Electrochemical Processes Standard Hydrogen Potential

The standard potential of reaction (6), which takes place in acid solutions, is 1.23 V vs. standard hydrogen electrode (SHE). Reaction (7), in alkaline solutions, has a potential of 0.40 V vs. SHE. Both reactions are 1.23 V positive to the reversible potential of the hydrogen evolution reaction (HER) in the respective media. Therefore, the theoretical decomposition voltages of certain electrochemical processes can be reduced by 1.23 V if an oxygen-consuming cathode is substituted for the conventional hydrogen-evolving type. Examples of these processes [5] are ... 

The standard electrode potentials for some common metals are given in Table 19.1. Note that the half-cell reactions are written as reduction processes the metal ions are gaining electrons. The standard electrode potentials are therefore sometimes known as standard reduction potentials. This arrangement of metals (and hydrogen) in order of decreasing standard electrode potential is known as the electrochemical series. It is very similar in arrangement to the activity series (Chapter 9). 

Values of the equilibrium potential, for known redox couples under standard conditions may be conveniently listed, in order, as an electrochemical series (Table 10.1). From this table it can be inferred that, under standard conditions only and considering only the listed equilibria, certain corrosion processes may be feasible, e.g. the copper dissolution reaction (10.23) has a more positive potential than that of the hydrogen evolution reaction (10.9) and therefore spontaneous corrosion (reaction (10.24)) is not possible in deaerated uncomplexed, acid... 

---