Download overpotential and battery basics and more Slides Electrochemistry in PDF only on Docsity!
Overpotential
- (^) Overpotential is the potential difference between half reaction thermodynamically determined reduction potential at which redox event is experimentally observed.
- (^) Measuring the potential at which a given current density.
- (^) The overpotential increases with growing current density as described by the Tafel equation.
Tafel equation
- (^) Electrochemical kinetics relating the rate of an electrochemical reaction to the overpotential.
- (^) A single electrode the Tafel equation. Ƞ = Overpotential b= Tafel slope i = Current density A/m 2 i 0 =Exchange current density A/m 2
Butler–Volmer equation
-. It describes how the electrical current on an electrode depends on the electrode potential, considering that both a cathodic and an anodic reaction occur on the same electrode. where:
- i: electrode current density , A/m^2 (defined as j = I/S )
- io: exchange current density , A/m^2
- E: electrode potential , V
- Eeq: equilibrium potential, V
- T: absolute temperature , K
- n: number of electrons involved in the electrode reaction
- F: Faraday constant
- (^) R: universal gas constant
- c: so-called cathodic charge transfer coefficient, dimensionless
- : so-called anodic charge transfer coefficient, dimensionless
- Ƞ : activation overpotential ( E – Eeq)
Butler -vomer plot
Open-Circuit Voltage Characteristics
- (^) The open-circuit voltage for a battery system is a function of temperature and electrolyte concentration.
- (^) The open-circuit voltage is also affected by temperature.
Working and Counter Electrodes
- (^) The electrode at which the reaction of interest occurs is called the working electrode
- (^) The electrode at which the other (coupled) reaction occurs is called the counter electrode
- (^) A third electrode, called the reference electrode may also be used.
Faraday’s First Law: The amount of current passed through an electrode is directly proportional to the amount of material liberated from it. By definition, one coulomb of charge is transferred when a 1-amp current flows for 1 second. Faraday second law: The amount of current passed through an electrode is directly proportional to the chemical equivalent
Faradays' law Formula: m = M I t /n F m - mass of substance M - molecular weight of the substance I - current passed (A) t - time for which the current is passed (s) n - number of electrons transferred F - Faraday constant The amount of chemical change is proportional to the amount of current passed
Heat transfer
Transfer of heat energy from one body to another body. Modes:
- (^) Conduction
- (^) Convection
- (^) Radiation
Conduction :
- (^) Heat is transferred from one molecule to another molecule by the help of inbetween molecule. Example: Heat exchanger Convection:
- (^) Heat is transferred without indirect contact. Example: boiling water Radiation:
- (^) Receive the heat energy from without any medium. Example: Radio waves
X-RAY DIFFRACTION:
- (^) Structures , phases , other structural parameters such as average grain size , crystallinity can be identified Uses: (^) It is used to determine the atomic spacing. (^) Measure of sample purity. (^) Identification of unknown crystalline material. (^) Determination of unit cell.
