Highly Selective TEMPO Catalyzed Bulk Electrooxidation of Isopropanol to Acetone for Application in Electrochemical Heat Pumping

Air conditioning, space heating, and refrigeration account for approximately 40% of electricity usage in the U.S. residential and commercial building sector. Therefore, the develop-ment of more energy efficient heat pump technologies remains an ongoing pursuit with widespread practical implications. Electro-chemical looping heat pump (ELHP) technology has emerged as an attractive alternative to conventional vapor compression systems (VCS), theoretically promising significant improvements in both performance and energy consumption. However, efficient ELHPs require selective facilitation of redox reactions that interconvert working fluids with minimal energy input. In this work, we report on the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) mediated oxidation of isopropanol (IPA) to acetone as a promising system for ELHP. We characterized the performance of seven different TEMPO derivatives for mediated electrocatalytic IPA to acetone conversion. 4-Methoxy-TEMPO emerged as the most promising candidate which selectively oxidized IPA to acetone in basic pH as confirmed via electrochemical methods and 13C NMR. Coupling experimental results with DigiElch simulations helped in characterizing the rate constant for the reaction as 6 M-1 s-1 and a turnover frequency of 3.1 s-1 at pH 10. Bulk electrolysis measurements followed by 13C NMR highlighted the selectivity of the catalyst (similar to 100%), even at IPA concentrations as high as 0.5 M IPA, making them ideal for use in practical ELHP. This work introduces a methodology to identify suitable catalysts for efficient ELHP and other bulk conversion methods based on concepts of highly selective mediated electrocatalysis.