Formation of C-N Bond in Carbon Monoxide Electrolysis
Formation of C-N Bond During Carbon Monoxide Electrolysis acetamides across the amines tested, providing strong evidence that acetate forms from nucleophilic hydroxide attack of the ketene intermediate, which competes with the amines. Matthew Jouny and Feng Jiao* a b Center of Catalytic Science and Technology, Department of Chemical and Biomolecular CO CO - e- e - - Engineering, University of Delaware, Newark DE 19716 (USA) Amide PrOH AcO EtOH C2H4 H2 Amide PrOH AcO EtOH C2H4 H2 *[email protected] 350 350
) 100 ) 100 300
300 2 2 Introduction 80 250 80 250 The electrochemical conversion of carbon dioxide (CO2) is a promising technology 200 200 60 60 for the sustainable production of fuels and chemicals. Multi-carbon (C2+) products are 150 150 particularly favorable due to their high value and significant market potential [1]. Highly 40 40 100 100
alkaline electrolytes have been shown to facilitate CO2 reduction to C2+ products [2]. However, Faradaic efficiency (%)
Faradaic efficiency (%) 20 20 Current density (mA/cm the inevitable reaction between CO2 and hydroxide to form carbonates hinders process 50 Current density (mA/cm 50 sustainability. This can be remedied by decoupling the electrolysis through the carbon 0 0 0 0 monoxide (CO) intermediate, where CO2 is initially reduced to CO in neutral conditions, which -0.40 -0.45 -0.50 -0.55 -0.60 -0.65 -0.45 -0.50 -0.55 -0.60 -0.65 -0.70 has been shown with high selectivity [3]. The produced CO can then be efficiently converted to Potential (V vs. RHE) Potential (V vs. RHE) c C2+ products in highly alkaline conditions. Amide n-Propanol Acetate CO Ethanol Ethylene H2 Recently, we demonstrated CO electrolysis to C2+ products with >90% selectivity at e- Amide PrOH AcO- EtOH C H H d 350 industrially relevant reaction rates and showed that acetate likely forms through nucleophilic 2 4 2 350 0.8 hydroxide attack of a reactive intermediate [4]. However, only four major C2+ products 0.7 100 300 ) (ethylene, ethanol, n-propanol, and acetate) are produced through conventional CO/CO2 2 100 300 electrolysis. We hypothesized that performing CO electrolysis in the presence of other 0.6 80 250 Ethylene nucleophilic species could lead to additional reaction products, greatly expanding the scope of 0.5 Alcohols 200 possible CO electrolysis products, which would facilitate the commerciality of the technology. 0.4 Acetate 250 60 80 ) Amide 2 Here, we demonstrated that concept by using amines to form C-N bonds during CO 150 0.3 electrolysis, leading to the production of acetamides, which are useful polymerization solvents. 40 100 0.2 200
Faradaic efficiency (%) 20 0.1
Current density (mA/cm 60 Materials and Methods 50 Molar Production Fraction CO electrolysis was performed in the presence of four amines: ammonia gas and 0.0 0 0 150 -0.40 -0.45 -0.50 -0.55 -0.60 -0.65 None 5M solutions of methylamine, ethylamine, and dimethylamine, using a three-compartment flow NH3 CH3NH2 Et-NH2 NH(CH3)2
electrolyzer as previously reported [4]. Copper nanoparticles (25 nm) deposited on a gas Potential (V vs. RHE) 40 Amine Faradaic efficiency (%)
Figure 1: CO electrolysis performance data for acetamides production from 5M solutions Current density (mA/cm diffusion electrode were used as the cathode, while the IrO2 anode was separated using an 100 FAA-3 anion exchange membrane. Gas products were quantified using gas chromatography, (with 1M KCl) of A) methylamine, B) ethylamine, and C) dimethylamine, and (D) molar production fractions of different products at 200 mA/cm2 for each amine source and liquid products were quantified using NMR. Supplemental Density Functional Theory 20 (DFT) calculations were performed using the Vienna ab initio simulation program. 50 Significance Results and Discussion We demonstrate the first C-N bond formation in CO/CO2 electrolysis, providing a facile alternative process to produce acetamides, as well 0 as identifying nucleophilic attack of CO0 CO electrolysis using a 2:1 ratio of NH3/CO gas feed in 1M KOH led to the -0.45 -0.50 -0.55 -0.60 -0.65 -0.70 electrolysis intermediates as a platform for further heteroatomic compound formation. production of acetamide with a peak Faradaic efficiency (selectivity) of 38% and a total current Potential (V vs. RHE) density of 300 mA/cm2 at a modest potential of -0.68 V vs. RHE. The overall CO reduction selectivity was 90%. DFT calculations suggested acetamide formation through nucleophilic References amine attack of a ketene, *C=C=O, intermediate. Additional acetamides were formed from 1. Jouny, M., Luc, W. & Jiao, F. Ind. Eng. Chem. Res. 57, 2165 (2018). their respective amines (Figure 1a-c), where amide formation was correlated to the 2. Lv, J.-J., et. al, Advanced Materials 30, 1803111 (2018). nucleophilicity of the amine precursor (Figure 1d). Acetate production varied inversely to 3. Luc, W., Jouny, M., Rosen, J. & Jiao, F. Energy Environ. Sci. 11, 2928 (2018). 4. Jouny, M., Luc, W. & Jiao, F. Nature Catalysis 1, 748 (2018).