MM 222 Lecture 5 PDF
Document Details
Uploaded by AwestruckChlorine
Tags
Related
- Electrochemistry: Principles, Methods, and Applications PDF
- PHA6122 Pharmaceutical Analysis 2 - Introduction to Instrumental Methods of Analysis PDF
- Electrochemical Methods of Analysis PDF
- Analytical Chemistry Lecture Notes PDF
- Non-Traditional Machining Methods (AMP 1-3 PDF)
- Electrochemical Methods - Chapter 11 PDF
Summary
This lecture covers half-cell reactions and cell voltage concepts in electrochemistry, including galvanic and electrolytic cells. It also discusses electrochemical methods, explaining overpotential and mass transport.
Full Transcript
Recap Examples of half cell and full cell reactions Cell voltage; and potential vs. reference Example regarding operation as galvanic and electrolytic cell; based on prior concepts Examples of cells where no equilibrium can be achieved in one of the ‘half cells’ Half cell...
Recap Examples of half cell and full cell reactions Cell voltage; and potential vs. reference Example regarding operation as galvanic and electrolytic cell; based on prior concepts Examples of cells where no equilibrium can be achieved in one of the ‘half cells’ Half cell reactions If potential of the Pt electrode is made more -oxidation/reducti negative w.r.t. Ag/AgBr (reference) electrode; on currents electron flow is from the electrode to protons in solution; i.e., cathodic current onset of current flow occurs when potential of Pt electrode is close to E° for the H+/H2 reaction; which is, 0 V vs. NHE or -0.07 V vs. Ag/AgBr Note: Presently, the more usual convention is to denote cathodic current as –ve; unlike in here Background limit, culminating in EPt (V vs. AgBr) Note: Since EAg/AgBr = 0.07 V vs. NHE, the potential axis can be converted to EPt (V vs. NHE) by adding 0.07 V to each value of potential. ELECTROCHEMICAL METHODS Fundamentals and Applications; by Allen J. Bard and Larry Half cell reactions -oxidation/reduction currents - overpotential Same cell, but with the Pt replaced with a mercury electrode: When the potential of Hg is made negative, there is no current flow in the region where thermodynamics predict H2 evolution. Indeed, the potential must be brought to considerably more negative values before this reaction takes place. Hence, at Hg, the rate of hydrogen evolution reaction is much lower than at Pt. So, considerably higher electron energies (viz., more negative potentials) must be applied to make the reaction occur at a measurable rate => ELECTROCHEMICAL Hg shows METHODS "a higher Fundamentals overpotential and Applications; forJ. Bard by Allen the and hydrogen Larry Adding other cations/species to electrolyte In general, when the potential of an electrode is moved from its open- circuit value (OCV) to more negative potentials, the substance that is likely be reduced first is the oxidant in the couple with the least negative (or most positive) reduction potential. However; for though, Power of electrode surface; i.e., electrocatalysis Cd(Hg): cadmium amalgam ELECTROCHEMICAL METHODS Fundamentals and Applications; by Allen J. Bard and Larry Rate and Pathway of general electrode reaction O + ne ↔ R C is equivalent to 6.24 x 1018 electrons) A particular current density is driven by a certain over-potential; which can be considered as a manifestation of: ηmt (mass-transfer overpotential), ηct (charge-transfer overpotential) and ηrxn (overpotential associated with any preceding reaction) ELECTROCHEMICAL METHODS Fundamentals and Applications; by Allen J. Bard and Larry R. Faulkn