Standard hydrogen electrode

• The electrode is connected to a standard hydrogen electrode (SHE) to constitute a cell
• It consists of a platinum electrode coated with a layer of platinum black.

• The electrode is immersed in an acidic solution and the pure hydrogen gas is bubbled through it.
• The concentration of the reduced form and the oxidized form of hydrogen is sustained at unity with following conditions:
• Pressure of hydrogen gas = 1 bar
• Concentration of hydrogen ion in the solution = 1 molar

Ecell = Ecathode – Eanode

Ecell = Ecathode – 0 = Ecathode

• The measured Emf of the cell:

Pt| H2 (1 bar)| H+ (1M) || Cu2+ (1M)| Cu is 0.34 V.

The positive value of the standard electrode potential signifies the easy reduction of Cu2+ ions than H+ ions.

• The measured Emf of the cell

Pt| H2 (1 bar)| H+ (1M) || Zn2+ (1M)| Zn is -0.76 V.

The negative value of the standard electrode potential signifies that the hydrogen ions oxidizes the zinc (or it can be said that zinc can reduce hydrogen ions).

• An electrode with standard electrode potential greater than zero is stable in its reduced form compared to hydrogen gas.
• Whereas an electrode with negative standard electrode potential is less stable in its reduced form compared to hydrogen gas.
• This decreases the standard electrode potential which in turn decreases the oxidizing power of the specific electrode on the left and increases the reducing power of the electrode to the right of the reaction.