山东大学：《物理化学》课程教学资源（讲义资料）7.8 Electrode potential-for students

87.8 Electrode potential Out-class extensive reading IraN. Levine, pp 426 Section 14.7 standard electrode potentials Section 14.8 concentration cells Section 14.9 liquid-junction potential

§7.8 Electrode potential Out-class extensive reading: Ira N. Levine, pp. 426 Section 14.7 standard electrode potentials Section 14.8 concentration cells Section 14.9 liquid-junction potential

87.8 Electrode potential Goals for this class (I) Explain the origin of interfacial charge (2)Compare the important models for electric double layer (3) Principle for defining a relative standard (4)Applying Nernst equation for electrode (5) Enumerate the ways to lower/eliminate liquid junction potential

Goals for this class (1) Explain the origin of interfacial charge; (2) Compare the important models for electric double layer; (3) Principle for defining a relative standard. (4) Applying Nernst equation for electrode. (5) Enumerate the ways to lower/eliminate liquid junction potential. §7.8 Electrode potential

87.8 Electrode potential 7.8.1 How does electrode potential establish? Cu half-cell (cathode; reduction) 12 BBS. CDSTM. CN Zn half-cell (anode; oxidation) electromotive forces potential difference Daniell cell

7.8.1 How does electrode potential establish? Daniell cell electromotive forces potential difference §7.8 Electrode potential

87.8 Electrode potential 7.8.1. Interfacial charge and electrode potential 1)Metal-metal interface 2)Liquid-liquid interface: Liquid junction is the interface between two miscible electrolyte solutions Work function contact potential HCI KCI HCI KCI n 4++(++ H ( Oenone ⑥ KCl solution HCI solution liquid junction potential, liquid potential, diffusion potential

1) Metal-metal interface: Work function contact potential 7.8.1. Interfacial charge and electrode potential KCl solution HCl solution 2) Liquid-liquid interface: Liquid junction is the interface between two miscible electrolyte solutions. liquid junction potential, liquid potential, diffusion potential §7.8 Electrode potential

87.8 Electrode potential 7.8.1. Interfacial charge and electrode potential 3)Liquid-metal: Cu2++2e-、Cu exchange current, electrode potential

3) Liquid-metal: exchange current, electrode potential 7.8.1. Interfacial charge and electrode potential §7.8 Electrode potential

87.8 Electrode potential 7.8.2. Models of electric double layer 1)Holmholtz double 2) Gouy-Chappman layer 3)Stern double layer layer (1853) (1910,1913) (1924) Compact double layer Diffuse double layer Absolute electrode potential

7.8.2. Models of electric double layer 1) Holmholtz double layer (1853) Compact double layer 2) Gouy-Chappman layer (1910, 1913) Diffuse double layer 3) Stern double layer (1924) §7.8 Electrode potential Absolute electrode potential

87.8 Electrode potential 7.8.3 Electromotive forces and relative electrode potential Cu'(s)IZn(s)znSO,(mi) CuSo4(m) Cu(s) E Positive E E E=E+(1)+(+2)=9+++(q1912 E

7.8.3 Electromotive forces and relative electrode potential Cu’(s)Zn(s)ZnSO4 (m1 )CuSO4 (m2 )Cu (s) E =  c + − + j + + E =  c + (l,1 - − ) + ( + - l,2 )=  + - − +  c + ( l,1 -  l,2 ) E =+ −− Negative Positive + - j §7.8 Electrode potential

87.8 Electrode potential 7.8.3 Electromotive forces and relative electrode potential Absolute potential potentiometer arbitrary reference E=mpr Only the difference between two electrodes Can the absolute potential of electrode be unmeasured? i.e. electromotive of the cell can be measured

Absolute potential 7.8.3 Electromotive forces and relative electrode potential Only the difference between two electrodes, i.e., electromotive of the cell can be measured. Can the absolute potential of electrode be unmeasured?  m l  = − §7.8 Electrode potential

87.8 Electrode potential 7.8.3 Electromotive forces and relative electrode potential (2) Normal/Standard Hydrogen Electrode (NHE/SHE) In 1953, iupac defined normal hydrogen electrode (NHE) as the reference for measurement of electrode potential. IUPAC conventions (I)pure hydrogen gas at standard pressure (2) platinized platinum foil electrode (3)acidic solution with activity of H equals 1 mH,1mol kg ,rH=l,a definition e H+/H2=0.000000V

(2) Normal/Standard Hydrogen Electrode (NHE/SHE) In 1953, IUPAC defined normal hydrogen electrode (NHE) as the reference for measurement of electrode potential. IUPAC conventions (3) acidic solution with activity of H+ equals 1. (2) platinized platinum foil electrode (1) pure hydrogen gas at standard pressure 1 H H H m a + + + 1.0mol kg , 1, 1  − =  = = definition  H+ /H2 = 0.000000 V. 7.8.3 Electromotive forces and relative electrode potential §7.8 Electrode potential

87.8 Electrode potential 7.8.3 Electromotive forces and relative electrode potential ( 3) Relative standard electrode potential NHE‖Cu2(a=0.1)Cu NHE unknown electrode reduction potentials The potential of electrode can be obtained by combination of nhe and any other unknown E=0.342V electrode into an reversible electrochemical cell without liquid junction potential with Cu2+/cu +0.342V NHE serving as negative electrode and the unknown electrode as positive electrode Cu2++2e-、Cu The sign and the value of the emf of the cell is thus the sign and value of the potential of the (reduction)(standard)electrode potential unknown electrode Cf. Levine, p 431-435

(3) Relative standard electrode potential The potential of electrode can be obtained by combination of NHE and any other unknown electrode into an reversible electrochemical cell without liquid junction potential with NHE serving as negative electrode and the unknown electrode as positive electrode. The sign and the value of the emf of the cell is thus the sign and value of the potential of the unknown electrode. - NHE || unknown electrode + Cf. Levine, p. 431-435 7.8.3 Electromotive forces and relative electrode potential reduction potentials. NHE  Cu2+ (a=0.1)Cu E = 0.342 V 2 Cu /Cu  + = +0.342V (reduction)(standard) electrode potential Cu2+ + 2e− Cu §7.8 Electrode potential