Electrode of the Third Kind Electrodes that merely serve as sources or sinks for electrons Common names: redox inert unattackable EXAMPLES metals: Pt, Au, GC, graphite, HOPG, Hg semiconductors: Si, GaAs, In-SnO,/glass Response for pt in contact with Fe2+ Fe3+ in solution 一E=EC0.059(V)log([e2+]/Fe3+])
Electrode of the Third Kind • Electrodes that merely serve as sources or sinks for electrons • Common names: redox, inert, unattackable • EXAMPLES: – metals: Pt, Au, GC, graphite, HOPG, Hg – semiconductors: Si, GaAs, In-SnO2 /glass • Response: – for Pt in contact with Fe2+, Fe3+ in solution: – E = E0 - 0.059 (V) log ([Fe2+]/[Fe3+])
Electrode of the fourth Kind Electrodes that cannot be classified as 1-3 EXAMPLES Chemically modified electrodes(CMEs)
Electrode of the Fourth Kind • Electrodes that cannot be classified as 1-3 • EXAMPLES: – Chemically modified electrodes (CME’s)
Reference electrodes Purpose: provide stable potential against which other potentials can be reliably measure d Criteria stable(time, temperature reproducible ( you, me) potential shouldnt be altered by passage of small current= not polarizable easily constructed conⅴ enient for use
Reference Electrodes • Purpose: provide stable potential against which other potentials can be reliably measured • Criteria: – stable (time, temperature) – reproducible (you, me) – potential shouldn’t be altered by passage of small current = not polarizable – easily constructed – convenient for use
SHE Advantages Disadvantages · International standard· Convenience EO≡0V Pt black easily · One of most poisoned by organics reproducible potentials sulfide. cyanide. etc +lmv Hydrogen explosive Sulfuric and hydrochloric strong acias
SHE Advantages • International standard E0 0 V • One of most reproducible potentials + 1 mV Disadvantages • Convenience – Pt black easily poisoned by organics, sulfide, cyanide, etc. – Hydrogen explosive – Sulfuric and hydrochloric strong acids
Practical reference electrodes Aqueous Nonaqueous ·SCE Agt /Ag Ag/AgCl pseudoreferences Pt, Ag wires Ferrocene
Practical Reference Electrodes Aqueous • SCE • Ag/AgCl Nonaqueous • Ag+ /Ag • pseudoreferences – Pt, Ag wires • Ferrocene