Electrode Kinetics of Solvated Electrons in Liquid Ammonia

Electrode reaction of ammoniated electrons was investigated with voltammetry, potentiometry and chronoamperometry. Experiments were conducted on Pt, Au and W electrodes in 0.5 M LiI, NaI, KI, CsI and KBr solutions of liq. NH₃. The results in dilute solutions (< 10<^?4 M) do not reflect the differences in alkali metal, electrode metal and supporting electrolyte and are explained by a simple one-electron transfer process whose transferring species is a free solvated electron and its ion-pair with a metal cation in a rapid equilibrium. The formal standard potential is ?2.155 ± 0.005 V vs. Pb/Pb(NO₃)₂ (0.05 M) at ?40°C in liq. NH₃ involving 0.5 M alkali metal iodide. The lower limit of the averaged diffusion coefficient is 0.7 × 10^?4 cm² s^?1. At higher metal concentrations (> 10^?2 M), a two-electron transfer process tends to prevail, which is explained by considering the dimer of ion-pairs as the diffusing species.