Ammonia Fuel: A Pathway for Carbon-Neutral of the Transportation Sector

Global warming is the most significant challenge to society due to the increasing carbon dioxide level in the atmosphere nowadays. Accelerating the deployment of zero-carbon fuel is imperative in the transportation field, one of the major sources of carbon emissions. The effort on clean energy represented by hydrogen has been made by showing good breakthroughs in some applications; however, many technical and economic challenges exist for large-scale commercial applications. Ammonia, as another zero-carbon fuel, is an efficient storage and transportation medium for hydrogen component and shows greater application potential. Compared to hydrogen, ammonia has more mature storage and transportation technologies, superior related infrastructure, and a further systematic transportation network. In the review, the current mainstream technology routes of ammonia synthesis, the storage and transportation, and the future development trends are summarized. Carbon emissions and costs for the processes are brought into focus. Additionally, the combustion and emission generation mechanisms with technical routes for ammonia as a direct fuel are discussed. The current opportunities and challenges are then analyzed for ammonia as a zero-carbon fuel. The prospect of utilizing ammonia both as a direct fuel and a carrier for hydrogen in transportation is being explored, along with an architecture of the zero-carbon energy system for transportation based on the ammonia fuel.