Hydrogen fuel cell. Computer illustration of the interior of a hydrogen fuel cell. This is a clean and efficient power source. Hydrogen is liberated from a natural source such as methanol or natural gases. It is then pumped into the cell (blue arrows), where the hydrogen nuclei (blue, inset) are separated from their electrons (yellow, inset). The electrons flow around a conducting loop (beige) as an electric current which can be harnessed. The hydrogen nuclei pass through a membrane (yellow, inset) and combine with the ele- ctrons and oxygen from the air (pale blue arrows) to form steam (white) as the major waste product.