Abstract
In this report, dual bandgap CoCo2O4 nanostructured films were spin-coated at different preheat temperatures (PHT) using different solution molarities (SM), Sn doping and La/Sn double doping levels. In addition to chemical compositions, various methods were used to investigate the structural, morphological, roughness, and optical properties. All the films are polycrystalline CoCo2O4, for simplicity Co3O4, spinel (AB2O4) cubic phase. The doping levels of Sn and La/Sn have strongly affected the surface morphologies and roughness parameters. PHT, SM, Sn% and La% show significant changes in lattice parameters, crystallite sizes, transmittance and reflectance spectra. Two bandgaps were detected in the range of 1.3–1.45 eV and 1.72–2.08 eV. With increasing PHT and decreasing SM, the refractive indices decreased and substantially modified with the inclusion of Sn and La in the matrix Co3O4. Among the applied electrodes for photoelectrochemical (PEC) hydrogen generation, the La/Sn-doped Co3O4 photocatalyst displays a catalytic H2 output rate of 134.50 mmol h−1/cm2 @-1Vwith IPCE% of ~52% @ 460 nm. The supreme values of ABPE% are 3.21%@-0.24V and 3.75%@-0.57V, which are the highest values yet for Co3O4-based photocatalysts. Interestingly, this photoelectrode shows photogenerated current densities of ~ −1.57 mA/cm2 at 0 V and −48.42 mA/cm2 at -1V, and photocurrent onset over −0.361 V. The PEC surface areas and Tafel slopes are also studied for the identification of the mechanism of PEC H2 production. The La/Sn doped-Co3O4 photoelectrode has been further tested for stability and reusability. This work has provided a new viewpoint to design highly active Co3O4-based photocatalysts for solar light-driven H2 generation.
•Novel nanostructured undoped, Sn-doped, and Sn/La co-doped Co3O4 photoanodes are designed.•Morphological, structural and optical parameters and constants are investigated and calculated.•The La/Sn doped-Co3O4 photoelectrode shows PEC H2 production rate of 134.50 mmol h−1/cm2 @-1V and Jph of −1.57 mA/cm2 at 0 V.•High efficiencies are obtained; IPCE% ~52%@460 nm, ABPE% of 3.21%@-0.24V and 3.75%@-0.57V. .•EC surface area, Tafel slopes, stability, and reusability are studied.