Ammonia as a Potential Energy Vector in the Burgeoning Hydrogen Economy

Abstract

The adoption of green hydrogen economy is an indispensable necessity in the current global scenario of environment and energy security. In this endeavor, ammonia is poised to play a key vector of hydrogen to mitigate the challenges arising from transportation, storage and safety. Besides containing a high volumetric and gravimetric hydrogen density, NH3 decomposition into H2 for onsite utilization as a distributed energy source is devoid of greenhouse gases production. In this endeavor, significant technological advancements have been made for in situ production of H2 from NH3 decomposition and the use of NH3 in fuel cell devices to produce electricity. The ammonia decomposition methods to produce H2 mainly involve thermocatalytic, oxidative, electrocatalytic and photocatalytic, among which the catalyst assisted thermal cracking of NH3 has been widely investigated. The research progress in electrolysis of NH3 has been notable in the last couple of years and provides a low‐cost alternative to produce H2 at room temperature. In the area of device development, solid oxide fuel cells (SOFC) have witnessed rapid development in the performances and stability, as ammonia is completely decomposed into H2 and N2 at high operating temperature above ~700 °C.

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“…H-SOFCs have demonstrated significant performance improvements [ 24 , 25 , 26 , 27 ], with the power output largely dependent on the oxygen reduction reaction (ORR) kinetics happening near the cathode. Lowering the operating temperature enhances the significance of ORR kinetics [ 28 , 29 , 30 ], a complex procedure involving the adsorption and dissociation of O 2 followed by first proton–electron transfer for acidic media and, similarly, the adsorption of O 2 followed by first and second proton–electron transfer in basic media, which creates water by reducing oxygen molecules at the cathode [ 31 ]. The ORR primary response can be shown as follows: O 2 + 4e − + 4H + → 2H 2 O …”

“…Understanding these fundamental steps is challenging due to their rapid and complex nature, making direct experimental observation during cell operation difficult. Experimental data can provide insights into the ORR mechanism and the RDS, but first-principles calculations are also valuable for verifying this knowledge from an atomistic perspective [ 31 , 32 ]. In first-principles calculations, a system of atoms is treated as a system of electrons and nuclei.…”