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Hydrogen (H2) is considered to be a future fuel because of its high energy density and could replace fossil fuels. It can be produced in a greener way by using abundant solar light and saline water and applying a photoelectrochemical (PEC) pathway. To produce green H2, WO3 2D nanosheets are developed, and their performance in saline water splitting is studied under PEC conditions. WO3 is very efficient in absorbing visible light from solar irradiation; however, it suffers from low charge-transfer rates, which inhibits its PEC performance. To increase the charge transportation ability, WO3 is sensitized with sulfur/nitrogen-codoped carbon dots (SNCDs). Impedance analysis indicates an enhanced charge transportation ability of the formed heterostructure. The best-obtained heterostructure of WO3 and SNCDs exhibits nearly 1.62 times more photocurrent density than bare WO3. Bare WO3 nanosheets can produce a photocurrent density of 1.59 mA/cm2 at 1.39 V vs Ag/AgCl. The best-obtained heterostructure of WO3 and SNCDs can produce photocurrent density of 2.57 mA/cm2 at 1.39 V vs Ag/AgCl. A type II staggered heterostructure of WO3/SNCDs leads to improved PEC activity. Enhanced carrier density and lowered charge-transfer resistances are observed from Mott–Schottky and PEC impedance analyses, respectively. The carrier density increases nearly 84 times in the heterostructure. The heterostructure exhibits effective photostability under uninterrupted illumination for 2 h. [ABSTRACT FROM AUTHOR]

Photoelectrochemical water splitting is a greener approach to produce hydrogen (H2) as an efficient chemical fuel for the future with high energy density. However, it is extremely challenging to develop suitable semiconductor materials with desired efficiency and stability, which can be applied for practical applications. Looking at the theoretical efficiency and the solar spectrum, it is clear that visible-light-active semiconductors are the most appealing candidates. Herein, CdIn2.2Sy (CIS), a visible light-active semiconductor, is explored as a photoanode for PEC water splitting. The thin nanosheets of CIS are grown vertically through a hydrothermal method. These can efficiently absorb visible light through multiple reflections and scattering of light inside the material and enhance the light–matter interaction. As a result, the developed CIS thin nanosheets produce a maximum photocurrent density of 3.97 mA/cm2 at "1.6" V versus RHE under continuous back illumination. On the other hand, CIS attains a maximum photoconversion efficiency of ∼1.72% at "0.60" V versus RHE. Furthermore, to improve the efficiency and stability, "S" and "N" codoped C-dots (S, N-CDs) are adorned on the CIS photoanode. The "S" and "N" codoped C-dots and CIS form the type-II heterostructure, which efficiently boosts the charge separation and transportation of photogenerated electrons and holes. The transient decay time becomes longer in the case of heterostructure compared to bare CIS. The heterostructure generates 11.2 mA/cm2 photocurrent densities at an applied potential of "1.6" V versus RHE. At the same time, the heterostructure CIS/S, N-CDs-B achieves a ∼2.08-fold higher photoconversion efficiency compared to bare CIS nanosheets and is stable up to 1500 s under continuous back illumination. The present work offers an approach for designing an efficient and stable photoanode for PEC water splitting. [ABSTRACT FROM AUTHOR]

To attain a sustainable energy source, in the present study, a visible light active semiconductor, ZnIn2.2Sy is developed initially and surface engineering is carried out to grow Cd-ZnIn2.2Sy following a multistep method. A hydrothermal technique is followed for the synthesis of vertically grown 2D nanosheets of visible light active photoanode ZnIn2.2Sy. Further, the cation exchange method is followed to synthesize Cd-ZnIn2.2Sy nanosheets for photoanodic application in photoelectrochemical (PEC) water splitting. In PEC water splitting, vertically grown 2D nanosheets of Cd-ZnIn2.2Sy show improved photoactivity compared to bare ZnIn2.2Sy by virtue of surface engineering. The vertically grown 2D-nanosheets efficiently absorb visible light through multiple reflection and scattering which results in more light and matter interaction. The optimized Cd-ZnIn2.2Sy nanosheets can generate a photocurrent density of 5.85 mA/cm2 at an applied potential "0.78" V vs RHE under back illumination. The photoconversion efficiency legitimizes the superiority of Cd-ZnIn2.2Sy nanosheets, η% is ∼3.10 at 0.53 V vs RHE for Cd-ZnIn2.2Sy whereas, in the case of ZnIn2.2Sy it is only 2.74% at 0.51 V vs RHE. After the development of Cd-ZnIn2.2Sy, the carrier density enhances nearly 4 times that ZnIn2.2Sy. Cd-ZnIn2.2Sy avails higher carrier density, faster charge transportation, and a wide space charge layer. The widening of the space charge layer is confirmed from the calculation of flat band potential. Both ZnIn2.2Sy and Cd-ZnIn2.2Sy nanosheets show excellent stability under continuous back illumination for 1 h. [ABSTRACT FROM AUTHOR]