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Graphene/metal oxide (rGO/MOx) heterostructures hold great promise for energy storage, yet a full understanding of their synthesis remains elusive. Herein, a general, efficient, and scalable synthesis strategy is designed for the preparation of various rGO/MOx heterostructure materials featuring robust interfacial interactions. The heterogeneous nucleation growth mechanism of metal oxides on graphene is elucidated through ex situ characterization and theoretical simulation. The surface of graphene oxide (GO) is enriched with reactive oxygen‐containing functional groups, serving as potent nucleation sites that facilitate the rapid and heterogeneous nucleation of MOx grains. Simultaneously, a stable interface (C−O−M bond) is in situ formed between graphene and adsorbed metal ions during heat treatment, producing rGO/MOx heterostructure materials. Notably, the resultant rGO/CoO heterostructure material is employed as an anode and LiCoO2 as a cathode to assemble a soft packaging quasi‐solid‐state battery, which has demonstrated an impressive energy density of 341.4 Wh kg−1 and maintains outstanding capacity retention at 93.4% after 300 cycles at a 1C current. These findings provide valuable insights into the preparation and potential applications of rGO/MOx heterostructure materials for energy storage. [ABSTRACT FROM AUTHOR]

Organic–inorganic halide perovskites are widely investigated for various optoelectronics devices such as photodetectors and solar cells. However, Pb‐based perovskite photodetectors perform poorly because of insufficient mobility and absence of an effective photoconductive gain mechanism. Herein, ZnON/perovskite heterostructures are demonstrated to realize the fabrication of high‐performance hybrid phototransistors. Additionally, a guanidinium iodide (GuI), alternating‐cation‐interlayer (ACI)‐type organic spacers, are utilized as an interface passivation layer. It is shown that the GuI interface layer reduces the defect density of the ZnON surface as well as the bulk perovskite film and promotes the separation and transport of photo‐generated charge carriers. Devices fabricated with the GuI interface passivation layer have a response speed of 0.1 s, excellent responsivity of 5.97 × 106 A W−1, and ultra‐high specific detectivity of 1.28 × 1018 Jones, the highest value among previously reported perovskite‐based hybrid phototransistors. This work provides valuable insights into the design and fabrication of high‐performance metal oxide/perovskite heterostructures with promising applications in future optoelectronic devices. [ABSTRACT FROM AUTHOR]

The Tauc plot is a method originally developed to derive the optical gap of amorphous semiconductors such as amorphous germanium or silicon. By measuring the absorption coefficient α(hν) and plotting (αhv)12$(\alpha {hv})^{\frac{1}{2}}$ versus photon energy hν, a value for the optical gap (Tauc gap) is determined. In this way non‐direct optical transitions between approximately parabolic bands can be examined. In the last decades, a modification of this method for (poly‐) crystalline semiconductors has become popular to study direct and indirect interband transitions. For this purpose, (ahν)n (n = 12$\frac{1}{2}$, 2) is plotted against hν to determine a value of the electronic bandgap. Due to the ease of performing UV–vis measurements, this method has nowadays become a standard to analyze various (poly‐) crystalline solids, regardless of their different electronic structure. Although this leads partially to widely varying values of the respective bandgap of nominally identical materials, there is still no study that critically questions which peculiarities in the electronic structure prevent a use of the Tauc plot for (poly‐) crystalline solids and to which material classes this applies. This study aims to close this gap by discussing the Tauc plot and its limiting factors for exemplary (poly‐) crystalline solids with different electronic structures. [ABSTRACT FROM AUTHOR]

Flexible electronics have seen extensive research over the past years due to their potential stretchability and adaptability to non‐flat surfaces. They are key to realizing low‐power sensors and circuits for wearable electronics and Internet of Things (IoT) applications. Semiconducting metal‐oxides are a prime candidate for implementing flexible electronics as their conformal deposition methods lend themselves to the idiosyncrasies of non‐rigid substrates. They are also a major component for the development of resistive memories (memristors) and as such their monolithic integration with thin film electronics has the potential to lead to novel all‐metal‐oxide devices combining memory and computing on a single node. This review focuses on exploring the recent advances across all these fronts starting from types of suitable substrates and their mechanical properties, different types of fabrication methods for thin film transistors and memristors applicable to flexible substrates (vacuum‐ or solution‐based), applications and comparison with rigid substrates while additionally delving into matters associated with their monolithic integration. [ABSTRACT FROM AUTHOR]

Selectivity for specific analytes and high‐temperature operation are key challenges for chemiresistive‐type gas sensors. Complementary hybrid materials, such as reduced graphene oxide (rGO) decorated with metal oxides enables realization of room‐temperature sensors with enhanced sensitivity. However, sensor training to identify target gases and accurate concentration measurement from gas mixtures still remain very challenging. This work proposes hybridization of rGO with CuCoOx binary metal oxide as a sensing material. Highly stable, room‐temperature NO2 sensors with a 50 ppb of detection limit is demonstrated using inkjet printing. A framework is then developed for machine‐intelligent recognition with good visibility to identify specific gases and predict concentration under an interfering atmosphere from a single sensor. Using ten unique parameters extracted from the sensor response, the machine learning‐based classifier provides a decision boundary with 98.1% accuracy, and is able to correctly predict previously unseen NO2 and humidity concentrations in an interfering environment. This approach enables implementation of an intelligent platform for printable, room‐temperature gas sensors in a mixed environment irrespective of ambient humidity. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) have become a promising candidate in a myriad of applications, such as light‐emitting diodes, solar cells, lasing, photodetectors, photocatalysis, transistors, etc. This is related to the synergy of their excellent features, including high photoluminescence quantum yields, narrow and tunable emission, long charge carrier lifetimes, broad absorption spectrum along with high extinction absorptions coefficients, among others. However, the main bottleneck is the poor stability of the MHPs under ambient conditions. This is imposing severe restrictions with respect to their industrialized applications and commercialization. In this context, metal oxide (MOx) coatings have recently emerged as an efficient strategy toward overcoming the stabilities issues as well as retaining the excellent properties of the MHPs, and therefore facilitate the development of the related devices' stabilities and performances. This review provides a summary of the recent progress on synthetic methods, enhanced features, the techniques to assess the MHPs@MOx composites, and applications of the MHPs@MOx. Specially, novel approaches to fabricate the composites and new applications of the composites are also reported in this review for the first time. This is rounded by a critical outlook about the current MHPs' stability issues and the further direction to ensure a bright future of MHPs@MOx. [ABSTRACT FROM AUTHOR]

Designing carbon nanotubes (CNTs)‐based materials are attracting great attention due to their fantastic properties and greater performance. Herein, a new CNTs network triggered by metal catalysts (e.g., Co, Ni, or Cu) is constructed on metal oxide (e.g., MnO) microparticles, giving rise to a high‐performance Co‐MnO@C‐CNTs anode in lithium‐ion batteries (LIBs). An extremely high capacity of 1050 mAh g−1, extraordinary rate capacities over 10 A g−1, and a long lifespan over 500 cycles are demonstrated. The great features of Co‐MnO@C‐CNTs anode are further confirmed in LIBs when the nickel‐rich cathode (e.g., LiNi0.8Co0.1Mn0.1O2) is used and charged at a high voltage over 4.5 V. A high‐capacity retention of 71.5% can be maintained at 1 C over 150 cycles. The superior performance relates to the CNTs network, which not only acts as an "expressway network" for fast ion/electron transportation but also buffers structural variation. Moreover, the metal nanoparticles can also enhance the electrical conductivity and catalyze the (de‐)lithiation of metal oxide, resulting in higher reversibility and long‐term cyclability. This study opens a new avenue to prepare CNTs‐based functional materials and also explores the potential applications of metal oxide‐based anode for high‐performance batteries. [ABSTRACT FROM AUTHOR]

Solar‐driven photo‐to‐chemical conversion is an interesting approach for energy harvesting and storage with high sustainability. To achieve high photo‐to‐chemical conversion efficiency, it is important to develop cost‐effective and stable catalysts with high activity. Metal oxides provide an interesting platform for the development of efficient catalysts owing to their abundance, high stability, and tunable band edges. Their performance highly depends on the rational design of heterostructures with engineered electronic structures, modified charge migration behavior, tailored interfacial properties, and amplified electromagnetic fields. All these enable the achievement of efficient light harvesting, promoted charge separation and transport, and accelerated surface reactions. Herein, a recent study on rationally designed metal oxide heterostructures for enhancing photo‐to‐chemical energy conversion via photocatalytic and photoelectrochemical systems is reviewed. The approaches to enhance their conversion efficiency are as follows: 1) surface modification via loading of plasmonic metals and other photosensitizers; 2) surface regulation, including morphology, defect, and dopants; 3) interfacial assembly with metal oxides, other metal compounds, and metal‐free materials. Moreover, the underlying reaction mechanisms of metal oxide‐based heterostructures and how they affect the energy conversion efficiency are discussed. Finally, the challenges and perspectives on the development of metal oxide‐based heterostructures and associated photo‐to‐chemical devices are presented. [ABSTRACT FROM AUTHOR]

Significant advances are realized in perovskite‐converted hybrid light‐emitting diodes (pc‐HLEDs). However, long‐living devices at high efficiencies still represent a major milestone with average stabilities of <200 h at ≈50 lm W−1 under low applied currents (<15 mA). Herein, a dual metal oxide‐coated CsPbBr3@SiO2/ZrO2 composite is prepared in a one‐pot synthesis through the kinetic control of the sol–gel reaction, followed by a gentle drying process in air. These hybrid nanoparticles show photoluminescence quantum yields of ≈65% that are stable under temperature, ambient, and irradiation stress scenarios. This is translated to pc‐HLEDs with a near‐unity conversion efficiency at any applied current, high efficiencies around 75 lm W−1, and one of the most remarkable stabilities of ≈200 and 700 h at 100 and 10 mA, respectively. In addition, the device degradation mechanism is thoughtfully rationalized comparing devices operating under ambient/inert conditions. As such, this work provides three milestones: i) a new room temperature one‐pot protocol to realize the first SiO2/ZrO2 metal oxide coating that effectively protects the emitting perovskite nanoparticle core, ii) one of the most stable and efficient pc‐HLEDs operating under ambient condition at any applied current, and iii) new insights for the degradation of pc‐HLEDs. [ABSTRACT FROM AUTHOR]

Exfoliating graphite to graphene has attracted great attention due to the fantastic properties of graphene available for designing graphene‐based materials or devices. Besides the classic solution method, herein a unique role of TiO2 in exfoliating graphite to be graphene layers effectively is reported. As a paradigm, this discovered effect of TiO2 is significant for preparing high‐performance graphene‐modified SiOx‐based anode in lithium‐ion batteries (LIBs), in which the graphite is in situ exfoliated mechanically by TiO2 to be multilayered graphene (i.e., MLG) and then the SiOx is wrapped by the MLG to construct a SiOx/TiO2@MLG. In this case, an extremely high capacity of 1484 mAh g−1, long lifespan over 1200 cycles at 2 A g−1, as well as good performance in full LIBs (vs nickel‐rich cathode) are demonstrated. It is confirmed that the MLG can enhance electric conductivity, mitigate electrolyte decomposition, and alleviate volume effect of the SiOx effectively. This result is hard to be achieved using other kinds of metal oxide besides TiO2. It is hoped that the SiOx/TiO2@MLG is practical for pursuing LIBs with an energy density beyond 300 Wh kg−1. In addition, it is believed the ingenious strategy is applicable for designing more functional materials with greater capabilities. [ABSTRACT FROM AUTHOR]

2D nanoscale oxides have attracted a large amount of research interest due to their unique properties. Here, a facile synthetic approach to prepare graphene-mimicking, porous 2D Co3O4 nanofoils using graphene oxide (GO) as a sacrificial template is reported. The thermal instability of graphene, as well as the catalytic ability of Co3O4 particles to degrade carbon backbones, allow the fabrication of porous 2D Co3O4 nanofoils without the loss of the 2D nature of GO. Based on these results, a graphene mimicking as a route for large-area 2D transition metal oxides for applications in electrochemical energy storage devices is proposed. As a proof of concept, it is demonstrated that graphene-like, porous 2D Co3O4 nanofoils exhibit a high reversible capacity (1279.2 mAh g−1), even after 50 cycles. This capacity is far beyond the theoretical capacity of Co3O4 based on the conversion mechanism from Co3O4 to Li2O and metallic Co. [ABSTRACT FROM AUTHOR]

The polysulfide shuttle reaction has severely limited practical applications of Li-S batteries. Recently, functional materials that can chemically adsorb polysulfide show significant enhancement in cycling stability and Coulombic efficiency. However, the mechanism of the chemisorption and the control factors governing the chemisorption are still not fully understood. Here, it is demonstrated for the first time that the surface acidity of the host material plays a crucial role in the chemisorption of polysulfide. By tailoring the surface acidity of TiO2 via heteroatom doping, the polysulfide-TiO2 interaction can be fortified and thus significantly the capacity fading be reduced to 0.04% per cycle. The discovery presented here sheds light on the mechanism of this interfacial phenomenon, and opens a new avenue that can lead to a practical sulfur/host composite cathode. [ABSTRACT FROM AUTHOR]

Perovskite solar cells have achieved the highest power conversion efficiencies on metal oxide n‐type layers, including SnO2 and TiO2. Despite ZnO having superior optoelectronic properties to these metal oxides, such as improved transmittance, higher conductivity, and closer conduction band alignment to methylammonium (MA)PbI3, ZnO is largely overlooked due to a chemical instability when in contact with metal halide perovskites, which leads to rapid decomposition of the perovskite. While surface passivation techniques have somewhat mitigated this instability, investigations as to whether all metal halide perovskites exhibit this instability with ZnO are yet to be undertaken. Experimental methods to elucidate the degradation mechanisms at ZnO–MAPbI3 interfaces are developed. By substituting MA with formamidinium (FA) and cesium (Cs), the stability of the perovskite–ZnO interface is greatly enhanced and it is found that stability compares favorably with SnO2‐based devices after high‐intensity UV irradiation and 85 °C thermal stressing. For devices comprising FA‐ and Cs‐based metal halide perovskite absorber layers on ZnO, a 21.1% scanned power conversion efficiency and 18% steady‐state power output are achieved. This work demonstrates that ZnO appears to be as feasible an n‐type charge extraction layer as SnO2, with many foreseeable advantages, provided that MA cations are avoided. [ABSTRACT FROM AUTHOR]

In article number 1806144, Jing Wei and co‐workers demonstrate a general self‐templating strategy for the synthesis of mesoporous metal oxide spheres with tunable compositions and metal‐mediated inner architectures via thermal decomposition of metal‐phenolic coordination polymers. Such materials can be used as a sensing platform for detection of volatile organic compounds and nucleic acids with high sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

The development of a general strategy to synthesize mesoporous metal oxide spheres (MMOSs) with tailorable compositions and architectures is desirable and challenging. Herein, a general self‐template strategy is demonstrated for the synthesis of MMOSs with tunable compositions (i.e., ZnO, Al2O3, Co3O4, Fe2O3, CuO) and metal‐mediated inner architectures via thermal decomposition of metal‐phenolic coordination polymers (MPCPs). The metal species in MPCPs can obviously influence the decomposition temperature of the polymer networks (Td). The inner architectures of MMOSs are determined by Td and the crystallization temperature of metal oxides (Tc). The MMOSs show solid inner architectures when Td > Tc or Td < Tc and hollow structure when Td ≈ Tc. Encouraged by their high surface area and accessible mesopores, gas sensors based on MMOSs (i.e., ZnO) are fabricated, which shows a low working temperature (250 °C) for detection of ethanol gas. The MMOSs (i.e., Co3O4) can further be used to fabricate sensing platform for detecting DNA analogue of miRNA‐21 (a biomarker abnormally expressed in most of solid tumors). Such MMOSs show high sensitivity (0.19 × 10−9m) and can even efficiently distinguish the target DNA from single‐, double‐ and triple‐base mismatched DNA. Mesoporous metal oxide spheres (MMOSs) with various compositions (ZnO, Al2O3, Co3O4, Fe2O3, CuO) and metal‐mediated inner architectures are synthesized via a general self‐template strategy using metal‐phenolic coordination polymers as a precursor. Such MMOSs can be used as a sensing platform for detection of volatile organic compounds (i.e., ethanol) and nucleic acids with high sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

In article number 1802717, Choongik Kim, Myung‐Gil Kim, and co‐workers describe rad‐hard solution‐processed metal‐oxide semiconductors by investigating the effect of high‐energy proton irradiation. Although the oxygen vacancy generation from proton irradiation typically results in device performance degradation, a structurally flexible a‐ZTO based device with an organic passivation layer exhibits stable electrical performance for irradiation up to 1015 cm−2 doses. [ABSTRACT FROM AUTHOR]

The effect of 5 MeV high‐energy proton irradiation on solution‐processed metal‐oxide thin‐film transistors (TFTs) is investigated. The electrical characteristics of the devices are measured before and after proton irradiation with radiation doses of 1013, 1014, and 1015 cm−2. TFTs based on zinc oxide (ZnO) and amorphous indium gallium zinc oxide (a‐IGZO) exhibit a significant negative shift in their threshold voltage values (ΔVth ≤ −30 V) or transitioned to the conductor state as the proton radiation dose increased. For a‐ZnO and IGZO, this change in the electrical characteristics originates from the formation of proton‐irradiation‐induced oxygen vacancies in the metal‐oxide semiconductor layer. On the other hand, amorphous zinc tin oxide devices with an optimized composition exhibit relatively stable electrical characteristics when subjected to proton irradiation. Furthermore, the back‐channel passivation of oxide‐semiconductor TFTs with an n‐type organic semiconductor layer significantly improves the device stability under proton irradiation. This study demonstrates that solution‐processed metal‐oxide semiconductors have significant potential as rad‐hard large area electronic devices for nuclear and aerospace applications. The effect of 5 MeV high‐energy proton irradiation on three types of solution‐processed metal‐oxide thin‐film transistors is investigated. The change in electrical characteristics originates from the formation of proton‐irradiation‐induced oxygen vacancies in the metal‐oxide semiconductor layer, where amorphous zinc tin oxide exhibits minimal negative shift in their threshold voltage values. This study demonstrates rad‐hardness potential for solution‐processed metal‐oxide semiconductors. [ABSTRACT FROM AUTHOR]

Carbon nanotubes and titania, highly corrosion‐resistant materials, are successfully assembled into high surface area microparticles (162 m2 g−1) in one step using low‐power ultrasound. The composite microparticles are electrically conductive (>0.4 S cm−1). The microparticles are deposited as an electrical layer (<2.5 µm) on a stainless‐steel mesh gas diffusion layer using a tribochemical coating technique. Long‐term durability testing in 0.5 m H2SO4 at 80 °C confirms the corrosion resistance of the catalyst coating. This coating method may have wider applicability for other electrical and electrochemical devices that require thin corrosion‐resistant coatings. A thin catalyst layer is deposited on a stainless‐steel mesh gas diffusion layer via a tribochemical coating technique using composite titanium dioxide and carbon nanotube microparticles as a precursor. The resulting coating is catalytically active and highly corrosion resistant. This coating technique may have further applicability for other electrical applications. [ABSTRACT FROM AUTHOR]