Performance assessment of electrochemical ammonia synthesis using photoelectrochemically produced hydrogen

In this study, an effective hydrogen production for electrochemical ammonia synthesis is performed using a photoelectrochemical hydrogen production reactor. A photoelectrochemical cell is built by electrodepositing photosensitive Cu₂O particles on a cathode stainless steel plate. The produced hydrogen is supplied to a molten salt electrolyte-based electrochemical ammonia synthesis reactor at ambient pressure where nitrogen gas is co-supplied from a nitrogen tank. Using photoelectrochemically produced hydrogen, the electrochemical synthesis of ammonia is successfully accomplished. The reactions of nitrogen and hydrogen gases occur in a molten salt ambient consisting of molten hydroxides (NaOH and KOH), whereas the reaction temperature is varied in the range of 180°C to 260°C to investigate the impact of temperature on the performance. The porous nickel-meshed electrodes with an effective area of 25 cm² are used as cathode and anode. The hydrogen production process is characterized under both concentrated light and non-concentrated light conditions. The maximum Coulombic efficiency for ammonia synthesis is calculated to be 14.2% with an ammonia production rate of 4.41 × 10⁻⁹ mol/s cm² via nano-Fe₃O₄ catalyst.