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In this paper, we report the effects of temperature on the deterioration of graphite-based negative electrodes during the long-term cycling of lithium-ion batteries (LIBs). After cycling 75 Ah pouch-type LIB full cells at temperatures of 45°C (45-Cell) and 25°C (25-Cell) until their end of life, we expected to observe changes in the negative electrode according to the temperature. The thickness of the negative electrode of the cell was greater after cycling; that of the electrode of 45-Cell (144 μm) was greater than that of the electrode of 25-Cell (109 μm). Cross-sectional scanning electron microscopy analysis confirmed that by-products caused this increase in the thickness of the negative electrode. The by-products that formed on the surface of the negative electrode during cycling increased the surface resistance and decreased the electrical conductivity. Voltage profiles showed that the negative electrode of 25-Cell exhibited an 84.7% retention of the initial capacity, whereas that of 45-Cell showed only a 70.3% retention. The results of this study are expected to be relevant to future analyses of the deterioration characteristics of the negative electrode and battery deterioration mechanisms, and are also expected to provide basic data for advanced battery design.

The Sb2S3-based photoanode is combined with a silicon photocathode for implementing a bias-free photoelectrochemical tandem device driving hydrogen evolution reaction coupled with IOR, affording operation current density of 4 mA cm−2.

An optimum weight fraction of manganese oxides is hybridized with covalent organic nanosheets (CONs) by redox reactions. The optimized hybrid exhibits the facile electron transfer to catalytic sites on manganese oxides for oxygen reduction reaction.

Among many types of low-dimensional inorganic nanostructures, nanostructured MnO2 provides unique advantages in designing and synthesizing efficient electrode and catalyst materials for novel energy storage technologies. The low cost, high redox potential, theoretically high energy storage capacity, environmentally friendliness, and rich deposits provide MnO2 nanomaterials with a high level of economic feasibility for various renewable energy-related applications, like electrodes for metal-ion batteries/metal–sulfur batteries/metal–O2 batteries/supercapacitors and electrocatalysts for oxygen evolution/oxygen reduction/CO2 reduction/N2 fixation. In this review, a wide spectrum of the energy-related applications of diverse nanostructured MnO2 materials is systematically surveyed along with versatile synthetic methods of these metal oxides and chemical design strategies to improve their electrochemical functionalities. Future research perspectives for nanostructured MnO2 materials are provided to offer insightful directions for the exploration of next-generation energy storage/conversion systems.

Sodium ion batteries (SIBs) is an attractive prospect for energy storage in applications ranging from portable devices to large scale energy storage grids. However practical application of SIBs is ...

Three-dimensional (3D) carbon nitrides (C3N4) show excellent photocatalytic performance for the hydrogen evolution reaction (HER) under visible light irradiation. 3D C3N4 can be produced by the hig...

Exfoliated two-dimensional (2D) nanosheets of inorganic solids exhibit various unique characteristics such as unusually high morphological and structural anisotropy, great diversity in composition and structure, and tunable physicochemical properties. The large 2D surface area and high electrochemical activity of inorganic nanosheets render them as potential materials for supercapacitor electrodes. The electrode performance of these nanosheets can be further improved by their hybridization with highly conductive and/or electrochemically active species. This review focuses on the application of 2D inorganic nanosheets as supercapacitor electrodes and versatile building blocks for synthesizing novel hybrid electrode materials. The crucial roles of 2D inorganic nanosheets in high-performance electrode materials for supercapacitors are discussed and several intriguing examples of 2D inorganic nanosheet-based electrode materials have also been provided. The perspective for future research in this field is discussed along with various strategies to optimize the electrode performance of 2D inorganic nanosheet-based hybrid materials.

A defect engineering of inorganic solids garners great deal of research activities because of its high efficacy to optimize diverse energy‐related functionalities of nanostructured materials. In this study, a novel in situ defect engineering route to maximize electrocatalytic redox activity of inorganic nanosheet is developed by using holey nanostructured substrate with strong interfacial electronic coupling. Density functional theory calculations and in situ spectroscopic analyses confirm that efficient interfacial charge transfer takes place between holey TiN and Ni−Fe‐layered double hydroxide (LDH), leading to the feedback formation of nitrogen vacancies and a maximization of cation redox activity. The holey TiN−LDH nanohybrid is found to exhibit a superior functionality as an oxygen electrocatalyst and electrode for Li−O2 batteries compared to its non‐holey homologues. The great impact of hybridization‐driven vacancy introduction on the electrochemical performance originates from an efficient electrochemical activation of both Fe and Ni ions during electrocatalytic process, a reinforcement of interfacial electronic coupling, an increase in electrochemical active sites, and an improvement in electrocatalysis/charge‐transfer kinetics., Here the development of a novel synthetic route to defect‐optimized high‐performance electrocatalyst via the hybridization‐driven in situ creation of crystal defects, is reported. The holey TiN−LDH nanohybrid with strong interfacial electronic coupling shows outstanding oxygen electrocatalytic activity for Li−O2 batteries, which is attributable to the feedback formation of nitrogen vacancies and the maximization of cation redox activity upon hybridization.

Highlights The g-C3N4 monolayer in the perfect 2D limit was successfully realized, for the first time, by the well-defined chemical strategy based on the bottom-up process. The most striking evidence was made from Cs–high resolution transmission electron microscopy measurements by observing directly the atomic structure of g-C3N4 unit cell, which was again supported by the corresponding high resolution transmission electron microscopy image simulation results. We demonstrated that the newly prepared g-C3N4 monolayer showed outstanding photocatalytic activity for H2O2 generation as well as excellent electrocatalytic activity for oxygen reduction reaction. Abstract The exfoliation of bulk graphitic carbon nitride (g-C3N4) into monolayer has been intensively studied to induce maximum surface area for fundamental studies, but ended in failure to realize chemically and physically well-defined monolayer of g-C3N4 mostly due to the difficulty in reducing the layer thickness down to an atomic level. It has, therefore, remained as a challenging issue in two-dimensional (2D) chemistry and physics communities. In this study, an “atomic monolayer of g-C3N4 with perfect two-dimensional limit” was successfully prepared by the chemically well-defined two-step routes. The atomically resolved monolayer of g-C3N4 was also confirmed by spectroscopic and microscopic analyses. In addition, the experimental Cs-HRTEM image was collected, for the first time, which was in excellent agreement with the theoretically simulated; the evidence of monolayer of g-C3N4 in the perfect 2D limit becomes now clear from the HRTEM image of orderly hexagonal symmetry with a cavity formed by encirclement of three adjacent heptazine units. Compared to bulk g-C3N4, the present g-C3N4 monolayer showed significantly higher photocatalytic generation of H2O2 and H2, and electrocatalytic oxygen reduction reaction. In addition, its photocatalytic efficiency for H2O2 production was found to be the best for any known g-C3N4 nanomaterials, underscoring the remarkable advantage of monolayer formation in optimizing the catalyst performance of g-C3N4.

The hybridization of conductive nanospecies has garnered significant research interest because of its high efficacy in improving the diverse functionalities of nanostructured materials. In this study, a novel synthetic strategy is developed to optimize the defect structure, structural ordering, and energy‐related functionality of nanostructured‐materials by employing a multilayer multicomponent two‐dimenstional (2D) graphene/metal oxide/graphene nanosheet (NS) as a versatile hybridization matrix. The hybridization of the robust trilayer, polydiallyldiammonium (PDDA)‐anchored reduced‐graphene oxide (prGO)/metal oxide/prGO NS effectively enhance the structural ordering and porosity of the hybridized MoS2/MnO2 NS through suppression of defect formation and tight stacking. In comparison with monolayer rGO/RuO2 NS‐based homologs, the 2D superlattice trilayer prGO/RuO2/prGO NS hybrids deliver better functionalities as a hydrogen evolution electrocatalyst and as a supercapacitor electrode, demonstrating the merits of hybridization with multilayer NSs. The advantages of using multilayer multicomponent conductive NSs as hybridization matrices arise from the enhancement of charge and mass transport through the layer flattening or defect suppression of the hybridized NSs and the increase in porosity, as evidenced by density functional theory calculations. Finally, the universal utility of multilayer NSs is confirmed by investigating the strong effect of the stacking order on the electrocatalytic functionality of MoS2/rGO/RuO2 films fabricated through layer‐by‐layer deposition., A new concept of synthetic strategy to improve various energy functionalities and mass/charge transports of nanostructured materials is developed by employing multilayer conductive graphene/inorganic/graphene nanosheet (NS) as an emerging versatile hybridization matrix. The universal usefulness of hybridization with multilayer multicomponent NSs in exploring high‐performance functional materials originates from optimization of the defect structure, structural ordering, and porosity of hybridized species.

The search for new high-performance dielectric material receives continued research interest. Several mechanisms for high permittivity have been proposed such as BaTiO3-based perovskites or CaCu3Ti4O12. Nevertheless, developing thin films with such high performance remains a highly challenging task. However, reducing the BaTiO3-based film thickness raises the leakage current and suppresses dielectric responses because of a low-permittivity interfacial ‘dead-layer’. Here, we propose a new materials design route to great permittivity behavior in atomically-thin films, where charge engineering of layered perovskites generates giant polarizability and results in 2-dimensional materials with colossal permittivity. Firstly, we present a concrete example Dion-Jacobson type KSr2 − xBixNb3O10 and its cation-exchanged form HSr2 − xBixNb3O10, which exhibit a stable colossal permittivity and a low dielectric loss. Also, Sr2(1−x)Bi2xNb3O10 (x = 0.1) nanosheets attain by chemical exfoliation method with a high dielectric permittivity of over 500, the highest among all known dielectrics in the ultrathin films (2Nb3O10, the dielectric permittivity exhibits two times higher value due to higher polarizability of Bi ions and leads larger dielectric permittivity. Density functional theory calculations suggest that the substitution of high-valent Bi ions with lone pairs are responsible for the colossal permittivity. Our results provide a strategy for achieving new high-k nanodielectrics for use in nano-scaled electronics.

The synergetic combination of defect engineering and graphene coupling enables to develop an effective way of exploring efficient bifunctional electrocatalyst/electrode materials. Defect-engineered amorphous MoO2 -reduced graphene oxide (rGO) nanohybrid was synthesized by soft-chemical reduction of K2 MoO4 in graphene oxide colloids. Mo K-edge X-ray absorption spectroscopy clearly demonstrates the rutile-type local atomic structure of amorphous MoO2 with significant oxygen vacancies and intimate electronic coupling with rGO. The defect-introduced MoO2 -rGO nanohybrid shows excellent bifunctionality as electrocatalyst for hydrogen evolution reaction and electrode for sodium-ion batteries, which are superior to those of crystalline MoO2 -rGO homologue. The beneficial effect of simultaneous defect control and rGO coupling can be ascribed to the provision of oxygen vacancies acting as active sites, the increase of electrical conductivity, and the improvement of reaction kinetics.

Polynary transition-metal atom catalysts are promising to supersede platinum (Pt)-based catalysts for oxygen reduction reaction (ORR). Regulating the local configuration of atomic catalysts is the key to catalyst performance enhancement. Different from the previously reported single-atom or dual-atom configurations, a new type of ternary-atom catalyst, which consists of atomically dispersed, nitrogen-coordinated Co-Co dimers, and Fe single sites (i.e., Co

Interstratified 2D nanohybrids of chromium hydroxide-molybdenum disulfide with improved electrode functionality are synthesized by the self-assembly of anionic monolayered MoS2 nanosheets with cationic chromium hydroxide nanoclusters. The intercalative hybridization of MoS2 with chromium hydroxide nanoclusters leads to a significant increase of basal spacing as well as to the formation of an open porous stacking structure. This is the first example of metal hydroxide nanocluster-pillared transition metal dichalcogenide (TMD) hybrid materials. According to extended X-ray absorption fine structure analysis, open tetrameric chromium hydroxide nanoclusters are stabilized in-between metallic 1T'-MoS2 monolayers. In comparison with the pristine MoS2 material, the chromium hydroxide-pillared molybdenum disulfide nanohybrids show remarkably improved charge storage capacity with excellent rate performance for lithium ion batteries, highlighting the beneficial effect of pillaring with metal hydroxides on the electrode performance of MoS2. The improvement of electrode functionality upon hybridization is attributable to the increase of basal spacing, the stabilization of metallic 1T'-MoS2 content, the improvement of charge transfer kinetics, and the stabilization of the open porous structure upon electrochemical cycling. The present study clearly demonstrates that an electrostatically-driven self-assembly between exfoliated TMD nanosheets and cationic inorganic nanoclusters can provide an effective way of synthesizing heterostructured hybrid electrode materials with improved performance.

A phase transformation route to porous 2D Mn3O4 nanosheets is developed by heat treatment of exfoliated layered MnO2 nanosheets. The calcination of MnO2 nanosheets at an elevated temperature of ≥ 500 °C in Ar atmosphere leads to the formation of porous 2D nanosheets as well as to reductive phase transition to low-valent Mn3O4. The formation of spinel-structured Mn3O4 phase with mixed tetrahedral and octahedral local symmetries is obviously evidenced by micro-Raman and X-ray absorption spectroscopies. An elevation of heating temperature enlarges the surface pore of 2D nanosheet and lowers the average oxidation state of Mn ion. In comparison with Mn3O4 crystal, the porous 2D Mn3O4 nanosheets show higher electrode activities for lithium ion batteries (LIBs) with larger discharge capacities, better rate characteristics, and excellent cyclabilities, emphasizing the advantage of porous 2D nanosheet morphology in optimizing the electrode functionality of metal oxide. The present study underscores the validity of the present phase transformation route in exploring novel high-performance metal oxide–based LIB electrode materials.

An effective methodology to explore highly efficient oxygen electrocatalysts and electrodes for Li−O2 batteries is developed via intimate layer-by-layer hybridization between mesoporous carbon layer and highly anisotropic 2D metal oxide nanosheets. The obtained multilayer hybrid nanosheets of mesoporous carbon−layered MnO2 display outstanding functionalities as oxygen electrocatalysts with low overpotential and as the electrodes of Li−O2 batteries with huge discharge capacity of ˜7000 mAhg−1 at 200 mAg− 1 and improved cyclability. The excellent electrocatalyst/electrode bifunctionality of the present material is attributable to enhanced electron transfer kinetics, maximized active sites, promoted electrocatalysis kinetics, and stabilization of unstable Mn3+ species. This multilayer hybrid nanosheet structure is advantageous for facilitating reversible formation/decomposition of discharged product during cycling in Li−O2 batteries via promoted electrolyte−oxygen diffusion. The present study underscores that exfoliated metal oxide nanosheet can be used as an efficient immobilization matrix for synthesizing novel 2D multilayer hybrid nanosheets with synergistically-improved electrocatalyst/electrode functionalities.

Highly anisotropic 2D nanosheets of inorganic solids with nanometer-level thickness attract a great deal of research activity because of their unique merits in exploring novel high performance photocatalysts applicable for environmental purification and production of renewable clean energy. The 2D inorganic nanosheets possess many valuable properties such as tailorable band structures and chemical compositions, large surface areas, well-defined defect-free surface structure, and tunable electrical conductivities. Due to these unique advantages of 2D inorganic nanosheets, these materials can be used as promising building blocks for hybrid-type photocatalysts with optimized band structures, expanded surface areas, improved charge separation behaviors, and enhanced reaction kinetics. Of prime importance is that unusually strong electronic coupling can occur between very thin 2D inorganic nanosheets and hybridized nanospecies, leading to the synergistic optimization of electronic and optical properties, and thus the remarkable enhancement of photocatalytic activity. Depending on the type of component nanosheets, diverse examples of inorganic nanosheet-based photocatalysts are presented along with the in-depth discussion about critical roles of inorganic nanosheet in these hybrid photocatalysts. Future perspectives in the researches for 2D inorganic nanosheet-based photocatalysts are discussed to offer useful directions for designing and synthesizing novel high performance photocatalysts applicable for renewable energy production and environmental purification.

Although progress has been made to improve photocatalytic CO2 reduction under visible light (λ>400 nm), the development of photocatalysts that can work under a longer wavelength (λ>600 nm) remains a challenge. Now, a heterogeneous photocatalyst system consisting of a ruthenium complex and a monolayer nickel-alumina layered double hydroxide (NiAl-LDH), which act as light-harvesting and catalytic units for selective photoreduction of CO2 and H2 O into CH4 and CO under irradiation with λ>400 nm. By precisely tuning the irradiation wavelength, the selectivity of CH4 can be improved to 70.3 %, and the H2 evolution reaction can be completely suppressed under irradiation with λ>600 nm. The photogenerated electrons matching the energy levels of photosensitizer and m-NiAl-LDH only localized at the defect state, providing a driving force of 0.313 eV to overcome the Gibbs free energy barrier of CO2 reduction to CH4 (0.127 eV), rather than that for H2 evolution (0.425 eV).

High-performance oxygen electrocatalysts have attracted tremendous research attention because of their crucial roles in diverse renewable energy technologies such as metal–oxygen batteries, fuel cells, and water electrolyzers. In this study, a novel lattice manipulation strategy for the exploration of highly active electrocatalysts was established via self-assembly between exfoliated MXene and layered double hydroxide (LDH) nanosheets (NSs). Electrostatically-driven self-assembly between cationic Co–Fe-LDH and anionic MXene NSs yielded intimately-coupled Co–Fe-LDH–MXene nanohybrids with porous stacking structures and significant interfacial charge transfer. The self-assembled Co–Fe-LDH–MXene nanohybrid delivered excellent electrocatalyst functionality with a lowered overpotential of 252 mV at 10 mA cm−2 that is much better than those of the precursor Co–Fe-LDH and MXene NSs. The outstanding electrocatalytic activity of the self-assembled Co–Fe-LDH–MXene nanohybrid highlights a high efficacy of the self-assembly methodology in exploring high-performance electrocatalysts. In situ surface enhanced Raman scattering analysis during electrocatalysis found that the enhanced redox activity of metal cations achieved by intimate electronic coupling with ultrathin conductive MXene NSs mainly contributes to the improved performance of the Co–Fe-LDH–MXene nanohybrids for oxygen evolution reaction.

Hybridization with conductive nanospecies has attracted intense research interest as a general effective means to improve the photocatalytic functionalities of nanostructured materials. To establish universal design rules for high‐performance hybrid photocatalysts, correlations between versatile roles of conductive species and interfacial interaction between hybridized species are systematically investigated through fine‐control of intersheet distance between photocatalytically active TiO2 and metallic reduced graphene oxide (rGO)/RuO2 nanosheets. Molecular‐level tailoring of intersheet distance and electronic coupling between 2D nanosheets can be successfully achieved by restacking of colloidal nanosheet mixture with variable‐sized organic intercalants. While the shortest intersheet distance between restacked TiO2 and rGO nanosheets leads to the highest visible‐light‐driven photocatalytic activity, the best UV–vis photocatalyst performance occurs for moderate intersheet spacing. These results highlight the greater sensitivity of photoinduced electronic excitation to the intersheet distance than that of interfacial charge transfer. The rGO nanosheet can function as effective charge transport pathway and cocatalyst within ≈1.7 nm distance from the semiconducting nanosheet, and as efficient stabilizer for hybridized photocatalyst within ≈1.8 nm. The present study underscores that the intercalative restacking of colloidal nanosheet mixture with intercalants enables molecular‐level control of distance between 2D inorganic/graphene nanosheets, which provides a rational design strategy for high‐performance hybrid photocatalysts., Molecular‐level control of intersheet distance and electronic coupling between 2D graphene/inorganic nanosheets can be achieved by restacking colloidal nanosheet mixture with variable‐sized intercalants. The optimal conditions for the efficacy of conductive nanosheet as photosensitizer, electron reservoir, charge transport pathway, cocatalyst, and stabilizer can be established with restacked organic–semiconductor–conductor nanohybrids, providing novel rational design strategy for high‐performance hybrid photocatalysts.

2D nanostructured materials, including inorganic and graphene nanosheets, have evoked plenty of scientific research activity due to their intriguing properties and excellent functionalities. The complementary advantages and common 2D crystal shapes of inorganic and graphene nanosheets render their homogenous mixtures powerful building blocks for novel high-performance functional hybrid materials. The nanometer-level thickness of 2D inorganic/graphene nanosheets allows the achievement of unusually strong electronic couplings between sheets, leading to a remarkable improvement in preexisting functionalities and the creation of unexpected properties. The synergetic merits of atomically coupled 2D inorganic-graphene nanosheets are presented here in the exploration of novel heterogeneous functional materials, with an emphasis on their critical roles as hybridization building blocks, interstratified sheets, additives, substrates, and deposited monolayers. The great flexibility and controllability of the elemental compositions, defect structures, and surface natures of inorganic-graphene nanosheets provide valuable opportunities for exploring high-performance nanohybrids applicable as electrodes for supercapacitors and rechargeable batteries, electrocatalysts, photocatalysts, and water purification agents, to give some examples. An outlook on future research perspectives for the exploitation of emerging 2D nanosheet-based hybrid materials is also presented along with novel synthetic strategies to maximize the synergetic advantage of atomically mixed 2D inorganic-graphene nanosheets.

Interstratified 2D nanohybrids of chromium hydroxide-molybdenum disulfide with improved electrode functionality are synthesized by the self-assembly of anionic monolayered MoS2 nanosheets with cationic chromium hydroxide nanoclusters. The intercalative hybridization of MoS2 with chromium hydroxide nanoclusters leads to a significant increase of basal spacing as well as to the formation of an open porous stacking structure. This is the first example of metal hydroxide nanocluster-pillared transition metal dichalcogenide (TMD) hybrid materials. According to extended X-ray absorption fine structure analysis, open tetrameric chromium hydroxide nanoclusters are stabilized in-between metallic 1T'-MoS2 monolayers. In comparison with the pristine MoS2 material, the chromium hydroxide-pillared molybdenum disulfide nanohybrids show remarkably improved charge storage capacity with excellent rate performance for lithium ion batteries, highlighting the beneficial effect of pillaring with metal hydroxides on the electrode performance of MoS2. The improvement of electrode functionality upon hybridization is attributable to the increase of basal spacing, the stabilization of metallic 1T'-MoS2 content, the improvement of charge transfer kinetics, and the stabilization of the open porous structure upon electrochemical cycling. The present study clearly demonstrates that an electrostatically-driven self-assembly between exfoliated TMD nanosheets and cationic inorganic nanoclusters can provide an effective way of synthesizing heterostructured hybrid electrode materials with improved performance.

This study explored for the first time the application of two-dimensional (2D) ruthenium oxide (RuO2) nanosheets (NSs) for organic decomposition through peroxymonosulfate (PMS) activation. RuO2 NSs outperformed not only the corresponding RuO2 nanoparticles (NPs) but also other common PMS activators such as transition metal oxides and carbonaceous nanomaterials, which is ascribed to facile electron transfer on 2D nanosheets, higher surface area and porosity, and favorable interaction with PMS on the hydrophilic surface. Aside from the higher PMS activation efficiency, the potential advantages of RuO2 NSs include (i) optimized performance under weakly acidic and neutral conditions and (ii) capability to utilize both PMS and PDS as radical precursors unlike Co3O4. In addition, RuO2 NSs/PMS could decompose both aromatic (e.g., bisphenol A, benzoic acid, and ranitidine) and non-aromatic compounds (e.g., dichloroacetate) to a significant extent, which is in marked contrast to the carbon nanotube–PMS system of which the efficiency sensitively depends on the kind of substrate. The generation of a sulfate radical (SO4˙−) as a main oxidant (from PMS decomposition) was corroborated by not only an outstanding inhibition effect of methanol (a sulfate radical scavenger) but also the formation of the sulfate radical adduct in the electron paramagnetic resonance (EPR) spin-trapping test. As a practical method of utilizing RuO2 NSs, RuO2 NSs could be coupled with magnetic Fe3O4, which enabled not only the facile recovery of the catalyst after use but also the robust catalytic performance without losing the activity during repeated use. Despite the high material cost of RuO2, such superiorities can make it an effective, stable, and reusable PMS activator.

Efficient bifunctional electrocatalysts of V- and Co-substituted α-MnO2 materials can be synthesized by one-pot hydrothermal reaction of ion-adducts V3+/Co2+–MnO4−, leading to the successful substitution of both V and Co ions in the α-MnO2 lattice. According to extended X-ray absorption fine structure analysis, the substituted V ion is stabilized in highly distorted local symmetry whereas the substituted Co ion has regular octahedral local environment. Both the V- and Co-substituted α-MnO2 materials exhibit excellent bifunctional electrocatalytic functionalities with lowered overpotentials and enhanced current densities for oxygen evolution (OER) and oxygen reduction reactions (ORR), underscoring the beneficial role of cation substitution in enhancing the bifunctional electrocatalytic activity of α-MnO2. The Co-substituted α-MnO2 shows higher bifunctional oxygen electrocatalyst functionality than does the V-substituted homologue, which is attributable to the greater improvement of charge transfer kinetics upon the Co substitution than the V one. The poorer charge transfer property of V-substituted α-MnO2 can be ascribed to highly distorted local symmetry of V ion, which is unfavorable for increasing band width and depressing bandgap energy. Taking into account many advantages of the oxides of V, Mn, and Co elements such as low price, rich abundance, and environmentally benignity, the present study underscores that the partial substitution of neighboring 3d metal ion having regular octahedral symmetry can provide an effective and environmental friendly way of optimizing the oxygen electrocatalytic activity of manganese oxide.

2D nanostructured fullerene (C60) nanosheets (NSs) with a strong electron-withdrawing ability are employed as a hybridization matrix for improving the electrode performance of an inorganic solid. The electrostatically-driven self-assembly of anionic C60 NSs with cationic Ni–Fe-layered double hydroxide (LDH) NSs yields a strongly-coupled nanohybrid of C60–LDH. The hybridization between fullerene and Ni–Fe-LDH NSs leads not only to the formation of a mesoporous stacking structure but also to the occurrence of strong interfacial electron transfer from Ni–Fe-LDH to C60. The obtained C60–Ni–Fe-LDH nanohybrids deliver much greater specific capacitances with better rate characteristics than the graphene–Ni–Fe-LDH nanohybrid and the pristine Ni–Fe-LDH, highlighting the superior role of fullerene as a hybridization matrix over graphene in improving the supercapacitor electrode performance of the LDH material. Such remarkable advantages of fullerene incorporated are attributable to the increase of porosity, the significant contribution of the redox process of fullerene, the improvement of charge transfer kinetics, and the enhancement of surface electrophilicity due to an electronic coupling with electron-withdrawing fullerene. The present study underscores that hybridization with fullerene provides an effective way of exploring a new family of high-performance electrochemistry-related functional nanohybrids.

An effective chemical way to optimize the oxygen electrocatalyst and Li-O2 electrode functionalities of metal oxide can be developed by the control of chemical bond nature with the surface anchoring of highly oxidized selenate (SeO4 2- ) clusters. The bond competition between (Se6+ -O) and (Mn-O) bonds is quite effective in stabilizing Jahn-Teller-active Mn3+ state and in increasing oxygen electron density of α-MnO2 nanowire (NW). The selenate-anchored α-MnO2 NW shows excellent oxygen electrocatalytic activity and electrode performance for Li-O2 batteries, which is due to the improved charge transfer kinetics and reversible formation/decomposition of Li2 O2 . The present study underscores that the surface anchoring of highly oxidized cluster can provide a facile, effective way of improving the oxygen electrocatalyst and electrochemical performances of nanostructured metal oxide in Li-O2 cells.

Mesoporous carbon nitrides (MCN) with C3 N4 stoichiometry could find applications in fields ranging from catalysis, sensing, and adsorption-separation to biotechnology. The extension of the synthesis of MCN with different nitrogen contents and chemical structures promises access to a wider range of applications. Herein we prepare mesoporous C3 N5 with a combined triazole and triazine framework via a simple self-assembly of 5-amino-1H-tetrazole (5-ATTZ). We are able to hybridize these nanostructures with graphene by using graphene-mesoporous-silica hybrids as a template to tune the electronic properties. DFT calculations and spectroscopic analyses clearly demonstrate that the C3 N5 consists of 1 triazole and 2 triazine moieties. The triazole-based mesoporous C3 N5 and its graphene hybrids are found to be highly active for oxygen reduction reaction (ORR) with a higher diffusion-limiting current density and a decreased overpotential than those of bulk g-C3 N4 .

A critical role of bond competition in tailoring Mn valence state and bifunctional electrocatalyst activity of manganese oxide is evidenced by the remarkable improvement of the electrocatalyst activity of α-MnO2 upon the partial substitution of electronegative Ru4+ ion. The replacement of Mn4+ ion with more electronegative Ru4+ one is quite effective in weakening adjacent (Mn−O) bonds in terms of bond competition, leading to the stabilization of Jahn-Teller active Mn3+ species, as well as in providing electrocatalytically active Ru sites. The resulting Ru-substituted α-Mn1−xRuxO2 nanowires show much higher electrocatalyst activities for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) than does the physical mixture of α-MnO2 and RuO2, indicating the main role of (Mn−O) bond covalency in the optimization of the bifunctional electrocatalyst activity of manganese oxide. The present study underscores that, like the previous strategy of structural disorder enhancement, the substitution of highly electronegative cation can provide a novel efficient way of improving the electrocatalyst performance of manganese oxide via the bond competition between adjacent (Ru−O) and (Mn−O) bonds.

A superior efficiency of MXene (Ti3C2) nanosheet as a hybridization matrix over graphene is evidenced by comparative investigation on uniformly-stacked MnO2–Ti3C2 and MnO2–reduced graphene oxide (rGO) nanohybrids. Density functional theory calculation and spectroscopic analyses demonstrate a stronger interfacial electronic coupling and greater charge transfer of polar MnO2 with hydrophilic Ti3C2 nanosheet than with hydrophobic rGO one, which maximizes the hybridization effect with the conductive nanosheet. Also, hybridization with Ti3C2 nanosheet is more effective in enhancing the ion diffusivity and porosity of MnO2 than that with strongly self-stacking rGO, which is attributable to weaker self-stacking tendency of Ti3C2. Due to these hybridization effects, the MnO2–Ti3C2 nanohybrid delivers larger specific capacitance with improved rate performance than does the MnO2–rGO nanohybrid, underscoring higher efficiency of MXene hybridization in improving electrode performance. This study clearly demonstrates that exfoliated MXene nanosheet can act as a superior hybridization matrix over rGO to explore strongly-coupled nanohybrids with improved energy-related functionality.

Magic-sized clusters represent materials with unique properties at the border between molecules and solids and provide important insights into the nanocrystal formation process. However, synthesis, doping, and especially structural characterization become more and more challenging with decreasing cluster size. Herein, we report the successful introduction of Co2+ ions into extremely small-sized CdSe clusters with the intention of using internal ligand field transitions to obtain structural insights. Despite the huge mismatch between the radii of Cd2+ and Co2+ ions (>21%), CdSe clusters can be effectively synthesized with a high Co2+ doping concentration of ∼10%. Optical spectroscopy and mass spectrometry suggest that one or two Co2+ ions are substitutionally embedded into (CdSe)13 clusters, which is known as one of the smallest CdSe clusters. Using magnetic circular dichroism spectroscopy on the intrinsic ligand field transitions between the different 3d orbitals of the transition metal dopants, we demonstrate that the Co2+ dopants are embedded on pseudotetrahedral selenium coordinated sites despite the limited number of atoms in the clusters. A significant shortening of Co-Se bond lengths compared to bulk or nanocrystals is observed, which results in the metastability of Co2+ doping. Our results not only extend the doping chemistry of magic-sized semiconductor nanoclusters, but also suggest an effective method to characterize the local structure of these extremely small-sized clusters.

A novel, rational, and efficient way to explore high-performance electrocatalysts was developed by controlling the reaction kinetics of the rate-determining step (RDS). Density functional theory (DFT) calculations demonstrate that the RDS for the oxygen evolution reaction driven by transition metal hydroxides/oxides, i.e., surface adsorption of OH−/OOH• species, can be significantly promoted by increasing the electrophilicity of electrocatalysts via hybridization with electron-withdrawing inorganic nanosheets. As predicted by DFT calculation, the hybridization of Ni–Fe-layered double hydroxide (LDH)/Ni–Co-LDH, with RuO2 nanosheets (1.0 wt%) leads to significant lowering of the overpotentials to 207/276 mV at 10 mA cm−2, i.e., one of the smallest overpotentials for LDH-based materials, with the increase in the current density. The necessity of a very small amount of RuO2 nanosheets (1.0 wt%) to optimize the electrocatalyst activity highlights the remarkably high efficiency of the RuO2 addition. The present study underscores the importance of kinetic control of the RDS via hybridization with electron-withdrawing species for exploring novel efficient electrocatalysts. Platinum and other precious metals currently used in fuel cells may ultimately be replaced by nanostructured catalysts designed with the help of computers. Catalysts are essential for speeding up the oxygen evolution reaction in fuel cells, a normally slow extraction of electrons and protons from water molecules. A team led by Hyungjun Kim from the Korea Advanced Institute of Science and Technology in Daejon and Seong-Ju Hwang from Ewha Womans University in Seoul have now used computer simulations to optimize inexpensive oxygen evolution catalysts made from transition metal hydroxides. Their calculations predicted that these normally multilayered catalysts could split water faster if exfoliated into individual sheets and attached to a ruthenium nanostructure. Fabrication of these materials revealed they had significantly higher active surface areas and improved energy efficiency compared to typical metal hydroxide catalysts. A rational way to explore economically feasible high-performance electrocatalyst for OER is developed by improving the reaction kinetics of rate-determining step via the hybridization with electron-withdrawing RuO2 nanosheet. Even with very low RuO2 content, self-assembled Ni–Fe-/Ni–Co-layered double hydroxide (LDH)–RuO2 nanohybrids show very small overpotentials of 207/276 mV at 10 mA cm−2 for oxygen evolution reaction with greatly improved current densities.