CO2 Electrolyzer to Produce Formic Acid Using Flue Gas at Industry Relevant Current Density

Abstract

The electrochemical conversion of carbon dioxide (CO2) into valuable fuels and feedstocks has gained great attention recently due to the global urgency to mitigate the rapid climate change. A wide variety of chemicals can be obtained through the electrochemical CO2 reduction reaction (CO2RR). Among all the chemicals generated through CO2RR, formic acid has attracted great interest because of its wide applications in silage preservation in agriculture, as an antibacterial agent in animal food additives, as a chemical additive in leather and tanning processing, as a chemical component in textile dyeing and finishing, as a reagent in pharmaceutical and chemical synthesis, and as deicing agents and a component in drilling fluids. Recently, the use of formic acid as a feedstock for biorefineries has also attracted increasing interest.Over the past decade, much effort has been devoted to the prospects of electrochemical CO2 conversion to formic acid. However, issues including low current density, low selectivity, low energy efficiency, lack of long-term stability evaluation, and production of formate salts instead of formic acid remain as the great challenges for the development and commercialization of this technology. Additionally, up to date, most of the electrochemical CO2 reduction work has been conducted in idealized laboratory conditions, such as feeding pure CO2 gas in the electrochemical cell. However, when CO2 is emitted with flue gas, reduced CO2 composition and different contaminants are present. If one wants to use flue gas as the source of CO2 for CO2RR to reduce CO2 emission and embrace circular economy, it is critical to identify the potential effect of the contaminants and CO2 composition on CO2RR. Thus, appropriate treatments and catalysts can be developed to mitigate the detrimental effects if any when a flue gas stream is used as the source of CO2.Recently, Dioxide Materials (DM) has developed an electrolyzer technology that can directly convert CO2 to pure formic acid using a three-compartment CO2 electrolyzer. In this work, we will present our recent efforts on how to run CO2 electrolyzers to produce pure formic acid using a flue gas as CO2 source at an industry relevant current density (200 mA/cm2). The testing results showed that the CO2 electrolyzer could directly produced formic acid with concentration and Faradaic efficiency (FE) up to 16 wt% (3.6 M) and 91%, respectively, depending on the operation conditions. We also investigated how the CO2 composition and impurities in the flue gas affect the electrolyzer performance. The electrolyzer operation results with 14, 50, 100 vol% CO2 at 200 mA/cm2 indicated that the electrolyzer shared similar performance with 50 and 100 vol% CO2 while the one with 14 vol% CO2 showed slightly lower performance. Among the impurities (O2, NOx and SOx) tested, O2 presents the most detrimental effect on CO2 electrolzyer performance. The detailed effects of O2, as well as NOx and SOx on the electrolyzer performance will be presented. Lastly, the long-term (1000 h) performance of the electrolyzer at different conditions and the strategy to maintain the performance will be discussed, as well as the ongoing efforts to test the device at a coal fired power plant. Figure 1