Fundamentals of Electrochemistry Flashcards
1
Q
Disciplines in Electrochemistry
A
- Batteries & Energy storage
- Corrosion Science & Technology
- Electrochemical Deposition
- Electrochemical Engineering
- Fuel Cells, Electrolyzers & Energy Conversion
- Organic & Bioelectrochemistry
- Physical / Analytical Electrochemistry
- Electrochemical Sensors
2
Q
Corrosion Science & Technology - Subcategories
A
- corrosion
- passivity
- coatings
3
Q
Electrochemically Deposition - Deposed
A
- metals
- oxides
- semiconductors
4
Q
Organic Biochemistry - Subunits
A
- enzymatic electrochemical reactions
- microbial electrochemical reactions
5
Q
Physical & Analytical Electrochemistry - subunits
A
- electrocatalysts
- photoelectrochemistry
- interfacial science
6
Q
Electrochemical Senors
A
- wearable devices
- implantable devices
- environmental sensors
7
Q
Differences in energy storage technologies
A
- storage principle
- mechanical
- electrical
- thermal
- chemical
- storage/discharge time
- associated power & energy
- installation potential (pumped hydro naturally limited)
- round-trip efficiencies
8
Q
Necessaties for current flow from electrochemical reaction
A
- a driving force -> electrochemical potential
- electron giver
- electron receiver
- electron conductor
- ion conductor
9
Q
Electrolytes
A
- used as ionic conductors
- Requirements
- chemically stable
- high ionic conductivity
- low mass
- non-volatile
- safe
- Relevant ionic conductors
- aqueous
- non-aqueous
- polymeric
- ceramic
- Characteristics of ionic conductivity
- (solvated) ions move due to electric field
- ionic conductivity π = f(ion concentration(proportional), ion mobility πβπβ, temperature Tβπβ)
10
Q
Electrodes
A
- electric conductors
- Requirements
- chemical stability
- large surface area
- low electronic resistance
- low mass
- low cost
- Relevant electronic conductors
- metals
- various carbonaceous materials
- Characteristics of ionic conductivity
- electrons are transported through a material
- electronic conductivity π = f(temperature Tβπβ, charge mobility πβπβ, time between collisions πβπβ)
- Highest conductivity: Copper at 0Β°C
11
Q
kinds of electrochemical cells
A
- electrolysis cells
- ΞG > 0
- electrical energy is used to drive non-spontaneous reaction
- electrical energy -> chemical energy
- galvanic cells
- ΞG < 0
- spontaneous reaction occurs & electrical energy is released
- fuel cells & batteries
- chemical energy -> electrical energy
12
Q
Electrochemical Interface
A
- when Electrode gets in contact with Electrolyte
- both phases are affected
- electrochemical double layer is created (1-10nm)
- acts like capacitor
- very high electric fields
- major potential drop
13
Q
Standard Hydrogen Electrode SHE
A
- used as a reference for standard potentials, tabulated
- positive: reaction proceeds spontaneously as written versus SHE; increased preference for taking up electrons (thermodynamically favourable)
- negative: reverse reaction would proceed spontaneously versus SHE; decreased preference for taking up electrons
- standard potential -> set to be 0V
- in real applications reversible hydrogen electrode (RHE) more commonly used
- standard potential depends on pH
- Convenient for measure of the half cell reactions
14
Q
Losses of Cell Voltage
A
- actual measure cell voltage (=applied potential) is sum of thermodynamic standard potentials of both electrodes & losses that occur:
- ohmic resistances -> ohmic losses
- slow kinetics -> activation losses
- ineffective mass transport ->mass transport losses
- get more pronounced with higher currents
15
Q
Thermochemical equilibrium potential
A
- no current flow between the electrodes
- each side reaction is in equilibrium as well (reversible)
16
Q
Current Flow
A
- wanted in real application
- current is proportional to reaction rate (kinetics of reactions!!)
- Electrocatalysis: catalysts at electrodes speed up reaction
- reactant concentration increase or reactant temperature increase can have the same effect
- current usually normalised by surface area
- at high currents vicinity of surface gets depleted of reacting species & concentration gradient occurs -> diffusion layer forms
17
Q
Modes & Relevance of Mass Transport
A
- migration
- movement in electrical field (charged species)
- driving force: electrochemical potential gradient - diffusion
- movement due to concentration differences
- driving force: chemical potential gradient - convection
- naturally/forced through temperature gradients
- due to e.g. stirring - reactants need to reach electrode surface region for a reaction to occur
- can all occur in a electrochemical cell
18
Q
Take Away messages B)
A
- diverse applications of electrochemistry
- increasing relevance in an electrified economy
- electrochemical reactions
- involve electrical currents
- involve a spatial separation of a reduction & an oxidation reaction (electron flow) - electrodes & electrolytes conduct charge differently (electrically vs. ionically)
- interface between the two phases
- electrochemical double layer - standard equilibrium potential of an electrode
- thermodynamic description (βG)
- quoted via the standard hydrogen electrode as a reference point
- Nernst equation allows determination at non-standard conditions - cell potential combines the reduction & oxidation processes
- measured potentials deviate from the thermodynamic description
- losses in the cell due to kinetic limitations, ohmic resistances & transport losses βoverpotentialsβ
19
Q
properties affecting the electrochemical reaction (-> current)
A
- applied voltage
- electrode (material, surface, catalystβ¦)
- electrolyte (speciesβ concentration, conductivityβ¦)
- ambient conditions
- transport of active species to the electrode
- side reactions
