Efficient Photoelectrochemical Reduction of Carbon Dioxide to Formic Acid: A Functionalized Ionic Liquid as an Absorbent and Electrolyte

Photoelectrochemical (PEC) reduction of carbon dioxide (CO2) is a potential method for production of fuels and chemicals from a C1 feedstock accumulated in the atmosphere. However, the low solubility of CO2 in water, and complicated processes associated with capture and conversion, render CO2 conversion inefficient. A new concept is proposed in which a PEC system is used to capture and convert CO2 into formic acid. The process is assisted by an ionic liquid (1‐aminopropyl‐3‐methylimidazolium bromide) aqueous solution, which functions as an absorbent and electrolyte at ambient temperature and pressure. Within this PEC reduction strategy, the ionic liquid plays a critical role in promoting the conversion of CO2 to formic acid and suppressing the reduction of H2O to H2. At an applied voltage of 1.7 V, the Faradaic efficiency for formic acid production is as high as 94.1 % and the electro‐to‐chemical efficiency is 86.2 %. Capture and conversion: A functionalized ionic liquid (IL) was used as an absorbent and electrolyte in photoelectrocatalytic reduction of CO2. The IL was critical for promoting conversion of CO2 to formic acid (FA) and suppressing reduction of H2O to H2. A 94.1 % faradaic efficiency and 86.2 % electro‐to‐chemical efficiency were achieved at 1.7 V for FA production. PEM=proton exchange membrane.