Coupling of LaFeO<sub>3</sub>–Plasma Catalysis and Cu<sup>+</sup>/Cu<sup>0</sup> Electrocatalysis for Direct Ammonia Synthesis from Air
Yi Cui, Hui Ying Yang, Chengyi Dai, Pengju Ren, Chunshan Song, Xiaoxun Ma
Abstract
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 (N2) under mild reaction conditions exhibits only low efficiency for NH3 synthesis because of the low water solubility of N2 and the high energy of the triple bond in molecular N2. Here, we use an N2 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 N2 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+/Cu0 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.