Interfacial engineering and electronic structure modulation of two-dimensional WSe₂ towards improved electrocatalytic hydrogen evolution

Tungsten diselenides (WSe₂) are regarded as highly desirable catalysts for various electrochemical reactions, owing to their tuneable conductivity and high electrochemical stability. A variety of strategies are continuously being explored to tune their electrochemical properties and to further enhance their electrocatalytic performance. Interface engineering is an ingenious approach for enhancing the electrocatalytic properties of transition metal dichalcogenides (TMDs). Thus, in the present investigation, we intend to tune the interlayer spacing of WSe₂ nanosheets (NSs) for modulating their electronic properties and to examine its influence on the electrocatalytic hydrogen evolution reaction (HER). Initially, WSe₂ NSs with different interlayer spacing were obtained either without or with different organic inclusion compounds, <i>viz</i>. oleyl amine (OA), glucose (Glu) and ammonium oxalate (AOx), incorporated during the solvothermal synthesis. The prepared WSe₂ NSs were systematically characterized using different structural and morphological investigations. The WSe₂ prepared without any inclusion compound exhibited an interlayer spacing of 0.62 nm, whereas WSe₂-OA, WSe₂-Glu and WSe₂-AOx showed interlayer spacing of 0.59, 0.69 and 0.75 nm, respectively. The inherent electrochemical characteristics of the prepared WSe₂ NSs and their electrocatalytic efficacy towards the HER were studied in 0.5 M H₂SO₄. Among these, WSe₂-AOx demonstrated impressive catalytic performance with a low overpotential of 268 mV at a current density of 10 mA cm^-2 and a low Tafel slope of 94 mV dec^-1. The superior electrocatalytic activity observed with WSe₂-AOx is attributed to the largest interlayer spacing which exposed abundant catalytic sites on the basal planes, thereby accelerating the kinetics of the HER. Notably, WSe₂-AOx displayed excellent cycling stability for 1000 cycles and impressive long-term stability up to 12 h in 0.5 M H₂SO₄.