ENERGY AND ENVIRONMENT THE ECONOMY OF HYDROGEN HYDROGEN FOR A GREENER FUTURE from fossil fuels PRODUCTION OF HYDROGEN from electrolysis of water FUEL CELLS Fuel cell vehicles WHAT FUTURE FOR HYDROGEN?
CLIMATE CHANGE HYDROGEN FOR A GREENER FUTURE • The quality of our environment is affected by many factors, amongst which are our personal (and government’s) choices regarding the use of fuels. • Fuels give off numerous emissions that many say are bringing about great climate changes, because of thegreenhouse effect, of global warming. • All economic activity that requires energy consumption contributes to these emissions producinggreenhouse gases.
CLIMATE CHANGE Why are greenhouse gases dangerous for the environment? Greenhouse gas … … is a gas in the atmosphere that freely allows radiation from the sun to reach the earth’s surface, but traps the heat radiated back from the earth’s surface towards space. The heating effect is analogous to the manner in which the glass of a greenhouse traps the sun’s radiation to warm the air inside the greenhouse.
Solutions? CLIMATE CHANGE H 2 Hydrogen has the best potential of becoming the fuel of the future. Hydrogen can be produced from sustainable, renewable sources and may contribute to meeting the growth in world energy demand. Hydrogen is a carbon-free energy carrier. When used in fuel cells, there are no harmful emissions. The use of energy may lead to climate changes. It is thus necessary to make the transition to cleaner and environmentally favourable energy carriers.
H CLIMATE CHANGE Hydrogen for a greener future 2 • Hydrogen may create freedom in the use of energy for transportation, in a similar way that internet made mass communication available to anyone with a PC and a phone line. • Production of hydrogen is relatively simple compared to • processes used to make, obtain, conventional fuels. • As a result, nobody will be able to control the supply of • hydrogen.
H HYDROGEN 2 The economy of hydrogen At the beginning of the seventies, the world energy situation was upset by two events: the Yom Kippur War and the petroleum crisis that ensued and the MIT report on the limits of development. Before After Abundance of energy Run out of energy Low prices High prices Low environmental awareness Environmental movements Consequences Search for new sources of energy Nuclear Renewable
H Hydrogen may be produced from different sources: 2 • Gas:Natural gas or bio-gas hydrogen sources with steam reforming or partial oxidation. • Oil:Hydrogen is produced with steam reforming or partial oxidation from fossil or renewable oils. • Coal:With gasification technology, hydrogen may be produced from coal. • Alcohols:Derived from gas or biomass are hydrogen rich and may be reformed to hydrogen. • Power:Water electrolysis from renewable sources. • Wood:Pyrolysis technology for hydrogen from biomass. • Algae:Methods of utilizing photosynthesis for hydrogen production.
CO + H2O CO2 + H2 CH4 + H2O CO + 3 H2 H HYDROGEN 2 Production of H2 from fossil fuels All fossil fuels can be converted into hydrogen with reactions of reforming or of partial oxidation. At present the most used reaction is the reforming with steam of natural gas: The reaction is endothermic. It requires high temperatures and the use of a catalyst. It is followed by the reaction of water shift … … and by the absorption of the carbon dioxide produced. Reforming reactions have been used for more than a century, in the industrial production of hydrogen (ammonia, petrochemical industry).
How is hydrogen produced by electrolysis? H 2 • In water electrolysis the water molecules are split into hydrogen and oxygen gases. These gases are produced when an electric current flows through an electrolyte from an anode to a cathode. The electrolyte is water mixed with a substance to optimize electrical conductivity. • The hydrogen and oxygen gases produced are separated, purified, compressed and stored in gas bottle battery banks or other storage vessels.
2H2O 2H2 + O2 H HYDROGEN 2 Production of H2: electrolysis of water With an electrochemical system functioning in reversal to the generator (electrolyser) the following reaction takes place: Because the reaction is not spontaneous, energy is provided: water is decomposed into its elements supplying electric energy. The electrolysis of water is used in order to produce small amounts of very pure hydrogen, or in specific situations such as India, Aswan and Norway. Its possibility to be integrated with the production of electrical energy from renewable sources is very interesting because it could reduce the cost of storage and transport and make its use easier.
H FUELCELLS 2 Fuel cellsare electrochemical systems able to convert chemical energy coming from a fuel directly into electric energy. A fuel cell operates like a battery as it produces electricity (energy) through an electrochemical process. But unlike the battery, it consumes substances from the surrounding air and therefore is able to work continuously without interruption until a fuel (hydrogen or methanol) and an oxidiser (oxygen or air) have been produced. Electricity is produced from the chemical reaction between hydrogen and the oxygen which is pumped into the fuel cell from the surrounding air.
H FUEL CELLS 2 • There are several types of fuel cells with different features and grades of development. • Fuel cells are classified either according to type of electrolyte: • alkaline - AFC • polymer electrolyte – PEFC • molten carbonate – MCFC • phosphoric acid – PAFC • solid oxide - SOFC • or to the operative temperature (high and low temperature).
- Anode material: platinum • + Cathode material: activated Ni • Cells material: graphite, plastic • Supply: pure oxygen and hydrogen at • moderate pressure • + Cathode H2 + 2OH- 2 H2 O + 2e • - Anode ½ O2 + H2O + 2e 2OH- • Total reaction H2 + ½ O2 = H2O Anode - Cathode + Electrolyte FUEL CELLS ALKALINE CELL (AFC) This type of FC directly converts chemical energy into electric energy. Electrolyte: KOH 30-40 % watery; temperature: 80 – 100 C
ALKALINE CELL (AFC) Cathode + Anode - O2 H2 O2 H2 + steam Electrolyte
FUEL CELLS H 2 POLYMER ELECTROLYTE FUEL CELL (PEFC) • This fuel cell consists of two thin, porous electrodes, an anode and a cathode, separated by a polymer membrane electrolyte that passes only protons. • Catalysts coat one side of each electrode. • After hydrogen enters, the anode catalyst splits it into electrons and protons. • The electrons travel off to power a drive motor, while the protons migrate through the membrane to the cathode. • Its catalyst combines the protons with the returning electrons and oxygen from the air to form water. Picture
H FUEL CELLS 2 Areas of application of fuel cells: Isolated application 0.5 – 10 kW Joint generation 50kW – 2MW Supply power 2 – 20 MW Transport 5 – 200 kW
H FUEL CELLS 2 Environmental impact of fuel cells The chart below compares the production of pollutants per kWh of energy (electricity)produced in normal power systems, with the production of a fuel cell power system using hydrogen obtained through reforming of natural gas. Pollutant Traditional SystemFC CO2 (g) 500 - 900 250 NOx (mg) 550 - 2400 50 SO2 (mg) 200 – 1200 50 Dusts (mg) 40 – 180 20 Noise very low
FUEL CELL VEHICLES H 2 The use of hydrogen fuel cell cars and trucks could help ensure a future in which personal mobility – the freedom to travel independently – could be sustained indefinitely, without damaging or destroying the environment or depleting Earth’s natural resources. This new technology could help solve the increasingly frequent environmental emergencies, created by city traffic: if we want to continue to drive, in our own vehicles, on the roads then we must change the way we power them.
H FUEL CELL VEHICLES 2 • It requires energy to extract hydrogen from substances, which is done either by reforming hydrocarbon molecules with catalysts or by splitting water with electricity. • This energy has to come from somewhere. Some generation sources (such as natural gas, oil, coal burning, power stations, etc.), produce carbon dioxide and other greenhouse gases. • Other methods of producing energy do not produce as many or, in some cases, any greenhouse gas.
H FUEL CELL VEHICLES 2 • When using pure hydrogen, a fuel-cell car is a zero-emission vehicle. This solution is, therefore, ideal for urban transport in highly polluted areas. However there is the problem of where and how the hydrogen is produced, as this is a process which could create pollution. • If the hydrogen is produced on board a vehicle by reforming fossil fuels some, but less, SO2, NOx emissions, dust and hydrocarbons are produced than would be by an internal combustion engine. For carbon dioxide the values (expressed in g/km) are: DIESEL 150 PETROL 200 FC NG 60 * FC PETROL 90** Considering the environmental impact the ideal solution is the production of hydrogen from renewable sources. *Fuel cell using natural gas; ** fuel cell using petrol
H How fuel cells work in a vehicle? 2 • Fuel cells convert hydrogen gas into electricity cleanly, making non polluting vehicles, powered by electric drive motors, possible. Not only would cars become cleaner, they could also be safer, more comfortable, more personalised – and even perhaps less expensive to buy and to run. • Furthermore, these fuel-cell vehicles could be help make a shift towards a “greener” energy economy based on hydrogen, revolutionising the energy industry.
H How fuel cells work in a vehicle? 2 • To understand why this technology could be so revolutionary, consider the operation of a fuel-cell vehicle, a vehicle with an electric traction drive. The motor gets power from a fuel-cell unit and not from an electrochemical battery. • Electricity is produced when electrons are stripped from hydrogen fuel travelling through a membrane in the cell. The resulting current runs the electric motor, which turns the wheels. The hydrogen protons then combine with oxygen and electrons to form water.
H How fuel cells work in a vehicle? 2 • Fuel cell cars are considered clean because they do not give off harmful emission. Indeed, their only by-products are heat and water (and if the fuel is methanol, carbon dioxide too). • Electricity produced by the chemical reaction in a single fuel cell has got too little voltage to be useful, so several fuel cells are combined to form a fuel stack, and produce a higher voltage. • Then, stacks can be combined in • modules to obtain a generator with even • higher voltages.
H HYDROGEN FOR A GREENER FUTURE 2 • Hydrogen could be the fuel of the future. But many obstacles have yet to be overcome before it will be able to match the expectations regarding convenience and performance, that customers have come to expect from internal combustion cars. • One of the biggest hurdles is to develop safe and effective onboard hydrogen storage technology. There are various ways of storing hydrogen, including liquid, compressed gas and solid-state methods (metal-hydride storage). All have potential, but pose problems. • A longer-term solution could come from nanotechnology (for example • the nanostructure of carbon), but nano materials for FC will likely take • years to be developed.They are often isolated molecules whose • properties arise from limited interactions.
Hydrogen will remain only a potential fuel for the future unless an energy supply system is developed (hydrogen fuelling infrastructure). HYDROGEN FOR A GREENER FUTURE H 2 • Large numbers of fuel cell vehicles must have adequate fuel available to run them. • A potentially costly hydrogen generation and distribution network is a prerequisite to commercializing fuel cell cars and trucks, but we won’t be able to create the required infrastructure unless there are significant numbers of FC vehicles on the roads. • Key solutions can be subsidy funding, incentives for developing refuelling stations, creation of uniform standards and more general education about this topic.
A hydrogen refueling station for cars and buses in Reykjavik, Iceland