Electrochemical Reduction of Carbon Dioxide II. Design, Assembly, and Performance of Low Temperature Full Electrochemical Cells

In this paper, we report the performance of a full electrochemical cell which directly converts carbon dioxide to fuels at room temperature and ambient pressure. The design of this cell features a buffer layer of liquid-phase electrolyte circulating between the ion exchange membrane and the cathode Sn catalyst layer. In the absence of the buffer layer, hydrogen was the predominant product with a faradaic efficiency nearly similar to 100%. Incorporating a buffer layer with an electrolyte, e.g. 0.1 M KHCO3, substantially promoted the formation of formate and CO, while suppressing hydrogen production. When the anode was fed with hydrogen, the onset of formate production occurred at 0.8 V, with a faradaic efficiency of 65% and a partial current density of -1 mA cm(-2); at which the energy efficiency toward formate production was 50%. The highest faradaic efficiency observed toward formate formation was over 90% at -1.7 V corresponding to a partial current density of -9 mA cm(-2). When the anode was fed with aqueous reactant (e.g. 1 M KOH solution), the formate production began at -1.2 V with a partial current density of -1 mA cm(-2), corresponding to a faradaic efficiency of 70% and an energy efficiency of 60%. In this case, the highest faradaic efficiency toward formate formation was 85% at -2.0 V with a partial current density of -6 mA cm(-2). Our studies show that this full electrochemical cell with a circulating liquid-phase electrolyte buffer layer enables production of formate at an overpotential of similar to-0.2 V regardless of the gaseous or aqueous reactants at the anode side. (C) 2013 The Electrochemical Society. All rights reserved.