Effects of electrolytes on the electrochemical reduction of CO2 to C2H4: a mechanistic point of view

The most attractive strategy to mitigate energy shortages and environmental pollution caused by fossil fuel consumption and CO2 emissions is to utilize renewable clean energy and convert CO2 into high value-added chemical products. However, it has been proven that activation and reduction of CO2 is a great challenge because of their thermodynamic stability and kinetic inertness. Recently, electrochemical conversion has emerged as one of the most flourishing means of converting CO2 into chemicals, ranging from common C-1 products (i.e. CO and formate) to C2+ products (i.e. ethylene, ethanol, and oxalic acid). The product distribution, i.e. the ratio of C-1 to C2+, is primarily determined by the electrode potential, cathode catalyst and electrolyte. Among them, the electrolyte plays a significant role in the total reaction efficiency and product selectivity. Here, we give a mini-review of the recently reported effects of various electrolytes on the selectivity to C2+ products (especially ethylene) in the electroreduction of CO2 and propose the mechanism of C-C coupling and possible reaction pathways, aiming to better understand the role of electrolytes in the electroreduction of CO2 to C2+ products and to provide insights into the field of process optimization for the electrochemical conversion of CO2 to high value-added chemicals and fuels. In recent years, ionic liquids have received widespread attention due to their high solubility for CO2 and the designability of their structures. They are generally considered as a green and efficient medium for homogeneous and heterogeneous catalytic reactions under ambient conditions. Here, we also briefly introduce some studies on ionic liquids used in the electrochemical reduction of CO2

Effects of electrolytes on the electrochemical reduction of CO2 to C2H4: a mechanistic point of view

The most attractive strategy to mitigate energy shortages and environmental pollution caused by fossil fuel consumption and CO2 emissions is to utilize renewable clean energy and convert CO2 into high value-added chemical products. However, it has been proven that activation and reduction of CO2 is a great challenge because of their thermodynamic stability and kinetic inertness. Recently, electrochemical conversion has emerged as one of the most flourishing means of converting CO2 into chemicals, ranging from common C-1 products (i.e. CO and formate) to C2+ products (i.e. ethylene, ethanol, and oxalic acid). The product distribution, i.e. the ratio of C-1 to C2+, is primarily determined by the electrode potential, cathode catalyst and electrolyte. Among them, the electrolyte plays a significant role in the total reaction efficiency and product selectivity. Here, we give a mini-review of the recently reported effects of various electrolytes on the selectivity to C2+ products (especially ethylene) in the electroreduction of CO2 and propose the mechanism of C-C coupling and possible reaction pathways, aiming to better understand the role of electrolytes in the electroreduction of CO2 to C2+ products and to provide insights into the field of process optimization for the electrochemical conversion of CO2 to high value-added chemicals and fuels. In recent years, ionic liquids have received widespread attention due to their high solubility for CO2 and the designability of their structures. They are generally considered as a green and efficient medium for homogeneous and heterogeneous catalytic reactions under ambient conditions. Here, we also briefly introduce some studies on ionic liquids used in the electrochemical reduction of CO2

Effect of Halide Anions on the Electroreduction of CO2 to C2H4: A Density Functional Theory Study

The halide anions present in the electrolyte improve the Faradaic efficiencies (FEs) of the multi-hydrocarbon (C2+) products for the electrochemical reduction of CO2 over copper (Cu) catalysts. However, the mechanism behind the increased yield of C2+ products with the addition of halide anions remains indistinct. In this study, we analysed the mechanism by investigating the electronic structures and computing the relative free energies of intermediates formed from CO2 to C2H4 on the Cu (100) facet based on density functional theory (DFT) calculations. The results show that formyl *CHO from the hydrogenation reaction of the adsorbed *CO acts as the key intermediate, and the C-C coupling reaction occurs preferentially between *CHO and *CO with the formation of a *CHO-CO intermediate. We then propose a free-energy pathway of C2H4 formation. We find that the presence of halide anions significantly decreases the free energy of the *CHOCH intermediate, and enhances desorption of C2H4 in the order of I->Cl->Br->F-. Lastly, the obtained results are rationalized through Bader charge analysis

Effect of Halide Anions on the Electroreduction of CO2 to C2H4: A Density Functional Theory Study

The halide anions present in the electrolyte improve the Faradaic efficiencies (FEs) of the multi-hydrocarbon (C2+) products for the electrochemical reduction of CO2 over copper (Cu) catalysts. However, the mechanism behind the increased yield of C2+ products with the addition of halide anions remains indistinct. In this study, we analysed the mechanism by investigating the electronic structures and computing the relative free energies of intermediates formed from CO2 to C2H4 on the Cu (100) facet based on density functional theory (DFT) calculations. The results show that formyl *CHO from the hydrogenation reaction of the adsorbed *CO acts as the key intermediate, and the C-C coupling reaction occurs preferentially between *CHO and *CO with the formation of a *CHO-CO intermediate. We then propose a free-energy pathway of C2H4 formation. We find that the presence of halide anions significantly decreases the free energy of the *CHOCH intermediate, and enhances desorption of C2H4 in the order of I->Cl->Br->F-. Lastly, the obtained results are rationalized through Bader charge analysis

Selective separation of Nd from La/Ce/Pr using phosphate-based ionic liquids: Solvent extraction studies and density functional theory

Since neodymium (Nd) has similar physicochemical properties to lanthanum (La), cerium (Ce) and praseodymium (Pr), their efficient separation and purification is very difficult. Three new phosphate-based ionic liquids (ILs): N,N-dimethyloctylamine bis(2-ethylhexyl)phosphate ([N-1,N-1,N-8,N-H][DEHP]), N,N-dimethyldecylamine bis(2-ethylhexyl)phosphate ([N-1,N-1,N-10,N-H][DEHP]), N,N-dimethyldodecylamine bis(2-ethylhexyl)phosphate ([N-1,N-1,N-12,N-H] [DEHP]) were synthesized and evaluated for selective separation of Nd(III) from aqueous solution. The influences concentration of Nd(III), phase volume ratio (O/A), cation chain length of ILs, extraction time, extraction temperature, salt concentration, solution acidity have on the performance of ILs for extraction separation of Nd(III) from aqueous solution were systematically investigated. It was found that the extraction efficiency (E) of Nd(III) using [N-1,N-1,N-8,N-H][DEHP] was close to 100% at pH of 4, and that it only required 10 min to reach extraction equilibrium at 303 K. Meanwhile, the separation factors (beta) values of beta Nd/La, beta Nd/Ce, beta Nd/pr using [N-1,N-1,N-8,N-H][DEHP] were all higher than 3. The density functional theory (DFT) results indicated that the interaction between [N-1,N-1,N-8,N-H][DEHP] and Nd were stronger than that between La, Ce and Pr. In addition, almost 100% of Nd(III) could be recycled from the loaded [N-1,N-1,N-8,N-H][DEHP] phase using 0.16 mol center dot L-1 hydrochloric acid via one step, and the E of Nd(III) by regenerated [N-1,N-1,N-8,N-H][DEHP] remained about 97% after eight cycles. Moreover, the extraction mechanism of Nd(III) using [N-1,N-1,N-8,N-H][DEHP] was complexation mechanism based on infrared spectroscopy and slope analysis. This work furnishes a strategy for selective separation of Nd(III) using phosphate-based ILs without diluent

Selective separation of Nd from La/Ce/Pr using phosphate-based ionic liquids: Solvent extraction studies and density functional theory

Since neodymium (Nd) has similar physicochemical properties to lanthanum (La), cerium (Ce) and praseodymium (Pr), their efficient separation and purification is very difficult. Three new phosphate-based ionic liquids (ILs): N,N-dimethyloctylamine bis(2-ethylhexyl)phosphate ([N-1,N-1,N-8,N-H][DEHP]), N,N-dimethyldecylamine bis(2-ethylhexyl)phosphate ([N-1,N-1,N-10,N-H][DEHP]), N,N-dimethyldodecylamine bis(2-ethylhexyl)phosphate ([N-1,N-1,N-12,N-H] [DEHP]) were synthesized and evaluated for selective separation of Nd(III) from aqueous solution. The influences concentration of Nd(III), phase volume ratio (O/A), cation chain length of ILs, extraction time, extraction temperature, salt concentration, solution acidity have on the performance of ILs for extraction separation of Nd(III) from aqueous solution were systematically investigated. It was found that the extraction efficiency (E) of Nd(III) using [N-1,N-1,N-8,N-H][DEHP] was close to 100% at pH of 4, and that it only required 10 min to reach extraction equilibrium at 303 K. Meanwhile, the separation factors (beta) values of beta Nd/La, beta Nd/Ce, beta Nd/pr using [N-1,N-1,N-8,N-H][DEHP] were all higher than 3. The density functional theory (DFT) results indicated that the interaction between [N-1,N-1,N-8,N-H][DEHP] and Nd were stronger than that between La, Ce and Pr. In addition, almost 100% of Nd(III) could be recycled from the loaded [N-1,N-1,N-8,N-H][DEHP] phase using 0.16 mol center dot L-1 hydrochloric acid via one step, and the E of Nd(III) by regenerated [N-1,N-1,N-8,N-H][DEHP] remained about 97% after eight cycles. Moreover, the extraction mechanism of Nd(III) using [N-1,N-1,N-8,N-H][DEHP] was complexation mechanism based on infrared spectroscopy and slope analysis. This work furnishes a strategy for selective separation of Nd(III) using phosphate-based ILs without diluent

Hydrogen bond donor functionalized poly(ionic liquid)s for efficient synergistic conversion of CO2 to cyclic carbonates

The development of metal-free, high effective and recyclable catalysts plays a pivotal role in transforming CO2 into high value-added products such as cyclic carbonates. In this paper, we introduced the hydrogen bond donor (HBD) groups into poly(ionic liquid)s via free radical polymerization, which successfully combined the HBD and ionic liquids (ILs) into one heterogeneous catalyst. The HBD could synergistically activate epoxides with hydroxyl functionalized ionic liquids and efficiently catalyze the cycloaddition of CO2 into cyclic carbonates. The yield of propylene carbonate (PC) reached 94% (at 105 degrees C, 2 MPa CO2, 3 h), which far exceeded poly(ionic liquid)s without HBDs functionalization (PC yield 72%), and even approached bulk ionic liquids (PC yield 95%). Moreover, HBD-functionalized poly(ionic liquid)s (HPILs) exhibited excellent recyclability after five runs and afforded wide substrate scope. According to the experimental results, H-1 NMR spectra and density functional theory (DFT) calculations showed 2-hydroxyethyl methacrylate (HEMA) and the hydroxyl of ILs would form strong H-bonds with epoxides contributing to the ring-opening process of epoxides, and a possible HBD and nucleophilic anion synergistically catalytic mechanism was proposed. The method herein paved a brand new way for green technology and utilization of poly(ionic liquid)s