Solar power is one of the most promising forms of creating “green” energy. But could we take the process a step further and generate other kinds of energy using the sun’s rays?
CUHK Professor Jimmy Yu Chai-mei believes he has found the answer. By using chemicals such as cadmium sulfide and, separately, simple elements such as red phosphorus, the chemist has produced promising results in generating energy by splitting water molecules using sunlight.
Water splitting does not occur in the absence of catalysts. Professor Yu has been examining ways of expediting that process by adding a photocatalyst that will speed up the decomposition of the water molecules to produce hydrogen, functioning much as chlorophyll in a plant, using sunlight to induce a chemical reaction. The hydrogen can then be stored and used in power plants or as fuel for vehicles.
Hydrogen power holds plenty of potential because it contains no carbon. On combustion, water molecules are formed, which are harmless to the environment. That makes it preferable to typical fossil fuels, which do contain carbon and so in combustion form greenhouse gases such as carbon dioxide.
There are hundreds if not thousands of materials that can function as photocatalysts. Titanium dioxide can act as a photocatalyst – but it only works when irradiated with ultraviolet light.
Professor Yu has discovered that adding the semiconductor cadmium sulfide, a highly active catalyst, into the equation allows the titanium dioxide to extend its photo-response to the shorter bandwidths of visible light.
Subsequently Professor Yu and his team have also shown that red phosphorus, the most stable and commonly found of three forms of that element, can help break up water. Phosphorous makes up around 0.1 percent of the Earth’s crust, so there are hundreds of billions of tons of it that can be extracted fairly easily and cheaply. “It is always available, that’s the beauty of it. It will never be used up,” says Professor Yu.
Put red phosphorus into water at room temperature and expose it to sunlight, and you will see bubbles of hydrogen forming. “We were the first people to observe that property of red phosphorus,” Professor Yu says.
The chemist sees that as the most elegant method of inducing photocatalysis, using a stand-alone element rather than a compound. “Simple is beautiful,” Professor Yu says. It marks the first time a single element had been used as a photocatalyst. “That’s as simple as you get.”
Thanks to the finding, Professor Yu made the ranks of the “World’s Most Influential Scientific Minds” in 2014, as compiled by Reuters.
Now the challenge is to scale up the process. So the chemist hopes engineers can take those findings and achieve sustainable clean energy production.
“We are hardly at a commercial scale yet,” Professor Yu says. But he hopes his laboratory experiments can inspire others. “We hope to offer some possible solutions.”
by Alex Frew McMillan