Variation of Ni and Mg dopants in spinel ZnIn2(O,S)4 microflower to generate NiIn− and MgIn− substitutional defects for a high-rate visible-light-induced hydrogen generation

• Published in: Journal of environmental chemical engineering 2023-10, Vol.11 (5), Article 110500
• Main Authors: Abdullah, Hairus, Shanmugasundaram, Sethupathi, Ahmed, Mohamed Tarek, Shuwanto, Hardy, Krishna, S.K., Kuo, Dong-Hau
• Format: Article
• Language: English
• Subjects: Heterojunction; Hydrogen evolution; Photocatalyst; Visible light; ZnIn2S4
• ISSN: 2213-3437
• DOI: 10.1016/j.jece.2023.110500

Carbon-free based fuels are a promising solution to overcome the world energy crisis and environmental pollution. Therefore, hydrogen fuel is a critical and sustainable energy source to replace the limited carbon-based fossil fuels, which can be generated using a simple photocatalysis method. Herein, we demonstrated that Ni- and Mg-doped ZnIn2(O,S)4 (NMZI) photocatalysts prepared with a hydrothermal process performed an unprecedented HER rate without a noble-metal cocatalyst under visible-light illumination. The amounts of Ni and Mg dopants in NMZI were varied and the as-prepared NMZI were characterized with SEM, TEM, XRD, Raman, FTIR, XPS, EPR, DRS, PL, EIS, TPC, CV, and tested for photocatalytic HER. It was found that the Ni and Mg co-dopants induced substitutional surface defects of ZnIn−, NiIn−, and MgIn−. As a result, the formation of oxygen vacancy (VO2+) compensated the induced defect charges, which are crucial in the HER mechanism. EDS, ICP, and XPS analyses suggest a non-stoichiometric Zn(Zn,Ni,Mg,In)2(O,S)3.5 with Zn, Ni, and Mg occupying In sites in the structure. The NMZI catalyst could achieve a maximum HER rate of 9.4 mmol/g․h under visible-light illumination. It is believed that the HER performance improvement is due to the defect formation on NMZI catalyst that subsequently enhances the optical, electrochemical, and photocatalytic properties. The photocatalytic HER mechanism has been elucidated and discussed thoroughly in this work. [Display omitted] •Zn(Zn,Ni,Mg,In)2(O,S)4−x microflower is prepared with simple hydrothermal process.•The spinel microflower can evolve 9.43 mmol/g˖h H2 under visible-light illumination.•Good stability in generating hydrogen with only a 3% degradation is demonstrated.•Equal molar Ni and Mg dopants optimize the HER catalytic activities.•Oxygen vacancy sites compensate for the negative-charged defects of Ni and Mg dopants.