Microchannel reactor is a novel electrochemical device to intensify CO2 mass transfer with large interfacial areas. However, if the catalyst inserted in the microchannel is wetted, CO2 is required to diffuse across the liquid film to get access to reaction sites. In this paper, a hydrophobic polytetrafluoroethylene (PTFE)-doped Ag nanocatalyst on a Zn rod was synthesized through a facile galvanic replacement of 2Ag++Zn → 2Ag + Zn2+. The catalyst layer, which was PTFE incorporated into the Ag matrix, was detected to distribute uniformly on the Zn substrate with a thickness of 77 μm. Consequently, the PTFE-doped electrode demonstrated enhanced activity with an optimal 96.19% CO faradaic efficiency (FECO) in the microchannel reactor. Typically, the catalyst could maintain over 90% FECO even at the current density of 24 mA cm-2, which was nearly 30% higher than that of a similar catalyst without PTFE. In addition, influences of the concentration of PTFE and deposition time were also investigated, determining that 1 vol % of PTFE and 30 min of coating yielded best electrocatalytic efficiency. To achieve a further breakthrough of CO2 mass transfer limitations, reactions were applied under relatively high pressures (3-15 bar) in a single-compartment high-pressure cell. The maximum CO partial current density (jCO) can reach 106.76 mA cm-2 at 9 bar.
Keywords: CO2 electroreduction; high pressure; hydrophobicity; microchannel reactor; modified electrodes.