Today’s experimental hydrogen fuel cells use so much platinum that there is not enough of the precious metal to replace all the world’s petrol engines.

As Kazuo Okamoto, the new head of research and development at Toyota, Japan’s biggest car maker, says: “With the current type of technology, we know already that (platinum supplies) will not be sufficient.”

And the problem cannot be solved by just digging up more of the metal in SA, which has the bulk of the world’s reserves. At the current 60g or so of platinum in each fuel cell, the world’s 780-million cars and trucks would use 46800 tons of the metal — just below the 47570 tons estimated to be still in the ground. And this assumes each vehicle has only 100hp, the same as the base diesel engine in a Volkswagen Golf, well below the 362hp of a BMW 7-Series luxury saloon.

There is no crisis yet. No car maker has sold a hydrogen vehicle, and only a few dozen are on the road, mainly at research centres in Japan and California. But manufacturers are committed to cutting the cost of hydrogen cars, with General Motors (GM) — the biggest car maker — planning a production-viable vehicle by 2010. Toyota, the second-largest producer, wants to lower the cost from more than $1m a car today to $50000 by 2015, when it plans to begin sales.

“There is no other alternative to hydrogen,” Okamoto says. “So one day (precious metals) will be a big problem. That will be the barrier to hydrogen.”

The possibility of a platinum shortage is already a critical issue for manufacturers spending vast sums on hydrogen research. More pressingly, it is also a major cost issue as 60g of platinum adds almost $2000 to the cost of a fuel cell. The only way to make the new technology competitive is to cut precious metal use.

Dan O’Connell, a GM fuel cell engineer, says he is confident that the company can cut platinum usage by two to three times.

But others are less concerned about platinum supplies. A study by consultants TIAX, for the US energy department, has claimed platinum will not run out. It believes platinum use will drop 75% to 15g a fuel cell once hydrogen cars became viable.

Katsuhiko Hirose, head of Toyota’s fuel cell project, points to the developments made in catalytic converters, which use platinum to clean up car exhaust fumes. He says when California adopted laws requiring catalytic converters, manufacturers sounded similar warnings as the devices needed more than 100g of platinum each. Thirty years on, platinum use has fallen 99%.

Car makers the world over are searching for alternatives, although palladium, a cheaper metal used in exhaust catalysts, does not work.

David Hart, head of fuel cell and hydrogen research at Imperial College, London, recognises the problems. But, he says, “There is a possibility of enzymatic catalysts which wouldn’t need platinum at all.”

So far the future demand for platinum in fuel cells has had little effect on miners and investors in the metal. But once fuel cells take off, the price of platinum could lead to short-term price spikes before new mine investment increases output, according to the US study.

Any shortage is likely to be eased by recycling. Already more platinum each year comes from exhaust catalysts in old cars than from any single mine.

But TIAX found that even with recycling, if fuel cells power 80% of cars by 2050, miners will be unable to extract platinum fast enough.

On the assumption that half of all cars are hydrogen-powered by then, and the amount of platinum needed falls sharply, there will be no shortage. But the key unknown factor is the future popularity of fuel-cell cars.

Ironically, if manufacturers are too successful in selling vehicles designed to solve the shortage of one resource, oil, they may run into a shortage of another.