This report describes the synthesis of a layered molybdenum disulfide (MoS2)–tungsten disulfide (WS2) heterostructure onto fluorine doped tin oxide covered glass substrates using a combination of chemical bath deposition and RF sputtering techniques. FESEM images revealed that the MoS2–WS2 heterostructure surface consisted of a cauliflower structured array of grains with spherical structures. The vertically aligned atomic layers were explored by transmission electron microscopy images for MoS2–WS2 heterostructure. Hydrogen evolution reaction (HER) kinetics show overpotentials of 151 and 175 mV @ 10 mA/cm2 with Tafel slope values of 90 and 117 mV/decade for pristine MoS2 and WS2 electrocatalysts, respectively. Improved electrocatalytic activity for HER was established with overpotential 129 mV @ 10 mA/cm2 and Tafel slope 72 mV/decade for the MoS2–WS2 heterostructure. The MoS2–WS2 heterostructure electrocatalyst showed robust continuous HER performance over 20 h in an acidic solution. This improved electrochemical performance emerges from the elevation of electron–hole separation at the layer interfaces and sharing of active edge sites through the interface. This study provides the basis to develop new applications for transition-metal dichalcogenides heterostructures in future energy conversion systems.

Hydrazine fuel-cell technology holds great promise for clean energy, not only because of the greater energy density of hydrazine compared to hydrogen but also due to its safer handling owing to its liquid state. However, current technologies involve the use of precious metals (such as platinum) for hydrazine oxidation, which hinders the further application of hydrazine fuel-cell technologies. In addition, little attention has been devoted to the management of gas, which tends to become stuck on the surface of the electrode, producing overall poor electrode efficiencies. In this study, we utilized a nano-hill morphology of vertical graphene, which efficiently resolves the issue of the accumulation of gas bubbles on the electrode surface by providing a nano-rough-edged surface that acts as a superaerophobic electrode. The growth of the vertical graphene nano-hills was achieved and optimized by a scalable plasma-enhanced chemical vapor deposition method. The resulting metal-free graphene-based electrode showed the lowest onset potential (−0.42 V vs saturated calomel electrode) and the highest current density of all the carbon-based materials reported previously for hydrazine oxidation.

The development of stable and efficient oxygen evolutional electrocatalysts is fundamental to the production of hydrogen by water electrolysis. However, so far the majority of electrocatalysts require a substantial overpotential (η) (approximately >250 mV) to catalyze the bottleneck oxygen evolution reaction (OER). To overcome this large overpotential for OER, herein we report the growth of nickel–cobalt–selenide (NiCoSe2) nanosheets over 3D nickel foam (NF) via a facile and scalable electrodeposition method. The resulting 3D NiCoSe2/NF hybrid electrode requires an overpotential of merely 183 mV to reach the current density (J) of 10 mA cm–2. To the best of our knowledge, this is the lowest η value reported so far for any earth-abundant material-based OER electrocatalyst to attain the same current density. Moreover, a significant reduction in Tafel slope (88 mV dec–1) is observed between bare NF and NiCoSe2/NF. Hence, as a result, the 3D hybrid NiCoSe2/NF OER electrode outperforms the previously reported electrocatalysts including the expensive state-of-the-art OER electrocatalysts like RuO2 and IrO2. Such enhancement in the OER catalytic efficiency of NiCoSe2 nanosheets over NF can be attributed to its enormous electrochemical active surface area (ECSA) (108 cm2), large roughness factor (270), highly conductive NF substrate, and the presence of multiple catalytically active OER species (NiOOH and CoOOH) on its surface. In addition, 3D hybrid NiCoSe2/NF electrocatalyst was tested for hydrazine oxidation for its bifunctional utilization. Much lower onset potential values (−0.7 V vs SCE) and high current densities (>200 mA cm–2) are observed for 3D hybrid NiCoSe2/NF when benchmarked against bare NF (−0.4 V and <50 mA cm–2). Furthermore, 3D hybrid NiCoSe2/NF OER electrode shows excellent stability of 50 h for continuous OER in strongly alkaline solutions while maintaining its enormous ECSA, chemical composition, and structural morphology. The excellent bifunctional electrocatalytic activity, long-term stability, and facile preparation method enable NiCoSe2/NF hybrid electrode to be a viable candidate for its widespread use in various water-splitting technologies.

Iridium on vertical graphene nano-hills emerges as a highly active and robust catalyst for the total water splitting reaction in both acidic and alkaline electrolytes.

In recent times, two-dimensional transition-metal dichalcogenides (TMDs) have become extremely attractive and proficient electrodes for dye-sensitized solar cells (DSSCs) and water electrolysis hydrogen evolution as alternatives to the scarce metal platinum (Pt). The active TMD molybdenum selenide (MoSe2) and tungsten disulfide (WS2) are inspiring systems owing to their abundance of active sulfur and selenium sites, but their outputs are lacking due to their inactive basal planes and ineffective transport behavior. In this work, van der Waals interrelated MoSe2/WS2 hybrid structures were constructed on conducting glass substrates by chemicophysical methodologies. For the first time, the constructed MoSe2/WS2 structures were effectively used as a counter electrode for DSSCs and an active electrode for hydrogen evolution to replace the nonabundant Pt. The assembled DSSCs using the designed MoSe2/WS2 heterostructure counter electrode provided a superior power-conversion efficiency of 9.92% and a photocurrent density of 23.10 mA·cm–2, unmatchable by most of the TMD-based structures. The MoSe2/WS2 heterostructure displayed excellent electrocatalytic hydrogen evolution behavior with a 75 mV overpotential to drive a 10 mA·cm–2 current density, a 60 mV·dec–1 Tafel slope, and an over 20 h durable process in an acidic medium. The results demonstrated the advantages of the MoSe2/WS2 hybrid development for generating interfacial transport and active facet distribution and enriching the electrocatalytic activity for DSSCs and the water-splitting hydrogen evolution process.