A well-designed honeycomb Co3O4@CdS photocatalyst derived from cobalt foam for high-efficiency visible-light H2 evolution

Abstract

Well-designed honeycomb Co₃O₄@CdS (H-Co₃O₄@CdS) was fabricated via a one-step strategy for efficient water splitting. During the decoration of CdS, honeycomb Co₃O₄ (H-Co₃O₄) with macropores was formed simultaneously. H-Co₃O₄ could enhance CdS visible-light absorption capacity conspicuously and narrow its band gap from 2.08 to 1.03 eV. Therefore, H-Co₃O₄@CdS presented a remarkable H₂ production of up to ca. 16 320 μmol g⁻¹ h⁻¹ (λ > 420 nm), nearly 7.3 times higher than that of pristine CdS, indicating the excellent synergistic effect between H-Co₃O₄ and CdS. Through various photoelectricity tests (e.g., PL spectra, EPR, photoelectric responsiveness and impedance), it could be found that the distinguished H₂ evolution was attributed to the improved charge carrier separation and electron generation. What's more, the enhanced H₂ production of H-Co₃O₄@CdS is related to the improved specific surface area (83.49 m² g⁻¹) and pore volume (0.247 cm³ g⁻¹) as well. Density Functional Theory (DFT) calculations confirmed that CdS has the function of diverting electrons, and the orbital energy level of absorbed H₂O molecules showed obvious migration due to the accumulation of electrons. Besides, the d-band of Co could induce more electrons to traverse the Fermi level. Subsequently, more electrons could be transferred from Co₃O₄ to CdS and break the O–H₁ bond. Compared to the H-Co₃O₄@CdS system, the d-band center of the Co atoms in H-Co₃O₄@CdS–H₂O shifted from −5.83 to −2.58 eV, thereby demonstrating that Co₃O₄ served as an electron reservoir for charge redistribution in the photocatalytic water splitting process. In the end, a practicable mechanism for H-Co₃O₄@CdS about H₂O dissociation and H₂ desorption was proposed.