While, standard reduction potentials always refer to the standard hydrogen electrode (SHE), with [ H ] = 1 M corresponding to a pH 0, and E red H+ ⊖ ⊖ fixed arbitrarily to zero by convention, it is no longer the case at a pH of 7. Then, the reduction potential E red of a hydrogen electrode operating at pH 7 is -0.413 V with respect to the standard hydrogen electrode (SHE).