Effects of Different Electro Chemical Cells, Particle Size and Local pH on CO2 Reduction Reaction

In effort to mitigate global warming, electrochemical reduction of carbon dioxide is extensively studied as a promising technique to decrease the atmospheric carbon dioxide level. This technique recycles gaseous carbon dioxide into reusable form of energy by applying electrical energy while allowing the gas to react with a catalyst. Many types of metallic nano-catalyst, ranging from gold, copper, platinum and etc., have been shown in researches to successfully regenerate fuels such as carbon monoxide, hydrocarbons. There have been many scientific efforts to optimize the condition in which electrochemical reduction yields more of the wanted product energy form, and less of unwanted products, or byproducts. The focus is not only in higher yields of reusable energy but also in efficiency in yielding the results. Gold nanoparticles in electrochemical reduction of CO2 is studied quite abundantly, and known as a fact that the reaction will produce carbon monoxide (CO) for the most of the time in reasonable overpotentials. From electrochemical reduction of water, hydrogen evolves. So we took the advantage of this characteristic ҈ of gold nanoparticles, and choose to conduct our study on gold. Many factors affect the efficiency of the electrochemical reduction reaction. Considering many factors, diffusivity was one major factor that could affect the reaction. Traditionally, scientist worked on H-cell for electrochemical reduction project. It had catalyst immersed in aqueous solutions to help ion transfer. However, the limitation was in the diffusivity of CO2. The diffusivity of CO2 is Water (H2O) is around 2.3x10-9 m2/s, where as the diffusivity in air is 1.4x10-5 m2/s. The diffusivity is almost 5000 larger in air. So we came up with a design to create an interface where CO2 can migrate to the catalyst surface via gas phase but keep protons and other constituents migrate via liquid phase, namely, gas diffusion electrolyzer (GDE). Another factor that may affect the efficiency is the local pH during the reaction. Since gold nanoparticles generate H2 gas during it’s the reduction from hydrogen evolution reaction (HER), the local pH tends to increase during the experiment. So we hypnotized that if the local pH increased would lead to suppression of HER, and thus follow up with a increased selectivity for CO. We hypothesize that increase in gas diffusivity into the catalyst, catalytic surface area, and local pH will positively affect the electrochemical reduction of carbon dioxide. My work looks into the aspects of the nature of the electrochemical cell by comparing two cell types that differ in carbon dioxide diffusivity, by comparing different catalyst sizes of gold nanoparticles that differ in surface to volume ratio, and local pH in which the reaction takes place. Through this work, we will get an insight of how to develop efficient electrochemical reduction conditions