Electrochemical kinetics 87.11 Polarization of electrode
§7.11 Polarization of electrode Electrochemical kinetics
87.11 Polarization of electrode What are we going to learn? Ideal vs real electrochemical processes Concepts: overvoltage, polarization, overpotential; concentration/diffusion polarization eectrochemical polarization Method: overpotential measurement; Rules: (1) polarization direction (2)Tatel equation Model: exchange equilibrium Theoretical treatment: Master equation, Butler-Volmer equation Applications: electrolysis, battery, corrosion protection
What are we going to learn? Ideal vs. real electrochemical processes. Concepts: overvoltage, polarization, overpotential; concentration/diffusion polarization, electrochemical polarization Method: overpotential measurement; Rules: (1) polarization direction; (2) Tafel equation; Model: exchange equilibrium Theoretical treatment: Master equation, Butler-Volmer equation Applications: electrolysis, battery, corrosion protection §7.11 Polarization of electrode
87.11 Polarization of electrode 7.11.0 Introduction Surface region Electrode process em. IXn ransier Fast equilibrium and rate-determining step Desorption/ adsorption Diffusion--concentration polarization EC rxn I Bulk solution Electrochemical reaction -electrochemical R polarization Desorption/adsorption R RS Chem. rxn Mass R transfer
7.11.0 Introduction Electrode process: Fast equilibrium and rate-determining step Diffusion—concentration polarization; Electrochemical reaction – electrochemical polarization §7.11 Polarization of electrode
87.11 Polarization of electrode 7.11.0 Introduction Electrochemical kinetic parameters Reaction rate: current density nFr/mol s nFkc A Activation energy: overpotential k T 4G+anFAo anFd k eXI p( h )=ko exp RT RT
7.11.0 Introduction Electrochemical kinetic parameters: 1 / mol s n i nFr nFkc j A A A − = = = , 0 0 exp( ) exp( ) k TB G nF c nF k k h RT RT + = − = − Reaction rate: current density Activation energy: overpotential §7.11 Polarization of electrode
87.11 Polarization of electrode 7.l1.1. Decomposition voltage and overvoltage 1.229 0.401 0.000 H,O 170V 1.229v -0.828 1.0 2.0E 02468101214pH Electrolysis of water Reversible decomposition Effective decomposition voltage voltage
7.11.1. Decomposition voltage and overvoltage Electrolysis of water Reversible decomposition voltage Effective decomposition voltage §7.11 Polarization of electrode