Introduction to electrochemical systems Sähkökemian peruseet KE Tanja Kallio C213 CH 1

Introduction to electrochemistry

Electrochemical cell load electrically charged species medium + =electrolyte ions complex ions molecules water organic solvent ceramics molten salts ionic liquids membranes electrodes external circuit load or measuring equipment

Electrochemical reaction electrode e-e- electrochemical reaction = heterogeneous redox reaction The rate of an electrochemical reaction depends on the potential of the electrode

Redox-reactions in the cell load Pt acidic aqueous electrolyte H 2 SO 4, HClO 4, … Anode H 2  2H + + 2e - E o = 0.00 V Cathode O 2 + 4H + + 4e -  2H 2 O E o = 1.23 V reaction of interest = working electrode counter electrode reference electrode auxillary electrode I = nFr Q = It = nzF

Metal bonding, Fermi level and work function Fermi Dirac distribution Fermi level P(E) = 1/2

Potential and voltage  inner or galva potential  outer or voltapotential  surface potential faasi  charge in vacuum

Electrode potential, potential difference and voltage electrode probability for finding an electron solution EfEf electrod potential + - electrode occupied states unoccupied occupied states unoccupied Ef’Ef’ 01 solution energy

Electron transfer on the electrode EfEf electrode occupied states unoccupied Ef’Ef’ energy HOMO LUMO e-e- HOMO LUMO e-e- electrode a molecule in a solvent Ag + (aq) + e -  Ag

Potential window

polarizability ideally nonpolarizable ideally polarizable reaction rate ~  reaction rate ~ 0 Li 4 Ti 5 O 7 electrode for lithiun ion battery ultra capacitor