Electrochemical production of syngas from CO₂ at pressures up to 30 bar in electrolytes containing ionic liquid

Electrochemical CO₂ reduction in a reactor that can operate up to 100 bar and 80 °C, with a configuration similar to that of an alkaline electrolyser, for hydrogen production suitable to be used industrially is reported for the first time. The effect of pressure on the co-electrolysis of CO₂ and water was studied. The successful scale-up from a previously reported batch process to electrodes of ca. 30 cm² geometrical area (30-fold factor) that combines the use of pressure and an ionic liquid-based electrolyte is presented. Also for the first time, the potential of the system under study to achieve high conversions of CO₂ to avoid a purification step of syngas from unreacted CO₂ is shown. An inexpensive commercial foil of the common metal zinc was employed. A semi-continuous operation yielded syngas productivities in the range of 0.02-0.04 mmol cm^-2 h^-1 at ca. -1.2 V vs. QRE Ag/Ag⁺. When an electrolyte consisting of 90 wt% H₂O and 10 wt% 1-ethyl-3-methylimidazolium trifluoromethanesulfonate was used, selectivities for CO in the range of 62% to 72% were obtained at 10 bar pressure, whereas selectivities of 82% were obtained at 30 bar pressure. H₂/CO ratios in the range of 1/1 to 4/1 at 10 bar pressure suitable for the synthesis of a variety of fuels, such as hydrocarbons, methanol, methane and chemical building blocks, were observed. An energy efficiency of 44.6% was calculated for a H₂/CO ratio of 2.2 suitable for the synthesis of methanol.