Chemical energy ⇔ electric energy Electrochemistry content in this course: Ox + e - ⇔ Red Charged surfaces ⇔ What is electrochemistry about? Electrochemistry in practice Electrode Electronics, Physics Electrolyte (liquid or solid) Chemistry • Metal, carbon • Semiconductor • Membrane • Ions • Molecules Materials properties Chemical information Adsorbed molecules Reactions Surface charge Capacitance Current/ potential source Electrochemistry at interfaces Charge transport via ions Charge transport via conduction electrons Electrode Solution φ x 0 0.1-10 nm φ M φ S Field strength: ∆E/∆x ≈ 1 V/ 1 nm ≈ ≈ MV-GV/m ! ∆E, ca -2 ... +2 V Potential drop at the interface φ M φ S 0 Adsorption influences properties such as capacitance and potential drop over the interface, as well as electrode reactions. We can take advantage of this to obtain information about the adsorbed layer!
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What is electrochemistry about? Electrochemistry in practice · A galvanic cell! The potential must be measured relative to another half cell! Galvanic cells Standard (reduction)
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Transcript
Chemical energy ⇔ electric energy
Electrochemistry content in this course:
Ox + e- ⇔ Red
Charged surfaces
⇔
What is electrochemistry about? Electrochemistry in practice
Electrode
Electronics, Physics
Electrolyte (liquid or solid)
Chemistry
• Metal, carbon• Semiconductor• Membrane
• Ions• Molecules
Materials properties Chemical information
Adsorbed moleculesReactions
Surface chargeCapacitance
Current/potential source
Electrochemistry at interfaces
Charge transportvia ions
Charge transport viaconduction electrons
Electrode Solution
φ
x0
0.1-10 nm
φM
φS
Field strength: ∆E/∆x ≈ 1 V/ 1 nm ≈≈ MV-GV/m !
∆E, ca
-2 ... +2 V
Potential drop at the interface
φM
φS
0
Adsorption influences propertiessuch as capacitance and potentialdrop over the interface, as well aselectrode reactions.
We can take advantage of this toobtain information about theadsorbed layer!
Electrode currents
electrode solution
Red
Ox + e-
Electrochemical reactionElectric double layer
electrode solution
--
--
-
+++++
e-
Faradaic current
Current flows across the interfaceat a rate determined by the electrode reaction.
Non-Faradaic current
Transient current as the chargingproperties at the interface are changed,charging current.
No charge transfer across the interface!
2.3 µA
An electrical circuit – An electrochemical cell
A
A+
B
B-
e-
+ -
Electrodes
+
Anode Cathode
-
e-e-e-
Potential E [Volt]
Current i [Ampere]
(e- per unit time)
Charge Q=It [Coulomb]
Ohm’s law R=U/i [Ohm]
Electric power P=UI [Watt]
Kirchoff’s law What happens at the electrodes?
Charge transfer
M E+
e-
Oxidation
M E
φ e-
Reduction-
φ
Electrode (M) Electrolyte (E)φ+
-Energy level (EF)
at the electrode electrons.
VacantMO
OccupiedMO
By varying theelectrode potential,reactions with theelectrolyte becomepossible. Zn