By Laura Shin
Posting in Energy
Since the 1970s, clean-energy advocates have dreamed of using the sun to split water into oxygen and hydrogen fuel. But one major obstacle kept this from becoming possible -- until now.
Since the 1970s, clean-energy advocates have dreamed of using the sun to split water into oxygen and hydrogen. Such a technique could allow solar energy to be stored as hydrogen fuel for use at nighttime or on cloudy days. But one major obstacle kept this from becoming possible -- until now.
Researchers at Stanford University have had positive results in overcoming this challenge with one solution, and they published their study in Nature Materials this week.
A vision -- and a challenge
The vision has always been to apply a voltage across two electrodes submerged in water, a process which would split water molecules into oxygen and hydrogen.
The technique is a clean-energy dream: it requires only water and electricity and produces pure oxygen and hydrogen.
Hydrogen is the cleanest-burning fuel and has shown promise in a number of renewable energy applications. However, researchers have not been able to overcome a main problem.
As materials science engineer Paul McIntyre put it in this Stanford Report article:
"In theory, water splitting is a clean and efficient energy storage mechanism. Unfortunately, solving one problem creates another. The most abundant solar electrodes we have today are made of silicon, a material that corrodes and fails almost immediately when exposed to oxygen, one of the byproducts of the reaction."
McIntyre and chemist Christopher Chidsey came up with a new approach. They coated their silicon electrodes with a protective, ultra-thin layer of titanium dioxide, which lets in sunlight and can efficiently transfer electricity, while simultaneously protecting the silicon.
In their experiment, the titanium dioxide allowed sunlight to stimulate the photosensitive silicon, which sent electrons flowing into the water, splitting hydrogen from oxygen. The hydrogen gas could then be stored until the sun is not shining. At that point, it could be released to reverse the process and recombined with water to produce electricity.
In their experiments, the researchers found that electrodes without titanium dioxide corroded and failed within a half hour, while the titanium dioxide-coated ones lasted eight hours without corroding or losing efficiency.
Watch the video:
via: Stanford Report
Jun 20, 2011
Forgive me, is this saying that they were shining light on silicon electrodes and splitting the water directly. I would have thought a solar cell would product the electricity and then the electricity would split the water using non-corrosive electrodes. Storing hydrogen really needs another step invented. Hydrogen is difficult to store, but comboned with carbon, it is the stuff hydrocarbons are made of, e.g. gasoline. Is there no way of combining the hdrogen with carbon dioxide to produce hydrocarbons? It would be benficial in two ways, capture carbon dioxide from the air, and produce a high quality fuel. So what if it is burned, it will add no net CO2 to the air, use surplus electricity, and reduce our dependence on foreign oil. I will patent this invention and become rich (or a target for elimination from the oil companies.)
Sounds like this process is in its very early stages. There are inherent problems with storing H2. With O2 nearby, watch out. I'm not getting too excited.
No one is saying anything about the oxygen that is also a product of water electrolysis. If the generated PURE oxygen is also stored, burning it with the generated pure hydrogen will provide much more power than burning it with diluted atmospheric oxygen (the atmosphere contains only 20% oxygen by volume). Burning pure hydrogen/oxygen will produce more heat, but it will have higher volumetric efficiency (more mpg) than using the diluted atmospheric oxygen. The added heat is a challenge, but our scientists will find a work-around for it (maybe use advanced ceramic combustion components).
Electrolysis has been around for a couple of centuries, what do the commercial grade electrolyzers like from GE or Siam electric use for their electrodes?
do we really understand the photosynthetic process? It really makes sugar for the plant with O2 as an unused byproduct. It seems to me that the splitting of the water is accomplished by using nitrates, phosphates, inferred and ultraviolet light being manipulated by the chlorophyll in the plant.
"The hydrogen gas could then be stored until the sun is not shining. At that point, it could be released to reverse the process and recombined with water to produce electricity." Are you talking about a fuel cell?
"In their experiments, the researchers found that electrodes without titanium dioxide corroded and failed within a half hour, while the titanium dioxide-coated ones lasted eight hours without corroding or losing efficiency." Does this mean you have to replace the dioxide every 8-hours? If so this is a small step in the right direction, but a long ways form economically viable. There is an old saying..."Hydrogen is the fuel of the future....and always will be"
is to eliminate losses due to resistance of wires, diodes etc and increasing efficiency by leaving out traces on top of the cell. If a cell in an array fails, or is just shaded, with no diodes the power from the rest could short through the failed one. So diodes are normally used, but each diode has a voltage loss. In a direct method like this, each cell is right in the water, with no wires, sun hits it and it bubbles H2 and O2. Shade it and it stops. If the TiO2 coating has low resistance, but prevents corrosion, on a small scale, put cells in a bottle, and pipe off the gasses, little chance of ignition from the electricity used. It could be even a closed sealed system with a fuel cell. On a bigger scale, cells arrayed in sealed trays with water, and again piping to collect gasses.
This isn't photosynthesis, it's a much simpler process than that. Scientists have been studying photosynthesis for decades, and they have a pretty good idea how it works, but it's not easy to copy. Plants still do it a lot better than we can.
I emailed the researcher. He said alternatively, you could burn the hydrogen in oxygen, making hot steam which you could then run through a turbine to recover the energy. This is typically done in large-scale industrial processes.
It could be a fuel cell on a grand scale to store massive amounts of hydrogen that can then be used to produce electricity. The system would use water as a feedstock to create hydrogen, but when the process is reversed and the stored hydrogen is "burned," the byproducts are just water and electricity. That water basically is the feedstock in a perpetual cycle, as long as the sun doesn't burn out. Laura
Hi kenmullins1, I should have been clearer in my post -- the test lasted for eight hours, and the dioxide did not corrode at all during that period. You're right that this is a small step and not yet near being commercially available. However, the test is significant because with the titanium dioxide, they were able to overcome an obstacle that had previously vexed researchers. Laura