To overcome the increasing energy demand worldwide, semiconductor-based photocatalytic H2 production by water splitting has gained much recognition as an alternative approach. However, the main drawbacks are lower visible light absorption and rapid recombination of photogenerated electrons–hole pairs in the semiconductor-based photocatalysts. This work reports the synthesis of CdS/ZnS heterostructures with varied compositions of each component via a single-step solvothermal method and calcination under vacuum. An optimized (CdS)0.4/(ZnS)0.6 composite exhibits the highest photocatalytic H2 generation rate of 830.95 μmol g–1 h–1, which is significantly higher than those of CdS nanorods (254.17 μmol g–1 h–1) and ZnS nanoplates (9.59 μmol g–1 h–1). The higher rate for H2 generation corresponds to better light absorption as well as efficient charge separation in the CdS/ZnS heterostructure. The photoelectrochemical study also confirms the effective charge separation in the CdS/ZnS heterostructure. Based on these results, a probable mechanism is suggested for photocatalytic H2 generation from the CdS/ZnS heterostructure.

Herein, a solution-based route is presented to fabricate Cu­(OH)2/Co­(OH)2 heterostructures directly on copper foil (CF) as a potential electrode material for supercapacitor application. First a CF is etched to form uniform Cu­(OH)2 nanobelt-like structures on its surface. Using the same CF as the substrate, Co­(OH)2 nanosheets are electrochemically grown on Cu­(OH)2 nanobelts to form a Cu­(OH)2/Co­(OH)2 heterostructure at room temperature. The electrodeposition duration determines the density of Co­(OH)2 nanosheets on the substrate. With an electrodeposition duration of 900 s, a maximum areal capacitance is achieved and thus the same duration is used for forming the heterostructure for device fabrication. An areal capacitance of 413 mF cm–2 is obtained for CF/Cu­(OH)2/Co­(OH)2, which is higher than those for CF/Co­(OH)2 (344 mF cm–2) and CF/Cu­(OH)2 (44 mF cm–2) at 5 mA cm–2. This demonstrates the direct use of a surface-modified binder-free electrode in supercapacitor applications. A more detailed analysis following Trasatti and Dunn’s method reveals the primary charge storage through the diffusion-controlled process. Additionally, the performance of an asymmetric supercapacitor device is demonstrated with CF/Cu­(OH)2/Co­(OH)2 as a positive electrode, activated carbon on CF as a negative electrode, and polyvinyl alcohol–KOH gel as the solid-state electrolyte. An areal capacitance of 113 mF cm–2 at 2.5 mA cm–2 is achieved with an energy density of 3.5 × 10–2 mW h cm–2 at a power density of 1.87 mW cm–2 with a 1.5 V voltage window. A capacitance retention of 81% is measured after 12,000 galvanostatic charge–discharge cycles.

A microwave-assisted hydrothermal method is demonstrated to synthesize Co3O4 nanostructures as the positive electrode and a graphene hydrogel as the negative electrode for a supercapacitor.

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A unique V-shaped MnO2 nanostructure is synthesized with a weak acid (acetic acid) using microwave-assisted hydrothermal technique. To improve the performance of MnO2 in supercapacitor application, its composite was prepared...