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On the road to renewable fuel

Greenhouse gasses in the atmosphere and fertilizers in the groundwater have negative consequences for our environment. With an electrochemical process they can be transformed to more valuable and useful substances like fuel and alcohol. Chemistry PhD candidate Elena Perez Gallent discovered how this process can be more efficient. On Thursday 1 February she defended her thesis.

At this moment we can capture and store substances that are harmful to our environment, like greenhouse gasses. Because the earth’s storage capacity is limited, a more sustainable solution is needed, says Perez Gallent. ‘Already since the ‘80s it is known that carbon dioxide can be electro-reduced to fuels like methane, ethylene and ethanol using electrocatalysis. How this works and how different factors influence the reaction is still under debate.’

Now the use of this method is not yet cost-efficient. According to Perez Gallent it is important to understand how different factors play a role in those processes to make it more efficient and selective. ‘However, the high complexity of the reaction makes this task arduous.’ Therefore, Perez Gallent analysed smaller parts of the process. ‘Like the Romans would say divide et impera, which means divide and rule.’

Copper

During electrocatalysis a catalyst absorbs the starting substances. This catalyst speeds up the reaction by forming intermediary products, so that less energy is needed to form the end products. ‘By using renewable energy sources like wind and solar energy this process will be even more sustainable,’ Perez Gallent adds. The electrocatalyst is placed in a liquid, the electrolyte. As soon as electricity passes through the electrolyte, the substances are converted into different products.

To convert carbon dioxide and nitrate into different products, various catalysts can be used. Perez Gallent chose copper because of its attractiveness to companies. ‘Copper can be applied for many different substances and is a cheaper alternative than the more often-used substances like platinum, palladium, or rhodium.’ Amongst other things, she studied how the acidity of the electrolyte and the structure of the copper surface affect the performance of carbon dioxide and nitrate reduction.

Square symmetry

Perez Gallent discovered an intermediary in the pathway where ethylene is formed from carbon dioxide. This intermediary was only hypothesized and never experimentally observed. Its formation proved sensitive to a copper surface with square symmetry. ‘The orientation of the surface copper particles changes their stability, making them more favourable to some intermediates for adsorption,’ Perez Gallent explains.

For nitrate Perez Gallent discovered that different products are formed in different acidities. In acidic conditions nitric oxide and ammonia are formed and in alkaline conditions hydroxylamine is formed. The latter one is favoured on a square-symmetry copper surface.

Never fuel again

Perez Gallent emphasizes the importance of fundamental research into these kinds of processes. ‘We are doing well developing electric and hydrogen cars. But there is still a long way to go before we can all use them, and before the industry and infrastructure is equipped for this. Besides, you will still have a harmful amount of carbon dioxide and nitrate in our environment. Ideally, we will have a device in our cars which will collect the gasses formed during the fuel combustion and transform them back to fuel. This way, we can decrease the amount of fuel and might never have to fuel again.’

Elena Perez Gallent’s promotion took place on Thursday the 1 February from 11:15 until 12:00 in the Academiegebouw (Rapenburg 73, Leiden).

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