Converting photons to fuel

Well, here's even more evidence about how we will be changing our world,
just as Kryon has stated we will....by changing the energy of the sun into
something we can use! This was found in the April, 1998 issue of Science.

RENEWABLE ENERGY:
A Record in Converting Photons to Fuel

Robert F. Service

It's the ultimate in clean energy: Generate fuel from water using only the
power of sunlight, and when the fuel burns, it gives off nothing but water.
Outlandish as it sounds, the dream was accomplished decades ago by using
solar energy to split water into its components, oxygen and hydrogen--a
powerful fuel that can be used to run everything from power plants to cars.
But as a commercial proposition, the process has been a nonstarter because
it's so inefficient and expensive. The two steps involved--generating
electricity from sunlight and using it to split water--normally take place
in separate devices, and energy is lost in between.

Now on page 425, researchers at the National Renewable Energy Laboratory
(NREL) in Golden, Colorado, have come up with a single device that
accomplishes both tasks and has set a world record in efficiency for
converting photons to fuel. The new solar-powered water splitter, built by
NREL chemists John Turner and Oscar Khaselev, converts about 12.5% of the
energy in sunlight to gaseous fuel--nearly double the previous record
achieved by a conventional two-step process.
Marye Anne Fox, a chemist at the University of Texas, Austin, calls this
efficiency "impressive." Fox's UT colleague Adam Heller adds that the new
device avoids one pitfall common to conventional solar water splitters: It
doesn't require the additional external energy that others need to get the
job done. The NREL device "is a stand-alone cell that is nicely efficient
and no longer needs external energy," says Heller. "It's a nice milestone."
Even so, it's not about to catalyze a wholesale switch from fossil fuels to
hydrogen, because the semiconductors at the heart of the new devices are
expensive; they are currently used only for specialized applications, such
as powering satellites.

Splitting water to create gaseous hydrogen and oxygen is quite simple.
Stick a pair of metal electrodes into water, apply a voltage across them,
and presto, oxygen gas is liberated at one electrode and hydrogen gas at
the other. The process, known as electrolysis, is commonly used to produce
pure hydrogen for making everything from food oils to computer chips. But
it's expensive and requires fossil fuels to generate the electricity that
powers the process. So energy researchers have long dreamed of using solar
energy to drive the electrolysis.

The basic principle of generating electricity from sunlight is, again, well
known. When photons from sunlight strike normally static electrons in some
semiconductor materials, they kick the electrons into a higher energy
level, allowing them to roam about. Left behind are electron vacancies, or
"holes," that act like positive charges that can also migrate through the
material. Additional semiconductor layers on either side of the absorbing
layer then channel the electrons and holes in opposite directions, creating
an electric current that can perform work or be stored in a battery. But,
unfortunately, combining this so-called photovoltaic effect with
electrolysis in a single device isn't simple.

First, there's a compatibility problem. Solar cells must sit in water in
order to split it into hydrogen and oxygen, but semiconductors that are
efficient light absorbers are often unstable in water. Then there's the
energy problem. A water molecule splits into hydrogen and oxygen atoms only
if each atom absorbs electrical charges packing very precise--and
different--amounts of energy. In conventional electrolysis, the metal
electrodes carry electrical charges with a wide energy range, allowing
those with just the right amount of energy to catalyze the split. But
semiconductors are more finicky. Charges in these materials can exist only
at well-defined energy levels, and "nature has not been kind to us in this
instance," says Turner. The only semiconductor materials that produce
electrical charges at just the right levels to generate both hydrogen and
oxygen are very poor absorbers of sunlight.

To overcome these problems, Turner and Khaselev constructed a sandwichlike
device that pairs the talents of two different semiconductor materials.
One--made from gallium indium phosphide--absorbs ultraviolet and visible
light and produces mobile electrons with the right energy to produce
hydrogen. The other--made from gallium arsenide--absorbs infrared light and
produces holes with the right amount of energy to produce oxygen. Gallium
indium phosphide is stable in water, so it can be used directly as an
electrode. But the unstable gallium arsenide layer is sealed with a
transparent epoxy coating to protect it, and the holes are shuttled to a
separate platinum electrode.

Although the new device appears to be efficient and stable, Turner
estimates that it would produce hydrogen at three times the cost of the
cheapest method for bulk production of hydrogen, in which hydrogen atoms
are stripped from natural gas by superheated steam. Turner and his
colleagues are now trying to engineer cheaper semiconductors to perform the
water-splitting reaction. If they succeed, the energy of the future may
finally find its way to the present.