2030

Artificial Photosynthesis

Akira Fujishima (b. 1942), Daniel George Nocera (b. 1957), Andrew B. Bocarsly (b. 1954)

Given the critical role photosynthesis plays in life on Earth, researchers have explored the process in detail, studying its efficiency, whether evolution has found the best system possible, and if humans can improve on it. These aren’t academic questions. There are two sides to the photosynthesis reaction, and large-scale artificial methods for either could change the world. The carbon dioxide fixation reaction (the conversion of CO₂ to sugar) could provide an instant new food source as well as a renewable fuel source and industrial chemical feedstock. This process would pull carbon dioxide from the air and turn it back into small organic compounds, essentially reversing the combustion that put it into the air in the first place. In 2008, American chemist Andrew B. Bocarsly demonstrated a conversion of carbon dioxide to methanol, and his “Liquid Light” technology aims to recycle CO₂ into useful industrial hydrocarbons. Given concerns about land use, food supplies, and the climate, this could be a world-changing advance.

The other half of the natural photosynthesis reaction is also being intensively studied: splitting water back into hydrogen and oxygen. This can be done with electricity, but accomplishing this conversion without hooking it up to the power lines is something else again. Japanese chemist Akira Fujishima’s 1967 discovery of titanium dioxide’s ability to catalyze this reaction has led to a great deal of research into its possibilities and those of other semiconductors (American engineer William Ayers demonstrated this with a silicon wafer cell in 1983, and a much more efficient version was invented by American chemist Daniel Nocera and coworkers in 2011). Efficient water splitting and hydrogen storage technology would be the key steps to using the gas as a nonpolluting fuel.

It’s too early to say which of the many competing technologies will be best. It seems safe to predict, though, that both processes could be driven by metal-containing catalysts. The challenge, and it’s a big one, will be to find catalytic systems that use metals that aren’t too exotic, have long lifetimes and high activity, and can be manufactured on a large scale. The task is enormous, but so are the benefits.

Vast amounts of carbon dioxide are fixed by plants. No one knows yet whether this process can be duplicated artificially, but it’s a prize being sought by research groups all over the world.