Solar Electrochemical Thermal Process (STEP) Ammonia: Optimization of the Electrolysis Conditions

In the solar thermal electrochemical process (STEP), sunlight is split into visible (for photovoltaic electricity) and thermal (unused, sub-bandgap) radiation using the full solar spectrum to efficiently drive high temperature electrolyzes. Electrolysis conditions for STEP ammonia are investigated. A mixed molten carbonate/hydroxide electrolyte with iron oxide catalyzes ammonia formation from water (steam) and air (nitrogen) via an iron intermediate. The higher temperature required for effective iron formation needs to be balanced by the lower temperature for effective hydration of the electrolyte. STEP ammonia is illustrated at a nickel anode and steel cathode at 650 °C in Li<sub>1.6</sub>Ba<sub>0.3</sub>Ca<sub>0.1</sub>CO<sub>3</sub> with 6m LiOH and 1.5m Fe<sub>2</sub>O<sub>3</sub>.