Enhanced electrochromic performance of carbon-coated V2O5 derived from a metal–organic framework

Abstract

In this study we synthesized a vanadium (V)-containing metal–organic framework (MOF) and used it as a template to prepare V2O5 NPs. We used MIL-47, a V-containing MOF having uniform C and V distributions, as a precursor for the preparation of carbon-coated V2O5 (C@V2O5) samples through annealing. The C@V2O5 structures were readily dispersed in poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) to form stable solutions, allowing the deposition of C@V2O5 on various substrates through simple low-temperature solution-based processes. The uniform coating of carbon on V2O5 was useful for two reasons: (i) the outer layer enhanced the electronic conductivity of a V2O5 electrode and its corresponding electrochemical properties and (ii) based on the electrochemical quartz crystal microbalance (EQCM) analysis, the carbon coating served as a buffer layer that allowed Li+ ion transport, but blocked migration of solvent into the V2O5 electrode, thereby improving the dimensional and electrochemical stability. Compared with the bare V2O5, C@V2O5 exhibited excellent electrochromic (EC) performance, with an EC contrast of 45.8%, a mean response time of 3.4 s, and a coloration efficiency of 89.3 cm2/C. C@V2O5 also displayed higher cycling stability (80.6% retention after 5000 cycles) and highly reversible ionic transport during redox reactions, compared with those of the bare V2O5.