Copper- and Zinc-based Catalysts for CO2 Electroreduction

Abstract

One strategy to mitigate climate change is the electrochemical conversion of CO2 to chemical building blocks using renewable electricity. An interesting product is ethylene, because it is commonly used e.g. for plastics production. To facilitate this conversion, a suitable catalyst is essential. Copper is the only metal catalyst that forms ethylene in significant amounts. However, improvements are necessary because many undesired by-products are formed simultaneously, and copper catalysts degrade over time. In this thesis, strategies to improve copper catalysts are investigated. In chapters 2 and 3, zinc and silver are added to the copper catalysts. Both metals form CO, which is an intermediate product in the conversion of CO2 to ethylene. Adding copper to CO-producing porous silver makes even a relatively small amount of copper active to ethylene, although copper dissolves into the electrolyte during the reaction. Chapter 4 investigates whether polymer layers on the copper surface can improve their catalytic performance and stability. The polymer Nafion improved the ethylene selectivity, likely by repelling bicarbonate ions near the copper surface. Nafion also mitigated agglomeration of copper particles, thereby improving their catalytic stability. Lastly, Chapter 5 shows that nickel catalysts can also form ethylene. Although their selectivity is low, they exhibit higher stability than copper catalysts. Furthermore, their selectivity can be improved by zinc addition. To summarize, this thesis describes different strategies to improve the selectivity and stability of catalysts for the electrochemical conversion of CO2 to ethylene.