Double redox aqueous capacitor with high energy output

Adam Slesinski, Sylwia Sroka, Sergio Aina, Justyna Piwek, Krzysztof Fic, M. Pilar Lobera, Maria Bernechea and Elzbieta Frackowiak, J. Mater. Chem. A, 2023, Accepted Manuscript. DOI:

The paper puts forward the concept of double redox electrochemical capacitor operating in an aqueous electrolyte. The redox activity of sulphur from insoluble Bi2S3 nanocrystals embedded in the negative electrode material (up to 10wt%) operated in 1 mol L-1 Li2SO4 electrolyte has been demonstrated. It is also shown that the performance is significantly boosted using MPA (3-mercaptopropionic acid) as a ligand attached to the nanocrystals surface, which allows for more efficient use of Bi2S3 redox active species. This redox activity is combined with the reactions of iodides which take place at opposite electrode using 1 mol L-1 NaI. This enables formation of discharge voltage plateau that effectively boosts the capacitance (275 F g-1), and thus energy density of the device thanks to relatively high cell voltage of 1.5 V. This performance is possible due to the advantageous electrode mass ratio (m-:m+ = 2:1), which helps to balance the charge. The device retains 73% of its capacitance at 10 A g-1 of discharge current. The different states of the redox species ensure their operation at separate electrodes in an immiscible manner without a shuttling effect. The specific interactions of the redox active species with carbon electrodes are supported by operando Raman spectroscopy.

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