Impact of the Dissolved Anion on the Electrocatalytic Reduction of CO2 to CO with Ruthenium CNC Pincer Complexes

The reactivity of three ruthenium electrocatalysts is shown to be modulated through the addition of anions for more selective and faster electrocatalysis. Controlled potential electrolysis studies confirm the generation of CO from CO2. The Faradaic efficiency increased for the three ruthenium catalysts studied through the introduction of Cl– to the reaction solution. Interestingly, a neutral ruthenium coordination complex with an associated chloride also gave equal or faster rates of catalysis upon Cl− addition. In this report, a systematic study on the effects of added halides (I−, Br−, Cl−, and F−) with varied counter cations (K+ and TBA+) with and without water is examined. Computational analysis provides insights into this interesting increase in FE based on anion addition. These results show anion addition to electrocatalysis reaction mixtures add an additional parameter to increase both rate and selectivity of catalysis with one example improving from 19 % FE to 91 % FE for CO production. The addition of halide anions to the electrocatalytic CO2 reduction reaction driven by ruthenium catalysts is found to dramatically influence the Faradaic efficiency and reaction rate. Faradaic efficiencies were found to change from 19 to 91 % in the most dramatic case upon addition of Cl−. Interestingly, computational results reveal an active catalyst with an associated halide is plausible where the halide is trans to the reactive site.