Water Enhancement of CO2Conversion on Silver in 1-Ethyl-3-Methylimidazolium Tetrafluoroborate

Abstract

Electrochemical recycling of carbon dioxide back to fuels and chemicals could be a viable method for CO₂ remediation if the efficiency of the process could be improved. One of the key challenges, though, is that the faradaic efficiency is low in the presence of water because water electrolysis is much easier than CO₂ electrolysis on most transition metal catalysts. Previous investigators have found that one can eliminate water conversion, by eliminating water from the system, but this has not proven to be practical. Here we present an alternate route, where EMIM-BF₄ is used to suppress water electrolysis. We observe that the addition of water to 1-ethyl-3-methyl imidazolium tetrafluoroborate (EMIM-BF₄) actually increased the efficiency of CO₂ conversion to CO. Indeed we find that little hydrogen is produced on silver in EMIM-Water solutions, provided the water concentration is no more than about 90% by mole. We observe an increase in rate of carbon monoxide (CO) production on silver and platinum as water is added to the electrolyte. We attribute this increase to the hydrolysis of tetrafluoroborate, which releases protons when mixed with water. Protons are shown to accelerate the reduction of CO₂ until a critical mole fraction of water is reached.