What is standard hydrogen electrode ?

A Standard Hydrogen Electrode (SHE) is an electrode that scientists use for reference on all half-cell potential reactions. The value of the standard electrode potential is zero, which forms the basis one needs to calculate cell potentials using different electrodes or different concentrations. SHE is composed of a 1.0 M H+(aq) solution containing a square piece of platinized platinum (connected to a platinum wire where electrons can be exchanged) inside a tube. 

During the reaction, hydrogen gas is then passed through the tube and into the solution causing the reaction:

2H+(aq) + 2e- <==> H₂(g)

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