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Characterization of the electrical properties of interfaces by impedance spectroscopy for clean energy devices
- 1. Characterization of the electrical properties of interfaces by impedance spectroscopy for clean energy devices Edmund Mills Major Professors: Sangtae Kim and YayoiTakamura
- 2. Projects • YSZ thin films with minimized grain boundary resistivity • Evaluating the rate-dependence of supercapacitor performance using Peukert’s equation • Direct Determination of Field Emission across the Heterojunctions in a ZnO/GrapheneThin-Film Barristor 1
- 3. Interfacial engineering for solid oxide fuel cell electrolytes 2 Ionic conductivity is enhanced in yttria-stabiled zirconia thin films Jun Jiang, Joshua L. Hertz ,J Electroceram (2014) 32,37–46
- 4. Investigation ofYSZ thin films MgO YSZ 20 nm Film growth Pulsed laser deposition ofYSZ thin films on MgO substrates Structural Characterization X-ray diffraction X-ray reflectivity HRTEM ElectricalCharacterization Impedance spectroscopy
- 5. Minimization of the grain boundary resistance ofYSZ thin films 4
- 6. Minimization of the grain boundary resistance ofYSZ thin films 5
- 7. Minimization of the grain boundary resistance ofYSZ thin films 6
- 8. Evaluating the rate-dependence of supercapacitor performance using Peukert’s equation
- 11. Rate-dependent capacitance: electrode porosity 10 Pore structure induces variability in surface accessibility to electrolyte ions
- 12. Rate-dependent capacitance 11 Zhi et al. “Highly conductive electrospun carbon nanofiber/MnO2 coaxial nano-cables for high energy and power density supercapacitors” Journal of Power Sources 208 (2012) 345–353
- 13. Rate-dependent capacitance 12 Zhi et al. “Highly conductive electrospun carbon nanofiber/MnO2 coaxial nano-cables for high energy and power density supercapacitors” Journal of Power Sources 208 (2012) 345–353
- 14. Peukert’s equation 13Supercapacitor rate-dependence • Used for batteries • Empirical • k = 1: rate independent capacity • k > 1: capacity decays at higher rates
- 15. Peukert’s equation 14Supercapacitor rate-dependence • Used for batteries • Empirical • k = 1: rate independent capacity • k > 1: capacity decays at higher rates
- 19. 18
- 20. Peukert’s equation 19Supercapacitor rate-dependence • Used for batteries • Empirical • k = 1: rate independent capacity • k > 1: capacity decays at higher rates
- 21. Peukert’s equation 20Supercapacitor rate-dependence • Used for batteries • Empirical • k = 1: rate independent capacity • k > 1: capacity decays at higher rates • Novel frequency dependent form for Impedance spectroscopy
- 24. Complex capacitance 23Supercapacitor rate-dependence (kdc = 1.06) (kdc = 1.01) (kdc = 1.29)
- 25. ac vs. dc determination 24Supercapacitor rate-dependence Impedance spectroscopy (ac) determination is consistent with dc
- 26. 25
- 27. Equivalent Circuit Modeling 26Supercapacitor rate-dependence
- 29. k and supercapacitor properties 28Supercapacitor rate-dependence
- 30. 29
- 31. Selected paper 1: Influence of carbon nanotube addition • Add CNTs to activated carbon electrodes • CNTs increase pore accessibility 30Supercapacitor rate-dependence Portet et al. “Influence of carbon nanotubes addition on carbon–carbon supercapacitor performances in organic electrolyte” Journal of Power Sources 139 (2005) 371–378
- 32. 31 1 1.05 1.1 1.15 1.2 0% 10% 20% 30% 40% 50% 60% Peukert'sconstant Wt% CNT CNTs Selected paper 1: Influence of carbon nanotube addition
- 33. Selected paper 2: MnO2 32Supercapacitor rate-dependence Zhi et al. “Highly conductive electrospun carbon nanofiber/MnO2 coaxial nano-cables for high energy and power density supercapacitors” Journal of Power Sources 208 (2012) 345–353 AAI-CNF CNF
- 34. Selected paper 2: MnO2 33Supercapacitor rate-dependence Zhi et al. “Highly conductive electrospun carbon nanofiber/MnO2 coaxial nano-cables for high energy and power density supercapacitors” Journal of Power Sources 208 (2012) 345–353 0.05 0.5 1 1.05 1.1 1.15 1.2 1.25 0% 10% 20% 30% 40% 50% 60% 70% ElectrodeResistivity(Ohm*cm) Peukert'sConstant MnO2 Loading 0.7 7 1 10 100 0% 10% 20% 30% 40% 50% 60% 70% ElectrodeResistivity(Ohm*cm) Peukert'sConstant MnO2 Loading AAI-CNF CNF
- 35. Selected paper 2: MnO2 34Supercapacitor rate-dependence Zhi et al. “Highly conductive electrospun carbon nanofiber/MnO2 coaxial nano-cables for high energy and power density supercapacitors” Journal of Power Sources 208 (2012) 345–353 1 10 0 0.5 1 1.5 2 2.5 Peukert'sconstant Electrode Resistiviy (Ohm*cm)
- 36. Relaxation time constant 35Supercapacitor rate-dependence k = 1.06
- 37. Summary Supercapacitor rate-dependence 36 • Developed novel method for determination of Peukert’s constant using impedance spectroscopy – Consistent with dc method of determination – Simple and precise • Demonstrated utility of Peukert’s constant for evaluation of supercapacitors – SCs follow Peukert’s law – Facilitates interpretation of rate-dependent capacitance
- 38. Direct Determination of Field Emission across the Heterojunctions in a ZnO/GrapheneThin-Film Barristor
- 43. Bias and temperature dependence 42 0 25 50 0 25 50 0.0 0.5 1.0 1.5 10 -5 10 -4 10 -3 10 -2 Vo (mV) Vth (mV) FE TFE (forward) TFE (reverse) TE CB -80 o C -60 o C -40 o C -20 o C 0 o C 20 o C 40 o C Current(A) Voltage (V) 15 20 25 30 0 250 500 Vo (mV) Vth (mV) A • Temperature-independent electrical characteristics • Indicates electron tunneling mechanism at the graphene-ZnO interface
- 44. Acknowledgements • Professors Sangtae Kim andYayoiTakamura • Kim andTakamura research groups • UC Davis CHMS department 43
- 45. 44
Editor's Notes
- At 500C
- Relative performance plot
- 1897
- Lead acid 1.1-1.3 Lithium ion 1.0 – 1.1
- Talk about IS
- Only 3 data points for N enriched porous carbon, maybe leading to innacuracy in k from dc method
- Utility for SCs: porosity, pseudocapacitance Equivalent circuit modeling, analysis of literature papers
- papers
- Measure reduced surface area with additional CNTs
- Iron acetylacetonate
- No Rct
- Reduced capacitance in more mno2 loaded samples: This was due to the fact that too thick oxide coating caused part of material to be electrochemically inactive, and jeopardized the charge transport. From the Nyquist plots, the capacitance retardation in the CNF@MnO2 samples was due to two problems: (i) high series resistance attributed to insufficient con- ductivity of the electrode, especially at a high MnO2 loading, and (ii) large charge transfer resistance at the carbon/MnO2 interface that inhibits the Na+ insertion/adsorption process in MnO2, leading to capacitance degradation at a high operation rate. The two problems were mitigated by the addition of AAI into CNF. The conductivity of the AAI-CNF (1.35 S cm−1 ) was almost 27 times higher than CNF (0.05 S cm−1 ) even at high MnO2 loading (59% of MnO2 loading), which minimized the series resistance of the electrode, reducing the IR loss. In addition, the AAI-CNF@MnO2 samples showed an almost linear shape in the Nyquist plot in the absence of an evident semicircle, which indicated a negligible charge transfer resistance. Benefited from the higher surface area of the AAI-CNF backbone, the C/MnO2 contact area can be enlarged and the interfacial resistance between carbon and MnO2 can be reduced, therefore the electron and ions can be more easily transferred.