Cobalt Phosphides Nanocrystals Encapsulated by P‐Doped Carbon and Married with P‐Doped Graphene for Overall Water Splitting

As one class of important functional materials, transition metal phosphides (TMPs) nanostructures show promising applications in catalysis and energy storage fields. Although great progress has been achieved, phase‐controlled synthesis of cobalt phosphides nanocrystals or related nanohybrids remains a challenge, and their use in overall water splitting (OWS) is not systematically studied. Herein, three kinds of cobalt phosphides nanocrystals encapsulated by P‐doped carbon (PC) and married with P‐doped graphene (PG) nanohybrids, including CoP@PC/PG, CoP‐Co₂P@PC/PG, and Co₂P@PC/PG, are obtained through controllable thermal conversion of presynthesized supramolecular gels that contain cobalt salt, phytic acid, and graphene oxides at proper temperature under Ar/H₂ atmosphere. Among them, the mixed‐phase CoP‐Co₂P@PC/PG nanohybrids manifest high electrocatalytic activity toward both hydrogen and oxygen evolution in alkaline media. Remarkably, using them as bifunctional catalysts, the fabricated CoP‐Co₂P@PC/PG || CoP‐Co₂P@PC/PG electrolyzer only needs a cell voltage of 1.567 V for driving OWS to reach the current density at 10 mA cm^?2, superior to their pure‐phase counterparts and recently reported bifunctional catalysts based devices. Also, such a CoP‐Co₂P@PC/PG || CoP‐Co₂P@PC/PG device exhibits outstanding stability for OWS. This work may shed some light on optimizing TMPs nanostructures based on phase engineering, and promote their applications in OWS or other renewable energy options.     

Origin of Fracture‐Resistance to Large Volume Change in Cu‐Substituted Co3O4 Electrodes

The electrode materials conducive to conversion reactions undergo large volume change in cycles which restrict their further development. It has been demonstrated that incorporation of a third element into metal oxides can improve the cycling stability while the mechanism remains unknown. Here, an in situ and ex situ electron microscopy investigation of structural evolutions of Cu‐substituted Co₃O₄ supplemented by first‐principles calculations is reported to reveal the mechanism. An interconnected framework of ultrathin metallic copper formed provides a high conductivity backbone and cohesive support to accommodate the volume change and has a cube‐on‐cube orientation relationship with Li₂O. In charge, a portion of Cu metal is oxidized to CuO, which maintains a cube‐on‐cube orientation relationship with Cu. The Co metal and oxides remain as nanoclusters (less than 5 nm) thus active in subsequent cycles. This adaptive architecture accommodates the formation of Li₂O in the discharge cycle and underpins the catalytic activity of Li₂O decomposition in the charge cycle.     

Defect Engineering of Chalcogen‐Tailored Oxygen Electrocatalysts for Rechargeable Quasi‐Solid‐State Zinc–Air Batteries

A critical bottleneck limiting the performance of rechargeable zinc–air batteries lies in the inefficient bifunctional electrocatalysts for the oxygen reduction and evolution reactions at the air electrodes. Hybridizing transition‐metal oxides with functional graphene materials has shown great advantages due to their catalytic synergism. However, both the mediocre catalytic activity of metal oxides and the restricted 2D mass/charge transfer of graphene render these hybrid catalysts inefficient. Here, an effective strategy combining anion substitution, defect engineering, and the dopant effect to address the above two critical issues is shown. This strategy is demonstrated on a hybrid catalyst consisting of sulfur‐deficient cobalt oxysulfide single crystals and nitrogen‐doped graphene nanomeshes (CoO_0.87S_0.13/GN). The defect chemistries of both oxygen‐vacancy‐rich, nonstoichiometric cobalt oxysulfides and edge‐nitrogen‐rich graphene nanomeshes lead to a remarkable improvement in electrocatalytic performance, where CoO_0.87S_0.13/GN exhibits strongly comparable catalytic activity to and much better stability than the best‐known benchmark noble‐metal catalysts. In application to quasi‐solid‐state zinc–air batteries, CoO_0.87S_0.13/GN as a freestanding catalyst assembly benefits from both structural integrity and enhanced charge transfer to achieve efficient and very stable cycling operation over 300 cycles with a low discharge–charge voltage gap of 0.77 V at 20 mA cm^?2 under ambient conditions.     

Rapid and Low‐Temperature Salt‐Templated Production of 2D Metal Oxide/Oxychloride/Hydroxide

2D materials have played an important role in electronics, sensors, optics, electrocatalysis, and energy storage. Many methods for the preparation of 2D materials have been explored. It is crucial to develop a high‐yield, rapid, and low‐temperature method to synthesize 2D materials. A general, fast (5 min), and low‐temperature (≈100 °C) salt (CoCl₂·6H₂O)‐templated method is proposed to prepare series of 2D metal oxides/oxychlorides/hydroxides in large scale, such as MoO₃, SnO₂, SiO₂, BiOCl, Sb₄O₅Cl₂, Zn₂Co₃(OH)₁₀ 2H₂O, and ZnCo₂O₄. The as‐synthesized 2D materials possess an ultrathin feature (2–7 nm) and large aspect ratios. Additionally, these 2D metal oxides/oxychlorides/hydroxides exhibit good electrochemical properties in energy storage (lithium/sodium‐ion batteries) and electrocatalysis (hydrogen/oxygen evolution reaction).     

Self‐Assembled Ruddlesden–Popper/Perovskite Hybrid with Lattice‐Oxygen Activation as a Superior Oxygen Evolution Electrocatalyst

The oxygen evolution reaction (OER) is pivotal in multiple gas‐involved energy conversion technologies, such as water splitting, rechargeable metal–air batteries, and CO₂/N₂ electrolysis. Emerging anion‐redox chemistry provides exciting opportunities for boosting catalytic activity, and thus mastering lattice‐oxygen activation of metal oxides and identifying the origins are crucial for the development of advanced catalysts. Here, a strategy to activate surface lattice‐oxygen sites for OER catalysis via constructing a Ruddlesden–Popper/perovskite hybrid, which is prepared by a facile one‐pot self‐assembly method, is developed. As a proof‐of‐concept, the unique hybrid catalyst (RP/P‐LSCF) consists of a dominated Ruddlesden–Popper phase LaSr₃Co_1.5Fe_1.5O_10‐δ (RP‐LSCF) and second perovskite phase La_0.25Sr_0.75Co_0.5Fe_0.5O_3‐δ (P‐LSCF), displaying exceptional OER activity. The RP/P‐LSCF achieves 10 mA cm^?2 at a low overpotential of only 324 mV in 0.1 m KOH, surpassing the benchmark RuO₂ and various state‐of‐the‐art metal oxides ever reported for OER, while showing significantly higher activity and stability than single RP‐LSCF oxide. The high catalytic performance for RP/P‐LSCF is attributed to the strong metal–oxygen covalency and high oxygen‐ion diffusion rate resulting from the phase mixture, which likely triggers the surface lattice‐oxygen activation to participate in OER. The success of Ruddlesden–Popper/perovskite hybrid construction creates a new direction to design advanced catalysts for various energy applications.     

Electrocatalytic N‐Doped Graphitic Nanofiber – Metal/Metal Oxide Nanoparticle Composites

Carbon‐based nanocomposites have shown promising results in replacing commercial Pt/C as high‐performance, low cost, nonprecious metal‐based oxygen reduction reaction (ORR) catalysts. Developing unique nanostructures of active components (e.g., metal oxides) and carbon materials is essential for their application in next generation electrode materials for fuel cells and metal–air batteries. Herein, a general approach for the production of 1D porous nitrogen‐doped graphitic carbon fibers embedded with active ORR components, (M/MO_x, i.e., metal or metal oxide nanoparticles) using a facile two‐step electrospinning and annealing process is reported. Metal nanoparticles/nanoclusters nucleate within the polymer nanofibers and subsequently catalyze graphitization of the surrounding polymer matrix and following oxidation, create an interconnected graphite–metal oxide framework with large pore channels, considerable active sites, and high specific surface area. The metal/metal oxide@N‐doped graphitic carbon fibers, especially Co₃O₄, exhibit comparable ORR catalytic activity but superior stability and methanol tolerance versus Pt in alkaline solutions, which can be ascribed to the synergistic chemical coupling effects between Co₃O₄ and robust 1D porous structures composed of interconnected N‐doped graphitic nanocarbon rings. This finding provides a novel insight into the design of functional electrocatalysts using electrospun carbon nanomaterials for their application in energy storage and conversion fields.     

Reduced Graphene Oxide‐Wrapped Co9–xFexS8/Co,Fe‐N‐C Composite as Bifunctional Electrocatalyst for Oxygen Reduction and Evolution

Searching for highly efficient bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) using nonnoble metal‐based catalysts is essential for the development of many energy conversion systems, including rechargeable fuel cells and metal–air batteries. Here, Co_9–xFe_xS₈/Co,Fe‐N‐C hybrids wrapped by reduced graphene oxide (rGO) (abbreviated as S‐Co_9–xFe_xS₈@rGO) are synthesized through a semivulcanization and calcination method using graphene oxide (GO) wrapped bimetallic zeolite imidazolate framework (ZIF) Co,Fe‐ZIF (CoFe‐ZIF@GO) as precursors. Benefiting from the synergistic effect of OER active CoFeS and ORR active Co,Fe‐N‐C in a single component, as well as high dispersity and enhanced conductivity derived from rGO coating and Fe‐doping, the obtained S‐Co_9–xFe_xS₈@rGO‐10 catalyst shows an ultrasmall overpotential of ≈0.29 V at 10 mA cm^?2 in OER and a half‐wave potential of 0.84 V in ORR, combining a superior oxygen electrode activity of ≈0.68 V in 0.1 m KOH.     

Multishelled NixCo3–xO4 Hollow Microspheres Derived from Bimetal–Organic Frameworks as Anode Materials for High‐Performance Lithium‐Ion Batteries

Metal–organic frameworks (MOFs) featuring versatile topological architectures are considered to be efficient self‐sacrificial templates to achieve mesoporous nanostructured materials. A facile and cost‐efficient strategy is developed to scalably fabricate binary metal oxides with complex hollow interior structures and tunable compositions. Bimetal–organic frameworks of Ni‐Co‐BTC solid microspheres with diverse Ni/Co ratios are readily prepared by solvothermal method to induce the Ni _x Co_{3? x} O₄ multishelled hollow microspheres through a morphology‐inherited annealing treatment. The obtained mixed metal oxides are demonstrated to be composed of nanometer‐sized subunits in the shells and large void spaces left between adjacent shells. When evaluated as anode materials for lithium‐ion batteries, Ni _x Co_{3? x} O₄‐0.1 multishelled hollow microspheres deliver a high reversible capacity of 1109.8 mAh g^?1 after 100 cycles at a current density of 100 mA g^?1 with an excellent high‐rate capability. Appropriate capacities of 832 and 673 mAh g^?1 could also be retained after 300 cycles at large currents of 1 and 2 A g^?1, respectively. These prominent electrochemical properties raise a concept of synthesizing MOFs‐derived mixed metal oxides with multishelled hollow structures for progressive lithium‐ion batteries.     

Recent Advances in Synthesis and Biomedical Applications of Two‐Dimensional Transition Metal Dichalcogenide Nanosheets

During recent decades, a giant leap in the development of nanotechnology has been witnessed. Numerous nanomaterials with different dimensions and unprecedented features have been developed and provided unimaginably wide scope to solve the challenging problems in biomedicine, such as cancer diagnosis and therapy. Recently, two‐dimensional (2D) transition metal dichalcogenide (TMDC) nanosheets (NSs), including MoS₂, WS₂, and etc., have emerged as novel inorganic graphene analogues and attracted tremendous attention due to their unique structures and distinctive properties, and opened up great opportunities for biomedical applications, including ultrasensitive biosensing, biological imaging, drug delivery, cancer therapy, and antibacterial treatment. A comprehensive overview of different synthetic methods of ultrathin 2D TMDC NSs and their state‐of‐the‐art biomedical applications, especially those that have appeared in the past few years, is presented. At the end of this review, the future opportunities and challenges for 2D TMDC NSs in biomedicine are also discussed.     

Uniformly grown PtCo-modified Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanosheets as a highly efficient catalyst for sodium borohydride electrooxidation

A facile hydrothermal synthetic method, followed by in situ reduction and galvanic replacement processes, is used to prepare PtCo-modified Co₃O₄ nanosheets (PtCo/Co₃O₄ NSs) supported on Ni foam. The prepared nanomaterial is used as an electrocatalyst for NaBH₄ oxidation in alkaline solution. The morphology and phase composition of PtCo/Co₃O₄ NSs are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The catalytic performance of PtCo/Co₃O₄ NSs is investigated by cyclic voltammetry (CV) and chronoamperometry (CA) in a standard three-electrode system. Current densities of 70 and 850 mA·cm^–2 were obtained at–0.4 V for Co/Co₃O₄ and PtCo/Co₃O₄ NSs, respectively, in a solution containing 2 mol·L^–1 NaOH and 0.2 mol·L^–1 NaBH₄. The use of a noble metal (Pt) greatly enhances the catalytic activity of the transition metal (Co) and Co₃O₄. Besides, both Co and Co₃O₄ exhibit good B–H bond breaking ability (in NaBH₄), which leads to better electrocatalytic activity and stability of PtCo/Co₃O₄ NSs in NaBH₄ electrooxidation compared to pure Pt. The results demonstrate that the as-prepared PtCo/Co₃O₄ NSs can be a promising electrocatalyst for borohydride oxidation.

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Countering the Segregation of Transition‐Metal Ions in LiMn1/3Co1/3Ni1/3O2 Cathode for Ultralong Life and High‐Energy Li‐Ion Batteries

High‐voltage layered lithium transition‐metal oxides are very promising cathodes for high‐energy Li‐ion batteries. However, these materials often suffer from a fast degradation of cycling stability due to structural evolutions. It seriously impedes the large‐scale application of layered lithium transition‐metal oxides. In this work, an ultralong life LiMn_1/3Co_1/3Ni_1/3O₂ microspherical cathode is prepared by constructing an Mn‐rich surface. Its capacity retention ratio at 700 mA g^?1 is as large as 92.9% after 600 cycles. The energy dispersive X‐ray maps of electrodes after numerous cycles demonstrate that the ultralong life of the as‐prepared cathode is attributed to the mitigation of TM‐ions segregation. Additionally, it is discovered that layered lithium transition‐metal oxide cathodes with an Mn‐rich surface can mitigate the segregation of TM ions and the corrosion of active materials. This study provides a new strategy to counter the segregation of TM ions in layered lithium transition‐metal oxides and will help to the design and development of high‐energy cathodes with ultralong life.     

Wet/Sono‐Chemical Synthesis of Enzymatic Two‐Dimensional MnO2 Nanosheets for Synergistic Catalysis‐Enhanced Phototheranostics

2D nanomaterials have attracted broad interest in the field of biomedicine owing to their large surface area, high drug‐loading capacity, and excellent photothermal conversion. However, few studies report their “enzyme‐like” catalytic performance because it is difficult to prepare enzymatic nanosheets with small size and ultrathin thickness by current synthetic protocols. Herein, a novel one‐step wet‐chemical method is first proposed for protein‐directed synthesis of 2D MnO₂ nanosheets (M‐NSs), in which the size and thickness can be easily adjusted by the protein dosage. Then, a unique sono‐chemical approach is introduced for surface functionalization of the M‐NSs with high dispersity/stability as well as metal‐cation‐chelating capacity, which can not only chelate ⁶⁴Cu radionuclides for positron emission tomography (PET) imaging, but also capture the potentially released Mn²⁺ for enhanced biosafety. Interestingly, the resulting M‐NS exhibits excellent enzyme‐like activity to catalyze the oxidation of glucose, which represents an alternative paradigm of acute glucose oxidase for starving cancer cells and sensitizing them to thermal ablation. Featured with outstanding phototheranostic performance, the well‐designed M‐NS can achieve effective photoacoustic‐imaging‐guided synergistic starvation‐enhanced photothermal therapy. This study is expected to establish a new enzymatic phototheranostic paradigm based on small‐sized and ultrathin M‐NSs, which will broaden the application of 2D nanomaterials.     

Defects‐Induced In‐Plane Heterophase in Cobalt Oxide Nanosheets for Oxygen Evolution Reaction

Cobalt oxides as efficient oxygen evolution reaction (OER) electrocatalysts have received much attention because of their rich reserves and cheap cost. There are two common cobalt oxides, Co₃O₄ (spinel phase, stable but poor intrinsic activity) and CoO (rocksalt phase, active but easily be oxidatized). Constructing Co₃O₄/CoO heterophase can inherit both characteristic features of each component and form a heterophase interface facilitating charge transfer, which is believed to be an effective strategy in designing excellent electrocatalysts. Herein, an atomic arrangement engineering strategy is applied to improve electrocatalytic activity of Co₃O₄ for the OER. With the presence of oxygen vacancies, cobalt atoms at tetrahedral sites in Co₃O₄ can more easily diffuse into interstitial octahedral sites to form CoO phase structure as revealed by periodic density functional theory computations. The Co₃O₄/CoO spinel/rocksalt heterophase can be in situ fabricated at the atomic scale in plane. The overpotential to reach 10 mA cm^?2 of Co₃O₄/CoO is 1.532 V, which is 92 mV smaller than that of Co₃O₄. Theoretical calculations confirm that the excellent electrochemical activity is corresponding to a decline in average p‐state energy of adsorbed‐O on the Co₃O₄/CoO heterophase interface. The reaction Gibbs energy barrier has been significantly decreased with the construction of the heterophase interface.     

Sugar Blowing‐Induced Porous Cobalt Phosphide/Nitrogen‐Doped Carbon Nanostructures with Enhanced Electrochemical Oxidation Performance toward Water and Other Small Molecules

Rational design of high active and robust nonprecious metal catalysts with excellent catalytic efficiency in oxygen evolution reaction (OER) is extremely vital for making the water splitting process more energy efficient and economical. Among these noble metal‐free catalysts, transition‐metal‐based nanomaterials are considered as one of the most promising OER catalysts due to their relatively low‐cost intrinsic activities, high abundance, and diversity in terms of structure and morphology. Herein, a facile sugar‐blowing technique and low‐temperature phosphorization are reported to generate 3D self‐supported metal involved carbon nanostructures, which are termed as Co₂P@Co/nitrogen‐doped carbon (Co₂P@Co/N‐C). By capitalizing on the 3D porous nanostructures with high surface area, homogeneously dispersed active sites, the intimate interaction between active sites, and 3D N‐doped carbon, the resultant Co₂P@Co/N‐C exhibits satisfying OER performance superior to CoO@Co/N‐C, delivering 10 mA cm^?2 at overpotential of 0.32 V. It is worth noting that in contrast to the substantial current density loss of RuO₂, Co₂P@Co/N‐C shows much enhanced catalytic activity during the stability test and a 1.8‐fold increase in current density is observed after stability test. Furthermore, the obtained Co₂P@Co/N‐C can also be served as an excellent nonprecious metal catalyst for methanol and glucose electrooxidation in alkaline media, further extending their potential applications.     

Strongly Coupled g‐C3N4 Nanosheets‐Co3O4 Quantum Dots as 2D/0D Heterostructure Composite for Peroxymonosulfate Activation

The development of effective approaches for the preparation of 0D quantum dots (QDs)/2D nanosheets (NSs) heterostructures, which have been proven to be favorable for heterogeneous catalysis, is highly desirable but remains a great challenge. Herein, 0D metal oxide nanocrystals–2D ultrathin g‐C₃N₄ nanosheets (Co₃O₄/CNNS) heterostructures are synthesized via a facile chemical reaction, followed by annealing in air. Ultrafine Co₃O₄ QDs (≈2.2–3.2 nm) are uniformly and tightly attached on the surface of g‐C₃N₄ nanosheets. Detailed characterization reveals that the specially designed unique 0D/2D structure is critical to the high photocatalytic performance for the degradation of tetracycline (TC) via peroxymonosulfate (PMS) activation. The optimal catalyst, namely, Co₃O₄/CNNS‐1100, exhibits excellent performance and ≈98.7% TC can be degraded under visible light irradiation. Moreover, TC degradation is almost completely insusceptible to several real water samples. Meanwhile, other dye pollutants can also be efficiently degraded by the Co₃O₄/CNNS‐1100/PMS/vis system. The quenching tests display that that the h⁺, ?OH, O₂^??, and SO₄^?? are responsible for TC removal. The improved photocatalytic performance can be attributed to the synergistic effect of the photocatalytic‐ and chemical‐processes in the PMS activation. This work gives an insight into the development of multifunctional 0D/2D nanocomposites for further potential applications which are not limited to environmental purification.     

One‐Step Route Synthesized Co2P/Ru/N‐Doped Carbon Nanotube Hybrids as Bifunctional Electrocatalysts for High‐Performance Li–O2 Batteries

The large‐scale commercial application of lithium–oxygen batteries (LOBs) is overwhelmed by the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) associated with insoluble and insulated Li₂O₂. Herein, an elaborate design on a highly catalytic LOBs cathode constructed by N‐doped carbon nanotubes (CNT) with in situ encapsulated Co₂P and Ru nanoparticles is reported. The homogeneously dispersed Co₂P and Ru catalysts can effectively modulate the formation and decomposition behavior of Li₂O₂ during discharge/charge processes, ameliorating the electronically insulating property of Li₂O₂ and constructing a homogenous low‐impedance Li₂O₂/catalyst interface. Compared with Co/CNT and Ru/CNT electrodes, the Co₂P/Ru/CNT electrode delivers much higher oxygen reduction triggering onset potential and higher ORR and OER peak current and integral areas, showing greatly improved ORR/OER kinetics due to the synergistic effects of Co₂P and Ru. Li–O₂ cells based on the Ru/Co₂P/CNT electrode demonstrate improved ORR/OER overpotential of 0.75 V, excellent rate capability of 12 800 mAh g^?1 at 1 A g^?1, and superior cycle stability for more than 185 cycles under a restricted capacity of 1000 mAh g^?1 at 100 mA g^?1. This work paves an exciting avenue for the design and construction of bifunctional catalytic cathodes by coupling metal phosphides with other active components in LOBs.     

Promoting Oxygen Evolution Reaction of Co‐Based Catalysts (Co3O4, CoS,CoP, and CoN) through Photothermal Effect

The increase of reaction temperature of electrocatalysts is regarded as an efficient method to improve the oxygen evolution reaction (OER) activity. Herein, it is reported that the electrocatalytic performance of dual functional (i.e., electrocatalytic and photothermal functions) Co₃O₄ can be dramatically improved via its photothermal effect. The operating temperature of the Co₃O₄ electrode is elevated in situ under near infrared (NIR) light irradiation, resulting in enhanced oxygen evolution activity due to its accelerated electrical conductivity, reaction kinetics, and desorption rate of O₂ bubbles from the electrode. In addition, photothermal effect can also enhance the electrocatalytic reaction rates of metal‐doped Co₃O₄ electrodes, indicating that it is able to significantly improve the OER activities of electrodes together with other modification strategies. With the assistance of the photothermal effect, the obtained Ni‐doped Co₃O₄ catalyst requires an extremely low overpotential of 208 mV to achieve a benchmark of 10 mA cm^?2 with a small Tafel slope, superior to most reported Co‐based catalysts. Significantly, the electrocatalytic performance of other electrodes with photothermal effect, such as CoN, CoP, and CoS, are also boosted under NIR light irradiation, indicating opportunities for implementing photothermal enhancement in electrocatalytic water splitting.     

Metal Oxide Hollow Nanostructures for Lithium‐ion Batteries

Metal oxide hollow structures have received great attention because of their many promising applications in a wide range of fields. As electrode materials for lithium‐ion batteries (LIBs), metal oxide hollow structures provide high specific capacity, superior rate capability, and improved cycling performance. In this Research News, we summarize the recent research activities in the synthesis of metal oxide hollow nanostructures with controlled shape, size, composition, and structural complexity, as well as their applications in LIBs. By focusing on hollow structures of some binary metal oxides (such as SnO₂, TiO₂, Fe₂O₃, Co₃O₄) and complex metal oxides, we seek to provide some rational understanding on the effect of nanostructure engineering on the electrochemical performance of the active materials. It is thus anticipated that this article will shed some light on the development of advanced electrode materials for next‐generation LIBs.     

Non‐3d Metal Modulation of a 2D Ni–Co Heterostructure Array as Multifunctional Electrocatalyst for Portable Overall Water Splitting

Portable water splitting devices driven by rechargeable metal–air batteries or solar cells are promising, however, their scalable usages are still hindered by lack of suitable multifunctional electrocatalysts. Here, a highly efficient multifunctional electrocatalyst is demonstrated, i.e., 2D nanosheet array of Mo‐doped NiCo₂O₄/Co_5.47N heterostructure deposited on nickel foam (Mo‐NiCo₂O₄/Co_5.47N/NF). The successful doping of non‐3d high‐valence metal into a heterostructured nanosheet array, which is directly grown on a conductive substrate endows the resultant catalyst with balanced electronic structure, highly exposed active sites, and binder‐free electrode architecture. As a result, the Mo‐NiCo₂O₄/Co_5.47N/NF exhibits remarkable catalytic activity toward the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), affording high current densities of 50 mA cm^?2 at low overpotentials of 310 mV for OER, and 170 mV for HER, respectively. Moreover, a low voltage of 1.56 V is achieved for the Mo‐NiCo₂O₄/Co_5.47N/NF‐based water splitting cell to reach 10 mA cm^?2. More importantly, a portable overall water splitting device is demonstrated through the integration of a water‐splitting cell and two Zn–air batteries (open‐circuit voltage of 1.43 V), which are all fabricated based on Mo‐NiCo₂O₄/Co_5.47N/NF, demonstrating a low‐cost way to generate fuel energy. This work offers an effective strategy to develop high‐performance metal‐doped heterostructured electrode.     

Nitrogen‐Doped Co3O4 Mesoporous Nanowire Arrays as an Additive‐Free Air‐Cathode for Flexible Solid‐State Zinc–Air Batteries

The kinetically sluggish rate of oxygen reduction reaction (ORR) on the cathode side is one of the main bottlenecks of zinc‐air batteries (ZABs), and thus the search for an efficient and cost‐effective catalyst for ORR is highly pursued. Co₃O₄ has received ever‐growing interest as a promising ORR catalyst due to the unique advantages of low‐cost, earth abundance and decent catalytic activity. However, owing to the poor conductivity as a result of its semiconducting nature, the ORR activity of the Co₃O₄ catalyst is still far below the expectation. Herein, we report a controllable N‐doping strategy to significantly improve the catalytic activity of Co₃O₄ for ORR and demonstrate these N doped Co₃O₄ nanowires as an additive‐free air‐cathode for flexible solid‐state zinc‐air batteries. The results of experiments and DFT calculations reveal that the catalytic activity is promoted by the N dopant through a combined set of factors, including enhanced electronic conductivity, increased O₂ adsorption strength and improved reaction kinetics. Finally, the assembly of all‐solid‐state ZABs based on the optimized cathode exhibit a high volumetric capacity of 98.1 mAh cm^‐3 and outstanding flexibility. The demonstration of such flexible ZABs provides valuable insights that point the way to the redesign of emerging portable electronics.