Structure-activity relationship toward electrocatalytic nitrogen reduction of MoS2 growing on polypyrrole/graphene oxide affected by pyridinium-type ionic liquids

MoS2 with different crystal structures and phase compositions have in-situ grown on the surface of pyridinium-type ionic liquids functionalized polypyrrole/graphene oxide (pyridinium-ILs/PPy/GO) and exhibited different electocatalytic performance towards Nitrogen reduction reaction (NRR), affected by the difference of crystal structure and phase compositions of MoS2 resulting from the induction of substituent groups in pyridinium. Combining the results of NRR performance tests with material characterizations determined by XRD, XPS and Raman spectra to explore the structure-activity relationship toward NRR of MoS2/pyridinium-ILs/PPy/GO, pyridinium-ILs with a group containing amino in the para- or ortho-position can be beneficial to induce 1T-MoS2 with good crystallinity, resulting in the satisfying NH3 yield, but poor stability, while the hydroxyl group at the para-position in pyridinium-ILs only induce 2H-MoS2 indexed to JCPDS file number 75-1539, not conducive to nitrogen fixation. Surprisingly, the most excellent NRR electroactivity is achieved by MoS2/pyridinium-ILs/PPy/GO synthesized using 2-amino-3-hydroxypyridine with the excellent lamellar hierarchical inorganic/organic micro-/nanostructures. It may be attributed to the confinement effect caused by the stereo hindrance composed of amino group at the ortho-position and hydroxyl group at the meta-position in pyridinium-ILs, resulting in 1T/2H-MoS2 nanoplates with rich defects indexed to JCPDS file number 37-1492 growing on pyridinium-ILs/PPy/GO. Therefore, the kind and position of substituent groups in pyridinium played an essential role for the crystal structure and phase compositions of MoS2 growing on pyridinium-ILs/PPy/GO, and further affected the NRR performance, which would provide a new thought and method for the reasonable design and performance optimization of electrocatalysts based on transition metal dichalcogenides for electrocatalysis.