Hydrogen Energy Generation from Sunlight

By Raymond Orbach

Is it possible to create synthetic photosynthesis?
Is it possible to create synthetic photosynthesis?

Elementary school children are taught that photosynthesis is the basis for life on Earth.  Plants take carbon dioxide (CO2) from the atmosphere, water and sunlight, and produce useful chemical energy – their “fuel” for growth and reproduction.  But is it possible to create synthetic photosynthesis?

Scientists at the University of Texas at Austin believe it is. The “Fuels from Sunlight” team hopes to show how to efficiently absorb sunlight and split water into clean hydrogen (H2) fuel without production of CO2, a greenhouse gas responsible for global warming.

The UT Austin team, headed by chemistry professor Allen Bard and chemical engineering professor Charles Mullins, lead the University’s Center for Electrochemistry, a multi-faculty collaboration devoted to research on fundamental and applied aspects of electrochemistry. The Center previously has received research support for work on electrochemical energy sources such as batteries and fuel cells, solar energy research and new materials.

The current industrial process for hydrogen generation using natural gas produces a molecule of CO2 for every four molecules of H2, while the production of hydrogen through photo-electro-catalytic splitting of water generates no CO2. This is significant, because the typical petroleum company uses large amounts of hydrogen for fuel production – up to one billion cubic feet/day. Carbon-free production of H2 would reduce emissions of CO2 from refineries by as much as 40%.

In addition, coatings for turbine blades used in electricity production have been developed that can withstand the very high temperatures associated with H2 combustion. This means H2 could be used to generate electricity in place of coal or natural gas (which generates about half the CO2 from electricity produced from coal).

Photomaterials are central to the development of any system for the conversion of sunlight to other forms of energy (chemical or electrical), and much of the UT Austin team’s effort is devoted to such discovery. The photomaterial has the function of efficiently capturing sunlight under irradiation and creating local electrical currents (reduction and oxidation sites) that split water into H2 and oxygen (O2) at reduction and oxidation sites.

In addition to suitable photomaterials, a commercially viable solar-hydrogen process would encompass energy capture, conversion and, to some extent, storage, in a single device. The key components in the development of such a system also include device architectures, and electrocatalysts. Although optimal materials remain to be found, there are no fundamental barriers to their discovery, and much has been learned from past work.

Hydrogen from sunlight is not 20–30 years off. Indeed, the UT Austin team believes there is a good chance that the discoveries of efficient photomaterials and electrocatalysts can be made within the next five years.

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Raymond Orbach, Ph.D, is Director, the Energy Institute at UT Austin.

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