An introduction to electrochemical CO 2 conversion and copper hollow fibre electrodes 1.1 Adding to the carbon cycle Being one of the main resources for plants and trees, carbon dioxide (CO2) acts as a building block for life on planet earth. [1] The supply of CO2 to the earth's atmosphere occurs through combustion of carbon containing species in the presence of air. Take the human body as an example, where carbon containing foods are taken in and combusted together with oxygen to yield energy and CO2. This CO2 is emitted to the atmosphere through breathing. In the many years that planet earth exists, a delicate cycle between CO2 supply and demand has evolved.In man-made combustion processes, carbon containing species are also combusted in the presence of air. These processes provide for energy, amongst others, and heavily rely on fossil-based fuels. [2] Utilization of these fossil-based carbon sources adds carbon to the atmosphere that was long stored in the earth's crust. The carbon cycle evolved to process a certain amount of CO2 each year, and the emission of additional fossilderived CO2 results in accumulation of CO2 in the atmosphere. [1]