HYDROGEN FUEL ALMOST A REALITY
If scientists could make houseplants know how to absorb sun and store the sun’s energy in chemical bonds, we could quit worrying about high gas prices.
A catalyst is needed that can take electricity and make it split water to make hydrogen gas as a clean fuel. More than 200 years ago, English chemists split water. It required two separate catalytic steps.
A positively charged electrode, an anode, swipes electrons from hydrogen atoms in the water. The proton then breaks away from its oxygen atoms. The anode then grabs two oxygen atoms and welds them together to make O2. The free proton, H, goes to the negatively charged electrode, a cathode, and hooks up with electrons to make H2.
The challenge has been to find an anode that links oxygen together. They always worked only under harsh chemical conditions or were made from too expensive metals, like platinum. To use solar energy to cover a large area a low cost catalyst is necessary.
A catalyst has been found that works under friendly environmental conditions. It is made made from cobalt and phosphorus, cheap and abundant elements.
Researcher Nocera and his team at MIT started with a stable electrode indium tin oxide, ITO. They spiked it with the cobalt and phosphorus phosphate. The ITO became positively charged, pulling electrons from the cobalt2+ turning it to cobalt3+. The cobalt3+ then teamed up with the negatively charged phosphate andprecipitated, forming a film of rocklike cobalt phosphate on the ITO. Another electron in the film is yanked from the cobalt3+ to make cobalt 4+.
The film makes the water splitting catalyst and swiped electrons from hydrogen atoms in the water. It grabs a single oxygen atom and welds them together, returning the cobalt4+ back to cobalt2+, and dissolves back again into water.
There are still two big hurdles to overcome. The catalyst needs excess electricity to start the water splitting reaction that can’t be recovered nor stored in the fuel. Also the catalyst can accept only low levels of electrical current. Since the catalysts are so easy to make and cheap, things look promising.
The costs of the cathodes are still too expensive and the researchers still need to link the electrodes to solar cells to make clean electricity. It is still not known if the catalyst can work in seawater.
The dream is to use the sun and oceans to fill our greatest needs. The attempt is to use sunlight to make hydrogen from seawater and then pipe it to large banks of fuel cells on shore that could convert it into electricity and fresh water.
Dreams do come true!
Source: Science, August 1, 2008
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