Electrolysis of liquid ammonia for hydrogen generation

Abstract

One route to efficient storage, transportation and utilization of renewable hydrogen is through its conversion into ammonia (NH₃). In order to examine the feasibility of an NH₃ fuel cycle, the electrolysis of NH₃ – both as a liquid and dissolved in N,N-dimethylformamide – was investigated using platinum electrodes. The current scaled with electrolyte concentration, but was nominally independent of composition, suggesting solution resistance limitations. NH₃ was found to be the chemical species oxidized at the anode which produced N₂, but also resulted in a poisoned electrode surface which introduced an additional overpotential of ∼0.5 V. Surprisingly, NH₄⁺ was the species reduced at the cathode via a one-electron transfer process to form , prior to H₂ generation, which resulted in an additional cathodic overpotential. In addition to establishing the two half reactions of liquid ammonia electrolysis, the formal potentials of the reactions and the kinetic overpotentials were quantified.