Energy Harvesting from CO2 emissions through Capacitive Mixing

During the last decade the awareness about climate change has been raised. The facts speak for themselves: CO2 levels in the air have never been higher, the temperature has risen about 1.18°C since the end of the 19th century and nineteen of the warmest years have occurred since 2000 [1]. The increase of CO2 concentration is mainly due to the use of fossil fuels and unlike gases like O2 or N2, CO2 is what is called a greenhouse gas, it absorbs heat, releasing it over time. This is why decarbonisation has become a global goal, the aim is to increase low-carbon power generation and decrease the use of fossil fuels. In this situation renewable energy sources become indispensable and eventhough the use of these is widespread there is still a need to make them more efficient and to try to find new ways to reduce the CO2 in the atmosphere. The aim of this thesis is to optimize a device based on Capacitive Mixing in order to harvest energy using carbon dioxide, while adsorbing the CO2 in the atmosphere. The technique used to do it, Capacitive Mixing, is mainly used for extracting energy from salinity gradients. When the water from the river (fresh water) goes into the sea (salt water), there is a spontaneous mixing of the two solutions and this makes the entropy increase. This entropy increase with equal entalphy means we have a free energy decrease. Using the Capacitive Mixing we can extract this energy: electrodes are charged in the high concentration (high capacitance) solution so that a given potential is reached and then they are discharged in the low concentration (low capacitance) one to a lower potential. Since we want to use CO2, we have to adapt this process changing the water by an electrolyte able to adsorb it. At first we have our high capacitance solution: the electrolyte. Flushing CO2 inside the cell we get our low capacitance solution and so that we recover our previous state we flush N2. This way we are able to replicate the CapMix process using an electrolyte and CO2 instead of using aqueous solutions.