However, platinum is scarce, difficult to mine and therefore very expensive. For instance, one of the biggest barriers to the adoption of fuel cells in hydrogen powered cars is their cost. Large quantities (about 30 grams) of this noble metal are still required for the electrodes in the fuel cells at which the chemical conversion processes take place. The pure platinum needed contributes about 40 per cent of the total unit cost. Without the catalytic effect of the platinum, it is not currently possible to achieve the necessary conversion rates. Researchers are working hard to find inexpensive alternatives to platinum catalysts for use in hydrogen fuel cells.