Green ammonia synthesis technology that does not require H2 gas: Reaction technology and prospects for ammonia synthesis using H2O as a direct hydrogen source

The Haber–Bosch (HB) process, utilizing hydrogen and nitrogen gases as raw materials, dominates industrial ammonia production. Alternative synthetic methods also typically require hydrogen and significant energy input, often leading to CO 2 emissions. This review examines hydrogen-gas-free ammonia synthesis methods. Various catalytic approaches, including plasma catalytic and catalytic electrochemical techniques, have been extensively studied. Additionally, increasing interest has emerged in “non-H 2 , non-catalytic ammonia synthesis reactions.” Finally, we discuss the potential of emerging green ammonia synthesis methods to address the challenges of existing techniques. • Plasma-driven nitrogen reduction via a plasma/liquid interface occurs at ambient condition, without a catalyst or H 2 . • Overview of catalytic and non-catalytic methods for ammonia synthesis without H 2 . • The key to plasma-driven ammonia synthesis is the efficient dissociation of nitrogen molecules, producing atomic nitrogen. • Collisional reactions in a nitrogen and noble gas plasma mixture led to the efficient production of atomic nitrogen.