1. Flame Synthesized Nanomaterials for Supercapacitor Applications
NanoEnergy Lab Group Meeting
Stanford, CA October 9, 2014
Flame Synthesized Nanomaterials for Supercapacitor Applications
Joaquin Camacho
NanoEnergy Lab
High Temperature Gas-Dynamics Laboratory
Mechanical Engineering Department
Stanford University

2. Supercapacitors HIGH-POWER ENERGY STORAGE DEVICE
POWER STABILIZATION AND BACKUP POWER
Computing and Electronics
conventional electrolytic capacitors have been replaced by supercapacitors to
increase efficiency and make more compact designs
Renewable Energy
buffers power for intermittent sources such as solar cells and wind turbines
smart grid regulation and power sources are possible with supercapacitor stabilization
TRANSPORTATION
Trains and Mass Transport
energy recovery by supercapacitors for converting braking energy to engine startup
Performance Cars
can provide short burst of power for acceleration in hybrid race cars
HOWEVER, HIGH-POWER IS ONLY HALF OF THE BATTLE….

3. Supercapacitors Tesla Roadster battery: AKA Electrochemical Capacitors
“The pack weighs 990 pounds, stores 56 kWh of electric energy, and delivers up to 215 kW of electric power. ”
P. Simon and Y. Gogotsi, Nature Materials, (2008)

4. Double-Layer Capacitance vs. Psuedo Capacitance
Electric Double Layer Capacitance (EDLC) – electrostatic energy storage by separating charge at the interface between electrolyte and electrode.
EDLC performance is maximized by increasing surface area of the interface
high surface area carbon structures are used such as nanotubes and graphene
energy densities up to 100 Wh / kg have been reported (kg active material)
Psuedo-capacitance – faradic energy storage through electron charge transfer by fast redox reactions, intercalation into the structure or electrosorption.
small particle sizes increase the active material usage of surface redox reactions.
transition metals- ruthenium oxides, iron oxides & manganese oxides most active
energy densities up to 110 Wh / kg have been reported (kg active material)

5. Manganese Oxide for High Performance Electrodes
abundant , environmentally friendly and relatively high specific capacitance
intercalation of electrolyte cations into the electrode structure:
adsorption of of cations onto the electrode surface:
improving electrode performance:
maximize the surface area
maximize intercalation
minimize diffusion resistance for ions into the electrode structure
maximize the conductivity of the electrode

6. Flame Stabilized on a Rotating Surface
Flame Assisted Chemical Vapor Deposition
Flame Stabilized on a Rotating Surface
method to synthesize nanoparticles and fabricate a thin porous layer in a single step
increasing precursor loading

7. Flame Assisted Chemical Vapor Deposition
mesoporous TiO2 thin films applied to novel devices

8. Flame Assisted Chemical Vapor Deposition
Particle size, surface area and degree of interconnected pores can be controlled and studied systematically in FSRS

9. Mn Oxide Precursor for Flame Synthesis
vaporization  thermal precursor breakdown  oxidation  condensation
methylcyclopentadienyl manganese tricarbonyl (MMT)
liquid at room temperature
boiling point – 500 K at 1 atm but at low concentrations vapor partial pressure is higher than saturation vapor pressure around 400K
in the flame: MMT  Mn + O2  Mn Oxide

10. Manganese Oxide Phase Diagram (Thermodynamics)
in oxygen rich flame synthesis conditions:
log( PO2 / 1 atm ) = log (0.10) = -1
the flame synthesis design is for particles around 10 nm in diameter
Mn3O4 is thermodynamically favored at temperatures above 900 K
N. Birkner and A. Navrotsky, Amer. Mineral., –1298 (2012)

11. Mn Oxide Flame Synthesis
substrate
Mn3O4 Stable above 1000K
Mn2O3 Stable 800K<T<1000K
MnO2 Stable below 800K
Does the thermodynamically stable product occur during flame synthesis?

12. Mn Oxide Flame Synthesis
1150 ppm MMT precursor
550 ppm MMT precursor

13. Mn Oxide Particle Characterization
X-ray Diffraction (XRD) λxray ~ Datoms
constructive interference of diffracted
x-rays are related to material crystal structure
BRAGGS LAW nλ = 2dsinθ

14. Mn Oxide Particle Characterization
XRD patterns show the phase of Mn Oxide is dependent on the MMT precursor concentration
Why is the thermodynamically favored product, MnO2 not observed?
during synthesis the particles deposit on the substrate at low temperatures
At what point in the flame does particle condensation occur?
different phases observed indicates that this occurs at different points for each ppm level
Can MnO2 be produced from extra post-processing steps of the flame synthesis products?
moderate temp annealing may oxidize the particles further as the phase diagram predicts

15. Mn Oxide Particle Characterization
Mn2O3 + ½ O2  2 MnO2 not observed
2 Mn3O4 + ½ O2  3 Mn2O3

16. Mn Oxide Flame Synthesis
Mn2O3 and Mn3O4 mesoporous thin films can be synthesized in the flame in one step
MnO2 is not obtained quickly by moderate to high temperature annealing in ambient air
FUTURE WORK:
Build electrochemical analysis ability and supercapacitor electrodes

17. Supercapacitor Development Plan
systematic preparation and characterization of novel supercapictor electrodes:
MnO2 based electrodes as a function of particle size
MnO2 based electrodes containing pre-intercalated Na+
MnO2 – carbon nanohybrid electrodes
Ni(OH)2 based electrodes are also of interest
Is the benchmark capacitance of 1000 F/g reachable?