Ammonia as a hydrogen carrier: A comprehensive analysis of electrolysis efficiency and its potential in sustainable energy systems

Hydrogen has garnered considerable interest as a clean fuel alternative in the pursuit of sustainable energy generation. An attractive hydrogen carrier candidate is ammonia, thanks to its 17.6 wt% hydrogen concentration and its well-developed manufacturing and transportation networks. This review focuses on ammonia and its properties, benefits, and drawbacks as a possible hydrogen energy carrier. The key findings of this study demonstrate that ammonia electrolysis is a feasible and effective technique for producing hydrogen, coupled with energy efficiencies varying from 30 to 60 %, which outperforms conventional water electrolysis techniques. Ammonia electrolysis represents an exceptional potential in optimizing clean hydrogen generation, given that the standard ammonia electrolysis requires only 1.55 Wh.g−1 hydrogen, in contrast to the 33 Wh g−1 by the water electrolysis, which showcases a 95 % energy savings. In addition, ammonia-based energy systems are advantageous since they make use of the substantial $60 billion worldwide ammonia market, thereby rendering them attractive options for less expensive energy storage. Aside from its merits, the lack of an indigenous infrastructure source constitutes a constraint, given that its generation is contingent upon the direct interaction between nitrogen and hydrogen via the Haber-Bosch process. To fully exploit the energy-carrying capabilities of ammonia, it is also necessary to overcome technical obstacles including degradation of catalysts, sluggish kinetics, and toxicity effects caused by impurities in ammonia feedstock.