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 CO₂ 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-H₂, non-catalytic ammonia synthesis reactions.” Finally, we discuss the potential of emerging green ammonia synthesis methods to address the challenges of existing techniques.