Sethupathi Shanmugasundaram,Hairus Abdullah,Noto Susanto Gultom,Hardy Shuwanto,Dong-Hau Kuo
Hydrogen is an inevitable energy source to replace fossil fuels in the future. Herein, we report Ni-doped ZnIn2(O,S)4/In(OH)3 heterojunction composites with different sulfur contents to support green hydrogen gas evolution. A simple one-step hydrothermal preparation process was carried out by simultaneously adding all chemical precursors during the synthesis of composites. The as-prepared composites were carefully characterized by XRD, FE-SEM, TEM, XPS, DRS, TPC, MS, EIS and CV techniques, which confirmed their performance in the hydrogen evolution reaction (HER) under visible-light illumination. With increasing sulfur content, XRD analysis indicated the gradual formation of Ni-doped ZnIn2(O,S)4 co-existing with the In(OH)3 phase. The highest hydrogen evolution rate of 2100 μmol g−1 h−1 under visible-light illumination was achieved in the presence of the Ni-doped ZnIn2(O,S)4/In(OH)3 composite. Its excellent photocatalytic performance is related to the good separation of photocarriers. XPS analysis suggests the formation of positively and negatively charged defects on catalyst surfaces which attract the photogenerated electrons and holes, respectively, thus leading to an extended photocarrier lifetime. Furthermore, the coupling effect with In(OH)3 provides a more positive conduction band (CB) relative to that of the Ni-doped ZnIn2(O,S)4 phase for facile electron transfer. A plausible HER mechanism based on the experimental data is proposed in this work.
Hairus Abdullah,Sethupathi Shanmugasundaram,Mohamed Tarek Ahmed,Hardy Shuwanto,S.K. Krishna,Dong-Hau Kuo
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 ZnIn 2 (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 Zn In − , Ni In − , and Mg In − . As a result, the formation of oxygen vacancy ( V O 2 + ) 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.
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