The standard hydrogen half cell, consists of hydrogen gas at 100kPa in contact with a platinum electrode which is dipped into an acidic solution (e.g. HCl) containing 1 moldm-3 of H+ ions at 298K.2H+(aq) + 2 e- ⇌ H2(g)It is always drawn on the left of a diagram or cell diagram. The standard electrode potential of a hydrogen electrode is 0V by definition. It is used as a reference standard for the measurement of the cell e.m.f.