Effect of microstructural changes in copper during the electrochemical conversion of CO2 to hydrocarbons

Effect of microstructural changes in copper during the electrochemical conversion of CO2 to hydrocarbons

Tripathi, Manas (TU Delft Mechanical, Maritime and Materials Engineering)

Gonzalez Garcia, Y. (mentor)
Asperti, S. (graduation committee)
Taheri, P. (graduation committee)

Delft University of Technology

Materials Science and Engineering

2022-01-31

Excess CO2 in the atmosphere has been a troublesome problem for humanity for the last few decades now. Academics, governments and industries are working together to tackle this problem to avert a global warming disaster. Research on many technologies is in progress to tackle global warming, with carbon capture being one exciting solution. The process of converting this captured carbon dioxide into something useful has gained momentum in research and academia since the 1980s. Out of the many catalysts worked upon to convert the excess CO2, copper has gained particular limelight because of its exceptional ability to reduce CO2 into valuable products such as methane, formic acid, ethane, methanol, to name a few.

The literature study associated with this project identified a knowledge gap between the present literature and the understanding of the microstructural impact on CO2 reduction. The thesis project studied the effect of microstructure changes on the electrochemical properties of copper and its subsequent impact on CO2 reduction capabilities to bridge the knowledge gap. Sigma- Aldrich copper of purity 99.999% was selected for this thesis work, and four samples: as received, electropolished, and two annealed samples were prepared. Optical microscopy and XRD measurements were used for microstructural characterization, and it was found that annealed samples lost their rolling direction, and their grain sizes increased. Evaluation of electrochemical behaviour through CV and EIS results indicated the formation of a complex triple passivation layer on the copper samples. Through evaluation of EIS results, we found that the electropolished sample had the most robust Cu2O layer.

From the CO2 reduction experiments, it was found that as-received samples had the highest F.E. for CO2 reduction, and non-electropolished samples had a high F.E. for hydrogen production. The performance of the electropolished sample stood out with a high F.E. of 46.3% for hydrocarbon production. The reason for this behaviour was, possibly, the presence of robust Cu2O layers that prevented the sample from catalyst poisoning and helped form a strong bond with CO* (carbon monoxide free radical).

The thesis opened up avenues for further research. By further investigation of factors like grain orientation and grain boundary density combined with XPS results, the understanding of the complex nature of passive layers formed on copper during CO2 reduction can be improved, which will ultimately help develop better catalysts.

CO2 reduction
Electrochemistry
CCUS
co2 conversion
Cyclic voltammetry
Electrochemical impedance spectroscopy

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Student theses

master thesis

© 2022 Manas Tripathi