Understanding Water Management in CO2 Recycling with Neutrons: ‘Power Naps’ for Electrolysers

(Neutrons for Society) A recent study uses high resolution neutron imaging at the ILL to examine water dynamics in a carbon dioxide electrolysis cells. Recently published in the journal ACS Energy Letters, the study has now been selected as research highlight in Nature Catalysis.

Global warming and environmental crisis due to anthropogenic activities call for the rapid implementation of measures to reduce the global carbon footprint. Carbon dioxide (CO2) capture and recycling through electrochemical reduction (electrolysis) may have a critical role when it comes to defossilizing the production of commodity chemicals.

While several transformation routes are being explored, CO2 electrolysis targeting carbon monoxide as a reaction product is close to commercial viability, with state-of-the-art electrolysers reaching high performance. The so-called ‘zero-gap’ electrolysers with an anion-exchange membrane (AEM) – see text box - is the cell setup closest to meeting commercial requirements. However, such devices still suffer from operational issues mainly due to the build-up of carbonate salt precipitates at the cathode and electrode flooding.

A recently published study examines the water transport in a CO2 electrolyser during operation. ILL’s instrument NeXT was used to obtain high-resolution neutron images at a pixel size of 4.2 μm of the water content in the cell, coupling the radiographic data with the overall electrochemical performance. The influence of gas humidification was studied, and pulsed operation is compared with constant current operation in 100 hours long measurements.

‘This is the first quantitative operando analysis of the water management in a CO2 electrolyser via high-resolution neutron imaging under industrially relevant working conditions’ says Joey Disch (University of Freiburg, Germany), who led the project, adding: ‘Operando studies play a vital role in understanding CO2 electrolysers and neutron imaging is an excellent method for operando investigation of water dynamics’.

‘The results demonstrate that pulsed operation increases stability, even with low electrolyte concentrations’, reveals Bohn, concluding: ‘During the resting period, pulsed operation introduces additional water to the cathode, which facilitates the removal of salt precipitates and mitigates uncontrolled electrode flooding,’ concludes Bohn.

Indeed, neutrons have shown that during the brief rest periods the amount of water at the cathode increases, especially at higher RH, which dissolves carbonate precipitates, preventing accumulation. While high efficiency is continuously achieved at lower RH, CO2 transport gets limited under 100% RH due to the increase in water content. At constant current, on the other hand, multiple flooding events are observed, especially under high humidification.

Researchers point out that optimising the pulse strategy parameters and the electrolyte could still lead to improvements in performance. Parameters like the potential during the resting period, the timing of the pulses, and different waveforms should be explored. Most importantly, the strategy’s transferability to cell stacks should be explored. The work published at this time is a first step rather than a final one. READ MORE; includes VIDEO