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Electrochemistry for renewable energy

Imagine we could convert the greenhouse gas CO2 into synthetic fuels using sustainable energy. This would enable us to reduce the amount of CO2 and at the same time store wind and solar energy in an innovative way. Chemist Akansha Goyal (Leiden University) is conducting fundamental research to make this possible. On March 31, she obtained her PhD under the supervision of Spinoza laureate Prof. Dr. Marc Koper.

In order to make the conversion of CO2 into chemical building blocks for fuels economically viable, the process must be very efficient. ‘We work with electrodes in a liquid with dissolved salts and CO2. We call this liquid the electrolyte,’ explains Goyal. ‘A metal electrode in the electrolyte serves as a catalyst for the reaction. Due to electrical voltage on the electrode, chemical reactions occur at the interface between the electrode and electrolyte. I mainly looked at the conversion of CO2 to CO, or carbon monoxide, which serves as a feedstock for more complex molecules.’

In addition to this carbon dioxide reduction reaction (CO2RR), another reaction occurs as well: the hydrogen evolution reaction (HER). ‘This reaction creates hydrogen, which in itself is also a useful energy carrier,’ Goyal notes. ‘But in this case it is a competing reaction that makes the conversion of CO2 to CO less efficient.’

The cover from the thesis of Dr. Akansha Goyal

What are the best reaction conditions?

Goyal conducted fundamental research into both the HER and the CO2RR. ‘You can influence these reactions in many ways,’ explains the chemist. ‘For example, through the type of metal of the catalyst or through the shape of the catalyst surface. But the electrochemical environment near the catalyst is also extremely important.'

There was much disagreement in the literature about the best reaction conditions. Goyal therefore decided to work under very well controlled conditions, with a completely flat catalyst surface. ‘I discovered, among other things, that the conversion of CO2 improves if you let the rotating ring-disc electrode, which controls convection in the liquid, rotate faster. The optimal reaction conditions also appear to depend on the precise composition of the electrolyte.’

‘Akansha has generated fundamentally new insights’

Her supervisor Prof. Marc Koper is enthusiastic about her research. ‘Akansha has really generated fundamentally new insights into how the electrolyte composition affects the reaction rates of both CO2RR and HER,’ he says. ‘This gives us completely new tools to improve the process.’

Isn't it more practical to make hydrogen?

Considering these fuels: wouldn't it be more practical to make hydrogen, allowing for a hydrogen economy? ‘Hydrogen is indeed part of the energy transition, which is why we also conducted research into the HER. But carbon-based fuels offer other advantages, such as a higher energy density and the fact that they can be liquid. Also, electrocatalysis of CO2 makes it economically attractive to convert this harmful greenhouse gas into useful substances.' But isn't CO2 released again once you use these fuels? ‘Not if you convert that CO2 back into fuels. Then you get a CO2-neutral cycle,' replies Goyal.

She expects it will take some time before the technology becomes widely applicable. ‘A lot of research is still necessary, especially for higher electrical current densities. Nevertheless, Shell, one of our research partners, is already building a first pilot CO2 electrolyzer. The future looks bright.’

Dr. Akansha Goyal completed her bachelor's degree in Chemistry at Delhi University. 'Back then I was already attracted to science, but there is little funding for fundamental research in India,' she says. That is why she obtained a scholarship for excellent students at Leiden University, where she completed a two-year master's degree in chemistry.

'During my master's, I received a European Erasmus+ grant that allowed me to do an internship in Scotland,' says the chemist. ‘It revolved around battery research. That is how I became interested in sustainable energy. When I returned to Leiden I did a small study with Marc Koper.' She liked it and when Koper offered her a PhD position, she gladly accepted it.

What are her future plans? ‘I now work as a postdoc and will be busy with ongoing research and writing reviews for some time. I also want to travel around with my family, who are coming to the Netherlands especially for my PhD defense. That’s very special to me, I last visited my family last year. I hadn't seen them for a long time before that due to the corona crisis.' Goyal plans to continue working in electrocatalysis. ‘I would like to increase the fundamental understanding of electrochemistry in order to contribute to the transition to a carbon-neutral energy cycle,’ she explains.

Text: Diana de Veld

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