Enhanced hydrogen evolution reaction for hydrothermally prepared g-C3N4/MoS2 heterostructure

Abstract

Hydrogen Evolution Reaction has recently gained a lot of attention as an affordable approach to address both environmental and energy-related concerns. In this context, this study focuses on advancement in the field of catalytic activity using the significant contribution of graphitic carbon nitride/molybdenum disulfide (g-C3N4/MoS2) heterostructure. Heterostructure is synthesized through a hydrothermal method, effectively combining the advantageous characteristics of both g-C3N4 and MoS2. Different characterisation techniques, including XRD, Raman spectroscopy, FE-SEM, XPS, UV-Vis Spectroscopy, and Mott-Schottky analysis were used to thoroughly examine structural, morphological, interfacial properties of pristine g-C3N4 and MoS2 and also their synthesized heterostructure, g-C₃N₄/MoS₂. XRD characterization is employed to investigate the crystal structure of the g-C3N4, MoS2 and the g-C₃N₄/MoS₂ heterostructure. In contrast, FE-SEM is used for surface morphological study of g-C3N4, which is found to have flaky sheets, MoS2 had flower like spherical globules, and g-C₃N₄/MoS₂ heterostructure was seen to have nanoflowers grown on the sheets of g-C3N4. Raman Spectroscopy characterization technique used to determine the vibrational modes of molecules. For MoS₂, in- plane (E2g1) and out- plane (A1g) were examined carefully to confirm the layered structure. For g-C₃N₄, a distinct band near 710 cm− 1 corresponding to tri-s-triazine rings, around 1350 cm− 1 and 1570 cm− 1 associated with disordered or graphitic carbons and other low-frequency modes of systems may also be observed. X-ray Photoelectron Spectroscopy (XPS) determined Mo 3d doublet peaks that confirmed the valence state of Mo in MoS₂, while the C 1s and N 1s spectra verified the preserved polymeric heptazine structure of g-C₃N₄. Furthermore, Mott-Schottky analysis was used to determine the flat band potential which combined with UV- Vis spectrum determined possible band diagram. The charge transfer between g-C₃N₄ and MoS₂ provided the formation of heterojunction. To evaluate the composite’s efficiency for water splitting, with attention given to HER, the composite g-C3N4/ MoS2 shows excellent HER activity with a low potential, high current density, and a favourable Tafel slope, signifying effective electrocatalytic performance. EIS analysis confirms that the reduced resistance contributed to improving charge transfer. Charge transfer resistance (Rct) values calculated by fitting the circuit results as 14,000 Ω, 2208 Ω and 967.6 Ω for g-C3N4, MoS2, and g-C3N4/ MoS2, respectively. The composite shows excellent HER activity with low overpotential, favorable Tafel slope, and reduced charge-transfer resistance. Chronoamperometry measurement performed also proved good electrochemical stability. It is demonstrated by these results that the combined properties of g-C3N4 and MoS2 lead to the formation of a heterostructure, i.e., suitable for electrocatalytic HER and hydrogen production.