Electrocatalytic energy conversion has been considered as one of the most efficient and promising pathways for realizing energy storage and energy utilization in modern society. To improve electrocatalytic reactions, specific catalysts are needed to lower the overpotential. In the search for efficient alternatives to noble metal catalysts, transition metal nitrides have attracted considerable interest due to their high catalytic activity and unique electronic structure. Over the past few decades, numerous nitride-based catalysts have been explored with respect to their ability to drive various electrocatalytic reactions, such as the hydrogen evolution reaction and the oxygen evolution reaction to achieve water splitting and the oxygen reduction reaction coupled with the methanol oxidation reaction to construct fuel cells or rechargeable Li-O₂ batteries. This Minireview provides a brief overview of recent progress on electrocatalysts based on transition metal nitrides, and outlines the current challenges and future opportunities.

Defect engineering is considered as one of the most efficient strategies to regulate the electronic structure of materials and involves the manipulation of the types, concentrations, and spatial distributions of defects, resulting in unprecedented properties. It is shown that a single-layered MnO₂ nanosheet with vacancies is a robust half-metal, which was confirmed by theoretical calculations, whereas vacancy-free single-layered MnO₂ is a typical semiconductor. The half-metallicity of the single-layered MnO₂ nanosheet can be observed for a wide range of vacancy concentrations and even in the co-presence of Mn and O vacancies. This work enables the development of half-metals by defect engineering of well-established low-dimensional materials, which may be used for the design of next-generation paper-like spintronics.

Electrocatalytic hydrogen evolution has been regarded as a promising strategy to realize efficient hydrogen production to face the energy crisis in the future. Hence, the design of hydrogen-evolving catalysts with high activity and low cost is imperative. In this Minireview article, state-of-the-art electrocatalysts for the hydrogen evolution reaction (HER) are overviewed, and the strategies for constructing ordered and disordered HER electrocatalysts are summarized in detail. By means of facet engineering, nanoscale, polymorph engineering accompanied by interface engineering, HER catalysts with an ordered structure could be optimized. For designing disordered catalysts, defect engineering, amorphization, elemental doping, and surface modification, as well as constructingan alloyed structure, could be effective to realize the beneficial modulation of active sites and electronic structure. This Minireview provides a structural perspective for the design of efficient HER electrocatalysts in the future.

Artificial all-surface-atomic 2D sheets can trigger breakthroughs in tailoring the physical and chemical properties of advanced functional materials. Here, the conceptually new all-surface-atomic semiconductors of SnS and SnSe freestanding sheets are realized using a scalable strategy. As an example, all-surface-atomic SnS sheets undergo surface atomic elongation and structural disordering, which is revealed by X-ray absorption fine structure spectroscopy and first-principles calculations, endowing them with high structural stability and an increased density of states at the valence band edge. These exotic atomic and electronic structures make the all-surface-atomic SnS sheet-based photoelectrode exhibit an incident photon-to-current conversion efficiency of 67.1% at 490 nm, much higher than the efficiencies of other visible-light-driven water splitting. A photocurrent density of 5.27 mA cm^-2, which is two orders of magnitude higher than that of the bulk counterpart, is also achieved for the all-surface-atomic SnS sheets-based photoelectrode. This will allow the manipulation of the basic properties of advanced materials on the atomic scale, thus paving the way for innovative applications.

Organolead halide perovskites have attracted extensive attentions as light harvesting materials for solar cells recently, because of its high charge-carrier mobilities, high photoconversion efficiencies, low energy cost, ease of deposition, and so on. Herein, with CH₃NH₃PbI₃ film deposited on flexible ITO coated substrate, the first organolead halide perovskite based broadband photodetector is demonstrated. The organolead halide perovskite photodetector is sensitive to a broadband wavelength from the ultraviolet light to entire visible light, showing a photo-responsivity of 3.49 A W⁻¹, 0.0367 A W⁻¹, an external quantum efficiency of 1.19×10³%, 5.84% at 365 nm and 780 nm with a voltage bias of 3 V, respectively. Additionally, the as-fabricated photodetector exhibit excellent flexibility and robustness with no obvious variation of photocurrent after bending for several times. The organolead halide perovskite photodetector with high sensitivity, high speed and broad spectrum photoresponse is promising for further practical applications. And this platform creates new opportunities for the development of low-cost, solution-processed and high-efficiency photodetectors.

Infrared (IR) harvesting and detection in red and near-IR (NIR) part of the solar spectrum have always been a long-term research area of intense interest. However, limited choices of current photoactive materials have significantly hampered the realization of ultrahigh IR sensitivity under room temperature conditions. The trigger for this requires the exploration of new photo­active materials and the ability to fabricate new photoactive structural design. Herein, a new oxide-catalogue photoconductive NIR detector with ultrahigh performance built by core/shell nanobeam heterostructures (CSNHs) with the inner single-domain monoclinic VO₂ (M) core and outer V₂O₅ shell, which is the first example of photoconductive IR detector made from transition metal oxides (TMOs), is presented. Benefited from the well-defined TMO hetero­junction interface, the ultrahigh responsivity (R_λ) of 2873.7 A W^-1 and specific detectivity (D*) of 9.23 × 10¹² Jones are achieved at room temperature (at 990 nm; 0.2 mW cm^-2), recording the best performance compared with those reported IR detectors based on heavy-metal-free materials, and even comparable/superior to those traditional ones made from materials including heavy metals. These findings pave a new way to design oxide heterostructures for intriguing applications in optoelectronic and energy harvesting nanodevices.

A promising family of mixed transition-metal oxides (MTMOs) (designated as A_xB_3-xO₄; A, B=Co, Ni, Zn, Mn, Fe, etc.) with stoichiometric or even non-stoichiometric compositions, typically in a spinel structure, has recently attracted increasing research interest worldwide. Benefiting from their remarkable electrochemical properties, these MTMOs will play significant roles for low-cost and environmentally friendly energy storage/conversion technologies. In this Review, we summarize recent research advances in the rational design and efficient synthesis of MTMOs with controlled shapes, sizes, compositions, and micro-/nanostructures, along with their applications as electrode materials for lithium-ion batteries and electrochemical capacitors, and efficient electrocatalysts for the oxygen reduction reaction in metal–air batteries and fuel cells. Some future trends and prospects to further develop advanced MTMOs for next-generation electrochemical energy storage/conversion systems are also presented.

A conceptually new all-solid-state asymmetric supercapacitor based on atomically thin sheets is presented which offers the opportunity to optimize supercapacitor properties on an atomic level. As a prototype, β-Co(OH)₂ single layers with five-atoms layer thickness were synthesized through an oriented-attachment strategy. The increased density-of-states and 100 % exposed hydrogen atoms endow the β-Co(OH)₂ single-layers-based electrode with a large capacitance of 2028 F g⁻¹. The corresponding all-solid-state asymmetric supercapacitor achieves a high cell voltage of 1.8 V and an exceptional energy density of 98.9 Wh kg⁻¹ at an ultrahigh power density of 17 981 W kg⁻¹. Also, this integrated nanodevice exhibits excellent cyclability with 93.2 % capacitance retention after 10 000 cycles, holding great promise for constructing high-energy storage nanodevices.

Seit kurzem findet eine Familie gemischter Übergangsmetalloxide (mixed transition-metal oxides, MTMOs; beschrieben durch A_xB_3−xO₄; A, B=Co, Ni, Zn, Mn, Fe usw.) mit stöchiometrischen oder gar nichtstöchiometrischen Zusammensetzungen (typischerweise in Spinellstruktur) weltweit Interesse. Diese MTMOs dürften dank ihrer ausgezeichneten elektrochemischen Eigenschaften große Bedeutung für kostengünstige und umweltfreundliche Technologien zur Energiespeicherung/-umwandlung erlangen. In diesem Aufsatz fassen wir die jüngsten Fortschritte beim rationalen Design von MTMOs mit steuerbaren Formen, Größen, Zusammensetzungen und Mikro-/Nanostrukturen sowie ihren Anwendungsmöglichkeiten zusammen, z. B. als Elektrodenmaterialien für Lithium-Ionen-Batterien und elektrochemische Kondensatoren oder als effiziente Elektrokatalysatoren bei der Sauerstoffreduktionsreaktion in Sauerstoff/Luft-Batterien und Brennstoffzellen. Zum Schluss diskutieren wir die weitere mögliche Entwicklung von MTMOs für die nächste Technologiegeneration der elektrochemischen Energiespeicherung/-umwandlung.

Hierarchical LiV₃O₈ nanofibers, assembled from nanosheets that have exposed {100} facets, have been fabricated by using electrospinning combined with calcination. The formation mechanism of hierarchical nanofibers was investigated by X-ray diffraction and scanning electron microscopy. Poly(vinyl alcohol) (PVA) played a dual role in the formation of the nanofibers: besides acting as the template for forming the fibers, it effectively prevented the aggregation of LiV₃O₈ nanoparticles, thereby allowing them to grow into small nanosheets with exposed {100} facets owing to the self-limitation property of LiV₃O₈. This nanostructure is beneficial for the insertion/extraction of lithium ions. Meanwhile, the {100} facets have fewer and smaller channels, which may effectively alleviate proton co-intercalation into the electrode materials. Hence, the hierarchical LiV₃O₈ nanofibers exhibit higher discharge capacities and better cycling stabilities as the anode electrode material for aqueous lithium-ion batteries than those reported previously. We demonstrate that these hierarchical nanofibers have promising potential applications in aqueous lithium-ion batteries.

Despite the promising applications of copper selenide nanoparticles, an in-depth elucidation of the inherent properties of tetragonal Cu₂Se (β-Cu₂Se) has not been performed because of the lack of a facile synthesis on the nanoscale and an energy-intensive strategy is usually employed. In this work, a facile wet-chemical strategy, employing HCOOH as reducing agent, has been developed to access single-crystalline metastable β-Cu₂Se hyperbranched architectures for the first time. The process avoids hazardous chemistry and high temperatures, and thus opens up a facile approach to the large-scale low-cost preparation of metastable β-Cu₂Se hyperbranched architectures. A possible growth mechanism to explain the formation of the β-Cu₂Se dendritic morphology has been proposed based on time-dependent shape evolution. Further investigations revealed that the metastable β-Cu₂Se can convert into the thermodynamically more stable cubic α-Cu_2−xSe maintaining the dendritic morphology. An increase in electrical conductivity and a tunable optical response were observed under ambient conditions. This behavior can be explained by the oxidation of the surface of the β-Cu₂Se hyperbranched structures, ultimately leading to solid-state phase conversion from β-Cu₂Se into superionic conductor α-Cu_1.8Se, which has potential applications in energy-related devices and sensors.

We found a linear relationship between the metal–insulator transition (MIT) temperature and the A⁺ ionic radius of the beta-A_0.33V₂O₅ bronze family, leading our attention to beta-K_0.33V₂O₅ which has been neglected for a long time. We have introduced a facile hydrothermal method to obtain the single-crystalline beta-K_0.33V₂O₅ nanorods. As expected, both the temperature-dependence of the resistivity and magnetization demonstrated MITs at about 72 K for beta-K_0.33V₂O₅, thus matching well with the linear relationship described above. The beta-K_0.33V₂O₅ was assigned as a new member of the beta-A_0.33V₂O₅ bronze family for their similar crystal and electronic structures and their MIT property; this addition enriches the beta-A_0.33V₂O₅ bronze family.

A new and universal synthetic strategy to hybridize metal oxides and conduct polymer nanocomposites has been proposed in this work. The simultaneous reaction process, which includes the generation of metal oxide layers, the oxidation polymerization of monomers, and the in situ formation of polymer–metal oxides sandwich structure is successfully realized and results in the unique hybrid polyaniline (PANI)-intercalated molybdenum oxide nanocomposites. The peroxomolybdate proved to play a dual role as the precursor of the inorganic hosts and the oxidizing agent for polymerization. The as-obtained hybrid nanocomposites present a flexible lamellar structure by oriented assembly of conductive PANI chains in the MoO₃ interlayer, and thus inherit excellent electrical performance and possess the potential of active electrode materials for electrochemical energy storage. Such uniform lamellar structure together with the anticipated high conductivity of the hybrid PANI/MoO₃ nanocomposites afford high specific capacitance and good stability during the charge–discharge cycling for supercapacitor application.

New-phased metastable V₂O₃ porous urchinlike micronanostructures were first fabricated on a large scale by a simple top-down strategy of pyrolyzing a vanadyl ethylene glycolated precursor in the absence of any templates or matrices. The pyrolysis mechanism was clearly revealed by synchrotron vacuum ultraviolet (VUV) photoionization mass spectra for the first time. The new-phased metastable V₂O₃ exhibits a body-centered cubic bixbyite structure and shows structural evolution from metastable cubic symmetry to thermodynamically stable rhombohedral symmetry V₂O₃ (R) above 510 °C. Furthermore, the prepared V₂O₃ porous urchinlike micronanostructures, as anode materials in aqueous lithium ion batteries, exhibit improved electrochemical properties with relatively high first discharge capacity and better cycle retention relative to thermodynamically stable V₂O₃ (R), which is derived from its unique microscopic crystal structure and macroscopic 3D framework with rigid morphology, porous structure, and high specific surface area.

Control over the different polymorphs of vanadium oxide that possess electrical switching properties is advancing rapidly as a result of the need to address energy-efficiency issues; an example of which is the intelligent regulation of infrared light demonstrated by these polymorphs. Recent advances in the development of new vanadium oxide structures as well as their promising electrical switching properties are summarized here. Theoretical analysis and experimental results suggest that the presence of infinite vanadium ion chains in the crystal structure plays a decisive role in determining the electrical properties of vanadium oxides. The successful synthesis of new vanadium oxide materials and their nanostructures not only promotes a mechanistic understanding of the temperature-driven electrical switching properties but also provides the right materials for constructing smart devices that can selectively filter out infrared light.

Magnetic nanoring structures are attractive for spintronic devices due to their unique attributes of well-defined and reproducible magnetic states originating from their characteristic geometry. Almost all previous magnetic nanorings have been exclusively limited to traditional ferromagnetic materials, and a magnetic semiconductor (MSC) nanoring structure has been reported rarely during the past decades. Here, it is demonstrated that room-temperature ferromagnetic Ag_1.2V₃O₈ nanobelts and nanorings may be achieved by controlled oxidation of the V⁴⁺ precursors in an Ag⁺-containing aqueous solution. The polarization-induced self-coiling of in situ formed Ag_1.2V₃O₈ nanobelts is responsible for the formation of the perfectly circular nanoring geometry. The NEXAFS spectra and the density functional calculations clearly reveal that the electron transfer originates from the hybridization of the doped Ag⁺ and V⁴⁺ atoms, causing ordering of the magnetic moments that give rise to the intrinsic ferromagnetism of the Ag_1.2V₃O₈ structure.

Vertically aligned BiVO₄ nanowall films on indium tin oxide (ITO) glass have been fabricated through a template-free hydrothermal method for the first time. Based on the structural understanding of both BiVO₄ and ITO, the lattice matches ({020}_BiVO4 and {040}_ITO, {200}_BiVO4 and {004}_ITO, respectively) and the similarity of metal atomic arrangement parallel to {001} planes turn out to be crucial for the fabrication of the nanowalls. Consequently, the growth of a BiVO₄ film begins from heteroepitaxy and undergoes an Ostwald ripening process to form an extended network, resulting in a c-orientation and exposing {010} facets. Through this process, it is much easier to obtain a range of nanowall films with different packing densities, as the surface state of ITO glass is alterable by adjusting the concentration of acid. The films can be directly used as an electrode, which exhibits an excellent response to visible light, especially light with low intensity, allowing for the electrical interconnection, highly active surface, appropriate orientation, and a good contact with the substrate. There are great benefits in improving the technique for detecting the weak light source signals.

Although about 200,000 metric tons of γ-MnO₂ are used annually worldwide for industrial applications, the γ-MnO₂ structure is still known to possess a highly ambiguous crystal lattice. To better understand the γ-MnO₂ atomic structure, hexagon-based nanoarchitectures were successfully synthesized and used to elucidate its internal structure for the present work. The structural analysis results, obtained from the hexagon-based nanoarchitectures, clearly show the coexistence of akhtenskite (ε-MnO₂), pyrolusite (β-MnO₂), and ramsdellite in the so-called γ-MnO₂ phase and verified the heterogeneous phase assembly of the γ-MnO₂ state, which violates the well-known “De Wolff” model and derivative models, but partially accords with Heuer's results. Furthermore, heterogeneous γ-MnO₂ assembly was found to be a metastable structure under hydrothermal conditions, and the individual components of the heterogeneous γ-MnO₂ system have structural similarities and a high lattice matches with pyrolusite (β-MnO₂). The as-obtained γ-MnO₂ nanoarchitectures are nontoxic and environmentally friendly, and the application of such nanoarchitectures as support matrices successfully mitigates the common problems for phase-change materials of inorganic salts, such as phase separation and supercooling-effects, thereby showing prospect in energy-saving applications in future “smart-house” systems.

Hyperbranched monoclinic BiVO₄ (h-BiVO₄) has been synthesized on a large scale and with good uniformity by a surfactant-free hydrothermal route. h-BiVO₄ consists of four trunks with branches distributed on opposite sides. From observation of the intermediates at an early stage of the reaction process, it can be seen that during formation h-BiVO₄ has different growth rates along the a, b, and c axes. Based on crystal structure analysis and experimental results, h-BiVO₄ shows preferential growth along the [100] direction, and subsequently, along the [010] and [001] directions. As-synthesized h-BiVO₄ exhibits excellent photocatalytic ability in the photodegradation reaction of an aqueous solution of RB under visible light. Electrochemical measurements predict that h-BiVO₄ possesses high sensitivity to formaldehyde and ethanol gases, favorable discharge capacity, and capacity retention, which indicate potential applications in the fields of sensing devices and lithium-ion batteries.

Novel double-shelled hierarchical ferrihydrite hollow spheres (Fe₁₀O₁₄(OH)₂⋅4 H₂O) were successfully synthesized on a large scale by using a facile medicine-inspired solution-phase approach. Sodium nitroprusside (SNP), an ordinary and inexpensive medicine for expanding blood vessels, served as both a ferric source and an in situ formed gas-bubble template with the presence of sodium dihydrogen phosphate as a pH regulator, coordinator, and stabilizer. A twice-gas-bubble template model has been proposed for the formation of the double-shelled hollow spheres to take advantage of the dissociation and hydrolyzation of the two kinds of ligands in the SNP precursor. The size of the double-shelled ferrihydrite hollow spheres can be tuned by varying the experimental parameters. As-obtained ferrihydrite is highly sensitive to ethanol gas, which indicates potential applications in the field of sensing devices.