Breakthrough artificial photosynthesis is getting closer

Imagine if we could do what green plants can do: photosynthesis. Then we could meet our enormous energy needs with deep green hydrogen and climate-neutral biodiesel. Scientists have been working on this for decades. Chemist Chengyu Liu will receive his doctorate on June 8 for another step that brings artificial photosynthesis closer. He expects it to be commonplace in fifty years.

In fact, we can already achieve photosynthesis the way green plants can. Solar energy converts CO. to2 and water in oxygen and chemical compounds that we can use as fuel. Hydrogen, for example, but also carbon compounds such as those found in gasoline. But the cost is greater than the value of the fuel it provides. If that changes, and we can massively scale up this artificial photosynthesis, then all our energy problems will be solved. than CO2 emissions from energy production become negative.

Promising, but we’re not there yet

While it sounds promising, we’re not there yet. Chengyu Liu, one of the dedicated researchers working on artificial photosynthesis: ‘Now that this topic is such a hot topic worldwide, I think the first real application will be a fact within twenty years. But that’s not all, he continues: ‘After the introduction of a new technology like this, it always takes decades before it becomes commonplace. It was the same after the invention of the steam engine in the nineteenth century. I suspect it will be another thirty to fifty years before it is widely used industrially.’

Real green hydrogen

We already have cars that run on hydrogen, with only water as exhaust gas. But it takes a lot of energy to make that hydrogen. The ‘green hydrogen’ we produce today only means that we get the energy to produce it from a windmill or solar panel, and not from coal, gas or oil. In photosynthesis, that energy comes directly from the sun, without a solar panel having to supply electricity first.

No fake trees, but huge surfaces needed

What would our world look like if artificial photosynthesis were the standard? Would we have artificial trees with artificial leaves everywhere to meet our energy needs? ‘You do indeed need huge surfaces to collect the light, CO2 gas and water (vapour). This can be done, for example, in the form of solar panels on roofs. Or we can place photosynthesis boxes in the desert, work during the day and collect water vapor in the evening. There must be many more different ways to use these kinds of settings. If we have successfully solved the pricing problem of the reactions themselves, the next step is to optimize devices for large-scale applications.’

Liu can already imagine it: ‘It would be nice if we could use seawater, because it is not scarce. We would then use a device that generates energy very cheaply with free sunlight, free seawater and free CO .2† Fossil energy would be comparatively much too expensive.’

Two components: water splitting and CO2 reduction

Artificial photosynthesis, like the natural variant in green plants, consists of two parts. One is water which splits into hydrogen and oxygen. The other is the reduction of carbon dioxide to energy-rich hydrocarbons. The aim is to realize these two components in one system that, on the one hand, contains the CO . reduces2 content of the air, and on the other hand produces fuels and oxygen.

The ideal catalyst: efficient, cheap and readily available

In his PhD research, funded by the China Scholarship Council, Liu focused on the first part of water splitting, where hydrogen and oxygen are produced. A reaction accelerator or catalyst can help to make that reaction more energy efficient. Liu: ‘I have developed strategies for designing more efficient catalysts, among other things. The ideal catalyst is not only efficient, but also inexpensive and readily available. For example, it should not be a rare metal that you have to get from somewhere with a lot of environmental damage.’

One of the best moments

Finding the ideal catalyst is one of the biggest challenges in the research field, says Liu. ‘One of the best moments in my research was when I found a new strategy to design a catalyst for hydrogen production, in the middle of a pH neutral environment.’

Two important results

According to Liu’s promoter Sylvestre Bonnet, Liu found two very important results during his PhD research. ‘Initially, he discovered that under photocatalytic conditions nickel porphyrin molecules can serve as catalysts for the extraction of electrons from water, a reaction called water oxidation. The most efficient catalysts that exist to date for this reaction are based on ruthenium or iridium, rare and expensive metals. As a result, they are not suitable for large-scale use.’

Liu’s second finding brings a very important and new fundamental insight into the design of catalysts for water splitting under pH-neutral conditions, Bonnet says. “We are currently hard at work with Francesco Buda’s group from the LIC to theoretically model the response and understand these counter-intuitive results. But I firmly believe that this result will lead to a much-cited article!’

Liu’s research yielded new design rules and ideas for achieving efficient artificial photosynthesis. ‘The results provide both fundamental insight and a practical strategy for finding new catalysts for water oxidation. I hope to continue my research. Ultimately, I want to be one of the researchers who arrives at a complete system of artificial photosynthesis.’

Supervisor Bonnet sees that Liu is there when researchers make a complete system of artificial photosynthesis realistic. “My feeling is that if one day people find a way to realize efficient artificial photosynthesis, or a way to make an artificial leave, Chengyu could be one of them. He has the passion, the insight, the excellent scientific attitude and has received an excellent education!’

Text: Rianne Lindhout

Image: Pixabay

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