Chemistry's crucial catalyst

Imagine if all of the fuel to power our homes and our cars came from sunlight. “Think of what kind of world that would be,” says Craig Hill, Goodrich C. White Professor of Chemistry.

Hill is at the forefront of scientists working to make this vision a reality. Along with colleagues from Emory and Germany's Institute of Solid State Research, he developed a stable, tunable water oxidation catalyst – a crucial component needed to generate solar energy cheaply and efficiently enough to go mainstream.

The idea is to eventually turn every home and car into an “artificial leaf,” by mimicking natural photosynthesis. “Geothermal power and wind power are great, but the most abundant source of energy is light,” Hill says. “Sunlight is the key to solving the dual problems of decreased fossil fuel resources and environmental pollution.”

Hill grew up in sunny Southern California. “I have always been inspired by the beauty and creativity that is intrinsic in nature,” he says, explaining what drew him to science. At the beach, he admired the action of waves, but surfing was not an option.

“I can get sunburned in minutes, literally,” says the red-headed Hill, who has survived two bouts of melanoma. “I got good at winter sports, like speed skating and skiing. I enjoy doing fast things.”

His work style also seems based on efficient movement. Munching on handfuls of organic mixed nuts in his Atwood office, he swivels to take calls, check e-mail and sign papers brought in by an assistant.

Hill just returned from a national lectureship in Switzerland, followed by talks in the Caribbean and Salt Lake City. At age 60, his star keeps rising. Among his many honors, he’s been elected a fellow of the American Association for the Advancement of Science, a Distinguished Fellow of the Victorian Institute of Chemical Sciences and co-chair of the National Science Foundation Workshop in Inorganic Chemistry for 2007–2009.

Hill joined Emory in 1983. Decades ago, he imagined many practical applications for catalysts to speed up gradual natural processes — like the oxidization of metals. “The red in Georgia clay is basically rust,” he says, explaining that iron in the soil, exposed to water and oxygen over time, becomes iron oxide. “We live in an oxidizing planet.”

Hill borrowed from nature’s principles to create complex molecular clusters called polyoxometalates, or POMs — inorganic catalysts for “greener” industry. He put together a consortium of scientists to develop an environmentally friendly paper production process — using POMs to break down wood pulp without discharging the usual toxic byproducts.

His love of nature helps fuel his interest in green chemistry. Hill is among a group of Emory scientists who go mountaineering together. “I like being in the outdoors and pushing the envelope,” he says. “When you get to the top of a really high mountain, it’s such a sense of accomplishment.”

His current research is focused on tapping sunlight for artificial photosynthesis, in collaboration with Tianquan Lian, William Henry Emerson Professor of Chemistry, and Jamal Musaev, director of the Cherry L. Emerson Center for Scientific Computation.

“We want to use sunlight to split water into oxygen and hydrogen,” he explains. Hydrogen becomes the fuel. Its combustion produces the by-product of water — which flows back into a clean, green, renewable cycle.

“The cycle is simplicity itself, but it’s not that easy to do,” Hill says. “Hydrogen is what we want — that’s the fuel. But you can’t get it without releasing oxygen. It has to be a balanced reaction.”

Three main technical challenges are involved: developing a light collector, a catalyst to oxidize water to oxygen and a catalyst to reduce water to hydrogen. All three components need improvement, but a viable water oxidation catalyst, or WOC, is the most difficult scientific challenge, Hill says. “You can’t have any organic structure in a WOC, because it will combine with oxygen and self-destruct. You’ll wind up with a lot of gunk.”

Hill and his team may have found a solution in the first prototype of a stable, molecular WOC. The chemists now plan to work with physicists and biologists at Emory and beyond, to find ways to refine and integrate all three of the components needed for artificial photosynthesis.

“Each of the three problems is sufficiently complex that no one research group can solve them all,” Hill says. Top scientists from around the world are racing for solutions. “Energy is one of the hottest topics in research right now,” Hill says. “It’s such a compelling area, it’s hard not to want to get involved.