For many city dwellers in China, the past year might have brought back some old memories they had long forgotten, when power cutoffs were a daily occurrence.

Up until the mid 1990s, power shortages were a major problem that plagued not only China's economy but also the daily life of every household.

The situation has been gradually reversed since then, with huge investment in power plants throughout the country gradually easing the problem. Ironically, industry then found itself facing power surplus over the following years, until things suddenly took a sharp turn last summer.

A growing number of provinces were forced to tighten down on power consumption because of the sharply increasing demand from industry. Daily power cutoffs returned, generating a public outcry for new energy sources.

Hydrogen, again, becomes a leading candidate as a clean, renewable energy source and has aroused interest not only among the research community but also among the general public.

Hydrogen burns without producing the sooty pollution and greenhouse gases associated with fossil fuels. Discussion over this matter has become so heated that even elementary school students have been encouraged to contribute to making the dream come true.

Last week, Beijing-based Feichi Luren Company, which specializes in solar energy research, donated 100 models of hydrogen-powered buses to an elementary school, to encourage the students to get involved in the design of hydrogen-powered buses. They claimed that such buses will be available for public transportation by the time of the 2008 Olympic Games in Beijing.

Also last week, Ouyang Minggao, a professor from Tsinghua University, said at an international symposium on hydrogen energy held in Shanghai that China is expecting to manufacture hydrogen- powered buses and cars between 2015 and 2020 that "will be market competitive." Ouyang is a researcher in the Department of Automobile Engineering of Tsinghua.

His words, although they may be a bit disappointing to those eager to see a quick breakthrough, may be regarded by his fellow researchers as bold, or even too bold.

For such vehicles to be market competitive, the hydrogen fuel that powers them must be as cheap and efficient as petrol, said Yu Ying, a researcher from the Beijing-based China University of Petroleum.

Yu has been doing research on hydrogen energy for two decades, focusing on methods to produce hydrogen in cost-efficient ways. "The major problem that impedes the application of hydrogen energy is not that we cannot generate it on a large scale," he said.

"We can do that.

"The real problem is that there is still no practical way to produce hydrogen that is competitive in price with petrol."

Few competitive methods

A variety of methods have been invented to produce hydrogen, which is widely used as an important industrial product, he said.

Unlike oil and coal, pure hydrogen does not exist naturally. The main source of hydrogen production at present is the hydrocarbon molecules in fossil fuel.

Producers generate some 45 million metric tons of hydrogen globally each year from fossil fuels. Almost half of this hydrogen goes to making ammonia, a major component of fertilizer and a familiar ingredient in household cleaners.

Refineries use the second largest chunk of hydrogen for chemical processes such as removing sulfur from petrol and converting heavy hydrocarbons into petrol and diesel fuel.

That situation has to be changed. Not only does the use of fossil fuel for making hydrogen create pollution, but fossil fuels eventually will run out, said Feng Wen, a researcher from the Guangzhou Institute of Energy Research.

"As long as hydrogen has to be produced by burning fossil fuels, you cannot say it is a clean and sustainable energy source," he said.

To make hydrogen a practical source of energy, new methods have to be developed to make hydrogen in a pollution-free manner, Feng added.

One of the best methods developed so far is called electrolysis, which splits water into hydrogen and oxygen with electricity.

Technically, the method has been in place for over 30 years and is able to meet the requirement of large-scale production. But the major problem is that, like using fossil fuels as a production method, the cost remains too high.

There is not only the high cost of the equipment. The consumption of electricity during the process is so enormous that "unless the cost of the electricity were zero, the hydrogen produced using current technologies could not compete with natural gas on the market," said Feng.

Yu from the China University of Petroleum noted that researchers worldwide are working to improve the process using various approaches, but the ultimate solution may lie with the technology of controlled nuclear fusion that may provide a steady and inexpensive supply of electricity for hydrogen production.

Scientists have also been looking into solar energy - using sunlight, the origin of most energy sources on Earth - for a possible answer. Its advantages are obvious. It is clean and renewable.

Trials have been conducted to make hydrogen with electricity generated from solar energy or using certain photocatalysts to break up water with sunlight.

The former approach also faces the problem of high cost, as the cost of electricity generated with solar energy is at least eight times that of natural gas on the present market, according to Feng.

Research on the second approach, known as photocatalysis, has boomed worldwide in recent years because of global energy shortages.

International efforts

Japanese scientist Akira Fujishima and his co-researchers published findings in Nature magazine nearly 30 years ago on their discovery that a type of titanium dioxide can break water molecules into hydrogen and oxygen at room temperature under ultraviolet light.

This discovery opened the door to research on efficient ways to extract hydrogen from water. But research in this area has since progressed slowly, as no satisfactory techniques have been developed for commercial manufacturing.

Visible-light photocatalysts are either unstable, decompose with prolonged use, or are inefficient in splitting water.

But a breakthrough was made last year when a research team from Japan developed a material that uses sunlight to break up water molecules.

Their findings were described in Nature magazine as having paved the way for the day when "hydrogen may be on tap just like natural gas."

Zou Zhigang, a Chinese researcher with the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan, and co- workers have developed a photocatalyst that seems to be very stable, showing no evidence of degradation after extended use.

While the material is not very efficient - over 99 per cent of light energy is wasted rather than used to split water - the findings look good when compared with those of other competitors, the article said.

The new material, like the majority of visible-light photocatalysts, is a metal oxide, containing indium, nickel and tantalum, which generate hydrogen and oxygen when immersed in water in sunlight.

The efficiency of the material generating hydrogen depends on the amount of nickel in it. Zou and his colleagues believe they can improve the efficiency by increasing the surface area of the photocatalyst, by making it porous for example, or grinding it into a fine powder, and by further tinkering with its chemical composition.

China's efforts

Chinese scientists are also picking up pace in the multi-route race.

Two weeks ago, a national research programme was initiated to develop technologies to generate hydrogen on large-scale using of solar energy.

The programme involves researchers from 10 research institutes and hopes to make breakthroughs in a couple of areas, according to Yu, who has been on the expert panel to review the proposal for the programme.

He revealed one of the most likely areas is the biological approach to generating hydrogen with wastewater.

Scientists have found that common sugar, or starch-bearing wastewaters, can be used to generate hydrogen when fermented with certain bacteria.

Technical challenges remain, however, as the researchers need to improve the hydrogen yield of their process, scaling it up for commercial use.

A research group from Harbin Industrial University in Northeast China's Heilongjiang Province reportedly made a breakthrough two years ago in this area.

They were reported to be the first in the world to have successfully conducted mid-stage trial production of hydrogen using this approach.

They have managed to attain a daily output of 250 cubic metres of hydrogen with a 50-cubic-metre metal container. At the same time, the sugar-bearing wastewater is cleaned up during the process.

Yu singled out this research project as the most promising under the national programme. "It is the nearest thing we have so far to a clean and inexpensive source of hydrogen energy," he said.