Mass-selecting and characterizing copper nanoparticles for electrochemical CO₍₂₎ reduction

The human reliance on fossil fuels has resulted in increased greenhouse gas emissions, which is causing widespread detrimental changes to the climate through global warming. One such greenhouse gas is CO₂, and reducing its emission quickly and efficiently is the key to mitigating the crisis at hand. To this end, renewable energy sources, such as solar and wind, are promising energy sources that can replace fossil fuel based ones. However, inherent to both solar and wind energy is the issue of intermittency, causing the need for efficient energy storage solutions.

Storing electric energy from renewable sources in chemical bonds by producing synthetic fuels and chemicals may be part of the solution. One way of accomplishing this, is through the electrochemical CO₂ reduction reaction, but more efficient catalysts are required. One such catalyst is copper, which is able to electrochemically produce fuels and chemicals, but suffers from poor selectivity between chemical products. By understanding the properties of copper catalysts, the design of catalysts with better selectivity and activity can be guided.

This thesis concerns the study of copper nanoparticle model systems for the electrochemical CO- and CO₂ reduction reactions. Here, the study of catalytic model systems is used to elucidate how properties like structure and binding of intermediates affect the electrochemical performance of catalysts.

One project focused on the implementation of the temperature programmed desorption technique, a method which yields information about the binding of gasses to surfaces. Using CO gas, a key intermediate in the electrochemical CO₂ reduction reaction, the binding characteristics to copper can be measured. In the project, the study of copper nanoparticles was the goal, but problems with temperature measurement and sample heating were identified. Key improvements were made on this front, through the design of a new sample holder, and the implementation of laser heating. The discovery of a thermal gradient on the surface, prompted further development in the form of a newly designed sample stage, expected to enable the accurate measurement of temperature.

In another project, the cleanliness requirements of the electrochemical measurements of CO- and CO₂ reduction on copper nanoparticles were explored. Here, detrimental effects on the validity of measurements were observed, stemming from small amounts of contaminants on the substrate. A variety of cleaning methods were explored, and a method for obtaining substrates with high levels of cleanliness was developed.

In the last project described in this thesis, the effect of varying the size of copper nanoparticles was investigated. Here, the goal was to investigate how the size impacts electrochemical activity and selectivity. The measurements, performing CO- and CO₂ reduction, showed a weak size effect. However, a high selectivity for the reduction of CO to the gaseous product ethylene was measured, with a possible correlation to structure.

The works presented in this thesis contribute to the investigation of catalysts with the goal of improving catalyst design.