Three-dimensional Hierarchical Porous Carbon Foam Derived from Chitosan Aerogel for Electrical Double Layer Capacitors (oral presentation, EC2.12.10, 2016 MRS Fall Meeting and Exhibit, Boston, MA, 2016)

1. Chitosan-derived Porous Carbon
Foams for Supercapacitors
Tianyu LIU
Li Lab
Department of Chemistry and Biochemistry
University of California, Santa Cruz
11/2016

2. UC Santa Cruz

3. Outline
 What Are Supercapacitors?
 Current Limitations of Supercapacitors
 Design and Fabrication of 3D Porous Carbon Foams
 Electrochemical Performance
 Summary

4. Background
(Supercapacitors)

5. Structure of Supercapacitors
Charge storage devices
Large surface area
5 μm
ZnO Nanowires
10 μm
Graphene Aerogel

6. Capacitance
Charge storage ability
Charge storage mechanisms
Electrical Double
Layer Capacitance
Pseudo-
capacitance
Activated Carbon,
CNT, Graphene etc.
Conducting polymers,
metal oxides etc.
𝑪𝒂𝒑𝒂𝒄𝒊𝒕𝒂𝒏𝒄𝒆 =
𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦
𝑃𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝑊𝑖𝑛𝑑𝑜𝑤

7. Motivation

8. Conventional Material - Low Capacitance
sourcetech411.com
Activated Carbon
(~100 F g-1)

9. Conventional Material - Poor Rate Capability
ACS Nano 2013, 7, (4), 3589-3597

10. Capacitance

11. Capacitance
Determining factors
0 r S
C
d
 

0
r
C
S
d







Dielectric constant
Electric constant (=8.854 pF/m)
Surface area (ion-accessible)
Separation b/w different chages
Capacitance

12. Enlarge (ion-accessible) surface area
0 r
C
d
S 

0
r
C
d
S







Dielectric constant
Electric constant (=8.854 pF/m)
Surface area (ion-accessible)
Separation b/w different chages
Capacitance
Capacitance

13. Rate capability

14. Rate Capability
2D Non-porous Electrode 3D Porous Electrode
VS.
Electrolyte Reservoir

15. The Keys (Take-home Message)
Capacitance
Rate
Capability
Large
Surface Area
Porous 3D
Structure
Excellent Electrical Conductivity

16. Design and Fabrication of 3D
Porous Carbon Foams
Liu and Zhang et al. Nano Res., 2016, 9, 2875-2888

17. Building 3D Structure
Chitosan
Glutaraldehyde

18. Building 3D Structure
Sample S (m2/g) Vmicro (cm3/g) Vmeso (cm3/g)
CF 8.9 0.002 0.030

19. Creating Porous Structure
K2CO3 → K2O + CO2
K2CO3 + 2C → 2K + 3CO
K2O + C → 2K + CO
Science 2011, 332, 1537-1541
Activation Processes

20. Creating Porous Structure
Sample S (m2/g) Vmicro (cm3/g) Vmeso (cm3/g)
PCF 1013.0 0.461 0.154
CF 8.9 0.002 0.030

21. Surface Area
Energ. Environ. Sci. 2011, 4, (9), 3342
Adv. Mater. 2014, 26, (17), 2676-2682
Name Surface Area
Carbon Cloth 5.3 m2•g-1
Graphite Powder 6 m2•g-1
Carbon Black ~100 m2•g-1
Porous Carbon Template ~200 m2•g-1
Graphene Aerogel ~500 m2•g-1
PCF 1013 m2•g-1

22. Electrical Conductivity
Potential-Current Plots Slope ∝ (Electrical Conductivity)-1

23. Capacitances & Rate Capability
PCF vs. CF

24. Capacitances & Rate Capability
PCF vs. CF
197.3 F/g
(@ 10 A/g) 179.4 F/g
(@ 50 A/g)
166.3 F/g
(@ 100 A/g)
PCF

25. Electrochemical Performance of
PCF Supercapacitor Devices

26. Device Assembly
PVA Powder H2O
+ → PVA Gel Electrolyte
← Separator
+ KOH
PCF

27. Excellent Performance
Rate Capability Cycling Stability

28. Ragone Plot
Energy Density (Wh•kg-1)
How much energy per kg material
can store
Power Density (W•kg-1)
How fast per kg material can
charge/discharge

29. Ragone Plot

30. Summary

31. Summary
Chitosan
Glutaraldehyde
K2CO3
3D Carbon
Foams
3D Porous
Carbon
Foams
Cross-link
Reaction
Chemical
Activation
Outstanding Capacitive
Performance

32. Acknowledgements
Prof. Feng Zhang
Prof. Yat Li Group, UCSC

34. Characteristics of Supercapacitors
More charges can be stored than conventional capacitors
>ca. 100-1000 F/g ca. 1 μF/g
Supercapacitors Conventional Capacitors

35. <
ca. seconds ca. hours
Li-ion BatteriesSupercapacitors
Faster charge and discharge rates than batteries:
More charges can be stored than conventional capacitors
>
Supercapacitors Conventional Capacitors
ca. 100-1000 F/g ca. 1 μF/g
Characteristics of Supercapacitors

36. N-doping

37. Cross-link Reaction

38. No Cross-linker

39. Freeze Dry

40. Thermogravimetric Analysis

41. BET

42. Electrical Conductivity
Raman Spectroscopy
D Band G Band
Graphitic regionsDefects
Decrease
electrical
conductivity
Increase
electrical
conductivity
IG/ID=0.503
IG/ID=0.345

43. Sheet Thickness

44. AFM
Average Roughness
Ra = 6.6 nm

45. TEM

46. Electrochemical Performance of PCF and CF
CyclicVoltammetry
(CV)
Chronopotentiometry
(CP)

47. Electrochemical Performance of PCF

48. Cycling Stability of PCF

49. Device Assembly
Gel electrolytes
Polymer (usually PVA)-based
Polyvinyl Alcohol Wikipedia
Electrolytes serve as the solute (e.g. LiCl, H2SO4, LiOH)

50. Electrochemical Performance
PCF – nearly ideal capacitive performance

51. Device Flexibility

52. Outlook
Liu and Zhang et al. Nat. Commun., Under Review