To this point we have purposefully refrained from identifying the proton donor and acceptor species. The specie responsible for an observed limiting current can be narrowed down by its respective •mol -1 •cm -1/3 (using 𝜐 = 0.01 cm 2 /s). For molecular hydrogen we obtain Eq. 38b. As the limiting current of the proton acceptor and donor species vary with pH, we naturally expect them to correspond to hydronium and hydroxyl ions and provide their expressions in Eq. 38c and Eq. 38d, respectively. The factor 𝑥 in the exponent will be explained shortly.