Cathodic nanoscale carbon chemically captures carbon Dioxide: Computational evidence through hybrid density functional theory

Abstract

Carbon dioxide (CO2) represents an industry-generated greenhouse gas, whose excessive presence in the atmosphere of the Earth is undesirable. Novel CO2 scavengers are being introduced nowadays to fix and valorize CO2 at the moment of its production. We herein invented an original solution for the CO2 chemisorption by the carbonaceous cathode at which voltage is applied. The electron-rich carbon atoms readily react with CO2 and produce carboxylated derivatives, which only remain stable as long as the external voltage remains applied. The kinetics and thermochemistry of the process are strongly sensitive to the electronic charge provided to the electrochemical setup. Upon increasing the carbonaceous cathode charge density from 21µCcm−2 to 127µCcm−2, the energy effect of the reaction decreases from 92 to −196 kJ mol−1. In turn, the height of the activation barrier decreases from 98 to 7 kJ mol−1. The voltage turnoff results in an activation barrier-free desorption of all the captured gas. The formation and ruination of the carbon(cathode)-carbon(CO2) covalent bond occur thanks to an additional electron. Otherwise, the reaction is thermochemically prohibited. By using a graphene quantum dot (GQD) as an idealized model of the nanoscale porous cathode, we report extensive characterization through geometrical, electronic, and energetic properties of the involved chemical transformations. Since the local atomic structures of GQD and various activated carbon species possessing nanopores are similar, the available cheaper carbonaceous materials should exhibit qualitatively the same scavenger performance. We argue that the invented method is technologically simple to implement and scale up.