ИСТИНА

The electrochemical reduction of carbon dioxide (CO2) currently receives global interest as one of the most promising approaches to mitigate and utilize CO2 gas, which is regarded as one of the major contributors to the greenhouse effect.[1] The main advantage of using an electrochemical approach for such CO2 conversion is that it can be combined with the use of renewable energy resources (solar, wind, hydro).[2] Ionic liquids (ILs) have recently gained significant attention as electrolyte for CO2 reduction due to several unique advantages: (i) ILs exhibit a selective and relatively high absorption of CO2; (ii) ILs suppress the parasitic hydrogen evolution reaction; (iii) ILs decrease the overpotential of CO2 reduction via stabilization of CO2 radical anion intermediate.[3] Therefore, ILs are proposed as the next generation of effective solvents for CO2 capture/sequestration and its conversion. However, the mass transport of CO2 in ILs is typically slow due to the relatively high viscosity of ILs. Recently we demonstrated that dilution of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]) with water improved the mass transport properties and boosted CO2 reduction reaction (CO2RR) to carbon monoxide (CO) on a silver electrode [4]. Now we compare the mass transport properties of CO2 and CO2RR in [BMIm][BF4] with those in ILs, 1-ethyl-3-methylimidazolium tricyanomethanide ([EMIm][TCM]) and 1-ethyl-3-methylimidazolium tetracyanoborate ([EMIm][TCB]), which have significantly lower intrinsic viscosity (Fig. 1). A pulsed-gradient spin-echo (PGSE) NMR spectroscopy is used to determine the concentration and diffusion coefficients of CO2 and other solution components. The effect of water addition is explored in the diffusion-controlled CO2RR in IL/water mixtures by means of voltammetry, chronoamperometry and rotating disc electrode techniques. The diffusion coefficients obtained from PGSE-NMR are compared with those obtained from electrochemical measurements. The formation of CO in CO2 electroreduction is confirmed by online gas chromatography.