Rich I. Masel

Electrochemical CO2 reduction reaction (CO2RR) to produce formic acid has attracted great interest recently since formic acid can be used as a feedstock for biorefineries. 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, poor long-term stability, and production of formate salts instead of formic acid remain as the great challenges for the development and commercialization of this technology. Recently, Dioxide Materials (DM) has developed an electrolyzer technology that can directly convert CO2 to pure formic acid with a three-compartment CO2 electrolyzer. In this work, DM will present our recent effort on improving the electrolyzer performance operating at industry relevant current density (200 mA/cm2). We have demonstrated 200 mA/cm² with 80% Faradaic efficiency for 1000 hours of operation. The effects of CO2 concentration and impurities in the flue gas on the electrolyzer performance will be discussed, as will ongoing efforts to test the device at a coal fired power plant. The long-term (1000 h) performance of the electrolyzer will also be presented.

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.

Electrochemical conversion of CO₂ to useful products at temperatures below 100 °C is nearing the commercial scale. Pilot units for CO₂ conversion to CO are already being tested. Units to convert CO₂ to formic acid are projected to reach pilot scale in the next year. Further, several investigators are starting to observe industrially relevant rates of the electrochemical conversion of CO₂ to ethanol and ethylene, with the hydrogen needed coming from water. In each case, Faradaic efficiencies of 80% or more and current densities above 200 mA cm⁻² can be reproducibly achieved. Here we describe the key advances in nanocatalysts that lead to the impressive performance, indicate where additional work is needed and provide benchmarks that others can use to compare their results.

This paper is a review on the application of imidazolium-based ionic liquids tethered to polymer backbones in the electrochemical conversion of CO₂ to carbon monoxide and formic acid. These tethered ionic liquids have been incorporated into novel anion ion exchange membranes for CO₂ electrolysis, as well as for ionomers that have been incorporated into the cathode catalyst layer, providing a co-catalyst for the reduction reaction. In using these tethered ionic liquids in the cathode catalyst composition, the cell operating current increased by a factor of two or more. The Faradaic efficiencies also increased by 20–30%. This paper provides a review of the literature, in addition to providing some new experimental results from Dioxide Materials, in the electrochemical conversion of CO₂ to CO and formic acid.

Electrochemical reduction of CO2 to formic acid has been attracting increasing interest in recent years due to the unique properties and potential applications of formic acid. Dioxide Materials has demonstrated the direct formation of formic acid in a 3-compartment CO2 electrolyzer with good performance. The electrolyzer was previously run with pure CO2. In the present work, the electrolyzer is operated with reduced CO2 concentration and the performance of electrolyzer is tested as a function of CO2 concentration. The testing results indicate decreased formic acid selectivity with reduced CO2 concentration. To improve the electrolyzer performance, a variety of strategies has been employed, including modification of electrolyzer design and components, adjustment of electrolyzer operation conditions. The electrolyzer performance (voltage, current, formic acid selectivity and production, and Faraday Efficiency) after modification has been evaluated and the results will be presented and discussed.

Carbon dioxide (CO₂) electrolysis provides a pathway to close the anthropogenic carbon cycle and store renewable energy, but the stability, selectivity, efficiency and rate of such process needs to be improved. In this paper, we explore the use of Sustainion imidazolium-functionalized membranes and ionomers to improve the performance of that process. Potentiometric runs at a fixed current of 200 mA/cm² using Sustainion membranes and ionomers showed that one can maintain 98% selectivity at about 3V applied potential for five months, with a voltage increase of only 3 μV/hour. Other runs showed stable performance at 400 and 600 mA/cm². These results pave the way for commercialization of CO₂ electrolysis, providing a viable pathway to recycle CO₂ back to fuels.

Water electrolyzers are being developed as a way of storing renewable energy, as a way to produce hydrogen for fuel cell automobiles, and as a route to renewable fuels and chemicals. In this paper the effect of changes in the cathode catalyst on the performance of an anion exchange membrane water electrolyzer with Sustainion® membranes running at 60 °C in 1 M KOH. We choose commercial catalysts for study: Raney nickel from W.R. Grace, NiFeCo and Ni₈Fe₂ from US Nano, NiMoB, FeCoBSi, Ni₈₀Mo₂₀ from Fraunhofer Institute for Manufacturing Technology (IFAM), and NiMo/C from Pajarito Powder(PP). They are all supported on nickel fiber paper. Surprisingly, Raney nickel showed the best performance. At a fixed cell voltage of 2.0 volts in 1 M KOH at 60 °C, we observe 2.9 A/cm² cell current with the Raney Nickel catalyst, compared to 2.3 and 2.1 A/cm² with the US Nano catalysts, 1.7, 1.65 and 1.1 A/cm² with the IFAM catalysts, 1.5 A/cm² with the Pajarito Powder catalyst, and 0.95 A/cm² with the nickel fiber paper alone. These results demonstrate that catalysts that catalysts that show superior performance in a conventional alkaline water electrolyzer, may not show performance superior to Raney nickel in an anion exchange membrane water electrolyzer. Figure 1

Anion exchange membrane fuel cells are of interest since they allow to use non-precious metal catalyst for both anode and cathode reaction. More than 2000 articles have been published on alkaline membrane fuel cells(1). There is one previous report indicating initial power densities of 1W/cm² but with no long term data(2). The best long term data shows a cell voltage decrease by about 25% over 800hr at a current density of 400mA/cm² and 60°C. Presently, Sustainion® 37 anion exchange membranes have demonstrate excellent stability in anion exchange membrane carbon dioxide (CO₂) and water electrolyzer(3-6). Carbon dioxide electrolyzer runs at pH 6-8 with 10mM KHCO3 in anode(3), while water electrolyzer runs at pH close to 14 with circulating 1M KOH at both anode and cathode at 60C(4-6). Both alkaline CO₂ and water electrolyzers have demonstrated 4000hr runs with only 1-6µV/hr increase in the cell voltage(3, 5). Here we report our preliminary results for fuel cells with Sustainion® 43 anion exchange membranes as shown in Figure 1. In this data, Pt/C catalysts were used as both cathode and anode, and humidified H₂ and O₂ were fed to anode and cathode, respectively. The cell operated at 60 °C with back pressure of 1 atm. The maximum power density was 0.44W/cm² and the maximum current density was 2A/cm². These initial results suggest that Sustainion® 43 membranes could be useful for alkaline membrane fuel cells. Figure 1 Cell voltage and power density as function of current density of the fuel cell with Sustanion anion exchange membrane and Pt/C for both anode and cathode. Back pressure: 1 atm; cell temperature at 60°C. D. R. Dekel, Journal of Power Sources, 375, 158 (2018). L. Wang, E. Magliocca, E. L. Cunningham, W. E. Mustain, S. D. Poynton, R. Escudero-Cid, M. M. Nasef, J. Ponce-Gonzalez, R. Bance-Souahli, R. C. T. Slade, D. K. Whelligan and J. R. Varcoe, Green Chemistry, 19, 831 (2017). R. B. Kutz, Q. Chen, H. Yang, S. D. Sajjad, Z. Liu and I. R. Masel, Energy Technology, 5, 929 (2017). Z. Liu, S. D. Sajjad, Y. Gao, J. Kaczur and R. Masel, ECS Transactions, 77, 71 (2017). Z. C. Liu, S. D. Sajjad, Y. Gao, H. Z. Yang, J. J. Kaczur and R. I. Masel, International Journal of Hydrogen Energy, 42, 29661 (2017). R. I. Masel, Z. Liu and S. Sajjad, ECS Transactions, 75, 1143 (2016). Figure 1