Small molecular fluorocarbons (FCs) and hydrofluorocarbons (HFCs), mainly used in refrigeration, are potent greenhouse gases that persist in our atmosphere. These chemicals are estimated to have thousands times greater global warming potential than that of carbon dioxide. Thus, there is significant need to develop efficient methods of decomposing these compounds. Electrochemical reduction can decompose fluorocarbons irreversibly, which is ideal for applying it to these greenhouse gas removal. The process of decomposition via electrochemical reduction can be easily studied using cyclic voltammetry. However, electron transfer (ET) reactions involving FCs and HFCs often have poor ET kinetics with large over-potential, and they occur at very negative voltages due to the large strength of the carbon-fluorine bond, together making the electrochemical reduction process ineffective for applications. Perfluorodecalin is currently studied as a model compound for fluorocarbon defluorination, as shown by Combellas et al in their early work. Preliminary results from reducing perfluorodecalin collected in this study have confirmed the sluggish nature of ET process and the large over-potential of the reduction. By utilizing an ET mediator, the reaction barrier for the electrochemical reduction can be lowered. Molecules with both an aromatic functional group and a perfluoroalkyl chain may perform well in the role of an ET mediator in this context. Theoretically, these functional groups together would provide an easier pathway for electrons to flow from a working electrode to a fluorocarbon compound in an electrochemical cell. The reduction of molecules with this structure have been examined in the past with widely varying reduction potentials due to the large diversity in structures possible. A mixture of 4-(perfluoroethyl)benzonitrile with perfluorodecalin showed a significant increase in the current and slope of the reduction wave compared to that of the perfluorodecalin reduction alone. This result indicates a probable ET mediating behavior of the 4-(perfluoroethyl)benzonitrile. Continuing to work towards designing a versatile and intelligent structure for an ET mediator or even an ET catalyst for this type of reductive defluorination will be important to improve the viability of reductive decomposition of FCs and HFCs in the future.

Defluorination of perfluorodecalin via electrochemical reduction

ACS Spring 2022

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