Chemically assembled 2D-van der Waals WSe2-WC heterostructured photo-anodes for electrochemical devices

Abstract

Structural, optical, nanomorphological, photoresponsive and electrochemical charge transport characteristics of chemically assembled 2D-layered Tungsten Selenide (WSe2)-Tungsten Carbide (WC) heterostructure were examined. WC exhibited an optical bandgap of ∼3.2 eV, which did not show any optical absorption in the visible spectrum, and WSe2 showed the same in the spectral range of 200 nm-950 nm with an optical bandgap of ∼1.3 eV. Chemical assembly of WSe2-WC heterostructure was made in which the weight fraction of WSe2 was varied to understand its role in WC. Among the 2, 4, 6 and 8 wt% of WSe2 in WC, we observed that 6 wt% exhibited a dominant absorption and fluorescence emission (∼600 nm). High-resolution transmission electron microscopic studies revealed the d-spacing values of 0.24 nm and 0.33 nm for WSe2 and WC, respectively. Further, the presence of W (4f), Se (2d) and C (1 s) were traced out and studied by X-ray photoelectron spectroscopy. Raman modes A1g and EAg1 at 150 cm−1 and 250 cm−1 asserted the presence of WSe2 in WC which exhibited A1g at 150 cm−1. In addition, the individual WSe2 and WC along with WSe2-WC heterostructures were subjected to X-ray diffraction to study the crystallite size and strain-induced broadening due to the lattice deformation that occurred at the WSe2-WC heterostructures. Incorporating WSe2 into WC increased the photo-responsive behaviour and facilitated the charge transport as envisaged from the electrochemical impedance spectroscopic studies.