Pseudocapacitive behaviour in sol-gel derived electrochromic titania nanostructures

Nanostructured thin films are widely investigated for application in multifunctional devices thanks to their peculiar optoelectronic properties. In this work anatase TiO2 nanoparticles (average diameter 10 nm) synthesised by a green aqueous sol-gel route are exploited to fabricate optically active electrodes for pseudocapacitive-electrochromic devices. In our approach, highly transparent and homogeneous thin films having a good electronic coupling between nanoparticles are prepared. These electrodes present a spongy-like nanostructure in which the dimension of native nanoparticles is preserved, resulting in a huge surface area. Cyclic voltammetry studies reveal that there are significant contributions to the total stored charge from both intercalation capacitance and pseudocapacitance, with a remarkable 50% of the total charge deriving from this second effect. Fast and reversible colouration occurs, with an optical modulation of similar to 60% in the range of 315-1660 nm, and a colouration efficiency of 25.1 cm(2) C-1 at 550 nm. This combination of pseudocapacitance and electrochromism makes the sol-gel derived titania thin films promising candidates for multifunctional 'smart windows'.

Automated summary

Nanostructured thin films synthesized by a green aqueous sol-gel route using anatase TiO2 nanoparticles show promising optoelectronic properties for the fabrication of optically active electrodes. These electrodes exhibit a spongy-like nanostructure with preserved nanoparticles size, resulting in a huge surface area, and demonstrate significant contributions from both intercalation capacitance and pseudocapacitance to the total stored charge. Fast and reversible coloration with high optical modulation and coloration efficiency makes the sol-gel derived titania thin films potential candidates for multifunctional 'smart windows'.