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
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
H 2 GAS SENSING: FORESIGHT US Department of Energy: Hydrogen Posture Plan,
H 2 SENSING: FORESIGHT International Organizations and Associations European Commission, Directorate for Energy and Transport, “clean Urban Transportation for Europe” Green car Congress, “European Commission Adopts 940M Fuel Cells and Hydrogen Joint Technology Initiative,” National Hydrogen Association “Key Hydrogen Message” US Department of Energy, Fuel cells and Infrastructure Technologies: Transition Strategies, by Sig Gronich US department of Energy, A national vision of America`s Transition to a Hydrogen Economy to 2030 and Beyond, HySA initiated by the South African Department of Science and Technology (DST) increase the South African Research in hydrogen and fuel cells, 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
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 ( % volume vs % 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
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 s/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
VO 2 MOTT OXIDE: ELECTRICAL PROPERTY d// EFEF ** 0.7 eV **
VO 2 MOTT OXIDE: CRYSTALLINE STRUCTURE Monoclinic VO 2 with a ~ nm, b ~ nm and c ~ 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
2 nm 20 nm 1m1m Hydrothermal synthesis ● Nanobelts: nm thickness range and a length ≥ 20μm. ● VO 2 (A): specific interspacing d (011) ~ nm. VO 2 MOTT OXIDE: STRUCTURAL PROPERTY
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
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
SENSITIVITY-RESPONSE TIME Sensitivity: Optimal at 90 ppm of H 2 at RT
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
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
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