Plants use sunlight, water and carbon dioxide to make food. Scientists want to copy this idea to make fuel. This is called artificial photosynthesis. It started with a Japanese discovery in 1972.

Light split water into hydrogen and oxygen. Hydrogen is a clean fuel. In 2021, Japanese scientists made hydrogen with panels as big as 100 square meters. But the panels used less than 1% of the sunlight's energy.

Leaves turn sunlight, water and carbon dioxide into sugar and oxygen. Artificial photosynthesis tries to copy this process to produce fuel. The field began in 1972, when Akira Fujishima and Kenichi Honda of the University of Tokyo reported that shining light on a titanium oxide electrode split water into hydrogen and oxygen. Hydrogen is attractive because burning it produces only water.

Since then, Japanese researchers have improved materials called photocatalysts. In 2021, a team led by Kazunari Domen reported a 100-square-meter panel system that produced hydrogen outdoors using sunlight and safely separated it from oxygen. However, the panels converted only about 0.76% of solar energy into hydrogen at best. Making the technology efficient, cheap and long-lasting is still a major challenge.

Artificial photosynthesis aims to imitate leaves by using sunlight to produce fuel, most commonly by splitting water into hydrogen and oxygen. Its origins lie in Japan: in 1972 Fujishima and Honda reported in Nature that a titanium oxide electrode exposed to ultraviolet-containing light could decompose water, a finding that sparked worldwide research on photocatalysts. Progress since then has been impressive but uneven. In 2020, Domen's group described a photocatalyst that used almost every absorbed photon of a specific ultraviolet wavelength to split water, yet because ultraviolet light makes up only a small fraction of sunlight, this did not translate into high overall efficiency.

In 2021 the same team operated a 100-square-meter panel array outdoors and safely separated hydrogen from the resulting gas mixture, but its solar-to-hydrogen efficiency peaked at only about 0.76%. Plants are not highly efficient either; their theoretical maximum for converting sunlight into biomass is estimated at roughly 4 to 6%. The real goal, therefore, is not to beat leaves but to produce fuel cheaply, at scale and over long periods, and that requires multiplying efficiency while keeping costs low.