Self-supporting electrode incorporating active Co sites for ultrafast ammonia production from nitrate reduction

Abstract

Electrocatalytic nitrate (NO3−) reduction reaction (NitRR) provides us a green solution to synthesize ammonia (NH3) and ease environmental problems. However, the development of robust electrodes with high NH3 yield rates and Faradaic efficiencies (FEs) is still challenging. Herein, we report a self-supporting electrode incorporating vertically aligned Co-based metal-organic framework (MOF) nanosheets (Co-NDC/NF), which facilitates electron and mass transfer for efficient NitRR to NH3 within a wide range of NO3− concentration (0.05−1.0 M). In 1.0 M KOH + 1.0 M KNO3 electrolytes, such Co-NDC/NF reaches a notable NH3 yield rate of 19,200 ug h−1 cm−2, a high FE of 93.9% and excellent electrochemical stability, which is superior to most electrocatalysts. A flow-through reactor with large-area Co-NDC/NF also achieves the continuous production of 1096 mg L−1 NH3 under an industrial current density. Furthermore, the rapid transformation of *NO2− to *NO and selective conversion of *NO to *NOH played critical roles in NitRR toward ultrafast NH3 production. Our research not only offers a facile fabrication procedure for high-performance electrode, but also gives new insights into the enhanced electron transfer and mass transport within MOF-based electrode in electrochemical reactions.