Share this article with friends
by Acad. Vladimir RUSANOV, Director, Institute of Hydrogen Energetics and Plasma Technologies, Russian Research Center KURCHATOVSKY INSTITUTE
The traditional power engineering, based on diesel fuel, methane, gasoline, kerosene, etc. now has an alternative-hydrogen energetics. It is based on the process of oxidation of hydrogen by oxygen of the air. This is accompanied by the release of heat (about 3 kWt/h per m3 of H2 ) and the production of water at not so high temperatures. This kind of reaction is obviously "most acceptable" from the ecological point of view.
One of the leading trends in world science now includes studies, development and perfection of methods of H2 production (including that from water and natural carbohydrates). And it is no less important to learn to use this "product" effectively, such as in fuel elements, and improve and perfect methods of its storage, transportation and safe handling. This range of problems relates to the general subject of hydrogen energetics*.
Its "basis" is this lightest of gases (1 m3 weighs approximately 0.1 kg) with small size of molecule (about 0.76 A). It is easily permeable and mobile and enters into a large number of reactions: with carbon, producing a large number of carbohydrates, with metals, producing hydrites; with halogens, oxygen, sulfur and phosphorus; it can be liquefied at a low temperature (of the order of -252°C). And its most remarkable compound associated with oxygen is water. Its vast resources on our planet act as "accumulators" and prac-
* See: V. Rusanov, "Hydrogen-Possibility of Technical Progress", Science in Russia, No. 4, 1998. - Ed.
tically inexhaustible sources of bound (with other substances) hydrogen.
So it looks as if an alternative to the energy crisis has already been found. But the new fuel so far remains rather expensive, which means that problem number one on the agenda is launching large-scale production of inexpensive hydrogen. Our country alone can require for the solution of global economic problems no less than 10 - 20 mn tons of it per year!
The traditional method of H2 production consists in its extraction from water by means of electrolysis. This does not cause considerable increases of temperature and there is a guarantee that the "final product" will be free from admixtures because nitrogen is not oxidized in this reaction. And there are several "types" of electrolysis: classical water-alkaline (on the basis of alkali), hard-oxide (on the basis of zirconium-yttrium ceramics) for temperatures from 800 - 1,000°C), solid-polymer (electrolyte-polymer membrane, transferring protons, i.e. hydrogen ions). The most progressive and accessible of these is the latter one, effective even at increased pressure. It does not require considerable amounts of energy-some 4 kWt/h/m3 H2 , has specific productivity (current density, achieved in the reaction) 1.2 A/cm2 , with the purity of the hydrogen produced being 99.99 percent.
Another possibility of H2 production consists in its extraction from natural fuels-methane, gasoline, kerosene, coal etc. which is characterized, as compared with electrolysis, by still lower energy consumption and considerably (by 2 - 3 times) lower cost of the final product. Let us consider as an example steam conversion (special treatment) of methane. Produced as a result is a mixture of hydrogen with carbon oxide, which, in its turn, is again treated with steam for its transformation into carbon dioxide and hydrogen. Thus closing stage is the transformation of the latter into pure "commercial quality" product. Similar cycles-steam-oxide conversion and partial oxidation of methane (complex process with minimal participation of oxygen) - pass through the similar main stages.
These methods of hydrogen production from the aforesaid organic compounds are now predominant on the world market, supplying more than 90 percent of the output. But all of them, as we can see, have several stages and produced at the closing stage in many cases, together with the required substance, is carbon dioxide and that creates the problem of its utilization.
In 1996 - 2004 researchers of our Institute studied the phenomenon of plasma catalysis of carbohydrates (intensification of their conversion due to special properties of the respective phase, accelerating the reaction). This method needs no traditional catalysts, which are indispensable in all of the aforesaid cases; apart from that, as compared with those other ones, it requires much lower amounts of electricity (up to 0.15 - 0.10 kWt/h/m3 H2 ), and possesses much higher specific productivity and "ecological correctness". Incidentally, systems based on this principle can become, among others, the prototypes of on-board hydrogen generators for cars.
As for energy supply for hydrogen-producing units, it can be arranged from the main power grids and from autonomous networks using, for example, hydrothermal, or hydro-power energy and solar and wind energy as well as that of tides.
A no less important trend in the field of energetics under consideration is the development of a power source of a new type - hydrogen fuel element. And what does it look like? Its cell consists of electrodes separated by a diffusion-dense cation-conducting membrane. Supplied upon them are oxygen (air) and hydrogen. Because of the electrochemical oxidation of the latter there is generated between the cathode and anode an electromotive force, which supports electric current in the outer chain (membrane has a layer of electrocatalysts boosting the process of oxidation). This kind of a power source can, for example, activate a car engine.
There is now a large set of respective fuel elements which differ by the composition of the electrolyte: water-alkaline, phosphorus-acidic, melt-carbonate, hard-oxide and polymer-membrane ones. The most "progressive" of them all is the last one and our Institute is one of its main "designers" in this country. Its basis is a cation-conducting membrane capable of carrying a hydrogen ion through a polymer and operating at 100°C. The efficiency of this kind of a power pack is about 70 percent - approximately two times higher than of an internal combustion engine. Low operating temperature rules out electrochemical oxidation of nitrogen by oxygen and provides for "clean" exhausts consisting of water vapors only. This makes such polymer-membrane fuel elements an optimal ecological choice for automobile transport and for autonomous power supply sources.
But there are still many problems on the way of the practical application of these ideas. Thus, for activating the process of electrochemical oxidation of hydrogen it is necessary to have catalysts (special films on polymer membrane) on the basis of metals of the platinum group (platinum, palladium), although in small amounts - 0.1 mg/cm2 , which makes such fuel elements somewhat more expensive. But the main cost component includes the production of cells-membrane-electrode blocks, and of the polymer membrane itself. As a result the initial price of these new power packs today is 2,000 - 3,000 US doll./kWt, and for large-scale commercial production it has to be reduced at least by ten times.
Intensive R&D work in this area of energetics is now in progress on a world scale. Test models of "hydrogen" automobiles have been developed in the United States, Germany and Japan and some firms, like the German Dymler-Crysler, are planning to launch commercial mass production of new automobiles by 2006.
Now, a look at the possibilities in this country. We can synthesize cation-conducting polymer which is as good as its foreign analogues. The potential of our defense industrial complex makes it possible to produce the necessary equipment of high parameters; the NORILSKY NIKEL* mining and metallurgical combine-the biggest producer of palladium in the world-can supply the strategic raw for the production of catalysts needed for the aforesaid processes. Consequently, Russia does have prospects of launching the production of transport equipment on the alternative types of propulsion. Incidentally, back in the early 1980s our specialists already developed and tested an automobile with hydrogen fuel elements**. Work in this area now continues at the OAO AvtoVAZ.
Summing it up, world progress puts into the forefront the problem of development of hydrogen energetics - the development of automobile transport and autonomous electric power plants on new fuel elements of this kind. This can be a major step forward for the whole of this country's national economy. And Russia does possess everything necessary for dealing with this objective.
* See: Ya. Renkas, "On the Road of Innovations and Investments", Science in Russia, No. 3, 2004. - Ed.
** See: A. Eidelman, "New Engines on Display", Science in Russia, No. 3, 2004. - Ed.
Permanent link to this publication:
LRussia LWorld Y G