Raman Spectroscopy of Active-Carbon Electrodes when Au Colloids Are Placed at the Electrolyte/electrode Interface

Surface enhanced Raman spectroscopy (SERS) was used to study active-carbon (A -C) electrodes in super-capacitors cells; these electrodes were functionalized with Au nanoparticles (AuNPs). We observed a large enhancement in the cell's specific capacitance as a function of the AuNPs concentration. Cell capacitance is a volumetric effect while SERS is susceptible to the local number of colloids. The intensity ratio between the D-line (defect line) and the graphitic line (G-line), ID/IG, of the A -C electrode proved to be a good marker, independent of the measurement point. Rather than a peak, typical of amorphous films, this ratio has a dip at a particular AuNPs concentration, which is shifted upon the presence of the electrolyte. It is suggested that the seemingly unrelated phenomena - the capacitance enhancement and the intensity dip - are the result of the formation of a quasi-2D array of AuNPs at the interface between the electrolyte and the electrode.