Techno-economic insights into ammonia as a hydrogen vector: synthesis, cracking, storage, and supply chain solutions

Abstract

Amid the global energy crisis, green hydrogen emerges as a potent energy carrier, yet the hydrogen economy grapples with economic viability, low volumetric energy density, storage, and safety issues that hinder its direct utilization. In this context, ammonia serves as an efficacious hydrogen carrier owing to its excellent volumetric and gravimetric hydrogen density, ability to be stored at low pressures and ease of catalytic decomposition, enabling onsite H₂ production without greenhouse gas emissions. The production of ammonia is primarily based on the Haber–Bosch process alongside electrochemical and thermochemical methods, while the decomposition of ammonia to hydrogen relies on thermal cracking, electro/photo-chemical, and plasma-assisted methods employing suitable catalysts, notably the extensively studied catalyst-assisted thermal cracking of NH₃. The present review explores diverse synthetic routes for the synthesis of ammonia and its storage strategies, catalyst-driven decomposition, and challenges associated with the development of proficient catalysts. Furthermore, this review ruminates on strategies used by the scientific community to scale up cutting-edge reactor technology for green NH₃ decomposition from early studies to the contemporary research outcomes, along with highlighting the bottlenecks to industrial entry and commercialization with respect to other hydrogen carriers, production and transport costs, and demand and supply constraints.