Upgrading the Optical and Catalytic Efficiency of CuCo₂O₄ Nanostructures via Composing with CuS or CdS for Hydrogen Generation

The present work examines the efficacy of CuCo₂O₄, CuCo₂O₄/CuS or CuCo₂O₄/CdS as catalysts for hydrogen generation via NaBH₄ hydrolysis. CuCo₂O₄, CuCo₂O₄/CuS and CuCo₂O₄/CdS nano samples were produced using hydrothermal and thermolysis techniques. X-ray diffraction (XRD) data manifested a single phase for all samples implying that the Cu, Cd, and S ions are integrated within the CuCo₂O₄ lattice, thereby forming a solid solution. Structure and microstructure analyses for all samples was performed using Rietveld analysis. The obtained UV–Vis diffuse absorbance revealed an enhanced visible light absorption for the 0.95CuCo₂O₄/0.05CuS sample. The CuCo₂O₄ sample possesses two optical band gaps (1.6, 2.1) eV. These bandgaps increased for the CuCo₂O₄/0.05CdS sample (1.66, 2.29) eV but decreased for CuCo₂O₄/0.05CuS sample (1.69, 1.87) eV. The catalytic effectiveness of CuCo₂O₄, CuCo₂O₄/CuS or CuCo₂O₄/CdS samples in promoting the hydrolysis of NaBH₄ under natural daylight circumstances in the laboratory was evaluated. The production rate of hydrogen using CuCo₂O₄/0.05CuS is nearly double that for pure CuCo₂O₄ and more than four times that of NaBH₄ self-hydrolysis. The activation energy of CuCo₂O₄ and of CuCo₂O₄/0.05CuS towards NaBH₄ were calculated to be 71.42 and 58.37 kJ mol⁻¹, respectively. The thermodynamic parameters including, activation enthalpy ΔH^‡, entropy ΔS^‡, and change in Gibbs free energy ΔG^‡ were calculated to predict the capability regarding the mechanistic pathway for the hydrolysis of NaBH₄ in the presence of different catalysts. A positive value of ΔS^‡ is found for the CuCo₂O₄ suggesting a dissociative mechanism, while a negative ΔS^‡ is found for CuCo₂O₄/0.05CuS suggesting a Langmuir–Hinshelwood associative mechanism.