Electron-transfer chemistry at electrodes: galvanic and electrolytic cells, the Nernst equation, batteries, and fuel cells. Bridges redox chemistry (L2) and classical EM (L1) via the Faraday constant.
electrochemistry
Galvanic cell
Electrochemical cell in which spontaneous redox drives electron flow through an external circuit, producing useful electrical work. Two…
Electrolytic cell
Electrochemical cell in which external electrical work drives a non-spontaneous redox reaction (ΔG > 0). Used in metal plating, aluminium…
Nernst equation
Concentration dependence of the electrode potential: E = E° − (RT/nF) ln Q. Governs battery voltage under load and pH-dependent electrode…
Battery
Stack of galvanic cells packaged for practical energy storage. Examples: Pb-acid, NiMH, Li-ion, solid-state Li, flow batteries.…
Fuel cell
Continuous-feed galvanic cell: fuel (H₂, methanol) and oxidant (O₂) are supplied separately, enabling indefinite operation. Types: PEM,…
Anode and cathode
The two electrodes of any electrochemical cell: the anode is where oxidation occurs (species loses electrons); the cathode is where…
Standard hydrogen electrode (SHE)
The reference half-cell for all electrode-potential measurements: Pt(s) | H₂(g, 1 atm) | H⁺(aq, 1 M); defined E° = 0.000 V by convention.…
Faraday's laws of electrolysis
Two quantitative laws (Faraday 1834): (1) the mass of substance deposited or liberated at an electrode is directly proportional to the…
Lithium-ion battery
Rocking-chair intercalation: LiCoO₂||graphite. 3.7 V, 250 Wh/kg. Goodenough/Whittingham/Yoshino Nobel 2019. LFP, NMC cathodes; Si anodes…
Solid electrolyte interphase (SEI)
Passivation layer formed on first charge from reductive decomposition of electrolyte at anode (Li₂CO₃, LiF, RCO₂Li). Critical for cycle…
PEM fuel cell
H₂/O₂ → H₂O + electricity at Pt/Nafion/Pt. Anode: H₂→2H+2e⁻; cathode ORR is kinetically slow. Automotive (Mirai, Nexo); Pt-loading…
Water electrolysis (PEM/SOEC)
2H₂O → 2H₂ + O₂; ΔG = 237 kJ/mol → 1.23 V thermodynamic, ~1.8 V practical. PEM (<100°C), alkaline, solid-oxide (700-900°C higher…
OER/ORR electrocatalysis
Oxygen-evolution RuO₂/IrO₂/NiFe-OH (4e⁻ water oxidation). Oxygen-reduction Pt, Pt-alloys, Fe-N-C. Descriptor-based catalyst design; volcano…
Butler–Volmer equation
i = i₀[exp(α_a Fη/RT) - exp(-α_c Fη/RT)]; controls electrode kinetics; Tafel at large η gives i ∝ exp(αFη/RT).
Tafel plot & exchange current
η = a + b log|i|; extrapolate to η=0 gives i₀; slope b = 2.303RT/αF; catalyst comparison.
Marcus–Hush electron transfer at electrodes
k_ET = A exp(-(λ+ΔG°)²/4λk_BT); inverted region; normal region typical for outer-sphere ET on electrodes.
Electrochemical impedance spectroscopy (EIS)
AC perturbation Z(ω); Nyquist, Bode plots; equivalent circuits (Randles, Warburg); mechanism & kinetics.
Cyclic voltammetry — kinetic analysis
Reversible ΔE_p = 59/n mV; quasi-reversible Nicholson ψ; EC mechanisms; Randles-Sevcik i_p ∝ √v.
OER, ORR, HER, HOR mechanisms
Sabatier volcano for HER (Pt apex); 4e⁻ OER limited by scaling relations among OHads/Oads/OOHads.
Li-ion battery chemistry
LiCoO₂/graphite, LFP, NMC cathodes; SEI formation; intercalation; ~300 Wh/kg commercial; 2019 Nobel.
Solid-state batteries
Solid electrolyte (sulfide, oxide, polymer) replaces liquid; enables Li-metal anode, higher E density; interfacial challenges.
Redox flow batteries
Liquid electrolyte tanks; VO²⁺/VO₂⁺ all-vanadium; energy/power decoupled; grid-scale storage.
Corrosion & passivation
Galvanic, pitting, crevice, stress corrosion; passivation via Cr₂O₃, Al₂O₃; Pourbaix diagrams predict stability.
Electrochemical CO₂ reduction
CO₂ + n e⁻ + n H⁺ → products; Cu unique for C-C coupling; Faradaic efficiency & selectivity challenges.