Development of high sensitivity electrochemical cell for in situ ESR spectroscopy focusing on carbon material selection indicator of organic energy device

In this study, the behaviour of carbon radicals has been observed in a laminate-type model cell of an electric double layer capacitor (EDLC) by using an in situ electron spin resonance (ESR) method and cyclic voltammetry (CV). The laminate-type model cell had a 70 mm length, 8 mm width and 1.5 mm thickness. It is first necessary to confirm that this model cell was able to be measured by ESR, because the model cell contained an electrolyte solution with a high dielectric loss. This problem was solved by adjusting the insertion distance in the resonant cavity to about 5 mm. The g-value of 2.0028 was calculated from each ESR spectrum, indicating that these signal peaks were identified in the radical of the carbon centre, and the ESR signal-to-noise ratio was 74. This finding indicated that this laminate-type model cell could be used for the in situ ESR measurement. This model cell was able to increase the sensitivity to fifteen times compared with the ESR cylindrical-sample-tube-type EDLC model cell developed by Ito and co-workers (Ref. 10). The cyclic voltammogram and the in situ ESR spectra were measured simultaneously by using the laminate-type model cell. The amount of the carbon radical increase as the CV cycle number increased. This finding indicated that the laminate-type model cell could be used for the simultaneous measurement of the cyclic voltammogram and the in situ ESR spectra.