Water Oxidation Catalyst

Artificial Photosynthesis: Solar Fuel Gets a Boost From an Improved Water Oxidation Catalyst

There is unprecedented interest in developing sustainable energy and solar energy is one of the best options for a sufficient and clean energy source. Previous methods to harness the energy of the sun have involved photovoltaics to generate electricity. However, electricity cannot meet the needs for mobility applications like ocean shipping and air transportation. These applications require high energy dense fuels. New approaches to harness solar energy are now focused on making solar fuel. In order to generate fuel from solar energy, or more specifically to create hydrogen fuel from water and sunlight, a catalyst is required. Emory researchers have developed a new water oxidation catalysts that oxidize water very rapidly, remain highly stable, and are easy to prepare with readily available materials. Prior catalysts have lacked practicality in terms of selectivity, speed, and stability, but these catalysts overcome these obstacles.

Craig Hill, PhD
Craig Hill, PhD

Hydrogen (a.k.a., atomic No. 1) makes up about three-fourths of all matter and is the lightest and most plentiful element in the universe. No wonder scientists have long searched for ways to transform hydrogen into a clean, sustainable solar fuel source.

The ultimate goal is to be able to split water into oxygen and hydrogen using only sunlight, through a process of artificial photosynthesis, and to use the resulting hydrogen as a clean fuel whose only byproduct is water. But this has proven more difficult, and expensive, than initially imagined. The challenges, say researchers, include developing a light collector, a catalyst to oxidize the water, and a catalyst to reduce the water to hydrogen.

Recently, Emory chemists have developed the most effective homogeneous catalyst so far for water oxidation, a crucial component of generating hydrogen fuel from water using only sunlight. They aim to mimic the natural process of photosynthesis with a carbon-free, molecular water oxidation catalyst (WOC).

Light Stimulated Oxygen Generation Using WOC

"This has really upped the standard from the other known homogeneous WOCs," says Emory inorganic chemist Craig Hill, PhD. "It's like a home run compared to a base hit." For this process to become viable, say the researchers, the water oxidation catalyst must have the "triple 's' qualities" of selectivity, stability, and speed. Homogeneity is necessary since it boosts efficiency and makes the WOC easier to study and optimize.

Nearly all of the previous WOCs developed by labs have had significant limitations, such as containing organic components that burn up quickly. A previous WOC developed by Hill's lab worked well, but was based on ruthenium, a relatively rare and expensive element. The new, groundbreaking WOC is based on inexpensive and abundant cobalt, and has proven to be even faster than any WOC previously invented.

Emory's Office of Technology Transfer licensing associate Justin Burns hopes "this discovery will be the foundation for a local green-tech company focused on hydrogen fuel generation."

Hill’s research is a component of the Emory Bio-inspired Renewable Energy Center, which aims to mimic natural processes to generate clean fuel. The next step involves incorporating the WOC into a solar-driven, water-splitting system.

The Emory team's breakthrough, which was published March 11, 2010 in the journal Science, was made in collaboration with the Paris Institute of Molecular Chemistry. Benjamin Yin, an undergraduate student in Hill's lab, is lead author on the paper, and Emory chemists Hill, Yurii Gueletii, Jamal Musaev, Zhen Luo and Ken Hardcastle are coauthors. The U.S. Department of Energy funded the work.

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