Optically Controlled Supercapacitors: Functional Active Carbon Electrodes with Semiconductor Particles

Supercapacitors, S-C-capacitors that take advantage of the large capacitance at the interface between an electrode and an electrolyte-have found many short-term energy applications. The parallel plate cells were made of two transparent electrodes (ITO), each covered with a semiconductor-embedded, active carbon (A-C) layer. While A-C appears black, it is not an ideal blackbody absorber that absorbs all spectral light indiscriminately. In addition to a relatively flat optical absorption background, A-C exhibits two distinct absorption bands: in the near-infrared (near-IR and in the blue. The first may be attributed to absorption by the OH- group and the latter, by scattering, possibly through surface plasmons at the pore/electrolyte interface. Here, optical and thermal effects of sub-mu m SiC particles that are embedded in A-C electrodes, are presented. Similar to nano-Si particles, SiC exhibits blue band absorption, but it is less likely to oxidize. Using Charge-Discharge (CD) experiments, the relative optically related capacitance increase may be as large as similar to 34% (68% when the illuminated area is taken into account). Capacitance increase was noted as the illuminated samples became hotter. This thermal effect amounts to <20% of the overall relative capacitance change using CD experiments. The thermal effect was quite large when the SiC particles were replaced by CdSe/ZnS quantum dots; for the latter, the thermal effect was 35% compared to 10% for the optical effect. When analyzing the optical effect one may consider two processes: ionization of the semiconductor particles and charge displacement under the cell's terminals-a dipole effect. A model suggests that the capacitance increase is related to an optically induced dipole effect.

Automated summary

The study investigates the optical and thermal effects of sub-micrometer SiC particles embedded in active carbon electrodes. Using Charge-Discharge experiments, it is found that the relative optically related capacitance increase can be significant. The research also shows that optical effects and thermal effects have different impacts on capacitance changes.