Electrochemical Impedance Spectroscopy.pptx
- 1. Electrochemical Impedance Spectroscopy (EIS) 1 Jahanzeb Ahmad (210312006) • Presented by: Prof. Sajid Ullah Khan and Class • Presented to:
- 2. Resistance and Impedance Resistance is an electrical circuit element which opposes the flow of current. The current may be AC as well as DC. Impedance is a collective name of a combination of resistor, inductor and capacitor generally. 2
- 3. 3 Electrochemistry as a circuit
- 4. ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY (EIS) EIS is a powerful method of analyzing the complex electrical resistance of a system. First examples of its use was reported at the end of the 1980s; however, the method has seen a huge improvement in recent years due to; Advances made in instrumentation and its extraordinary sensitivity Introduction. 4
- 5. Cont… It has been applied for studying electrochemical properties, for example • Charge transport across membranes & its interfaces • Electrode kinetics • Double layers studies EIS has been intensively used in areas, • Electrochemistry • Bio-medical applications • Material science and others • Bio-sensing • Energy storing and conversion systems (Fuel cells, Rechargeable batteries) • Corrosion mechanisms • Electrochemical synthesis 5
- 7. Basic Principle of Electrochemical Impedance Making EIS Measurements Apply a small potential (or current) AC signals (1 – 10 mV) of fixed frequency or for a wide range of frequencies. Measure the response and compute the impedance at each frequency. Plot Analyze 7
- 8. 8 EIS of a Resistor
- 9. 9 EIS of a Capacitor
- 10. 10
- 11. 11 Bode plot
- 12. 12 Nyquist Plot
- 13. 13 Nyquist Plot with Fit
- 14. Bode Plot: • Individual charge transfer processes are resolvable. • Frequency is explicit. • Small impedances in presence of large impedances can be identified easily. Nyquist Plot: • Individual charge transfer processes are resolvable. • Frequency is not obvious. • Small impedances can be swamped by large impedances. 14 Bode Plot vs Plot Nyquist
- 15. Electrochemical cells can be modeled as a network of passive electrical circuit elements. A network is called an “equivalent electrical circuit”, can be done using serial and parallel combinations of Circuit Elements Most of the circuit elements in the model are common electrical elements such as, Electrolyte Resistance (Rs, Ru) Double Layer Capacitance (Cdl) Electron Transfer Resistance (Ret) Warburg Impedance (Zw) Constant Phase element (Q) 15 Analyzing EIS: Modeling
- 16. Resistance of an ionic solution It depends on: Ionic concentration. Types of ions. Temperature. The geometry of the area in which current is carried. 16 Electrolyte Resistance
- 17. Ions from solution stick on the electrode surface. Charges of these ions separate the charges in electrodes. Separation is very small (order of angstroms) 17 Double layer Capacitance
- 18. Electrode reaction is composed of: • Charge transfer • Adsorption • Mass transport If no electron transfer occur, Rct becomes very large. If there is an electron transfer reaction, Rct becomes smaller. It connects in parallel with double layer capacitance C. 18 Charge Transfer Resistance (Rct)
- 19. Warburg Impedance: General impedance which represents a resistance to mass transfer, i.e., diffusion control. A Warburg typically exhibits a 45° phase shift. Constant Phase Element: A very general element used to model “imperfect” capacitors. CPE’s normally exhibit a 80-90° phase shift. 19 Other Modeling Elements
- 20. 20 Case Study-1
- 21. The Rct value in the Nyquist plot of the modified electrode was 44.9 Ω. The peak current in the CV curve of the modified electrode was 382.5 μA . After the antibody was attached to the modified electrode, an increase in Rct (360 Ω) and a decrease in peak current (220 μA) was observed. This was due to the hindering effect of insulating protein for electron transfer. Then, the blocking process and immuno-competition process further protect electron transfer of the electrodes. Further proving from CV peak, the current decreased to 157 μA after blocking and decreased to 108 μA after immuno-binding and Rct value increased upto 806 Ω. The stepwise increase in impedance value confirm the successful immobilization of GCE surface 21 Detection strategy of impedance immunosensor
- 22. 22 Case Study-2
- 23. 23 A fiber shaped, stretchable, TiO2 nanowire array based DSSC was reported firstly. EIS on this device show that the bending time at a bending radius of 2 cm and the stretching time at a strain of 50% had almost no effect on the photoelectric conversion efficiency The slight damage of the TiO2 layer leads to terrible electron combination, the stretching operation increases the internal resistance and charge-transfer resistance at the counter electrode, resulting in the decrease of FF and Jsc. Efficiency of solar cells is decreased when TiO2 layer is damaged. Cont…
- 24. Useful on high resistance materials Time dependent data is available Non- destructive Quantitative data available 24 Advantages and Disadvantages Expensive Complex data analysis for quantification
- 25. EIS has been used since decades in non-biological applications such as in Corrosion study. Electrochemical activity of Li-ion cells. Monitoring fuel cell performance, etc. However, EIS has gained recently much more popularity in biosensor applications that is used for a wide range of analyses owing to its Label-free measurements. Non-destructive technique. Excellent sensitivities. 25 Current trends and challenges
- 26. EIS technique has demonstrated its feasibility on the characterization of modified-surface electrode processes and determining diffusion kinetics, mass-transport parameters at electrodes interfaces. Mainly, (EIS) is becoming a sensitive technique for the analysis of the interfacial properties related to bio molecular recognition events on the transducer surface. The detection process involves the formation of a recognition complex between the sensing biomolecule and the analyze at the interface of the electronic transducer, which directly or indirectly changes the electrochemical impedance properties of the recognition surface. The foremost advantages of working with EIS based biosensors is the small amplitude perturbation from steady state, which makes it a non-destructive technique, as well as its label-free measurements and excellent sensitivities. Due to the affordability and availability of impedance instrumentation at the present time, a trend towards the development of impedimetric biosensors & NDT appears to be popular. These can be realized from the increase in the number of publications on this topic over the past few years. 26 Conclusion