From the Science Show on radio national:
Conventional hydrogen production is expensive. A cheaper method involves using algae. The algae live in a series of ponds. Hydrogen is collected as it bubbles to the surface. An advantage is microalgae can be located on non-arable land and dont compete with food production.
Normally algae use sunlight to split water into protons and elections. Combined with carbon dioxide from the atmosphere, the cell is able to produce all the biomolecules it requires. If the cultures are depleted of sulphur, the photosynthetic pathway switches to the production of hydrogen