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 CuCo 2 O 4 , CuCo 2 O 4 /CuS or CuCo 2 O 4 /CdS as catalysts for hydrogen generation via NaBH 4 hydrolysis. CuCo 2 O 4 , CuCo 2 O 4 /CuS and CuCo 2 O 4 /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 CuCo 2 O 4 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 0.95CuCo 2 O 4 /0.05CuS sample. The CuCo 2 O 4 sample possesses two optical band gaps (1.6, 2.1) eV. These bandgaps increased for the CuCo 2 O 4 /0.05CdS sample (1.66, 2.29) eV but decreased for CuCo 2 O 4 /0.05CuS sample (1.69, 1.87) eV. The catalytic effectiveness of CuCo 2 O 4 , CuCo 2 O 4 /CuS or CuCo 2 O 4 /CdS samples in promoting the hydrolysis of NaBH 4 under natural daylight circumstances in the laboratory was evaluated. The production rate of hydrogen using CuCo 2 O 4 /0.05CuS is nearly double that for pure CuCo 2 O 4 and more than four times that of NaBH 4 self-hydrolysis. The activation energy of CuCo 2 O 4 and of CuCo 2 O 4 /0.05CuS towards NaBH 4 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 NaBH 4 in the presence of different catalysts. A positive value of ΔS ‡ is found for the CuCo 2 O 4 suggesting a dissociative mechanism, while a negative ΔS ‡ is found for CuCo 2 O 4 /0.05CuS suggesting a Langmuir–Hinshelwood associative mechanism.