1. VO 2 NANOSTRUCTURES BASED CHEMORESISTOR FOR LOW POWER ENERGY CONSUMPTION HYDROGEN SENSING Energy Postgraduate Conference 2013 Ms. Aline SIMO Supervisor: Prof Malik Maaza Co-Supervisor: Prof Reginaldt Madjoe iThemba LABS/University of Western Cape

2. OUTLINE 1- H 2 Gas sensing foresight, Safety & Oxides 2- Gas Sensing Principle 4- VO 2 : Mott oxide and Room temperature H 2 sensing 5- Conclusions and follow up

3. H 2 GAS SENSING: FORESIGHT US Department of Energy: Hydrogen Posture Plan, www.fchea.org

4. H 2 SENSING: FORESIGHT International Organizations and Associations European Commission, Directorate for Energy and Transport, “clean Urban Transportation for Europe” http://ec.europa.eu/energy/res/fp6_projects/doc/hydrogen/deliverables/summary.pdf http://ec.europa.eu/energy/res/fp6_projects/doc/hydrogen/deliverables/summary.pdf Green car Congress, “European Commission Adopts 940M Fuel Cells and Hydrogen Joint Technology Initiative,” www.greencarcongress.com/2007/10/european-commis.htmlwww.greencarcongress.com/2007/10/european-commis.html National Hydrogen Association “Key Hydrogen Message” http://www.hydrogenassociation.org/pdf/keyHydrogenMessages.pdf http://www.hydrogenassociation.org/pdf/keyHydrogenMessages.pdf US Department of Energy, Fuel cells and Infrastructure Technologies: Transition Strategies, by Sig Gronich http://www.eere.energy.gov/hydrogenfuelcells/pdfs/transition_wkshp_strategies2.pdf. http://www.eere.energy.gov/hydrogenfuelcells/pdfs/transition_wkshp_strategies2.pdf US department of Energy, A national vision of America`s Transition to a Hydrogen Economy to 2030 and Beyond, http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/vision_doc.pdf http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/vision_doc.pdf HySA initiated by the South African Department of Science and Technology (DST) increase the South African Research in hydrogen and fuel cells, http://www.fuelcelltoday.comhttp://www.fuelcelltoday.com Publications and News The International Journal for Hydrogen Energy - This site a news service for the hydrogen industry, covering developments in fuel cells, technology, hydrogen supply, storage, projects and regulatory policy. Sensors & Actuators B: Chemical Alternative Energy News Hydrogen - This news site links to hydrogen articles across the internet and is updated with several new articles each day The Hydrogen and Fuel Cell Letter - This monthly newsletter, started in 1986, provides news from across the spectrum from across the hydrogen and fuel cells industry http://www.greencarcongress.com

5. H 2 GAS SAFETY Risk /Safety codes H 2 : Wide concentration range of flammability with 4-75% volume compared to gasoline 1-7.6% and wide detonation range (18.3-59% volume vs. 1.1-3.3% for gasoline) H 2 : Odorless and leaks not detectable by smell Ignition of a flammable mixture at small quantity and high diffusivity H 2 : reducing dependence on petroleum imports, pollution and greenhouse gas emissions H 2 : is amongst cleanest carrier energy with the highest specific energy offering long term solution being produced from Renewables Energies such as wind-powered electrolysis or solar. Requirements for an Effective Gas Sensor Sensitivity: Chemical Surface activity Selectivity: Gas identification Energy consumption

6. OXIDES SENSORS: DETECTION LIMT-TEMPERATURE CONSUMPTION MaterialsTarget Gas Lowest detection Concentration Response/Recovery SnO 2 NanowhiskersEthanol H 2 50 ppm (300 °C, S=23) 10 ppm (300, S=0.4) N/A 10min N/A Single nanowireH 2 Humidity 100 ppm (2, S=13) RH: 30% (30°C, S≈1.25) N/A 120-170s/20-60s NanorodsH2H2 100ppm (150 °C) N/A In 2 O 3 NanowiresEthanol 100ppm (370 °C, S≈2) 1ppm (250 °C, S≈2.57) 200ppb (RT) 5ppm (330 °C, S≈1.84) 10s/~20s N/A 2-3min/N/A 6s/11s NO 2 H2SH2S Ethanol Single NWH2SH2S 1ppm (120 °C) 48s/56s ZnONanorodsH2H2 500ppm (25 °C) 50ppb (RT, S≈1.7) 1ppb (300°C, S≈10) 50ppm (300 °C, S≈3.2) 100ppm (325°C, S≈20) 10min/ N/A N/A H2SH2S Ethanol Methanol Ethanol Single NWH2H2 200ppm (RT, S≈0.04) WO 3 nanowiresH2SH2S 1ppm (250°C, S≈48) 10ppb(room temperature N/A NH 3 TeO 2 nanowiresNO 2 10ppm (26 °C) 50ppm (26 °C) 10min > 30min N/A NH 3 H2SH2S CuOnanowiresCO 30ppm (300 °C, S≈0.07) 2ppm (300 °C, S≈0.15) N/A NO 2 nanoribbonsMethanol 5ppm (100 °C, S≈1.4) 5ppm (200°C, S≈1.2) 2-4s/3-7s 3-6s/4-9s Ethanol CdO nanowiresNO 2 1ppm (100 °C, S≈0.27)N/A

7. VO 2 MOTT OXIDE: ELECTRICAL PROPERTY d//  EFEF **  0.7 eV **

8. VO 2 MOTT OXIDE: CRYSTALLINE STRUCTURE Monoclinic VO 2 with a ~ 0.5753 nm, b ~ 0.4526 nm and c ~ 0.5383 nm, presenting semiconductor behavior at RT. Formation of an electron pair in the monoclinic structure results in semiconductor phase. It can inversely transit to tetragonal rutile and conducting VO 2 phase

9. 2 nm 20 nm 1m1m Hydrothermal synthesis ● Nanobelts: 20-150 nm thickness range and a length ≥ 20μm. ● VO 2 (A): specific interspacing d (011) ~ 0.600 nm. VO 2 MOTT OXIDE: STRUCTURAL PROPERTY

10. VO 2 SENSING MECHANISM O2O2 O2-O2- e- O2O2 O2-O2- O2-O2- O2-O2- O2-O2- O2O2 x Potential Barrier e- O2-O2- O2-O2- O2-O2- O2-O2- H2H2 H2H2 x

11. o Different H 2 partial pressures equivalent to 140, 90, 50, 14, 0.17 ppm of H 2 (N 2 carrier): Standard gas sensing BUT at RT. o Average response time are ~840, 890, 1080, 1020, 1050s for 140, 90, 50, 14 and 0.17 ppm of H 2 respectively. SENSING RESPONSE

12. SENSITIVITY-RESPONSE TIME Sensitivity: Optimal at 90 ppm of H 2 at RT

13. SELECTIVITY RESPONSE Low detection Limit, High Selectivity H 2 comparatively to CO, CO 2 at RT, Low Power Consumption. ● For Humidity: idem at RT (background level), ● H 2 S, NH 3, and C 2 H 5 OH gases: in progress

14. CONCLUSIONS AND FOLLOW UP -Synthesis of highly crystalline Pure VO 2 -Good response of cyclic gas concentrations activation -Detection limit 0.14ppm of Hydrogen gas at low temperature (low power consumption energy) -Highly selective comparatively to CO and CO 2 -Potential application as Mott Infrared Insulator transistor due to its ultrafast synchrotron radiation -Following to test other gases to confirm the selectivity of vanadium dioxide and enhance the working temperature

15. THANK YOU