MIL-101(Fe)@Nb2C MXene for efficient electrocatalytic ammonia production: an experimental and theoretical study

Abstract

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 (NO₃RR), with no process of N₂ adsorption, exhibits a higher NH₃ yield and FE. In this work, the MIL-101(Fe) is synthesized and composited with Nb₂C MXene, which exhibited excellent NRR and NO₃RR performance. For the NRR, the MIL-101(Fe)@Nb₂C achieved an ammonia yield of 8.92 μg h⁻¹ cm⁻² and a high FE of 20.77%. Meanwhile, for the NO₃RR, it achieved a large NH₃ yield of 199.68 μg h⁻¹ cm⁻² and a high FE of 89.9%. In addition, MIL-101(Fe)@Nb₂C exhibits excellent stability for the NRR and NO₃RR. DFT calculations proved that the interfacial interaction between Nb₂C and MIL-101(Fe) acquired a significant synergistic mechanism to improve the catalytic performance. Since the NH₃ yield and FE of the NO₃RR 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.