Smart electrochromic supercapacitors based on highly stable transparent conductive graphene/CuS network electrodes

A well-designed flexible ITO-free electrochromic supercapacitor was obtained using a hybrid graphene/CuS network on PET (G–CuS) as the transparent conductive electrode (TCE). This new type of TCE was produced by photolithography, chemical vapor deposition and a low temperature solvothermal reaction. The TCE achieves a sheet resistance (Rs) as low as ∼20 Ω sq−1 with a high transmittance of over 85%. In particular, the G–CuS TCE displays a remarkable flexible stability under bending stresses and an excellent chemical stability through the polyaniline (PANI) electrodeposition in acid solution. The PANI/G–CuS electrode gave a favorable area capacitance of 17.3 mF cm−2 at 0.025 mA cm−2 along with a large optical modulation of 40.1% (620 nm). More intuitively, a symmetrical supercapacitor of PANI/G–CuS was fabricated with H2SO4–PVA hydrogel as the electrolyte, and its noticeable color variation enables users to evaluate the level of stored energy by the naked eye in a predictable manner. This work may provide a practical route to the fabrication of stable TCEs in smart supercapacitors.