Optically Controlled TiO₂-Embedded Supercapacitors: The Effects of Colloidal Size, Light Wavelength, and Intensity on the Cells’ Performance

Optically controlled supercapacitors (S-C) could be of interest to the sensor community, as well as set the stage for novel optoelectronic charging devices. Here, structures constructed of two parallel transparent current collectors (indium-tin-oxide, ITO films on glass substrates) were considered. Active-carbon (A-C) films were used as electrodes. Two sets of electrodes were used: as-is electrodes that were used as the reference and electrodes that were embedded with submicron-or micron-sized titanium oxide (TiO₂) colloids. While immersed in a 1 M Na₂ SO₄, the electrodes exhibited minimal thermal effects (<3^◦ C) throughout the course of experiments). The optically induced capacitance increase for TiO₂-embedded S-C was large of the order of 30%, whereas S-C without the TiO₂ colloids exhibited minimal optically related effects (<3%). Spectrally, the blue spectral band had a relatively larger impact on the light-induced effects. A lingering polarization effect that increased the cell capacitance in the dark after prolonged light exposure is noted; that effect occurred without an indication of a chemical reaction.