Ammonia for hydrogen storage: challenges and opportunities

TLDR

Ammonia is a promising hydrogen carrier because of its high density, mature synthesis and distribution infrastructure, and zero CO₂ emissions, yet its toxicity and trace‑ammonia contamination pose significant challenges. The study outlines the remaining research challenges for ammonia as a hydrogen carrier. The authors propose storing ammonia in metal ammine salts. This storage strategy preserves high volumetric hydrogen density while mitigating handling problems.

Abstract

The possibility of using ammonia as a hydrogen carrier is discussed. Compared to other hydrogen storage materials, ammonia has the advantages of a high hydrogen density, a well-developed technology for synthesis and distribution, and easy catalytic decomposition. Compared to hydrocarbons and alcohols, it has the advantage that there is no CO2 emission at the end user. The drawbacks are mainly the toxicity of liquid ammonia and the problems related to trace amounts of ammonia in the hydrogen after decomposition. Storage of ammonia in metal ammine salts is discussed, and it is shown that this maintains the high volumetric hydrogen density while alleviating the problems of handling the ammonia. Some of the remaining challenges for research in ammonia as a hydrogen carrier are outlined.