Energy Storage - Electrochemistry Flashcards
Electrochemical Cells
These convert chemical energy into electrical energy through redox reactions.
Structure of EC cell?
Two electrodes, an electrolyte solution and a seperator.
Structure of the two electrodes?
Of two different materials, with ions in electrolyte solution that cna undergo redox reactions at electrodes.
What is the function of the seperator?
Allow for ion flow but prevent direct electrode contact.
What is the process of EC cell?
Anode undergoes oxidation where electrons flow through external circuit generating electrical currents.
What does anode oxidation allow for?
Negative charged electrolyte ions which are oxidised converting to higher oxidation states.
What is the process of the cathode solution of the EC cell?
Cathode is reduced, with external transfer of electrons to cathode surface, combining with positive charged electrolyte solution ions, reducing them, converting to lower oxidation state.
What causes reduction of the cathode?
Electron transfer from the anode.
What electrostatics govern ion flow in the electrolyte?
Potential difference between the electrodes generate electric fields, ions experiencing lorentz force.
Lorentz Force
This is the force exerted by a magnetic field onto a moving electrical charge.
What is lorentz force described by?
F = qE where q is charge and E is electric field strength.
What two forces is ion movement through electrolyte governed by?
Diffusion and migration(directed ion movement in response to electric fields)
What is diffusion and migration described by respecitvely?
Ficks Law and Nernst-Planck Equation
Equation of Ficks Law?
J = -D(dC/dx) where J is ion flux,, D the diffusion coefficient, dC/dx concentration graidnet.
Diffusion Coefficient
This is the proportion between flux and concentration gradient.
What does negative sign in ficks law indicate?
Movement from high to low concentraiton.
What is the Nernst-Planck equation?
J = -D(dC/dx) + qDC(E/RT) where R is gas constant, T temperature and J ion flux.
Nernst Planck Equation
This descibres motion of a charged chemical species in a fluid medium
What chemistry forces govern ion movement in electrolytes?
Reactions at electrodes by electron and ion transfer between electrode/electrolyte.
What is the basis of energy production in EC cells?
Electrolyte flow by redox reactions.
What happens when anode is oxidized by chemical reactions?
Cations and electrons are produced, whilst cathode reduced consuming an electron and an anion.
What do the anode-produced electrons do?
Combine with ions produced at the cathode.
What is electrolyte flow governed by?
Ohms law
Ohms Law
This says that electrical resistance is the ratio of applied voltage to the current between two electrodes in contact with a aterial.
Equation of Ohms Law?
I = V/R where I is current, V is voltage and R is conductor resistance.
What is the source of energy in EC cells?
The intermediaries fcailitaing electron transfer between electrodes, where energy is stored in electrode material chemical bonds.
Passivation
This is the creation of an outer layer of shield material pplied to a microcoating created by chemical reactions with base material.
Gibbs Free Energy Change
Describes maximum amount of work extracted from a reaction at constant temperature and pressure.
What does DeltaG relate to in EC cells?
Electromotive force and cell potential.
Denote DeltaG = -nFEcell
N is number of electrons, F is faraday constant and Ecell is cell potential
Faradaays Constant
This is the amount of electric charge carried by one mole, or avogadros number of electrons.
What does DeltaG determine?
Spontaneity of a reaction, if negative being exergonic whilst postive endergonic.
How does DeltaG relate to EC cells?
Positve cell potential means spontaneous flow from anode to cathode whilst negative means spontanoues from cathode to anode.
What is work exctracted from an EC cell calculated by?
Relationship between DeltaG and Ecell and equilibrium constant.
Equilibrium Constant
This expresses relationship between products and reactants of a reaciton at equilibrium.
What must G and Ecell be for electrical energy to be produced?
Negative and Positve.
Nernst Equation
This allows calculation of extent of reaction between two redox systems.
What is the formula for the NE?
Ecell = E^o - (RT/nF)1nQ (R is gas constant, T is absolute temperature, F is faradays constant, n is number of electrons transferred, and Q is reaction quotient.
Reaction Quotient
This measures relative amounts of products and reactants present during a raction at a particular point in time.
What is nernst equation based on?
Chemical Equilibrium and relationship of G and equilibrium constant.
What is G and Q at equilibrium?
0 and equal to EC
What does nernst equation calculate in EC?
Electrode potential of an EC cell, determining how concentraiton changes of the electroactive species affect electron potential, thus direction/magnitude of electron transfer in cell reaction.
Example of nernst equation applied to daniel cell?
If Zn+Cu2 –> Zn2+ + Cu with standard electrode potential of 1.10V, with Cu conc of 0.1m and Zn conc of 1.0m, and reaction quotient given by Zn/Cu, then 1.10V-0.059V with electrode potential of 1.04V
Electrode Potential
Meassures how easily a substance loses electrons.
Secondary Cells
These are rechargeable batteries.
Example of secondary cell?
Lithium-Ion batteries having anode and cathode, seperated by electrolyte where cathode made of metal oxide or polyanion, whilst anode of lithium containing material.
What laws are requierd for secondary cells?
Faradays Laws
Ohms Law
Kirchoffs Laws
What are the two faradays laws?
First states amount of chemical change produced by an electrical current is proportional to amount of electrical charge passing through the cell
Second states chemical change produced by an electrical current is proportional to the equivalent weight of the substnace being oxidised/reduced
What are the two Kirchoffs Law?
First says that at a junction in an electrical circuit, the sum of currents flowing into the junction is equal to the sum of currents flowing out of the junction.
Second says that any closed loop in a circuit, the directed sum of potential idifferences across componnets is zero.
