MIL-101(Fe)@Nb 2 C MXene for efficient electrocatalytic ammonia production: an experimental and theoretical study

The environment-friendly electrochemical nitrogen reduction reaction (NRR) is considered to be a promising alternative to the traditional Haber–Bosch process for ammonia production. However, the stability of nitrogen and competitive hydrogen evolution reaction (HER) lead to low faradaic efficiency (FE) and ammonia selectivity for the NRR. Compared with the NRR, the electrochemical nitrate reduction reaction (NO 3 RR), with no process of N 2 adsorption, exhibits a higher NH 3 yield and FE. In this work, the MIL-101(Fe) is synthesized and composited with Nb 2 C MXene, which exhibited excellent NRR and NO 3 RR performance. For the NRR, the MIL-101(Fe)@Nb 2 C achieved an ammonia yield of 8.92 μg h −1 cm −2 and a high FE of 20.77%. Meanwhile, for the NO 3 RR, it achieved a large NH 3 yield of 199.68 μg h −1 cm −2 and a high FE of 89.9%. In addition, MIL-101(Fe)@Nb 2 C exhibits excellent stability for the NRR and NO 3 RR. DFT calculations proved that the interfacial interaction between Nb 2 C and MIL-101(Fe) acquired a significant synergistic mechanism to improve the catalytic performance. Since the NH 3 yield and FE of the NO 3 RR are much higher than those of the NRR, it is vital to design NRR catalysts that can easily adsorb and activate nitrogen as well as inhibit the HER.