Bionic SiO2@Fc(COCH3)2 core-shell nanostructure for enhancing the electrochromic properties of ferrocene

Abstract

Although the properties of electrochromic materials (ECMs) have been enhanced using fabricated porous materials, the effect of materials porosity on such an enhancement remains unclear. Here, we report a novel ECMs with an adjustable pore hierarchy based on quasi-amorphous and ordered arrays of SiO2@Fc(COCH3)2. ECMs with different pore systems were generated by modifying Fc(COCH3)2 concentration and self-assembly temperature. The composition and core-shell structure of the SiO2@Fc(COCH3)2 nanospheres were confirmed through scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR) and EDX mapping. The influence of adjustable pore system on the electrochemical behavior was studied. Experimental results showed that the current density of the redox couple peaks of the quasi-amorphous porous SiO2@Fc(COCH3)2 films are considerably lower than those of the ordered porous films but are higher than those of the dense Fc(COCH3)2 films. At 550 nm, the transmittance variation of the quasi-amorphous porous SiO2@Fc(COCH3)2 film is 19%, whereas that of the ordered porous film is 35%. The coloration and bleaching times of the quasi-amorphous porous SiO2@Fc(COCH3)2 film are 17.1 s and 4.5 s, respectively, whereas those of the ordered porous film are only 16.5 s and 3.5 s, respectively. Furthermore, the porosities of the films are solved numerically by the finite-element method. For the ordered porous SiO2@Fc(COCH3)2 film, the porosity is 0.26, while the quasi-amorphous film became larger (0.31–0.41). This work is the first step in combining ferrocene derivative and colloidal crystal porous structures to develop a green, simple and efficient electrochromic process.