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When will the hydrogen age arrive?

Everywhere and yet nowhere, hydrogen abounds in the Universe and in the media, where it promises to power the fuel cells of tomorrow’s cars. Hydrogen is highly reactive and virtually impossible to find on Earth in a molecular state. However, since it can be isolated, stored and transported, hydrogen is set to become the number-one clean energy carrier of the future.

Développement de nouveaux catalyseurs pour pile à combustible. © CNRS Photothèque/Emmanuel Perrin
Development of new catalysts for fuel cells. © CNRS Photothèque/Emmanuel Perrin
Nanocornets de carbone, formant des structures de 80 à 100 nm de diamètre, qui pourraient offrir une solution de stockage efficace et sûre de l’hydrogène. © CNRS Photothèque/Fabienne Warmont
Carbon nanohorns, forming structures 80–100 nm in diameter, which could offer a solution for the safe and efficient storage of hydrogen. © CNRS Photothèque/Fabienne Warmont
Grain d’hydrure (éponge à hydrogène) observé par microscopie à balayage, montrant la fracturation du composé intermétallique suite à l’insertion d’hydrogène. L’utilisation de ce matériau est étudiée dans l’élaboration du réservoir d’hydrogène des piles à combustible. © CNRS Photothèque/Jean-Marc Joubert
Grain of hydride (hydrogen sponge) seen under a scanning microscope, showing the fracturing of the intermetallic compound after. © CNRS Photothèque/Jean-Marc Joubert
<strong>Production d’hydrogène électrocatalysé </strong>par des complexes de cobalt. © CNRS Photothèque/Emmanuel Perrin
Electrocatalytic hydrogen evolution by cobalt complexes. © CNRS Photothèque/Emmanuel Perrin

With one electron and one proton, hydrogen is the simplest and most abundant chemical element in the Universe, of which it is estimated to represent more than 75% of the elemental mass. The Sun and most of the stars are composed mainly of hydrogen.

What is more, the energy emitted by these stars comes from the thermonuclear fusion of hydrogen. Traces of hydrogen, a colourless, odourless, tasteless diatomic gas with the molecular formula H2, can be found in the atmosphere. As it is highly reactive, it bonds easily with other elements to form compounds such as water, sugar, proteins and even hydrocarbons.

At present, H2 is used mainly by the petrochemical industry to produce ammonia.

However, in the future it is planned to use hydrogen as an energy carrier like electricity, with the enormous advantage that it is easier to store than electricity.

Cells come up trumps

In a bid to escape the era of fossil energies, especially in the transport sector, all eyes are turned to the electric car. However, conventional storage batteries have serious drawbacks.

Apart from being rather bulky and having very limited autonomy, they tend to water. This ‘miracle’ is produced in the electro – the H+ ions cross the electrolyte to join the oxygen. As this is a highly exothermic reaction and yields an energy efficiency of up to 60 % (compared with 20–30% for conventional combustion engines), it can be envisaged for a range of highly attractive applications, especially cars.

The fuel cell concept was discovered by William R. Grove in 1839 but lay in a drawer gathering dust until the 1960s, when NASA retrieved it for the Gemini and Apollo space programmes. After that, the prospects for the fuel cell grew, and several cell variants emerged, either using different types of electrolyte, different operating temperatures or ‘fuels’ other than hydrogen (1). In the 1990s, the car industry released its first high-performance prototypes. Their proton exchange membrane fuel cells (PEMFC) use a platinum catalyst to reduce the reaction temperature to between 80°C and 100°C. At present, researchers are also investigating less expensive catalyst materials.

However, numerous obstacles stand in the way of creating a real hydrogen fuel chain in the transport sector: unlike oil, the ‘fuel’ in fuel cells does not actually exist on the planet, and the reactivity of this volatile gas raises safety issues for storage, transportation and distribution.

Snags with hydrogen production

At present, hydrogen is produced by its main consumers – that is to say, oil refineries and fertiliser factories. It is produced using one of three techniques for decomposing hydrocarbon: steam reforming, partial oxidation and autothermal reforming. Steam reforming involves dissociating carbonaceous molecules in the presence of steam and heat.

Although steam reforming offers high energy efficiency of 40%, it is an endothermic technique.

Partial oxidation is a reaction from the combustion of hydrocarbons. Although it has the advantage of being exothermic, partial oxidation produces less hydrogen. Autothermal reforming is a combination of the latter two techniques: the heat released by partial oxidation is fed back into the steam-reforming process to enhance energy efficiency.

However, not only do these techniques rely on a dwindling supply of hydrocarbons, they also produce greenhouse gases. In order to set ourselves on the path to clean and sustainable transport systems, it is therefore crucial to use alternative hydrogen-production techniques.

Hydro-alternative

One such alternative is hydrolysis – the electrolysis of water. When the H2O molecule is subjected to a direct electric current, its H and O components are isolated. The base elements – water and electricity – are available just about everywhere, at least in industrialised countries. However, it requires a lot of electricity to divide one of the world’s most stable molecules at ambient temperature. If the electricity has to come from conventional power stations, the environmental advantage is lost. And, economically speaking, division is not yet cost-effective enough compared with hydrocarbon-based reactions.

This makes high-temperature electrolysis (HTE) a more interesting alternative. At high temperature, the heat provides part of the energy required for the reaction, increasing energy efficiency. HTE consumes less electricity and presents real economic advantages, provided that the heat comes from a natural resource like the Sun.

The challenge of HydroSOL

Would it be possible to produce hydrogen without using electricity at all? This is the challenge that European research has been endeavouring to meet since 2002 with the HydroSOL project, which is 50 % financed by the European Commission. The project is coordinated by the Laboratory of Aerosol and Particle Technology of the Chemical Process Engineering Research Institute at the Centre for Research and Technology-Hellas (CPERI/CERTH) in Greece. Project researchers are developing an innovative thermochemical reactor that produces hydrogen using solar energy alone.

HydroSOL was awarded the European Union Descartes Prize for Research in 2007, as well as the International Partnership for Hydrogen Economy (IPHE) inaugural 2006 Technical Achievement Award. “The theoretical concept is very simple”, ex - plains Athanasios Konstandopoulos, HydroSOL coordinator and director of CERTH. “Con - centrated solar radiation is used to heat water and the resulting steam traverses the reactor, where the hydrogen and oxygen are separated at high temperature by oxidation-reduction.

The economic gains are enormous: the reagents are inexpensive and the sunny regions suited to hosting the solar tower power plants for this clean hydrogen-production met hod tend to be economically depressed areas.” The reactor is a refractory-ceramic monolith capable of absorbing solar radiation and reaching a temperature of 1 100 °C. The steam travels through the reactor’s honeycomb structure with its many tiny parallel channels. Each channel is coated with active nanoparticles which absorb and trap oxygen, leaving the hydrogen to continue on it way. In a second phase, solar heat releases the oxygen from the nanomaterial to regenerate it, allowing a new cycle to commence. “In order to test the reactor, we integrated it into a small pilot concentrated solar power station”, explains Athanasios Konstandopoulos. It was used to produce hydrogen continuously in 40 cycles over the space of two days. This successful project is continuing with HydroSOL-2, launched in 2005, again with European Commission funding. The plan is to inaugurate a 100 kW power station on 31 March 2008 on the site of the Almeria Solar Platform in Spain. The project aims to cut production costs to arrive at a selling price of 6 euro cents/kWh. “After two years of research, we ought then to design, or even build, a 1 MW-capacity pilot power station, which is a scale that is of interest to investors. We want to mass-produce hydrogen at a competitive price in the next 5–10 years”, says the coordinator.

Storing H2

Problems of storage and transportation are also holding back the introduction of hydrogen fuel. 14 times lighter than air, weight for weight, hydrogen contains more than twice the energy of natural gas and nearly three times that of oil. However, the memory of the fire that destroyed the Hindenburg zeppelin near New York in 1937 serves to remind us that this gas raises safety issues, being highly flammable in the presence of oxygen.

Hydrogen can be compressed (250–700 bars) in gas bottles or underground tanks – the most common form of storage. However, it requires energy to place gas under pressure and the storage tanks needed are still too large.

Although liquefaction (at a temperature of -253°C at atmospheric pressure) provides a solution to the volume problem of storing hydrogen, cryogenic techniques are also energy- consuming and require highly insulating storage materials (a field where lighter composites are increasingly supplanting steel).

However, in the future, hydrogen could well be stored in a solid state: a hydride can be made by filling the fractures in light metal alloys with hydrogen ions. Since this absorption reaction is exothermic, the host material then needs to be heated to release the hydrogen.

D.K. Ross, from the University of Salford (UK), is coordinating the European project HyTRAIN (2), a research training network that also provides a multidisciplinary forum to identify new candidate materials for hydrogen storage, as well as methods of synthesising them. “Solid-state hydrogen storage would avoid the risks of high-pressure storage, provided that the absorption/release reactions take place at an acceptable rate, which can be achieved at a moderate temperature”, explains Ross.

A Swiss–Norwegian team participating in the HyTRAIN project recently discovered an unstable form of LiBH4, which could be a useful candidate for solid storage. “However, these materials are still very difficult to handle”, cautions D.K. Ross. “The HyTRAIN project is also paving the way for hybrid tank designs that combine the solid storage and pressurised gas methods. The potential for solid hydrogen will be enormous if hydrogen energy takes off.

Nanostructured materials could be bulk stored for use in refuelling stations, for example.”

When will the hydrogen economy arrive?

A total of €470 million from the budget of the European Union's Seventh Framework Programme for 2007–13 (FP7) has been earmarked for research into hydrogen and fuel cells. According to several estimates, this new clean-energy carrier will start to replace hydrocarbons in the transport sector and stationary applications as from 2020. By then, Europe expects be using hydrogen to cover 5% of energy requirements for its transport sector.

This would appear to be a fairly modest objective. Could implementation be speeded up? 17 governments and the European Commission have been working in the IPHE since 2003 to hasten the transition to the running…

Delphine d’Hoop

  1. A cell using methanol for fuel, the direct methanol fuel cell (DMFC), is likely to introduce fuel cells into everyday life, to power telephones, portable computers and multimedia devices. These cells avoid a number of problems associated with hydrogen fuel and are already performing five times better than their lithium-ion counterparts.
  2. Proton Exchanger Membrane Fuel Cell.
  3. HYdrogen Storage Research TRAINing Network.

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Fuel cells in cities

Cellules de piles à combustible «tout solide» (Solid Oxide Fuel Cell) prêtes à être testées. Les chercheurs ont réussi à abaisser de 100 °C leur température de fonctionnement. © CNRS Photothèque/François Jannin Solid oxide fuel cells ready for testing. Researchers have succeeded in reducing their operating temperature by 100 °C. © CNRS Photothèque/François Jannin

In 2006, the first major experiment using hydrogen transport vehicles ended in success. The CUTE (Clean Urban Transport for Europe) project, in which nine European cities participated, involved running 27 buses on fuel cells. More than half of the hydrogen contained in the cells was produced using renewable energy. More than 4 million passengers were transported without a single incident and, more importantly, without any polluting emissions.

The CUTE partners were surprised at the efficiency, life span and reliability of the cells and decided to extend the experiment with HyFLEET:CUTE. The new project involves 31 participants around the world, including Iceland, Australia and China, and has been endowed with a budget of €43 million (€19 million of which comes from the European Commission) for operating some 47 hydrogen-powered buses. “Cooperation with other continents brings great benefits”, explains the project’s coordinator, Monika Kentzler. “It enables us to test the designs under a wide variety of conditions, whilst at the same time showcasing European technology and know-how.” HyFLEET:CUTE aims to develop not only hydrogen-powered vehicles, but also hydrogen-production and refuelling techniques. The cities involved will each set up their own refuelling system. Other techniques are being tested too. For instance, Berlin is operating 14 internal-combustionengine buses powered directly by hydrogen. “The two technologies are close to being marketed”, assures Monika Kentzler. “Although production capacities are still too small to meet the partners’ requirements, we expect to be able to satisfy them by 2015–20.

A significant research effort is also required in the area of infrastructure, to ensure quick, easy and reliable refuelling. In addition, we must develop costs of the hydrogen fuel chain as a whole.”




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