The Standard Hydrogen Electrode

The particular anode reaction chosen for the measurement of all standard cathode potentials is:

H2(g) --> 2e + 2H+(aq)

In order to anchor the scale, E0H+/H2 is arbitarily chosen to be 0

The reaction shown above can be made to occur in a Standard Hydrogen Electrode (SHE), which can be constructed as shown on p. 777 of the text.

 

This electrode consists of a piece of platinum, immersed in a 1M solution of a strong acid (a source of H+ (aq)), over which is bubbled gaseous hydrogen at 1 atm. The purpose of the platinum is to act both as a sink for electrons (injecting them into the external circuit) and as a catalyst for the above half-reaction.