Constructing interfacial polarization to improve electrocatalytic nitrogen reduction reactions in polyoxometalates-based metal-organic framework-derived Fe7S8-WS2-Co9S8 multi-phase heterostructures

Abstract

Electrocatalytic nitrogen (N2) reduction to produce ammonia (NH3) has received increasing attention. It is urgent to design highly active and environmentally friendly catalysts due to present electrocatalysts still suffering from poor stability and low catalytic efficacy. In this work, Fe7S8-WS2-Co9S8 multi-phase heterostructures are prepared by using a template-directed assembly approach. The uniform distribution of Fe7S8-WS2-Co9S8 nanosheets derived from polyoxometalate-based metal-organic frameworks (POMOFs) largely provides more reactive active sites and improves the enrichment efficiency of N2. Multi-phase heterojunction interface between Fe7S8, WS2 and Co9S8 enhances the interfacial polarisation and leads to electron transfer from WS2 to Fe7S8 and Co9S8, and further facilitated the reduction of N2 in the electron-rich Fe7S8, resulting in an ultrahigh NH3 yield of 51.21 μg·h·mgcat.−1 and a Faradaic efficiency of 34.12 %. Density Functional Theory (DFT) calculations indicate that Fe sites are favorable sites for N2 adsorption in Fe7S8-WS2-Co9S8 composites, and Fe7S8-WS2-Co9S8 is most likely to catalyze nitrogen reduction via the distal pathway. The current investigation provides a perspective for developing multi-phase heterogeneous catalysts for electrocatalytic NH3 from N2.