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preface to fifteenth edition

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8.140 SECTION 8<br />

TABLE 8.29<br />

Overpotentials for Common Electrode Reactions at 25C<br />

The overpotential is defined as the difference between the actual potential of an electrode at a given current<br />

density and the reversible electrode potential for the reaction.<br />

Current Density, A/cm 2<br />

Electrode<br />

0.001 0.01 0.1 0.5 1.0 5.0<br />

Overpotential, volts<br />

Liberation of H 2 from 1M H 2 SO 4<br />

Ag 0.097 0.13 0.3 0.48 0.69<br />

Al 0.3 0.83 1.00 1.29<br />

Au 0.017 0.1 0.24 0.33<br />

Bi 0.39 0.4 0.78 0.98<br />

Cd 1.13 1.22 1.25<br />

Co 0.2<br />

Cr 0.4<br />

Cu 0.35 0.48 0.55<br />

Fe 0.56 0.82 1.29<br />

Graphite 0.002 0.32 0.60 0.73<br />

Hg 0.8 0.93 1.03 1.07<br />

Ir 0.0026 0.2<br />

Ni 0.14 0.3 0.56 0.71<br />

Pb 0.40 0.4 0.52 1.06<br />

Pd 0 0.04<br />

Pt (smooth) 0.0000 0.16 0.29 0.68<br />

Pt (platinized) 0.0000 0.030 0.041 0.048 0.051<br />

Sb 0.4<br />

Sn 0.5 1.2<br />

Ta 0.39 0.4<br />

Zn 0.48 0.75 1.06 1.23<br />

Liberation of O 2 from 1M KOH<br />

Ag 0.58 0.73 0.98 1.13<br />

Au 0.67 0.96 1.24 1.63<br />

Cu 0.42 0.58 0.66 0.79<br />

Graphite 0.53 0.90 1.09 1.24<br />

Ni 0.35 0.52 0.73 0.85<br />

Pt (smooth) 0.72 0.85 1.28 1.49<br />

Pt (platinized) 0.40 0.52 0.64 0.77<br />

Liberation of Cl 2 from saturated NaCl solution<br />

Graphite 0.25 0.42 0.53<br />

Platinized Pt 0.006 0.026 0.05<br />

Smooth Pt 0.008 0.03 0.054 0.161 0.236<br />

Liberation of Br 2 from saturated NaBr solution<br />

Graphite 0.002 0.027 0.16 0.33<br />

Platinized Pt 0.002 0.012 0.069 0.21<br />

Smooth Pt 0.002 0.006* 0.26 0.38†<br />

Liberation of I 2 from saturated Nal solution<br />

Graphite 0.002 0.014 0.097<br />

Platinized Pt 0.006 0.032 0.196<br />

Smooth Pt 0.003 0.03 0.12 0.22<br />

* At 0.23 A/cm 2 . † At 0.72 A/cm 2 .<br />

The overpotential required for the evolution of O 2 from dilute solutions of HClO 4 , HNO 3 ,H 3 PO 4 or H 2 SO 4 on<strong>to</strong> smooth<br />

platinum electrodes is approximately 0.5 V.

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