Photocatalysis for Green Future ?
Photocatalysis is an innovative means of producing hydrogen from water using sunlight – and possibly turning carbon dioxide into methanol, as Tom Shelley reports. Success with that idea would solve, at one blow, both the problem of what to do with sequestered CO2 from burning fossil fuels and the problem of replacing them with a replacement ‘green’ fuels.
The basic process involves photons of light striking a very thin layer of semiconductor, typically only one micron thick, which produces electrons and holes – the same principle as that used in a photovoltaic cell. In a photocatalytic cell, however, the electrons combine with hydrogen ions in water at the cathode surface to produce hydrogen gas molecules, whereas the holes interact with water molecules at the anode surface, in order to produce oxygen and hydrogen ions, which have to be able to migrate through the material to the cathode. The cells can be made planar, as is the case with photovoltaic cells, or as particles, dispersed in water.
Whereas it is quite easy to make a device that produces small amounts of hydrogen, producing larger amounts has so far defeated many expert minds.
The key points are,
* New materials offer the possibility that photocatalytic conversion of water to hydrogen for fuel can be accomplished using a much wider part of the solar spectrum than at present
* The ideal material has not yet been found, but progress is being made and there are many more material combinations to try
* Photocatalytic destruction of organic pollutants and organisms is already a proven commercial technology, using ultra violet light, but can also be accomplished using sunlight
* There is also the possibility of using photocatalytic reduction of carbon dioxide to methanol
see more
The basic process involves photons of light striking a very thin layer of semiconductor, typically only one micron thick, which produces electrons and holes – the same principle as that used in a photovoltaic cell. In a photocatalytic cell, however, the electrons combine with hydrogen ions in water at the cathode surface to produce hydrogen gas molecules, whereas the holes interact with water molecules at the anode surface, in order to produce oxygen and hydrogen ions, which have to be able to migrate through the material to the cathode. The cells can be made planar, as is the case with photovoltaic cells, or as particles, dispersed in water.
Whereas it is quite easy to make a device that produces small amounts of hydrogen, producing larger amounts has so far defeated many expert minds.
The key points are,
* New materials offer the possibility that photocatalytic conversion of water to hydrogen for fuel can be accomplished using a much wider part of the solar spectrum than at present
* The ideal material has not yet been found, but progress is being made and there are many more material combinations to try
* Photocatalytic destruction of organic pollutants and organisms is already a proven commercial technology, using ultra violet light, but can also be accomplished using sunlight
* There is also the possibility of using photocatalytic reduction of carbon dioxide to methanol
see more
Labels: energy, fuel, hydrogen
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