Defect-engineered S-scheme charge transfer in TiO2/Zn0.5Cd0.5S heterojunction for high-efficiency photocatalytic hydrogen evolution

doi:10.1016/S1872-2067(25)64909-6

Abstract

Abstract:

Photocatalytic water splitting for H₂ evolution represents a viable approach to address energy and environmental challenges, but it still remains a significant challenge by inefficient light absorption, insufficient charge separation, and weak redox potentials. To tackle these problems, a defect-engineered S-scheme photocatalyst is designed and constructed by in-situ growing Zn_0.5Cd_0.5S nanoparticles on flower-like TiO₂ microspheres with oxygen vacancies (TiO₂-Ov) via a hydrothermal method, thus forming defect-engineered TiO₂-Ov/Zn_0.5Cd_0.5S S-scheme heterojunction. Remarkably, the optimal heterojunction achieves a superior H₂ evolution rate of 15.31 mmol g^-1 h^-1, surpassing those of TiO₂, TiO₂-Ov, Zn_0.5Cd_0.5S, and defect-free TiO₂/Zn_0.5Cd_0.5S by factors of 306.2, 56.7, 4.7, and 1.9, respectively. Notably, the presence of oxygen vacancies in TiO₂-Ov enables a broadened light absorption and introduces an intermediate energy level to provide an additional photo-induced charge transfer channel within the S-scheme heterojunction. Combining with defect engineering and S-scheme mechanism, the photocatalytic system significantly exhibits enhanced light-harvesting ability, accelerated the spatial separation and transfer of photo-induced charge, and preserved strong redox power. Simultaneously, the S-scheme charge transfer pathway in the TiO₂-Ov/Zn_0.5Cd_0.5S heterojunction is systematically validated through a combination of in-situ irradiated X-ray photoelectron spectroscopy, kelvin probe force microscopy, femtosecond transient absorption spectra, electron paramagnetic resonance, and density functional theory calculation. This work highlights the synergistic effect of defect engineering and S-scheme heterojunction in boosting photocatalytic H₂ evolution, offering insights for designing high-performance photocatalyst.

Key words: Defect engineering, TiO₂/Zn_0.5Cd_0.5S, S-scheme, Dual charge transfer pathways, Photocatalytic H₂ evolution

Baolong Zhang, Bin Sun, Xingpeng Liu, Wenyu Liu, Shaonan Gu, Guowei Zhou. Defect-engineered S-scheme charge transfer in TiO₂/Zn_0.5Cd_0.5S heterojunction for high-efficiency photocatalytic hydrogen evolution[J]. Chinese Journal of Catalysis, 2026, 84: 117-129.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(25)64909-6

https://www.cjcatal.com/EN/Y2026/V84/I5/117

Figures/Tables 9

Fig. 1. (a) Schematic diagram of synthesis process of TiO2-Ov/Zn0.5Cd0.5S. (b) XRD patterns of TiO2, TiO2-Ov, Zn0.5Cd0.5S, and TiO2-Ov/Zn0.5Cd0.5S heterojunction with different Zn0.5Cd0.5S content. (c) EPR spectra of TiO2, TiO2-Ov, and TZCS-50wt%.

Fig. 2. FESEM images of TiO2-Ov (a,b), Zn0.5Cd0.5S (c), and TZCS-50wt% (d,e). TEM image (f), HRTEM image (g), fast Fourier transform patterns (h), and elemental mappings (i-n) of Ti, O, Zn, Cd, and S of TZCS-50wt%.

Fig. 3. (a) XPS survey spectra of TiO2-Ov, Zn0.5Cd0.5S, and TZCS-50wt%. High-resolution XPS spectra of Ti 2p (b), O 1s (c), Zn 2p (d), Cd 3d (e), and S 2p (f) of TiO2-Ov, Zn0.5Cd0.5S, and TZCS-50wt% with and without light irradiation.

Fig. 4. UV-vis diffuse reflectance spectra (a) and Tauc plots (b) of TiO2, TiO2-Ov, Zn0.5Cd0.5S, and TiO2-Ov/Zn0.5Cd0.5S heterojunctions. Density of states and energy band structures of TiO2-Ov (c) and Zn0.5Cd0.5S (d). Mott-Schottky plots (e?g) and VB-XPS spectra (h) of TiO2, TiO2-Ov, and Zn0.5Cd0.5S. Corresponding to band structure diagram (i).

Fig. 5. Transient photocurrent spectra (a), EIS Nyquist plots (b), PL spectra (c), and LSV curves (d) of as-prepared samples.

Fig. 6. Photocatalytic H2 evolution (a) and photocatalytic H2 evolution rate (b) of as-obtained samples. Recycling H2 evolution tests (c) of TZCS-50wt%. Comparison of photocatalytic H2 evolution rate (d) of TiO2-Ov/Zn0.5Cd0.5S heterojunction with other reported photocatalysts. Structural model and H-adsorption free energy for Cd and S sites in Zn0.5Cd0.5S via DFT calculation (e).

Fig. 7. KPFM images (a,b) and corresponding to surface potential profiles (c) of TZCS-50wt% with and without light irradiation. Pseudo color plot (d), fs-TA (e), and normalized time profile (f) of TZCS-50wt%.

Fig. 8. EPR spectra of DMPO-?OH (a) and DMPO-?O2- (b) over TiO2-Ov, Zn0.5Cd0.5S, and TZCS-50wt% under light and dark conditions. DFT calculated electrostatic potentials of TiO2-Ov (c) and Zn0.5Cd0.5S (d). The charge density difference from front view (e) and planar-averaged charge density difference (f) of TiO2-Ov/Zn0.5Cd0.5S. Schematic diagram of S-scheme mechanism over TiO2-Ov/Zn0.5Cd0.5S heterojunction: before contact, after contact, and light irradiation (g).

Fig. 9. Proposed photocatalytic H2 mechanism of TiO2-Ov/Zn0.5Cd0.5S S-scheme heterojunction under simulated sunlight irradiation.

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Defect-engineered S-scheme charge transfer in TiO₂/Zn_0.5Cd_0.5S heterojunction for high-efficiency photocatalytic hydrogen evolution

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