Hydrogen made using sunlight a step closer

Chinese scientists have clearly mapped the basic mechanism behind turning water into hydrogen gas using sunlight and catalysts, paving the way for the green production of hydrogen on an industrial scale, according to a study published in the journal Nature on Wednesday.

Hydrogen is widely regarded as a clean and renewable fuel crucial for reducing greenhouse gas emissions and combating climate change. However, producing hydrogen on an industrial scale often requires natural gas, a non-renewable fossil fuel.

For decades, scientists have been trying to find a clean and easy way to produce hydrogen, preferably using water, which contains two hydrogen atoms and one oxygen atom.

In the 1970s, researchers discovered that certain catalysts can absorb energy from light to start a chemical reaction. This process is known as photocatalysis, and scientists later found that some photocatalysts can split water into hydrogen and oxygen gas using sunlight.

"Using photocatalysts to produce hydrogen is considered one of the most important and challenging chemical reactions in the field of chemical sciences," said Li Can, a researcher at the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences.

Li said the reaction is also regarded as the "holy grail" of chemistry, but the current efficiency of this reaction is too low and far from practical. One of the main reasons is the lack of understanding of its basic mechanisms, such as how electrical charges generated by sunlight are involved in the reaction process.

Photocatalysts' complex nanoscale features and electrical charge operating across a range of spatial and temporal scales, such as from a femtosecond (one millionth of one billionth, of a second), to seconds, are some of the major challenges when probing the essential mechanisms of photocatalysis, Li said.

As a result, the conversion rate of water to hydrogen using photocatalysts is about 1.5 percent, a major improvement compared to decades ago, but still drastically behind traditional production methods using fossil fuel, he added.

Now, Chinese scientists have cracked one of the biggest scientific mysteries behind using photocatalysts to make hydrogen. They used a combination of three techniques to reveal the complex process of how charge transfers in a cuprous oxide photocatalyst, a semiconductor material made of only one copper atom and one oxygen atom.

This breakthrough will allow scientists to improve the efficiency of photocatalysts and design better ones that may have potential industrial applications, said Li.

"If the conversion rate of a water-splitting reaction using photocatalysts can reach around 10 percent, then it would have a practical chance of replacing the current industrial production method," he said. "We still have quite a long way to go, but now that we know how the process works, we may see new breakthroughs in the coming years."

An anonymous peer reviewer for the study said the measurement of the mechanism will be of interest to the wider communities of catalysis, energy and materials science.