Electrochemical modelling of ammonia synthesis in molten salt medium for renewable fuel production using wind power

Abstract

Ammonia is one of the most abundantly used chemicals in the world, and it is a potential hydrogen carrier for possible solutions of hydrogen storage and transportation. The conventional method of ammonia production is energy-intensive that requires high pressure and it is dominantly dependent on fossil fuels for hydrogen and nitrogen production. With the electrochemical synthesis option, ammonia can be produced at atmospheric pressures and lower temperature levels. Hydrogen production via water electrolysis using renewable energy can further reduce carbon emissions. In this work, ammonia production via an electrochemical process in a molten salt medium is modelled through electrochemical impedance spectroscopy using several equivalent circuit models. Then, afterwards, for a case study in Qatar to produce renewable ammonia, wind data are used to predict the annual ammonia production rates where the wind turbine rated power is 6 MW. The electrochemical modelling results show that two main parameters emerged as the most influential on the modelling of the low frequencies region; the capacitance of the electrolyte, and the capacitance of the electrode. Furthermore, it is found that the Warburg diffusion limit showed little to negligible effect on the shape in the low-frequency region. The best performing model in terms of the goodness of fit is model 11 with a value of 4.75 × 10−7, which was modelled by 9 circuit elements (resistors, inductor, capacitors and Gerischer elements) and 12 adjustable parameters. Moreover, Models 11 and 12 reached a goodness of fit in the order of 10−7. Some models included a larger number of variables but offered poorer fit or insignificant improvement, which does not provide justification for the additional elements.