Coupling of LaFeO3-Plasma Catalysis and Cu+/Cu-0 Electrocatalysis for Direct Ammonia Synthesis from Air

Ammonia (NH3) is an essential commodity manufactured by the chemical industry. However, it is still mainly synthesized via the traditional Haber-Bosch process, which is energy consuming and produces large amounts of CO2. As one of the most promising alternatives, the electrochemical reduction of nitrogen (N-2) under mild reaction conditions exhibits only low efficiency for NH3 synthesis because of the low water solubility of N-2 and the high energy of the triple bond in molecular N-2. Here, we use an N-2 fixation strategy of "oxidation-reduction" based on a coupled plasma catalysis and electrocatalytic system. First, a perovskite LaFeO3 catalyst is used in a nonthermal plasma to oxidize N-2 to nitrate/nitrite (NOx-), which quickly dissolves in water for activation in the next step. The theoretical calculations indicate that the LaFeO3 with rich surface-reactive oxygen species has better activity and stability in the reaction than poor surface-reactive oxygen species, thereby enhancing the increase of NOx- production. Then NOx- is electrochemically reduced to NH3 using a Cu+/Cu-0 catalyst with considerable activity (3.0 mg h(-1) cm(-2)) and high faradaic efficiency (83.2%). The process only requires air and water as reactants. This strategy could provide a new and efficient pathway for NH3 synthesis directly from the air.