Sol–gel synthesis, structure, and morphology of M0.2Ni0.8MoO4 (M = Fe, Cu, and Zn) layered double hydroxide as a novel electrocatalysts for the hydrogen evolution reaction in alkaline media

Abstract

The fabrication of transition metal-based electrocatalysts with superior performance for the hydrogen evolution reaction (HER) remains a major challenge in the field of electrocatalysis. Here, the sol–gel method is used to synthesize three of M_0.2Ni_0.8Mo-LDH (where M is Fe, Cu, and Zn) layered double hydroxide precursors, which are then used as effective electrocatalysts for the alkaline HER. XRD, HRSEM, ATR-FT-IR, energy-dispersive X-ray, and thermokinetic analysis using TGA methods were used to characterize the structure of the prepared materials. Several investigations have been carried out with thermal kinetic analysis using the Coats–Redfern and Horowitz–Metzger equations. In comparison with Zn_0.2Ni_0.8Mo-LDH and Fe_0.2Ni_0.8Mo-LDH electrocatalysts, the results show increased electrocatalytic activity of Cu_0.2Ni_0.8Mo-LDH in alkaline conditions. For the Cu_0.2Ni_0.8Mo-LDH to supply a cathodic current density of 10 mA cm⁻² for the HER, an overpotential as low as 211 mV was needed. The Tafel slopes for different materials were measured, and the results show that the HER follows the Volmer–Heyrovsky reaction. The 3D Hirshfeld surface analysis indicates that van der Waals and dispersion forces play a significant role in the packing of the crystal, with specific interactions between different metal centers—Ni•••H, Mo•••H, and M•••H—being particularly influential. The percentages provided in range (13.6–30.6%) for Cu, (5.5–30.1%) for Zn, and (20.5–33.4%) for Fe—highlight the relative contributions of these interactions to the overall stability and structure of the crystal lattice involving Fe, Cu, and Zn.