Hydrogen: Number One Element, Number One Fuel
Dr. Tim Mays, Department of Chemical Engineering, University of Bath
Gro Harlem Brundtland (20 April 1939) is a Norwegian Social democratic politician, diplomat, and physician, and an international leader in sustainable development and public health. She has said that sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.
In 1983, Brundtland was invited by then United Nations Secretary-General Javier Pérez de Cuéllar to establish and chair the World Commission on Environment and Development (WCED), widely referred to as the Brundtland Commission, developing the broad political concept of sustainable development.
Source: World Bank. Economic growth puts a great strain on resources.
Increasing Energy Demand
Source: International Energy Agency. 1 quad = 1 quadrillion Btu = 1015 Btu =1.055 x 1018 J = 1.055 EJ; 528 EJ world energy consumption in 2009 ↔ 16.7 TW globally or 2.5 kW per person on average.
You can see from the above graphs that population growth and economic growth have, not surprisingly, caused an increasing energy demand.
Energy can’t be created or destroyed it simply gets moved around.
Energy Supply and Demand
The above left pie chart shows the primary energy supply and the above right pie chart shows the energy demand. We need more oil and gas than can supplied. Mtoe stands for million tons of oil equivalent (if using imperial units).
Enhanced Greenhouse Effect and Climate Change
Svante August Arrhenius (19 February 1859 – 2 October 1927) was a Swedish scientist, originally a physicist, but often referred to as a chemist, and one of the founders of the science of physical chemistry. He received the Nobel Prize for Chemistry in 1903. The Arrhenius equation, lunar crater Arrhenius and the Arrhenius Labs at Stockholm University are named after him.
He developed a theory to explain the ice ages, and in 1896 he was the first scientist to attempt to calculate how changes in the levels of carbon dioxide in the atmosphere could alter the surface temperature through the greenhouse effect.
400 pm CO2 is considered a danger point. Arrhenius predicted the temperature increase.
Marion King Hubbert (October 5, 1903 – October 11, 1989) was a geoscientist who worked at the Shell research lab in Houston, Texas. He made several important contributions to geology, geophysics, and petroleum geology, most notably the Hubbert curve and Hubbert peak theory (a basic component of Peak oil), with important political ramifications. He was often referred to as “M. King Hubbert” or “King Hubbert”.
(Actually running out of fuel is not a problem. The flooding caused by global warming will get us first)
The Hubbert peak theory says that for any given geographical area, from an individual oil-producing region to the planet as a whole, the rate of petroleum production tends to follow a bell-shaped curve.
The Hubbert curve is an approximation of the production rate of a resource over time. Basing his calculations on the peak of oil well discovery in 1948, Hubbert used his model in 1956 to create a curve which accurately predicted that oil production in the contiguous United States would peak around 1970.
The actual shape of a graph of real world production trends is determined by various factors, such as development of enhanced production techniques, availability of competing resources, and government regulations on production or consumption. Because of such factors, real world Hubbert curves are often not symmetrical.
Also: Hubbert Science 108 (1948) 589 and Hubbert Science 109 (1949) 103
With population and economic growth, increased energy demand, climate change and the fact we are running out of fossil and nuclear fuels can hydrogen help? It can, but not on its own.
Hydrogen: The Element
Atomic and Molecular Hydrogen
High excited stages are required to give the Bohr model.
There exists two different spin isomers of hydrogen diatomic molecules that differ by the relative spin of their nuclei. In the orthohydrogen form, the spins of the two protons are parallel and form a triplet state with a molecular spin quantum number of 1 (½+½); in the parahydrogen form the spins are antiparallel and form a singlet with a molecular spin quantum number of 0 (½–½).
Hydrogen is the simplest, smallest and lightest of all atoms. It was the first element formed in the Big Bang 13.7 billion years ago and remains the commonest element in the observable Universe (75 % by mass, 90 % by number of atoms).
Hydrogen is the third commonest element on the Earth’s surface but almost all of it is contained in chemical compounds.
1) In normal conditions free hydrogen is a colourless, odourless, tasteless, diatomic gas (H2) and it is an asphyxiant in very high concentrations.
2) Hydrogen combines with oxygen to produce water and energy. The word stems from the French: hydrogène, and Greek: hydro = water, genes = to beget).
3) In normal conditions the density of H2 is 0.08 g/L (air is 1.2 g/L).
4) Its normal boiling point is -253 °C and the density of liquid hydrogen is 71 g/L (water is 1,000 g/L).
5) The normal melting point is -259 °C and the density of solid hydrogen is 88 g/L (ice is 917 g/L).
6) H2 costs about 3x the cost of methane used to make it.
7) 1 kg H2 contains about the same energy as a gallon of petrol.
The history of hydrogen
Hydrogen has a high energy density. The first internal combustion engine was fuelled by hydrogen.
Hydrogen Chemical Energy
hydrogen + oxygen → water + energy
H2 + ½ O2 → H2O
Energy = 120 – 142 MJ kg-1 heat (combustion) = 1.23 V electrical potential + 24 MJ kg-1 heat (fuel cell)
The difference in energy is due to the different states: 120 MJ kg^-1 for gaseous water and 142 MJ kg^-1 for liquid water (3 times the energy obtained from fossil fuels).
Hydrogen forms very strong bonds.
Note: Only material product of the above reaction is water (Compare this with hydrocarbon + oxygen → water + carbon dioxide + energy)
A lot of energy per unit mass of hydrogen (Compare this with 40 to 55 MJ kg^-1 for combustion of hydrocarbons).
Electrolysis of water can be damaging if you use fossil fuels to generate the electricity.
The Carnot cycle is a theoretical thermodynamic cycle proposed by Nicolas Léonard Sadi Carnot in 1823 and expanded by in the 1830s and 40s. It can be shown that it is the most efficient cycle for converting a given amount of thermal energy into work, or conversely, creating a temperature difference (e.g. refrigeration) by doing a given amount of work. The efficiency of heat engines is dictated by the Carnot efficiency.
Nicolas Léonard Sadi Carnot (1 June 1796 – 24 August 1832) was a French military engineer and physicist, often described as the “father of thermodynamics”.
Jules Verne: The Mysterious Island (1874
“Yes, but water decomposed into its primitive elements,“ replied Cyrus Harding, “and decomposed doubtless, by electricity ——- . I believe, then, that when the deposits of coal are exhausted we shall heat and warm ourselves with water. Water will be the coal of the future”.
Jules Gabriel Verne (8 February 1828 – 24 March 1905) was a French novelist, poet, and playwright best known for his adventure novels and his profound influence on the literary genre of science fiction.
Hydrogen fusion inside the stars is very successful but the fusion experiments on Earth such as the International Thermonuclear Experimental Reactor (ITER) Caderache, SW France have not produced a single joule of energy.
Hydrogen (Chemical) Energy System
Hydrogen Energy Chain
30% efficiency is rather low but this isn’t an excuse not to do it.
Hydrogen End Use
The heat from hydrogen when it is burned can generate power in an: Internal combustion engine; Gas turbine; Jet engine; Rocket
The aim is to replace kerosene with hydrogen.
Electricity from hydrogen fuel cells can be used in vehicles in addition to the way electricity is used now.
Fuel cells are intrinsically more efficient than heat engines but costs need to be brought down and reliability and lifetimes need to be increased.
Hydrogen Fuel Cell
A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel.
There are two ways in which this can be done.
The less sensible involves burning fossil fuels to produce the electricity;
The electricity is transferred to our houses or a power point via the national grid;
The electric car is then plugged into the electricity supply. The process has a very poor efficiency and produces carbon dioxide;
The more sensible way would be to remove the hydrogen from any fossil fuel or water. It could be argued that this is not sensible in that electricity has to be used at some point in the process but you can use the electricity at any time of the day including night time when nobody will be using it (electricity has to be generated throughout the day as it is very difficult to start and stop the processes involved).
The hydrogen would need to be liquefied and stored in pressurized and thermally insulated containers.
The hydrogen would be used in a hydrogen fuel cell.
Honda 2008 FCX Clarity.
Fuel Cell Electric Vehicle (FCEV) is a type of hydrogen vehicle which uses a fuel cell to produce electricity, powering its on-board electric motor. Fuel cells in vehicles create electricity to power an electric motor using hydrogen (produced in one of several ways) and oxygen from the air.
Managing Renewable Electricity
Use the excess electricity to produce hydrogen. This is grid balancing.
Load balancing, load matching, or daily peak demand reserve refers to the use of various techniques by electrical power stations to store excess electrical power during low demand periods for release as demand rises. The goal would be for the power supply system to see a load factor of 1.
Unst is one of the North Isles of the Shetland Islands, Scotland. It is the northernmost of the inhabited British Isles and is the third largest island in Shetland after the Mainland and Yell. It has an area of 46 square miles (120 km^2).
It is also the home to the Promoting Unst Renewable Energy (PURE) Wind Hydrogen project, a community-owned clean energy system based on hydrogen production. This project is part of the Unst Partnership, the community’s development trust.
The graph above right shows how the electricity can be used to produce hydrogen when demand is low and the hydrogen in turn can be used to produce electricity when demand is high. We could even have hydrogen cells in the house.
Interim Observations about hydrogen
There are many possible sources of hydrogen.
Hydrogen can only ever yield as much energy as was used to produce it in the first place.
Hydrogen moves energy around (like electricity); strictly it is an energy vector or carrier
There is no CO2 at the point of use
Produces lots of energy per unit mass
Is creating new industries and supporting current ones
… but challenges remain including
Need sustainable production;
Need storage and distribution facilities;
Need to increase the numbers of end uses.
Cost and affordability – making the cost of producing it low enough to make it affordable.
Awareness and acceptability – making people and industry aware of it and accept it.
Safety, regulation, codes and standards – that is making the process and use safe and setting up regulation, codes and standards to make it so.
So the issues are:
Economics, safety (remember the Hindenburg), regulation, codes, standards, public awareness and acceptability, policy, infrastructure and Storage?
Energy security means the provision of affordable energy to society on demand
Hydrogen and hydrogen energy systems are currently expensive
But can we afford NOT to use hydrogen and other sustainable energy technologies?
The Stern Review (2006) claims that investment of 1% of GDP to manage climate change should be set against a likely 20% reduction in GDP if we do nothing
UK energy policy has no mention of hydrogen
Hydrogen has wide flammable range 4% – 75%
Range for natural gas is 4% – 15%
Range for gasoline is 1.4% – 5.6%
Very low ignition energy
Potential for detonation
Nearly invisible flame
Evidence of spontaneous ignition from venting
Chemicals industry has been using hydrogen safely on a large scale for many years.
Has developed procedures and standards but may not be relevant to new uses
“New” industry may operate in less well-controlled situations
There is evidence (Flynn, 2007) that public awareness of energy and climate change is widespread
But not so with the use of hydrogen which too many – even policymakers – is associated with the H-bomb and the Hindenburg if it registers at all
Hydrogen is better known in some areas (e. g. Teeside, Birmingham, S Wales) where there are visible and well-known hydrogen activities
Where concern is expressed, it is often about safety
Clear need for information on, understanding by and reassurance of both the public and policymakers on hydrogen energy.
UK Energy Policy
UK Energy Policy largely set by
Energy White Paper (2007) and The UK Low Carbon Transition Plan (2009) but there is no mention of hydrogen.
Courtesy: Air Products
The challenge is to store hydrogen in small, light containers as it has a very low density. It can be used as a liquid or a compressed gas.
Future methods of storage could include: Chemical storage; Storage in porous solids; Power to gas (electrolytic H2 mixed with natural gas); Underground storage.
Underground hydrogen storage is the practice of hydrogen storage in underground caverns, salt domes and depleted oil/gas fields. Large quantities of gaseous hydrogen have been stored in underground caverns by ICI for many years without any difficulties. The storage of large quantities of hydrogen underground in solution-mined salt domes, aquifers or excavated rock caverns or mines can function as grid energy storage which is essential for the hydrogen economy. Up to 10% natural gas is safely stored this way.
Cryo-adsorption is proving to be very interesting.
Cryo-adsorption is a method used for hydrogen storage where gaseous hydrogen at cryogenic temperatures (150 – 60 K) is physically adsorbed on porous material, mostly activated carbon. The achievable storage density is between liquid hydrogen (LH2) storage systems and compressed hydrogen (CGH2) storage systems.
The activated carbon has already been used in the healing of wounds and during the cold war Russia used it to take up radioactive nuclei.
Metal-Organic Frameworks are compounds consisting of metal ions or clusters coordinated to often rigid organic molecules to form one-, two-, or three-dimensional structures that can be porous. Metal-organic frameworks represent another class of synthetic porous materials that store hydrogen and energy at the molecular level. MOFs are highly crystalline inorganic-organic hybrid structures that contain metal clusters or ions (secondary building units) as nodes and organic ligands as linkers.
acre = 4,046 m^2 hectare = 10,000 m^2
For cryo-adsorption the structure of the absorber consists of an arrangement of Cu3BTC2 (copper (II)-benzene-1,3,5-tetracarboxylate). The copper sits in the centre of the benzene ring. The space within is 2nm across (about 2 atomic diameters) and acts like a sponge. This is where the hydrogen is stored at low temperatures.
In 2006, chemists at UCLA and the University of Michigan have achieved hydrogen storage concentrations of up to 7.5 wt% in MOF-74 at a low temperature of 77 K.
Power to Gas
Underground Hydrogen Storage
Underground hydrogen storage is the practice of hydrogen storage in underground caverns, salt domes and depleted oil/gas fields.
Hydrogen & Fuel Cell Research Hub
Penultimate Word including some difficult stuff
Common nanoporous materials
Activated carbon materials, Zeolites, polymers, and metal-organic frameworks
Metal-Organic Frameworks (MOFs) are compounds consisting of metal ions or clusters coordinated to often rigid organic molecules to form one-, two-, or three-dimensional structures that can be porous.
The pores are stable and can be used for the storage of gases such as hydrogen.
(a) Hydrogen production and storage by renewable resource, (b) hydrogen storage in metal doped carbon nanotubes, (c) storage in mesoporous zeolite: by controlling the ratio of different alkali metal ions (yellow and green balls), it is possible to tailor the pressure and temperature at which hydrogen is released from the material, (d) hydrogen storage in metal–organic framework (MOF)-74 resembles a series of tightly packed straws comprised mostly of carbon atoms (white balls) with columns of zinc ions (blue balls) running down the walls. Heavy hydrogen molecules (green balls) adsorbed in MOF-74 pack into the tubes more densely than they would in solid form.
Above left shows a unit cell of sodium zeolite with cage and cavity and above right shows hydrogen gas (red) adsorbed in an array of carbon nanotubes (grey). The hydrogen inside the nanotubes and in the interstitial channels is at a much higher density than that of the bulk gas.
Above left shows the structure and possible cation sites in zeolite faujasite containing aluminium and above right shows eight units surrounding a pore (yellow ball represents space available in pore) in the metalorganic framework called MOF-5. Each unit contains four ZnO4 tetrahedra (blue) and is connected to its neighboring unit by a dicarboxylic acid group.
Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. This process differs from absorption, in which a fluid (the absorbate) permeates or is dissolved by a liquid or solid (the absorbent). Note that adsorption is a surface-based process while absorption involves the whole volume of the material. The term sorption encompasses both processes, while desorption is the reverse of adsorption. It is a surface phenomenon.
The Langmuir adsorption model is the most common model used to quantify the amount of adsorbate adsorbed on an adsorbent as a function of partial pressure or concentration at a given temperature. It considers adsorption of an ideal gas onto an idealized surface. The gas is presumed to bind at a series of distinct sites.
Brunauer–Emmett–Teller (BET) theory aims to explain the physical adsorption of gas molecules on a solid surface and serves as the basis for an important analysis technique for the measurement of the specific surface area of a material. In 1938, Stephen Brunauer, Paul Hugh Emmett, and Edward Teller published the first article about the BET theory in the Journal of the American Chemical Society.
Hydrogen pore volumes
Hydrogen stored in the pores
Notts are metal-organic frameworks for storing hydrogen.
Bar is a non SI unit of pressure (100000 Pa = 0.1 MPa).
The slip model is a model of the molecular interaction between gas particles and the solid-surface atoms. It involves the kinetic theory of gases and van der Waals force (there are other factors involved if there is a chemical reaction between hydrogen and the surface). It is about hydrogen diffusing into the solid by slipping over a surface and into any cracks, dislocations and pores.
In physical chemistry, the van der Waals force (or van der Waals interaction), named after Dutch scientist Johannes Diderik van der Waals, is the sum of the attractive or repulsive forces between molecules (or between parts of the same molecule) other than those due to covalent bonds, the hydrogen bonds, or the electrostatic interaction of ions with one another or with neutral molecules or charged molecules.
23 November 1837 – 8 March 1923
The above graph shows how different conditions affect the density of hydrogen
The graphs below show how the volume of gas in a pore can affect how much is actually adsorbed.
Carbon-based adsorbents suggested for hydrogen storage include carbon nanotubes (CNTs), graphite nanofibers (GNFs), activated carbons (ACs), templated carbons (TCs), etc. Studies have shown that high surface area carbons (above 2000 m2/g) may store 5~10 wt % of hydrogen. However, these storage capacities are only observed at low temperatures (77 ~ 180 K) due to the weak interaction between hydrogen molecules and the material. At room temperature, the storage capacity drops to less than 1 wt% at 4 MPa (1 bar = 0.1 MPa)
When considering carbon nanotubes when all errors are minimized or eliminated from the measurements, the hydrogen storage capacities are below 0.3 wt % at 298 K and 10 MPa. This is far too low when considering other methods of hydrogen storage.
The hydrogen storage capacity of graphite Nanofibres was only 0.34 wt% at 77 K and 20 bar and 0.02 wt% at 300K and 20 bar.
Zlotea, C., Moretto, P. & Steriotis, T. A Round Robin characterisation of the hydrogen sorption properties of a carbon based material. Int J Hydrogen Energ 2009 34, 3044-3057.
Carbon graphite, graphene and activated carbon are possibilites for hydrogen storage.
The Clausius–Clapeyron relation, named after Rudolf Clausius and Benoît Paul Émile Clapeyron, is a way of characterizing a discontinuous phase transition between two phases of matter of a single constituent.
Zn4O units bridged by benzenedicarboxylate linkers.
Experimental excess isotherm: Poirier and Dailly, J Phys Chem C 112 (2008) 13047
The adsorption isotherm gives the amount of gas adsorbed in the nanopores as a function of the external pressure.
Excess adsorption is the number of molecules in the nanopores in excess of the amount that would be present in the pore volume at the equilibrium density of the bulk gas.
The adsorption isotherm for a pure gas is the relation between the specific amount adsorbed n (moles of gas per kilogram of solid) and P, the external pressure in the gas phase.
Adsorption isotherm describes the equilibrium of the adsorption of a material at a surface (more general at a surface boundary) at constant temperature.
Langmuir isotherm, Langmuir adsorption equation or Hill-Langmuir equation relates the coverage or adsorption of molecules on a solid surface to gas pressure or concentration of a medium above the solid surface at a fixed temperature.
Simulated total adsorption: Courtesy of Fröba Group (Michael Fischer), Department of Chemistry, University of Hamburg, Germany.