Harnessing the Power of Sunlight to Produce Fuels

A professor is teaming up with one of the most decorated chemists on the planet to harness the power of sunlight and produce fuels that could one day substitute for oil.

sunlight

A professor at the Cockrell School of Engineering is teaming up with one of the most decorated chemists on the planet to harness the power of sunlight and produce fuels that could one day substitute for oil.

In a race to develop materials that mimic photosynthesis, Buddie Mullins, professor of chemical engineering, and Allen Bard, professor of chemistry in the College of Natural Sciences, are researching ways to split water into its constituent atoms — hydrogen and oxygen — so that oxygen bubbles up into the air cleanly and hydrogen is captured and made available as fuel.

The benefits of such fuels, if they can be engineered, will be breathtaking. They'll be renewable into the far future, needing for their creation only water and modest amounts of metals, such as iron or titanium, we already have or can make in abundance. And they'll be vastly cleaner than the fuels we’re burning now, emitting no carbon dioxide.

What stands between this particular vision of a more sustainable future, however, is a kind of gauntlet of photoelectrochemical and structural challenges to find a material capable of splitting hydrogen from water.

Cockrell School of Engineering Professor Buddie Mullins holding a glass of water.

Professor Buddie Mullins is working with chemistry Professor Allen Bard to make fuel using sunlight.

Among other properties, the material would have to absorb as much as possible of the right regions of the solar spectrum. It would have to be efficient in its use of the energy it does absorb. It would have to be decently conductive. It would have to be sturdy. And, perhaps most important, it would have to be cheap to make and cheap to lay down over tens of thousands of square miles of solar fuel farms.

Based on his pioneering Scanning Electrochemical Microscope, Bard uses a system for rapidly synthesizing and screening new materials. The materials are heated up to the point where they oxidize, and then fed into the scanning microscope, which shines a bright light on the compounds, one at a time, to see which one produces the highest current.

Bard then takes the good candidates, and hands them over to Mullins, who manipulates them at the nano-level.

"Al has this terrific experimental strategy for trying to identify materials of promising compositions, but his process doesn't give you a lot of control over the morphology or structure of the material,” Mullins said. “His group drips a liquid onto a substrate and heats it up, but we have a lot more control over its morphology."

Mullins, given a lead by Bard, experiments with the new material's structure. He looks for nanoformations that, for example, increase the utility of a given compound, allowing it to more efficiently use the charge carriers (the electrons and holes) that are created in the material once a photon is absorbed.

Mullins feeds his discoveries back to Bard who then refines his production process. The best of the best compounds are integrated into a prototype solar fuel system to see if they can do the job. And so on. With each iteration, the researchers creep closer to the day when commercially viable solar fuels are available. They also, perhaps, contribute to the kind of big leap forward that occasionally happens in the materials development field.

"Think about high-temperature superconductors," Mullins said. "Until the late 1980s, people thought that the highest temp superconductor we were ever going to get would be about 20 or so Kelvin. Really cold. Then some guys at IBM in Zurich came up with a material that was a superconductor at 30 Kelvin, and that just turned that field on its ear. By 1988, they had superconductors up to 125 Kelvin and just blew everything apart. They got many times higher than what they'd thought possible.

"We use that field as an example because those high temperature superconductors are complicated materials. They're four or five or six elements, and we're thinking that the right material for photoelectrochemistry, to do this job, is going to be something really complicated like that. It'll be several different elements, with a unique structure that's never been synthesized before."

For Bard, the hunt for a material to split water has focused recently on metal oxides, which are appealing for a few reasons. They're cheap. They're sturdy. They're easy to find or make. And though they tend not to be very good on their own at doing many of the things that a successful "photomaterial" would have to do, they're very familiar to chemists, and there's a lot of accumulated experience of how to manipulate them.

College of Natural Sciences Professor Allen Bard in front of a chalk board.

College of Natural Sciences Professor Allen Bard is one of the most decorated chemist in the world.

"Our winning material right now is bismuth vanadium oxide, doped with some tungsten,” Bard said. “It's reasonably efficient, and it's very stable and pretty inexpensive. If we can get that up to 15 percent efficiency, with a material that's stable for 10 years and costs a couple dollars for a square meter, then we're competitive."

Bard is optimistic that workable systems will be found before the world runs out of fossil fuels in the next century or two. The question that remains, however, is whether such solutions will be found in time to avert the major effects of climate change. The answer to that question, Bard believes, depends more on the political will society can summon to the task of cutting emissions and funding research than it does on the skill of scientists like him.

Ray Orbach, director of The University of Texas at Austin's Energy Institute, said the greatest danger is passivity. The costs of passivity will be high. Animal species will go extinct and coastlines will be lost. Climate instability will lead to political instability.

"What we're talking about is the cumulative effect of all the carbon dioxide emitted since the beginning of the Industrial Revolution,” Orbach said. “It'll be catastrophic even for the wealthy countries."

Many of the effects of climate change are already visible, of course, but it's not yet too late, he said, to tilt the momentum back in the other direction. Solutions, like those Bard and Mullins are pursuing, can be found soon if the resources of The University of Texas at Austin and of other places like it are brought to bear with the intelligence and on the scale that problems of such magnitude deserve.

"I don't want to wait until 2030 or 2050," Orbach said. "I want to do something now."

This story by Daniel Oppenheimer, College of Natural Sciences, has been modified and originally ran at The University of Texas at Austin website.

Photo of Dr. Allen Bard: Marsha Miller

Sunlight graphic: David Steadman