Hybrid materials as cathode and carbon based materials as anode for asymmetric supercapacitor applications. Ncholu Manyala

Transcription

1 Hybrid materials as cathode and carbon based materials as anode for asymmetric supercapacitor applications Ncholu Manyala Department of Physics, Institute of Applied Materials, SARCHI Chair in Carbon Technology and Materials, University of Pretoria, Pretoria 0028, South Africa 1

2 Overview Outline Synthesis of hybrid materials Synthesis of carbon-based materials Results and discussion Conclusion 2

3 Why electrochemical capacitors (Supercapacitors) Due to the increasing demand for high-performance energy-storage systems alternative storage systems are considered. Supercapacitors are power devices with high power capability, long cyclic life, fast charge propagation dynamics with low maintenance cost. They are suitable for application in backup power sources, portable electronic devices, electric vehicles and hybrid electric vehicles (HEVs). Most of the available supercapacitor have energy density < 10 Wh/kg, when compared with batteries > 100 Wh/kg. Hence, there is the need to increase the energy performance of supercapacitors to be close to or even beyond that of batteries. 3

4 Batteries have low power density and high energy density Supercapacitors have low energy density but high power density Applications 4

5 Materials used for supercapacitor devices 5

6 Symmetric SCs Asymmetric SCs Symmetric SCs without hybrid behaviour Symmetrichybrid materials Asymmetrichybrid materials Asymmetric SCs without hybrid behaviour EDLCs Symmetric systems with Faradic materials One batterytype electrode Electrodes of capacitive nature 6

7 Specific capacitance (C sp ) of single electrode can be obtained using (CV curve) (CD curve) (CD curve) EDLC C sp I( v) dv mv V (Fg 1 ), C sp 2I A charge balance Q + = Q between the two electrodes should be done; where Q + and Q are the charges stored in the positive and negative electrodes, respectively. The charge stored by each electrode can be expressed as The energy density (E, in Wh kg -1 ) of supercapacitor can be calculated from specific capacitance E max C sp U (Wh Power density (P, in W kg -1 ) of a supercapacitor P V ( t) dt mv max 2 m m (Fg C C 1 ), sp sp U U kg Emax 1 (W kg ) t C sp Q Cspm V ) I t m V (Fg 1 ) 7

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9 Methane (CH 4 ) decomposition at 1000 o C Graphene nucleation/growth on NF High surface NF used as substrate for growth 9

10 1. Mn 3 (PO 4 ) 2 /GF 2. Co 3 (PO 4 ) 2.4H 2 O/GF 3. V 2 O 5 /GF 10

11 1. Activated carbon (AC) from coconut shell 2. Carbonization of Fe cations adsorbed onto polyaniline (C-FP) 11

12 Three composite materials have been used as positive electrodes and two carbon-based materials as negative electrodes in asymmetric supercapacitors: 1. Mn 3 (PO 4 ) 2 /GF//AC 2. Co 3 (PO 4 ) 2 /GF//C-FP 3. V 2 O 5 /GF//C-FP Mn 3 (PO 4 ) 2 /GF//AC AC Mn 3 (PO 4 ) 2 / GF Carbonbased materials Co 3 (PO 4 ) 2 /GF//C-FP Co 3 (PO 4 ) 2 / GF Composite materials C-FP V 2 O 5 /GF V 2 O 5 /GF//C-FP 12

13 XRD, SEM, CV & CD (in 6 M KOH electrolyte) of AC 13

14 SEM & TEM: Mn 3 (PO 4 ) 2 and Mn 3 (PO 4 ) 2 /GF 14

15 CV & CD (in 6 M KOH electrolyte) for Mn 3 (PO 4 ) 2 and Mn 3 (PO 4 ) 2 50 mvs 1 A g -1 15

16 Mn 3 (PO 4 ) 2 /GF//AC asymmetric device 16

17 EIS & Stability: Mn 3 (PO 4 ) 2 /GF//AC A g -1 17

18 CV & CD (in 6 M KOH electrolyte) for Carbonization of Fe cations adsorbed onto polyaniline (C-FP) Current density (A g -1 ) (c) 5 mv s mv s -1 Potential (V vs Ag/AgCl) 0,0 (d) -0,2-0,4-0,6-0,8-1,0 1 A/g 2 A/g 3 A/g 4 A/g 5 A/g ,2-1,0-0,8-0,6-0,4-0,2 0,0 Potential (V vs. SCE) -1, Time (s) 18

19 SEM & TEM: Co 3 (PO 4 ) 2.4H 2 O and Co 3 (PO 4 ) 2.4H 2 O/GF Pristine Composite Pristine Composite 19

20 CV & CD (in 6 M KOH as electrolyte) for Co 3 (PO 4 ) 2.4H 2 O and Co 3 (PO 4 ) 2.4H mv s 0.5 A g -1 20

21 Co 3 (PO 4 ) 2.4H 2 O/GF//C-FP asymmetric device 21

22 EIS & Stability: Co 3 (PO 4 ) 2.4H 2 O/GF//C-FP asymmetric A g -1 22

23 SEM & TEM: V 2 O 5 and V 2 O 5 /GF 23

24 CV & CD (in 6 M KOH electrolyte) for V 2 O 5 and V 2 O 5 /GF 24

25 V 2 O 5 GF//C-FP asymmetric device 25

26 Stability and EIS: V 2 O 5 /GF//C-FP asymmetric A g A g -1 26

27 Ragone Plot: Asymmetric devices 10 5 Mn 3 (PO 4 ) 2 /GF//AC Energy density (Wh kg -1 ) V 2 O 5 /GF//C-FP Co 3 (PO 4 ) 2 /GF//C-FP Power density (W kg -1 ) 27

28 Conclusion We have successfully synthesized hybrid (Mn 3 (PO 4 ) 2 /GF, Co 3 (PO 4 ) 2 /GF and V 2 O 5 /GF) materials using hydrothermal approach. Activated carbon from coconut shell and carbonization of Fe onto polyaniline (C-FP) were also synthesized The electrochemical performance of the metal oxides was improved in three electrode by incorporation of the graphene foam into the metal oxide matrix. The hybrid materials have been used as positive electrodes and the carbonbased materials as negative electrodes in asymmetric supercapacitors. The results showed that asymmetric supercapacitors based on hybrid materials and carbon-based materials have great potential for energy storage applications. 28

29 Ndeye Maty Ndiaye, Ph.D Student Abdulmajid Mirghni, Ph.D student 29

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31 Thank you 31

32 XRD & Raman: Mn 3 (PO 4 ) 2 and Mn 3 (PO 4 ) 2 /GF 32

33 XRD & Raman: Co 3 (PO 4 ) 2.4H 2 O and Co 3 (PO 4 ) 2.4H 2 O/GF 33

34 XRD, Raman & XPS: V 2 O 5 and V 2 O 5 /GF 34