Role of pressure and current density on the cathodic conversion of CO2 using Ag, Sn, Bi and Ni cathodes

Abstract

In recent years, there has been an increasing attention towards the cathodic reduction of pressurized CO2 (PrCO2CR) to produce various chemicals, such as formic acid or formate (FA), CO, synthesis gas and higher hydrocarbons. Recently, in the case of Ag cathode, it has been shown that the optimization of PrCO2CR requires an accurate selection of the couple current density (j) - pressure (). In particular, it was found that the faradaic efficiency in CO doesn’t always increase with the pressure; conversely, a maximum was observed for the plot faradic efficiency vs. . In this work, the PrCO2CR process was investigated using various commercial cathodes (Sn, Bi, Ag and Ni) in an undivided cell to evaluate the role of the and j for each cathode. It was found that the optimal and j values ranged from 30 and 55 bar and −150 and −190 mA cm−2, respectively, for both Sn, Bi and Ag cathodes. It was observed that the plot of the total faradaic efficiency towards all CO2 reduction products () vs gave a curve with a maximum for both Sn and Ag, while for Ni and Bi a monotonic increase of with was observed up to 55 bar. On the other hand, the plot vs j gave a curve with a maximum for all tested electrodes. The maximum value was achieved at higher j when higher pressures were used. Moreover, the effect of and j on the economic figures of the process was evaluated for Sn, Ag and Bi and best operating conditions were found for each cathode.