Dual purpose poly(3,4-ethylenedioxypyrrole)/vanadium pentoxide nanobelt hybrids in photoelectrochromic cells and supercapacitors

Abstract

Poly(3,4-ethylenedioxypyrrole) (PEDOP)/vanadium pentoxide (V₂O₅) nanobelt hybrid films were prepared for the first time. V₂O₅ nanobelts with a monoclinic structure were grown by a hydrothermal route and a PEDOT layer was coated onto V₂O₅ nanobelts by electropolymerization to yield the PEDOP/V₂O₅ hybrid. The hybrid showed a fourfold increment in electrical conductivity compared to the pristine oxide, and a work function of 4.71 eV (by Kelvin probe force microscopy), which was intermediate to that of PEDOP and V₂O₅. Both oxide and hybrid showed green-red luminescence. The PEDOP/V₂O₅ hybrid or V₂O₅ films were assembled into energy saving photoelectrochromic cells, by combining with a photovoltaic electrode of CdS/titania, and in response to 1 sun illumination for different durations, the hybrid showed a dynamic transmission modulation (ΔT), as it switched from a yellow to a dark green optical state, without the application of any external bias, by simply consuming the electrical current produced by the irradiated CdS/titania. The hybrid exhibited a maximum ΔT of 65.5% at 475 nm, which was greater by 82% compared to pristine V₂O₅ at the same wavelength. The ability of PEDOP to provide facile conduction pathways for fast and improved electron transfer and transport in the PEDOP/V₂O₅ hybrid, enhances the optical contrast produced. The versatility of the hybrid was established by assembling asymmetric supercapacitors with the hybrid or polymer or oxide and a liquid electrolyte. The synergistic effects of PEDOP (high electrical conductivity) and V₂O₅ nanobelts (large surface area) and their ability to store/release charge by undergoing reversible Faradaic reactions were reflected in a high specific capacitance of 224 F g⁻¹ delivered by the hybrid, higher by 83% and 69% relative to pristine V₂O₅ and PEDOP. The hybrid shows an energy density of 223 W h kg⁻¹ at a power density of 3.8 kW kg⁻¹, and an acceptable cycling performance with 90% capacitance retention after 5000 cycles. The PEDOP/V₂O₅ hybrid is useful for advanced next-generation self-powered electrochromic smart windows and supercapacitors.