Nitrogen-rich 1T′-MoS₂ layered nanostructures using alkyl amines for high catalytic performance toward hydrogen evolution

Abstract

The imminent global energy crisis and current environmental issues have stimulated considerable research on high-performance catalysts for sustainable hydrogen energy generation. Two-dimensional layered MoS2 has recently drawn worldwide attention because of its excellent catalytic properties for the hydrogen evolution reaction (HER). In the present work, we prepared nitrogen (N)-rich 1T' (distorted 1T) phase MoS2 layered nanostructures using different alkyl amines with 1-4 nitrogen atoms (methylamine, ethylenediamine, diethylenetriamine, and triethylenetetramine) as intercalants. The amine molecules intercalate at 10 atomic%, and simultaneously supply the N atoms that substitute the S atoms to produce the N-doped MoS2, whose composition is MoS2(1-x)Nx, where x = 0.1-0.26. MoS2 prepared with amines having more N atoms has enhanced catalytic HER performance: a Tafel slope of 36 mV dec-1 and 10 mA cm-2 at -160 mV (vs. RHE). First-principles calculations showed that the amine intercalation and N doping increase the density of states near the Fermi level in a narrow range and bring about an effective overlap of the dz2(Mo), pz(S), and pz(N) states. These factors in turn increase the carrier (electron) concentration and mobility for improved HER. The calculation also predicted that the most active site is S vacancies. The present work illustrates how the HER catalytic performance of 1T' phase MoS2 can be effectively controlled by the amine molecules.

Ionic Liquid‐Intercalated Metallic MoS2 as a Superior Electrode for Energy Storage Applications

“…[15,29] In addition, two weak peaks are present at 228.66 eV and 232.11 eV correspond to the Mo (3d 5/2 and 3d 3/2 respectively) suggesting the presence of 2H-MoS 2 . [13] Similarly, the presence of two strong peaks at 161.27 eV and 162.89 eV corresponding to the S (2p 3/2 and 2p 1/2 ) confirms the presence of sulfur in 1T-MoS 2 . Along with these two peaks, additional peaks were observed at 162.15 eV and 164.42 eV which are assigned to the S (2p 3/2 and 2p 1/2 respectively) of 2H-MoS 2 .…”

“…The close matching of the lattice parameter 'a' for 1T-MoS 2 (3.23 Å) with that of the reported 1T phase MoS 2 confirms the Mo is in octahedral configuration. [13] The intercalation of the IL leading to phase transformation is further supported by the decrease in the lattice parameter 'a' to 3.12 Å after annealing of the IL loaded 1T-MoS 2 @CC sample. Also the intensity ratio of (110)/(002) is higher for 2H-MoS 2 suggesting IL is capping in the Z-axis direction during the growth of 1T-MoS 2 and allowing the further growth in the XY-plane to obtain two dimensional MoS 2 .…”

“…Among different materials, transition metal dichalcogenides (TMDs) draw huge attention due to their unique properties. [13][14] Among the TMDs, MoS 2 is an ideal candidate to perform the HER at relatively low over potentials. [15] MoS 2 possesses layered structure where the Mo layer is sandwiched between two sulfur layers.…”

“…[16][17][18] MoS 2 crystallizes in two major phases named as 2H phase and 1T phase. [13,19] In the 2H phase, sulfur atoms were arranged in trigonal prismatic manner around the Mo center whereas in the 1T phase one of the sulfur plane (upper or lower) in the trigonal prism rotates about 60°to obtain octahedral geometry where the Mo atom occupies the octahedral hole. [14,20] Among these two phases, 1T phase exhibits superior electrochemical properties over the 2H phase.…”

“…[26] There were few reports on the bottom up approach to make the 1T-MoS 2 nanosheets using hydro/solvothermal methods and tested for electrocatalytic HER, supercapacitor and lithium ion battery applications. [13,19,27] For example, Gheng et al synthesized 1T-MoS 2 using hydrothermal method from MoO 3 , thioacetamide and urea and observed the enhancement in the electrocatalytic HER. [28] The intercalation of ammonium ions into the MoS 2 layers helps in the generation of 1T-phase by increasing the electron density at the Mo center.…”