A Photoelectrochemical cell for direct conversion of gaseous CO2 to self-growing graphenic carbon and hydrogenated carbon

Abstract

Limiting anthropogenic climate change to below 2 °C is one of the key challenges of the 21st century. Climate models suggest this cannot be achieved without drastically affecting the global economy unless carbon removal technologies, which are able to reduce absolute content of CO2 in the atmosphere, are deployed. This thesis is aimed at developing a technology to convert CO2 directly from gas phase to a solid product using non-concentrated sun light, thereby moving beyond mimicking nature’s leaf, integrating millions of years of fossilization into a real-time process. In this thesis, a novel electrolyte-less photoelectrochemical cell for direct conversion of gaseous CO2 to solid carbon using earth abundant materials is conceptualized, designed, realized, and tested. It was found that the proposed PEC is able to convert CO2 to a self-growing graphenic material, when placed in an environment where gaseous CO2, gaseous H2O, and light at natural intensity coexist. The proposed PEC was extensively experimented under different atmospheres using unassisted and assisted photoelectrochemical and electrochemical techniques. The product of CO2 conversion reaction was characterized using optical microscopy, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, X-ray Photoelectron Spectroscopy, Infrared spectroscopy, Raman spectroscopy, Atomic Force Microscopy, Laser profilometry, UV-Vis spectroscopy, and Time of Flight-Secondary Mass Spectroscopy. Extensive evidences were found confirming that CO2 was converted to a mixture of graphene and hydrogenated amorphous carbon which has self-growing properties through high sp2 carbon content and semiconducting properties. Furthermore, a reaction mechanism for such a conversion on the proposed PEC was suggested. Measures to improve performance of the developed PEC were suggested and deployed were possible.