FeS2/MoS2@RGO hybrid materials derived from polyoxomolybdate-based metal–organic frameworks as high-performance electrocatalyst for ammonia synthesis under ambient conditions

Abstract

The electrocatalytic nitrogen reduction reaction (NRR) provides a promising way for storage and sustainable utilization of ammonia. In order to reduce the cost of ammonia synthesis and promote large-scale production, it is very important to develop stable and highly active electrocatalysts. In this work, we demonstrate an iron-based metal–organic framework (MIL-100) and molybdenum-based polyoxometalate (PMo12) host–guest-assisted strategy for synthesizing nanostructured bimetallic sulfides through a one-pot hydrothermal synthesis process. FeS2/MoS2 particles are evenly distributed on reduced graphene oxide (RGO) with high conductivity, forming a well-defined nanoflower structure. Benefiting from the synergistic effect of FeS2, MoS2 (with inherent rich catalytically active sites and uniform nanoflower structure) and RGO, the as-synthesized FeS2/MoS2@RGO achieves electrocatalytic activity and stability towards NRR in both basic and acidic solutions. The electrochemical results show a high Faradaic efficiency (FE) of 38.6 % and NH3 yield rate of 41.1 μg h−1 mgcat-1 at −0.2 V with respect to a reversible hydrogen electrode (RHE) in acidic potassium sulfate, and FE of 9.62 % and NH3 yield rate of 10.35 μg h−1 mgcat–1 at −0.4 V vs. RHE in alkaline potassium hydroxide solution at room temperature. Density functional theory (DFT) calculation indicates that NRR on FeS2/MoS2 has optimized nitrogen binding and ammonia release which promotes the fast kinetics process through the distal mechanism, and the protonation of N2 to form *N2H species is the rate-determining step (RDS) with the maximum ΔG values (+0.43 eV). This work develop a general and promising method for the design of efficient and low cost pH-universal NRR electrocatalysts.