The standard hydrogen electrode (or SHE) is the reference half-cell for standard
electrode potentials.
One component of the SHE is 1.0 mol dm–3 H+(aq) ions, provided by an acid solution
at 298 K.
A platinum electrode is dipped into the acid solution.
The wire from the electrode passes through a glass tube, which extends into the
acid solution around the electrode.
The glass tube has holes to let bubbles of hydrogen gas escape.
A continuous stream of hydrogen gas at 298 K and 1 atm pressure is passed over
the platinum electrode.
Excess gas escapes through the holes in the glass tube.
A salt bridge, such as filter paper soaked in saturated potassium nitrate solution,
allows ions to pass to and from other half-cells.
The standard electrode potential for the SHE is defined as zero volts exactly.
Other electrodes involving gases are set up like this!!! (Cl- / Cl2(g))