Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows

1. Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows Ghouwaa Philander iThemba LABS Supervisor: Prof. M. Maaza Energy Postgraduate Conference 2013

2. Contents Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows • Breaking it down • Vanadium Dioxide • Thermochromism and Doping • Bringing it together • Smart Windows • Need • Material Synthesized • Conclusions and Future Work Energy Postgraduate Conference 2013

3. Vanadium Dioxide (VO2) Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows • VO2 undergoes a transition at 68°C from the semi-conducting monoclinic phase to the metallic rutile phase, the latter which is IR opaque. • VO2 exists in a number of morphologies with varying properties, dependant largely on method synthesis and growth. Whittaker et al. J. Phys. Chem. Lett. 2011, 2, 745–758 Energy Postgraduate Conference 2013

4. Thermochromism and Doping Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows • A compound that displays a reversible change in colour as a result of a change in temperature is ‘thermochromic’. • change in geometry • variation in coordination number • change in lattice formation • Doping is the process of introducing a ‘metal’, as an impurity, into the crystal structure which introduces additional energy levels. • Doping of VO2 compounds with tungsten reduces the naturally occurring transition temperature to even closer to room temperature. Energy Postgraduate Conference 2013

5. Smart Windows Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows Parkin and Manning. J. Chem. Ed. 2006, 83, 393-400 Energy Postgraduate Conference 2013

6. Need Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows • Heating, ventilation and air-conditioning, contribute an estimated 15% to South Africa’s current peak demand consumption. • 33% saving in energy consumption will be realisedif inside and outside temperature difference is maintained. (Eskom Communication Fact Sheet, January 2013) • Objective: To develop a cost effective chemical method to produce efficient and viable VO2 coatings with enhanced properties, for use in smart window applications. Energy Postgraduate Conference 2013

7. Material Synthesized Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows • A chemical method was used to synthesize a range of W-doped VO2 films from 0.5-2.5 wt%. • Polymer assisted deposition with annealing in an oxygen deficient environment. • Crystalline particle sizes ranged from 30-62 nm along the (011) plane. Variability in the dhkl showed evidence of W integration into the crystal lattice structure. Energy Postgraduate Conference 2013

8. Material Synthesized cont. Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows Energy Postgraduate Conference 2013

9. Material Synthesized cont. Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows • The phase transition is represented with a steep slope and takes place at approximately 33°C during the heating and cooling cycle. • Hysteresis gap of 8.8°C at 27 MΩ . Energy Postgraduate Conference 2013

10. Conclusions and Future Work Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows • The method has achieved its primary objective of producing thermochromic VO2 films with enhanced properties. • The reduced transition temperature achieved renders this material suitable for smart window applications. • Future work will include further optimization of this method, including IR modulation studies. THANK YOU Energy Postgraduate Conference 2013