Preparation and characterization of molybdenum trioxide/poly(3,4-ethylenedioxythiophene): Polystyrene sulphonate nanocomposites for electrochromic application

Electrochromic processes are mostly characterized by colour change arising from the energy of a chemical reaction involving electron transfer. Transition metal oxides of tungsten, molybdenum, iridium, and nickel show the most intense Electrochromic colour changes and photochemical stability of about 100 cycles compared to organic electrochromes which are susceptible to photochemical degradation. The prospect of conjugated polymers (comprising of metal oxides and polymers) has opened a new dimension on improving the Electrochromic performance of the transition metal oxides. In this work, solution growth methods were employed in preparing a MoO3/PEDOT: PSS composite layer by adding PEDOT: PSS into MoO3 aqueous dispersion resulting in an electrostatic interaction between MoO3 and PEDOT: PSS for electrochromic application. This composite has shown a long-term stability up to more than 550 cycles which shows higher potential specific capacitance than WO3/PEDOT: PSS. This approach has significantly improved the stability issue of MoO3 and enhances the potential of MoO3-based materials for electrochromic applications. The semi crystalline nature of MoO3-300 °C was further proved by FE-SEM observation of the MoO3 nanoparticles. The particle size shown in the images corresponds with FE-SEM result and polycrystalline structure was observed under high magnification. The polycrystalline nature of the MoO3 particles favors their electrochemical stability, while their small size facilitates their effective interactions with PEDOT: PSS. The electrochemical properties of MoO3, PEDOT: PSS and composite were further studied by cyclic voltammetry (CV) from -1 V to +1 V. MoO3 has a broad oxidation peak at -0.43 V and no obvious reduction peak in this range. PEDOT: PSS has an oxidation peak at -0.02 V and a reduction peak at -0.55 V. In the composite, the peak at -0.43 V becomes a shoulder and a new pair of redox peaks appear at -0.18 V/-0.09 V.