(A) novel electrochemical system with a permeable CNT membrane for facile conversion of $CO_2$

Abstract

Electrocatalytic $CO_2$ reduction (e$CO_2$R) has been highlighted as a novel strategy to mitigate the emission of $CO_2$ and to store renewable energy as a form of organic fuels simultaneously. In this study, $SnO_x$-doped carbon nanotubes were fabricated to the conductive and permeable hollow-fiber electrodes (Sn-CHM), and operated in gas-phase mode to overcome the dependence of catalysts on precious metals (e.g., silver, gold) and the low current density, which represents reaction rate during the CO production from the e$CO_2$R. Due to the enhanced $CO_2$ mass transport in gas-phase operation compared to conventional liquid-phase mode, Sn-CHM achieved the highest CO selectivity and current density among previously reported Sn-based electrodes. From the computational calculation based on the density functional theory (DFT), the highly charged surface of the Sn-CHM as a result of even distribution of SnOx particles on CNT structures significantly reduced the adsorption energy and stabilized key intermediates of the e$CO_2$R for CO production. The highest conversion efficiency and current density for syngas production among non-noble metals based catalysts were achieved by controlling operational parameters including $SnO_x$ loading, flow rate of $CO_2$ gas, and pH of electrolyte in the e$CO_2$R, and this was achieved under low overpotential comparing to noble metals.