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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]

To avoid a massive energy crisis in the near future, it becomes urgent to develop efficient catalysts for the oxygen evolution reaction (OER) in water splitting. For this purpose, a two dimensional (2D) heterostructure of Co3O4 and Co3S4 is prepared following a simple multi-step method that incorporates a wet-chemical technique followed by a hydrothermal method. Initially, 2D sheets of Co3O4 are synthesized using the wet-chemical method followed by calcination. Finally, the heterostructure Co3O4@Co3S4 is fabricated from the Co3O4 sheets following a simple Kirkendall process through sulfurization for electrochemical application. Slow anion exchange leads to development of a hollow core@shell 2D Co3O4@Co3S4 heterostructure. After sulfidation, the heterostructure of 2D sheets shows excellent conductivity and improved electrocatalytic activity for the OER compared to bare Co3O4. The best-obtained Co3O4@Co3S4 can produce a 20 mA cm−2 current density upon application of 1.647 V vs. RHE, which is ∼100 mV lower compared to bare Co3O4. Sulfidation of Co3O4 leads to the formation of hollow heterostructures with a ∼2.8 times higher electrochemically active surface area. Co3O4@Co3S4 is very stable, and it can produce an unaltered current density up to 1000 continuous cycles in the OER. [ABSTRACT FROM AUTHOR]

2D nanosheets of different metal chalcogenides have attracted potential interest due to their appealing physical and chemical properties. In this present study we have developed a novel approach for the synthesis of 2D sheets of MoS2 following a simple hydrothermal method. Using a simple wet‐chemical route, surface of 2D sheets of MoS2 are modified with AgPd alloy nanoparticles following galvanic exchange technique. Electrocatalytic activity towards hydrogen evolution reaction (HER) of MoS2, MoS2/Ag, and AgPd alloy was checked in a wide range of pH condition. In 0.5 M H2SO4, bare MoS2 nanosheets can generate 10 mA/cm2 current density upon application of only −0.329 V vs. reversible hydrogen electrode (RHE). After successful decoration of Ag nanoparticle, MoS2/Ag shows improved activity compared to bare MoS2 sheets. MoS2/Ag can generate current density 10 mA/cm2 only by applying −0.299 V vs. RHE. Further MoS2/AgPd‐1 can generate 10 mA/cm2 current density upon application of −0.229 V vs. RHE. So, from the result it is clear that the successive inclusion of Pd in place of Ag results in higher electrocatalytic activity. Again, MoS2/AgPd‐2 can generate 10 mA/cm2 current density upon application of only −0.215 V vs. RHE. All the metal and alloy nanoparticle decorated MoS2 show excellent stability in hydrogen evolution reaction. MoS2, MoS2/AgPd‐1 and MoS2/AgPd‐2 can generate unaltered current density up to 30 h. MoS2, MoS2/Ag, and AgPd alloy are developed as efficient HER catalyst in a wide range of pH condition. AgPd alloy nanoparticle is developed on the surface of MoS2, using MoS2/Ag as the precursor following galvanic exchange method. MoS2, MoS2/AgPd‐1 and MoS2/AgPd‐2 can generate unaltered current density up to 30 h. [ABSTRACT FROM AUTHOR]

The most important issue in water splitting is the development of efficient, abundant, and cost‐effective hydrogen and oxygen evolution catalysts. The development of an efficient electrocatalyst for the hydrogen evolution reaction (HER) under alkaline conditions is described here following a simple hydrothermal route. Here, a method for the synthesis of NiCo2S4/Co9S8, Co9S8, and NiCo2S4 nanotubes has been developed. The NiCo2S4/Co9S8 heterostructure has been introduced as an efficient electrocatalyst towards HER under alkaline conditions (1.0 m KOH). The vertically aligned nanotube heterostructure (NiCo2S4/Co9S8) shows the most efficient activity as compared to bare Co9S8 and NiCo2S4 nanotubes. The heterostructure of NiCo2S4 and Co9S8 shows a significant anodic shift in the onset potential compared to the bare counterpart. NiCo2S4/Co9S8 can generate a current density of 10 mA cm−2 upon application of only −0.172 V vs. RHE, whereas Co9S8 and NiCo2S4 require −0.293 V and −0.239 V vs. RHE, respectively. The heterostructure formation and the nanotube morphology of Co9S8 and NiCo2S4 facilitates a fast charge transportation which results in higher electrocatalytic activity. The hydrogen gas evolution rate of the NiCo2S4/Co9S8 heterostructure was determined to be 2.29 μmol min−1. The most important issue in water splitting is the development of efficient, abundant, and cost‐effective hydrogen and oxygen evolution catalysts. The development of an efficient electrocatalyst for the hydrogen evolution reaction (HER) under alkaline conditions is described here following a simple hydrothermal route. [ABSTRACT FROM AUTHOR]