Direct photoelectrochemical splitting of water by sunlight has already been achieved by many groups worldwide, including some at KACST and Cambridge, but existing methods are severely limited by low efficiencies and unstable catalysts that are prone to corrosion. They also have a technical problem known as a wide-bandgap, in which the materials are transparent for photons with energy lower than the gap between energy states (the bandgap) required to achieve the water-splitting reaction. A major aim of the project is to develop materials with narrow bandgaps that will allow absorption of visible light energy to split the water.
“Splitting water using visible light will be a key milestone,” says AlOtaibi. He explains that this would allow the energy in the full spectrum of light emitted by the sun to be harnessed. Another key aim is to find materials that are stable enough to resist corrosion.
Researchers on the project already have a good idea of what types of materials could solve the problems. They plan to make a variety of metal oxide catalysts made from a complex of different types of positively charged metal ions and negatively charged oxide ions. “We already have evidence of the type of oxides, forms of what we call perovskites, that hold great promise to solve the efficiency and corrosion problems at a reasonable cost,” says AlOtaibi.
The two key tasks for the project are synthesizing a variety of possible photochemical electrode materials, then studying their performance using advanced electrochemical techniques.
A process of nanostructuring — manipulating the fine structure of the materials at very small scales — will also be explored to further improve the performance of the most promising potential materials.
The project will also investigate the potential of these materials for use in photovoltaic cells that can serve to first generate electricity, which can then be used to split water in the less direct route. Through this, the researchers hope to develop an oxide-based photovoltaic cell integrated with the catalysts that can use the electricity to split water.
The incentive to succeed is enormous. Developing technology to greatly increase the contribution of solar energy to global power production could drastically cut the carbon dioxide emissions from burning fossil fuels. Cuts in these emissions on the scale that climate science experts say is needed to avoid disastrous global warming will demand such new technologies, rather than just changes in behavior. AlOtaibi also points out that the world’s energy consumption is expected to increase by more than 50 percent from 2010 to 2040.
“The technology is also perfectly suited to Saudi Arabia due to the local problems of the large amount of carbon dioxide emitted by the oil refining industry, and also the wastewater this industry generates,” says AlOtaibi.