Nanocomposite thin films for high temperature optical gas sensing of hydrogen
Inventors
Ohodnicki, JR., Paul R. • Brown, Thomas D.
Assignees
Publication Number
US-8411275-B1
Publication Date
2013-04-02
Expiration Date
2032-04-10
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Abstract
The disclosure relates to a plasmon resonance-based method for H2 sensing in a gas stream at temperatures greater than about 500° C. utilizing a hydrogen sensing material. The hydrogen sensing material is comprised of gold nanoparticles having an average nanoparticle diameter of less than about 100 nanometers dispersed in an inert matrix having a bandgap greater than or equal to 5 eV, and an oxygen ion conductivity less than approximately 10−7 S/cm at a temperature of 700° C. Exemplary inert matrix materials include SiO2, Al2O3, and Si3N4 as well as modifications to modify the effective refractive indices through combinations and/or doping of such materials. At high temperatures, blue shift of the plasmon resonance optical absorption peak indicates the presence of H2. The method disclosed offers significant advantage over active and reducible matrix materials typically utilized, such as yttria-stabilized zirconia (YSZ) or TiO2.
Core Innovation
The invention provides a method for hydrogen sensing in gases at temperatures above about 500° C. by detecting shifts in the plasmon resonance peak position of a hydrogen sensing material. This material comprises gold nanoparticles with an average diameter less than about 100 nanometers dispersed within an inert, wide bandgap matrix. The plasmon resonance optical absorption peak of this sensing material undergoes a blue shift to lower wavelengths upon exposure to diatomic hydrogen at high temperatures.
The hydrogen sensing material's matrix has a bandgap greater than or equal to 5 eV and an oxygen ion conductivity less than approximately 10−7 S/cm at 700° C. Typical inert matrix materials include SiO2, Al2O3, and Si3N4, including derivatives such as MgF2 doped SiO2 or mixtures of SiO2/Al2O3. The inert matrix acts primarily to prevent coarsening of gold nanoparticles at high temperatures and to tailor the effective refractive index for optimized sensing, especially when integrated with optical waveguide sensors.
The problem solved is the limitation of existing high temperature hydrogen sensing methods using gold nanoparticles embedded in reducible or oxygen conducting matrices, such as yttria-stabilized zirconia (YSZ) or TiO2. Those traditional methods require the presence of oxygen and depend on matrix reduction or oxygen vacancy changes for sensing, which limits selectivity and sensor responsiveness. This invention overcomes these limitations by using an inert matrix that does not interact directly with the gas atmosphere, enabling selective, stable, and direct sensing of hydrogen through interactions solely between the gold nanoparticles and hydrogen at elevated temperatures.
Claims Coverage
The claims include three independent claims covering methods of hydrogen monitoring at high temperatures using a gold nanoparticle-based hydrogen sensing material dispersed in an inert matrix. Three main inventive features are identified.
Hydrogen sensing material composition and properties
The sensing material comprises a plurality of gold nanoparticles, each comprised of elemental gold with an average nanoparticle diameter less than about 100 nanometers (in certain claims less than 50 nm). The nanoparticles are dispersed in an inert matrix stable at temperatures above 500° C., having a bandgap of at least 5 eV and an oxygen ion conductivity less than about 10−7 S/cm at 700° C. Exemplary matrices include SiO2, Al2O3, Si3N4, and their combinations and doped variants. The nanoparticle spacing is greater than about five times the average diameter to maintain electrical isolation.
Monitoring hydrogen via plasmon resonance peak shifts
Hydrogen is detected by illuminating the hydrogen sensing material with incident light (typically visible spectrum), collecting transmitted or reflected exiting light, and monitoring plasmon resonance peak positions using absorption spectroscopy. The presence of hydrogen induces a blue shift of the plasmon resonance peak, especially observable between about 500 nm and 600 nm, indicating hydrogen concentration in a high temperature gas stream above 500° C.
Integration with optical waveguides and fiber optic sensors
The method includes ascertaining the refractive index of the inert matrix and providing a waveguide (e.g., a fiber optic cable) with a core material having a higher refractive index than the matrix. The hydrogen sensing material is placed in contact with the waveguide core, allowing illumination of the sensing material via an evanescent wave generated in the core. Incident light is emitted into the waveguide, and exiting light is gathered at the other end for plasmon resonance monitoring. The matrix refractive index is tunable through doping or material combinations to optimize compatibility.
In summary, the claims cover a method for hydrogen sensing in high temperature gas streams using gold nanoparticles dispersed in an inert, wide bandgap matrix with low oxygen ion conductivity, detecting hydrogen via plasmon resonance peak blue shifts, augmented by integration into waveguide-based optical sensing platforms for enhanced selectivity and stability at elevated temperatures.
Stated Advantages
Enhanced thermal stability of the sensing material at temperatures greater than about 500° C.
Relative insensitivity or improved selectivity to hydrogen compared to other reducing gases.
Increased stability of gold nanoparticle diameter under high temperature conditions, reducing coarsening.
Ability to tune effective refractive indices of the nanocomposite film for compatibility with optical waveguide based sensors.
Reduced dependency on oxygen presence in the sensing environment, enabling effective hydrogen detection independent of oxygen partial pressure.
Documented Applications
Hydrogen sensing in high temperature gas streams above about 500° C.
Use in fossil fuel based energy production technologies such as coal gasification, solid oxide fuel cells, gas turbines, and advanced combustion systems.
Integration with optical waveguide based sensors including fiber optic cables employing evanescent wave absorption spectroscopy for in-situ hydrogen detection.
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