• UVM scientists seek answers to fuel cell economy
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     | March 12,2007
     

    An electron cyclotron resonance plasma enhanced sputtering system glows behind University of Vermont Professor Walter Varhue, left, and Post Doctorate and Fellow Mike Cross, right, at the Semiconductor Processing Lab on Saturday in Burlington. Varhue and a team of scientists are seeking an economical source of hydrogen for power.

    BURLINGTON — Imagine sunlight falling on a beaker of water with a fabricated membrane at the bottom that causes the water to split into the two elements that make it up — hydrogen and oxygen.

    You might just have solved a big riddle in the search for an economical and environmentally friendly source of hydrogen to power the "fuel cell economy," which is seen by some as a solution for the problems of climate change and oil depletion.

    Walter Varhue and a team of scientists at the University of Vermont are delving into the realm of nanotechnology — the science of very tiny things — in hopes of developing the material to make up that membrane.

    Varhue, a professor of electrical engineering, envisions hydrogen "farms," where arrays of panels would collect sunlight and convert it to energy capable of splitting water into hydrogen and oxygen.

    A single particle of sunlight contains enough energy to split water, but the conversion process isn't efficient, Varhue said. New materials brought by nanotechnology could solve this problem. "If the current efficiency of 6 percent can be increased to 10 percent, you could have farms across the country making hydrogen instead of growing corn."

    The panels would rely on nanotechnology because they would be constructed at the molecular level, taking just the required amount of energy from sunlight to serve as a catalyst in the conversion of water into its constituent elements.

    Nanotechnology has opened up big new frontiers in science because of the potential for things — when reduced to very small size — to do things they don't do easily at more normal volumes.

    If Varhue and his team are successful, their work could help solve one of what Varhue calls the three problems of hydrogen-powered fuel cells. One is production of the hydrogen, the second is storage and shipment of hydrogen and the third is use — or the still developing technology of fuel cells themselves.

    Fuel cells are electrochemical devices that combine hydrogen and oxygen to produce electricity, with water and heat as byproducts. Essentially, hydrogen is fed into one end — the anode — and reacts with a catalyst called an electrolyte. Its protons flow through the catalyst and join with oxygen on the other, cathode, end to form water. The hydrogen's electrons flow through a separate path to an electrical circuit.

    A big question for fuel cell enthusiasts has been where to get the hydrogen economically and in large volumes, and that's the question Varhue and the UVM team are trying to answer.

    "I'm not the only one who is working on this," he said in a recent interview. "All the world over is working on this right now."

    Varhue, 50, a father of three who raises cows, pigs and sheep on a farm in the Franklin County town of Georgia, brings a farmer's fix-anything spirit into his lab.

    He has used spare parts from the IBM semiconductor fabrication plant in Essex Junction and components he's ordered from catalogues to build a super-low-pressure vacuum chamber.

    For the sort of work Varhue is doing — growing "quantum dots" — the vacuum chamber must be as clear of contaminants as possible. And in this case, air is a contaminant.

    It takes three powerful pumps 10 seconds or so to get all the oxygen and nitrogen — the principal components of air — out of the chamber. Water vapor is another story.

    Molecules of water like to settle on the stainless steel walls of the vacuum chamber, Varhue said. It takes the vacuum pumps two weeks to get enough of the water vapor out of the chamber for the scientific work to go forward. "You can never get it all," he said.

    Much of the work to come up with a solar-powered hydrogen-producing membrane has focused on a material called titanium oxide, Varhue said. But so far, that material has been shown only to make use of about 6 percent of the energy in sunlight in the hydrogen-making process.

    Varhue's team has applied to the U.S. Department of Energy for a research grant — $750,000 a year for three years — on the hope that an alternative material can be developed to use more of the energy in sunlight. He calls the grant application extremely competitive and the chances of winning the grant slim, but worth a try.

    The plan is to "grow" crystals from four elements: gallium, zinc, nitrogen and oxygen in carefully controlled amounts. Those elements naturally join to form the crystals, which the scientists call "nanostructured catalysts for the photoelectrochemical production of hydrogen."

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