naming of energy storage devices after their own core materials: conventional batteries such as lead-acid batteries, which are named after the lead-based active material and the acidic electrolyte; nickelcadmium batteries named after the nickeland cadmium-based active materials; nickel-metal hybrid batteries named after the nickel-and metal hydride-based active materials; state-of-the-art lithium-ion batteries (LIBs), named after the lithiated host materials and lithium-ion carriers; and next-generation batteries such as sodiumion, lithium-sulfur, and lithium-air batteries, which are named after the lithium metal anode and sulfur or O 2 cathode. [4][5][6][7][8][9] In short, whenever energy storage materials made a breakthrough, new-generation energy storage devices appeared. Among electrochemical energy storage devices, supercapacitors (SCs), which can store charges at the surface, have advantages over LIB and conventional batteries in terms of high power, fast charging/ discharging rates, and long cyclability, as will be discussed in Section 2.1. However, the low energy density of SCs remains a critical challenge for emerging applications such as next-generation electronic systems, electrical vehicles (EVs), and renewable energy storage systems (ESSs). [10,11] Based on the long history of energy storage research, new and emerging materials are expected to provide solutions to this problem.Returning to the chronological development of SCs, SCs have been revolutionized by the emergence of new materials, as Two dimensional (2D) nanomaterials are very attractive due to their unique structural and surface features for energy storage applications. Motivated by the recent pioneering works demonstrating "the emergent pseudocapacitance of 2D nanomaterials," the energy storage and nanoscience communities could revisit bulk layered materials though state-of-the-art nanotechnology such as nanostructuring, nanoarchitecturing, and compositional control. However, no review has focused on the fundamentals, recent progress, and outlook on this new mechanism of 2D nanomaterials yet. In this study, the key aspects of emergent pseudocapacitors based on 2D nanomaterials are comprehensively reviewed, which covers the history, classification, thermodynamic and kinetic aspects, electrochemical characteristics, and design guidelines of materials for extrinsically surface redox and intercalation pseudocapacitors. The structural and compositional controls of graphene and other carbon nanosheets, transition metal oxides and hydroxides, transition metal dichalcogenides, and metal carbide/nitride on both microscopic and macroscopic levels will be particularly addressed, emphasizing the important results published since 2010. Finally, perspectives on the current impediments and future directions of this field are offered. Unlimited combinations and modifications of 2D nanomaterials can provide a rational strategy to overcome intrinsic limitations of existing materials, offering a new-generation energy storage materials toward a high and new p...

2D materials, their features and possible approaches to mitigating the challenges in Li–S batteries are discussed.

Photocatalytic water splitting is a sustainable technology for the production of clean fuel in terms of hydrogen (H2). In the present study, hydrogen (H2) production efficiency of three promising photocatalysts (titania (TiO2-P25), graphitic carbon nitride (g-C3N4), and cadmium sulfide (CdS)) was evaluated in detail using various sacrificial agents. The effect of most commonly used sacrificial agents in the recent years, such as methanol, ethanol, isopropanol, ethylene glycol, glycerol, lactic acid, glucose, sodium sulfide, sodium sulfite, sodium sulfide/sodium sulfite mixture, and triethanolamine, were evaluated on TiO2-P25, g-C3N4, and CdS. H2 production experiments were carried out under simulated solar light irradiation in an immersion type photo-reactor. All the experiments were performed without any noble metal co-catalyst. Moreover, photolysis experiments were executed to study the H2 generation in the absence of a catalyst. The results were discussed specifically in terms of chemical reactions, pH of the reaction medium, hydroxyl groups, alpha hydrogen, and carbon chain length of sacrificial agents. The results revealed that glucose and glycerol are the most suitable sacrificial agents for an oxide photocatalyst. Triethanolamine is the ideal sacrificial agent for carbon and sulfide photocatalyst. A remarkable amount of H2 was produced from the photolysis of sodium sulfide and sodium sulfide/sodium sulfite mixture without any photocatalyst. The findings of this study would be highly beneficial for the selection of sacrificial agents for a particular photocatalyst.

The assembly of two-dimensional conductive nanomaterials into hierarchical complex architectures precisely controlling internal open porosity and orientation, external morphology, composition, and interaction is expected to provide promising hosts for high-capacity sulfur cathodes. Herein, we demonstrate rod-like nanosulfur (nS) deposited onto radially oriented open-porous microspherical reduced graphene oxide (rGO) architectures for improved rate and cyclic capabilities of lithium− sulfur (Li−S) batteries. The combined chemistry of a spray-frozen assembly and ozonation drives the formation of a radially oriented open-porous structure and an overall microspherical morphology as well as uniform distribution and high loading of rod-like nS. Moreover, an optimum composition and strong bonding of the rGO/nS hybrid enables the optimization of redox kinetics for high sulfur utilization and high-rate capacities. The resulting rGO/nS hybrid provides a specific capacity and first-cycle Coulombic efficiency of 1269.1 mAh g −1 and 98.5%, respectively, which are much greater than those of ice-templated and physically mixed rGO/nS hybrids and radially oriented open-porous rGO/ bulk sulfur with the same hybrid composition. A 4C capacity of 510.3 mAhg −1 and capacity decay of 0.08% per cycle over 500 cycles (70.9% of the initial capacity over 300 cycles) also support the synergistic effect of the rod-like nS strongly interacting with the radially oriented open-porous rGO microspheres.

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CdS–SnS2 1D–0D core–shell heteronanostructures were designed for an efficient visible-light photocatalytic H2 evolution reaction.

Fabrication of core–shell heteronanostructures with excellent optical properties and light induced charge separation effects have recently emerged as promising materials for solar to hydrogen conversion. Here, one-dimensional CdS–Au/MoS2 hierarchical core/shell heteronanostructures (CSHNSs) have been successfully synthesized by a facile two-step hydrothermal method. Such heteronanostructures exhibit high efficiency and excellent stability toward hydrogen production. The introduction of Au nanoparticles on to CdS nanorods not only made a Schottky junction with strong plasmonic absorption enhancement but also directed the growth of few layered MoS2 nanosheets as a hierarchical protective shell around the CdS nanorods. These CdS–Au/MoS2 hybrid structures possess a large number of edge sites in the MoS2 layers which are active sites for hydrogen evolution reaction. As a result, the CdS–Au/MoS2 CSHNSs exhibit outstanding hydrogen evolution performance which is 7 times that of pure CdS nanorods. Also these CdS–Au/MoS2 CSHNSs showed greater stability after a long-time test (16 h), and 90% of catalytic activity still remained. The enhanced hydrogen evolution activity of CdS–Au/MoS2 CSHNSs was attributed to the improved visible light absorption and the formation of heterojunctions between CdS, Au, and MoS2 components, which increases the charge separation efficiency and thereby suppresses the electron–hole recombination.