative than the metals and less electronegative than the • nonmetals. • As its electron configuration 1s1 it can achieve a “noble gas” configuration by either gaining losing or sharing an electron: • As the H – H bond is extremely strong, 436 kJ/mol, • it is a relatively unreactive molecule. • Even thermodynamically favoured reactions of • hydrogen often require a catalyst to break the • strong H – H bond. Hydrogen does, however, • react with exothermically with oxygen and with fluorine

14. Catalytic Steam Reformation of hydrocarbons. • Methane, CH4, (or some organic material) reacts with steam at 900-1000 • °C to give CO and H2. Then CO reacts with more steam at 400-500 °C in • the presence of catalyst, giving more H2 gas • The purest hydrogen is obtained from the electrolysis of water, but is • prohibitively expensive for large-scale production. • The new fuel??? Alternative to oil?

15. Classes of Hydrogen Compounds • There are three general classes of hydrogen compounds: • Ionic hydrides in which hydrogen combines with elements from groups 1-2 • (except beryllium) to form ionic compounds: • Metallic hydrides (also called interstitial compounds) in which elements • from groups 3-10 “absorb” hydrogen. The hydrogen atoms fill holes in • the metallic lattice, distorting its structure if enough hydrogen is absorbed. • Covalent hydrogen compounds in which hydrogen • combines with elements from groups 11-17 (or beryllium) • to form covalent molecules:

16. Ionic Hydrides • Most ionic hydrides have a crystal structure like NaCl (mono • hydrides) or CaF2 (for dihydrides). • In this case the cations form the main • lattice as they are typically larger • than the hydride anions: • Ionic hydrides are strong bases, • reacting with acids (even those as weak • as water): • Ionic hydrides are typically sold as grey powders • suspended in mineral oil. The oil protects them • from reacting with moisture in the air though it • must be washed off (with solvent) if an accurate • amount is to be weighed. If an ionic hydride is • not stored properly, it turns white. What has • happened?

17. Metallic Hydrides • The hydrogen in metallic hydrides can act • as either “H+” or “H-”: • Transition metals are often used as catalysts for reactions in which • hydrogen is added to a double bond (e.g. hydrogenating vegetable oil to • make margarine). The hydrogen first reacts with the transition metal to • make a metallic hydride (more reactive than hydrogen gas). • The ratio of hydrogen : metal atoms in a metallic hydride is often fractional – not every hole in the lattice contains a hydrogen atom.

18. Covalent Hydrogen Compounds • Most of the “everyday” compounds containing hydrogen are covalent hydrogen • compounds. • When hydrogen is covalently bonded to a less electronegative element (like • aluminum), it has a partial negative charge and may behave like a hydride. • When hydrogen is covalently bonded to an element with similar electro- • negativity(like carbon), it is relatively neutral and tends not to be reactive: • When hydrogen is covalently bonded to a more electronegative element (like • oxygen), it has a partial positive charge and may behave as an acid.