2. Understanding Corrosion

2.5.4 Exchange Current Density [2/2]


The exchange current density for H+ + e H2 on Mercury is 10-14 A/cm2, but is several orders of magnitude higher on Platinum at 10-2 A/cm2. A large current density means a very stable potential which cannot be easily disturbed, hence, Platinized platinum is made a standard hydrogen electrode, so that the potential remains stable.

Figure below shows the exchange current density values for hydrogen reduction on Hg, Fe and Pt and overvoltage hc Vs i (current density).