Black Phosphorus and Carbon Nitride Hybrid Photocatalysts for Photoredox Reactions

The development of metal‐free photocatalysts with high efficiency, stability, and broadband solar absorption is a major challenge to realize green and sustainable chemical development. Recently, metal‐free nanohybrids (BP/CN) composed of black phosphorus (BP) and polymeric carbon nitride (CN) are emerged as photocatalytic hybrids with broadband light‐harvesting capabilities and higher photocatalytic performance. Herein, the latest progress of BP/CN hybrids for multifarious photoredox reactions is summarized. The different heterojunction types of BP/CN hybrid photocatalysts, including type I, type II, and multicomponent heterojunctions, are illustrated. Furthermore, the relevant applications of BP/CN hybrid photocatalysts for photocatalytic water splitting, CO₂ photoreduction, N₂ fixation, H₂O₂ production, pollutant decomposition, and bacterial inactivation are discussed. An overview of the challenge in this area and the directions for the future is presented.     

Synthesis of Leaf‐Vein‐Like g‐C3N4 with Tunable Band Structures and Charge Transfer Properties for Selective Photocatalytic H2O2 Evolution

Photocatalytic H₂O₂ evolution through two‐electron oxygen reduction has attracted wide attention as an environmentally friendly strategy compared with the traditional anthraquinone or electrocatalytic method. Herein, a biomimetic leaf‐vein‐like g‐C₃N₄ as an efficient photocatalyst for H₂O₂ evolution is reported, which owns tenable band structure, optimized charge transfer, and selective two‐electron O₂ reduction. The mechanism for the regulation of band structure and charge transfer is well studied by combining experiments and theoretical calculations. The H₂O₂ yield of CN4 (287 µmol h^?1) is about 3.3 times higher than that of pristine CN (87 µmol h^?1), and the apparent quantum yield for H₂O₂ evolution over CN4 reaches 27.8% at 420 nm, which is much higher than that for many other current photocatalysts. This work not only provides a novel strategy for the design of photocatalyst with excellent H₂O₂ evolution efficiency, but also promotes deep understanding for the role of defect and doping sites on photocatalytic activity.     

In Situ Grown Pristine Cobalt Sulfide as Bifunctional Photocatalyst for Hydrogen and Oxygen Evolution

Herein, transition metal chalcogenides of pristine cobalt sulfides are rationally designed to act as robust bifunctional photocatalysts for visible‐light‐driven water splitting for the first time. Through moderate solvothermal route, cobalt sulfides are synthesized in situ growth and observed by scanning electron microscope image analysis. Noteworthily, 3D hierarchical cobalt sulfides acting as bifunctional photocatalysts are implemented to catalyze the visible‐light‐driven oxygen evolution reaction and hydrogen evolution reaction. This efficient, earth‐abundant, and nonnoble water splitting catalyst for artificial photosynthesis is thoroughly analyzed by various spectroscopic techniques with the aim of investigating its photocatalytic mechanism under visible‐light illumination. The main catalyst of CoS‐2 exhibits considerable H₂ evolution rate of 1196 µmol h^?1 g^?1 and O₂ yield of 63.5%. The efficient activity is attributed to the effective electron transfer between the photosensitizer and catalyst, which is verified by transient absorption experiments. The effective electron transfer between the photosensitizer and catalyst during water oxidation is verified by the dramatic decline of [Ru(bpy)₃]³⁺ concentration in the presence of the catalyst CoS‐2. At the same time, transient absorption experiments support a rapid electron transfers from ³EY* (excited photosensitizer eosin‐Y) to the catalyst CoS‐2 for efficient hydrogen evolution.     

Ice‐Assisted Synthesis of Black Phosphorus Nanosheets as a Metal‐Free Photocatalyst: 2D/2D Heterostructure for Broadband H2 Evolution

A 2D/2D heterojunction of black phosphorous (BP)/graphitic carbon nitride (g‐C₃N₄) is designed and synthesized for photocatalytic H₂ evolution. The ice‐assisted exfoliation method developed herein for preparing BP nanosheets from bulk BP, leads to high yield of few‐layer BP nanosheets (≈6 layers on average) with large lateral size at reduced duration and power for liquid exfoliation. The combination of BP with g‐C₃N₄ protects BP from oxidation and contributes to enhanced activity both under λ > 420 nm and λ > 475 nm light irradiation and to long‐term stability. The H₂ production rate of BP/g‐C₃N₄ (384.17 µmol g^?1 h^?1) is comparable to, and even surpasses that of the previously reported, precious metal‐loaded photocatalyst under λ > 420 nm light. The efficient charge transfer between BP and g‐C₃N₄ (likely due to formed N? P bonds) and broadened photon absorption (supported both experimentally and theoretically) contribute to the excellent photocatalytic performance. The possible mechanisms of H₂ evolution under various forms of light irradiation is unveiled. This work presents a novel, facile method to prepare 2D nanomaterials and provides a successful paradigm for the design of metal‐free photocatalysts with improved charge‐carrier dynamics for renewable energy conversion.     

Photocatalyst Interface Engineering: Spatially Confined Growth of ZnFe2O4 within Graphene Networks as Excellent Visible‐Light‐Driven Photocatalysts

High‐performance photocatalysts should have highly crystallized nanocrystals (NCs) with small sizes, high separation efficiency of photogenerated electron–hole pairs, fast transport and consumption of photon‐excited electrons from the surface of catalyst, high adsorption of organic pollutant, and suitable band gap for maximally utilizing sunlight energy. However, the design and synthesis of these versatile structures still remain a big challenge. Here, we report a novel strategy for the synthesis of ultrasmall and highly crystallized graphene–ZnFe₂O₄ photocatalyst through interface engineering by using interconnected graphene network as barrier for spatially confined growth of ZnFe₂O₄, as transport channels for photon‐excited electron from the surface of catalyst, as well as the electron reservoir for suppressing the recombination of photogenerated electron–hole pairs. As a result, about 20 nm ZnFe₂O₄ NCs with highly crystallized (311) plane confined in the graphene network exhibit an excellent visible‐light‐driven photocatalytic activity with an ultrafast degradation rate of 1.924 × 10^?7 mol g^?1 s^?1 for methylene blue, much higher than those of previously reported photocatalysts such as spinel‐based photocatalysts (20 times), TiO₂‐based photocatalysts (4 times), and other photocatalysts (4 times). Our strategy can be further extended to fabricate other catalysts and electrode materials for supercapacitors and Li‐ion batteries.     

Simultaneously Tuning Band Structure and Oxygen Reduction Pathway toward High-Efficient Photocatalytic Hydrogen Peroxide Production Using Cyano-Rich Graphitic Carbon Nitride

The demands for green production of hydrogen peroxide have triggered extensive studies in the photocatalytic synthesis, but most photocatalysts suffer from rapid charge recombination and poor 2e⁻ oxygen reduction reaction (ORR) selectivity. Here, a novel composite photocatalyst of cyano-rich graphitic carbon nitride g-C₃N₄ is fabricated in a facile manner by sodium chloride-assisted calcination on dicyandiamide. The obtained photocatalysts exhibit superior activity (7.01 mm  h⁻¹ under λ  ≥  420 nm, 16.05 mm  h⁻¹ under simulated sun conditions) for H₂O₂ production and 93% selectivity for 2e⁻ ORR, much higher than that of the state-of-the-art photocatalyst. The porous g-C₃N₄ with Na dopants and cyano groups simultaneously optimize two limiting steps of the photocatalytic 2e⁻ ORR: photoactivity, and selectivity. The cyano groups can adjust the band structure of g-C₃N₄ to achieve high activity. They also serve as oxygen adsorption sites, in which local charge polarization facilitates O₂ adsorption and protonation. With the aid of Na⁺, the O₂ is reduced to produce more superoxide radicals as the intermediate products for H₂O₂ synthesis. This work provides a facile approach to simultaneously tune photocatalytic activity and 2e⁻ ORR selectivity for boosting H₂O₂ production, and then paves the way for the practical application of g-C₃N₄ in environmental remediation and energy supply.     

Trimetallic Mn‐Fe‐Ni Oxide Nanoparticles Supported on Multi‐Walled Carbon Nanotubes as High‐Performance Bifunctional ORR/OER Electrocatalyst in Alkaline Media

Discovering precious metal‐free electrocatalysts exhibiting high activity and stability toward both the oxygen reduction (ORR) and the oxygen evolution (OER) reactions remains one of the main challenges for the development of reversible oxygen electrodes in rechargeable metal–air batteries and reversible electrolyzer/fuel cell systems. Herein, a highly active OER catalyst, Fe_0.3Ni_0.7O_X supported on oxygen‐functionalized multi‐walled carbon nanotubes, is substantially activated into a bifunctional ORR/OER catalyst by means of additional incorporation of MnO_X. The carbon nanotube‐supported trimetallic (Mn‐Ni‐Fe) oxide catalyst achieves remarkably low ORR and OER overpotentials with a low reversible ORR/OER overvoltage of only 0.73 V, as well as selective reduction of O₂ predominantly to OH^?. It is shown by means of rotating disk electrode and rotating ring disk electrode voltammetry that the combination of earth‐abundant transition metal oxides leads to strong synergistic interactions modulating catalytic activity. The applicability of the prepared catalyst for reversible ORR/OER electrocatalysis is evaluated by means of a four‐electrode configuration cell assembly comprising an integrated two‐layer bifunctional ORR/OER electrode system with the individual layers dedicated for the ORR and the OER to prevent deactivation of the ORR activity as commonly observed in single‐layer bifunctional ORR/OER electrodes after OER polarization.     

Enhanced Electrocatalytic Oxygen Evolution Activity by Tuning Both the Oxygen Vacancy and Orbital Occupancy of B‐Site Metal Cation in NdNiO3

Perovskite oxides have been explored as promising electrocatalysts for the oxygen evolution reaction (OER), while a lack of understanding of key factors impacting the catalytic activity restricts their further design and development. Here, for the first time, the contributions of oxygen vacancy (V_O) and orbital occupancy of B‐site cations to the catalytic activity of NdNiO₃ films are systematically investigated. It is found that OER activity follows a typical volcano‐shaped dependence on the oxygen pressure. In the range of 0.2–10 Pa, proper concentration of V_O can provide a moderate bonding strength with intermediate hydroxyl OH* and the increased ratio of Ni³⁺/Ni²⁺ provides a more favorable occupancy of e_g orbital for the catalytic activity; while in the range of 10–60 Pa, insufficient concentration of V_O leads to an enhanced strength of hybridization between Ni 3d and O 2p band and thus deteriorated catalytic activity. The superior OER catalytic performance can be only achieved with both appropriate concentration of V_O and the ratio of B‐site metal cations with different valences.     

Cu?Co Bimetallic Oxide Quantum Dot Decorated Nitrogen‐Doped Carbon Nanotubes: A High‐Efficiency Bifunctional Oxygen Electrode for Zn–Air Batteries

The large‐scale production of metal–air batteries, an appealing solution for next‐generation energy storage, requires low‐cost, earth‐abundant, and efficient oxygen electrode materials, yet insights into active catalyst structures and synergistic reactivity remain largely unknown. Here, a new bifunctional oxygen electrode based on nitrogen‐doped carbon nanotubes decorated by spinel CuCo₂O₄ quantum dots (CuCo₂O₄/N‐CNTs) is reported, outperforming the benchmark of state‐of‐the‐art noble metal catalysts. Combining spectroscopic characterization and electrochemical studies, a prominent synergetic effect between CuCo₂O₄ and N‐doped carbon nanotubes is uncovered: the high conductivity, large active surface area, and increase in the number of catalytic sites induced by Cu doping (i.e., Cu²⁺ and Cu? N) can be beneficial to the overall electrocatalytic activities. Remarkably, the native flexibility of CuCo₂O₄/N‐CNTs allows its direct use as reversible oxygen electrodes in Zn–air batteries either with liquid alkaline electrolyte or in the all‐solid‐state configuration. The prepared devices demonstrate excellent discharging/charging performance, large energy density (83.83 mW cm^?2 in liquid state, 1.86 W g^?1 in all‐solid‐state), and long lifetime (48 h in liquid state, 9 h in all‐solid‐state), holding great promise in the practical application of rechargeable metal–air batteries and other fuel cells.     

CuCo Bimetallic Oxide Quantum Dot Decorated Nitrogen‐Doped Carbon Nanotubes: A High‐Efficiency Bifunctional Oxygen Electrode for Zn–Air Batteries

The large‐scale production of metal–air batteries, an appealing solution for next‐generation energy storage, requires low‐cost, earth‐abundant, and efficient oxygen electrode materials, yet insights into active catalyst structures and synergistic reactivity remain largely unknown. Here, a new bifunctional oxygen electrode based on nitrogen‐doped carbon nanotubes decorated by spinel CuCo₂O₄ quantum dots (CuCo₂O₄/N‐CNTs) is reported, outperforming the benchmark of state‐of‐the‐art noble metal catalysts. Combining spectroscopic characterization and electrochemical studies, a prominent synergetic effect between CuCo₂O₄ and N‐doped carbon nanotubes is uncovered: the high conductivity, large active surface area, and increase in the number of catalytic sites induced by Cu doping (i.e., Cu²⁺ and Cu?N) can be beneficial to the overall electrocatalytic activities. Remarkably, the native flexibility of CuCo₂O₄/N‐CNTs allows its direct use as reversible oxygen electrodes in Zn–air batteries either with liquid alkaline electrolyte or in the all‐solid‐state configuration. The prepared devices demonstrate excellent discharging/charging performance, large energy density (83.83 mW cm^?2 in liquid state, 1.86 W g^?1 in all‐solid‐state), and long lifetime (48 h in liquid state, 9 h in all‐solid‐state), holding great promise in the practical application of rechargeable metal–air batteries and other fuel cells.     

Oxygen Vacant Semiconductor Photocatalysts

Semiconductor photocatalysis acts as a sustainable green technology to convert solar energy for environmental purification and production of renewable energy. However, the current photocatalysts suffer from inefficient photoabsorption, rapid recombination of photogenerated electrons and holes, and inadequate surface reactive sites. Introduction of oxygen vacancies (OVs) in photocatalysts has been demonstrated to be an efficacious strategy to solve these issues and improve photocatalytic efficiency. This review systematically summarizes the recent progress in the oxygen vacant semiconductor photocatalysts. Firstly, the formation and characterizations of OVs in semiconductor photocatalysts are briefly introduced. Then, highlighted are the roles of OVs in the photocatalytic reactions of three types of typical oxygen-containing semiconductors, including metal oxides (TiO₂, ZnO, WO₃, W₁₈O₄₉, MoO₃, BiO_2-x, SnO₂, etc), hydroxides (In(OH)₃, Ln(OH)₃ (Ln=La, Pr, and Nd), Layered double hydroxides) and oxysalts (bismuth-based oxysalts and others) photocatalysts. Moreover, the advanced photocatalytic applications of oxygen vacant semiconductor photocatalysts, such as pollutant removal, H₂ production, CO₂ reduction, N₂ fixation and organic synthesis are systematically summarized. Finally, an overview on the current challenges and a prospective on the future of oxygen vacant materials is proposed.     

Oxygen Vacancy-Mediated Exciton Effect in Hierarchical BiOBr Enables Dichotomy of Energy Transfer and Electron Transfer in Photocatalysis

Using solar energy through green and simple artificial photosynthesis systems are considered as a promising way to solve the energy and environmental crisis. However, one of the important primary steps of photosynthesis, i.e., energy transfer, is long being ignored especially in inorganic semiconducting systems due to the small exciton binding energies. Herein, the simultaneous interrogation of the charge transfer and energy transfer steps in a photoexcitation process is proposed by utilizing few-layered nanosheet-assembled hierarchical BiOBr nanotubes with rich oxygen vacancies (OVs) as efficient multifunctional photocatalysts. Benefiting from the integrated 1D/2D structure and abundant OV defects, the excitonic effect strikes a delicate balance in the optimized BiOBr photocatalyst, showing not only improved charge carrier separation and transfer but also enhanced exciton generation. As a result, the hierarchical BiOBr nanotubes exhibit high efficiency toward photocatalytic CO₂ reduction with an impressive CO evolution rate of 135.6 µmol g⁻¹ h⁻¹ without cocatalyst or photosensitizer. The dominant reactive oxygen species of singlet oxygen (¹O₂) are discriminated for the first time, which originated from an energy transfer process, with electrophilic character, whereas the minor effect of superoxide anion radical (^•O₂⁻) with a nucleophilic rate-determining step in the photocatalytic aerobic oxidation of sulfides.     

Searching General Sufficient‐and‐Necessary Conditions for Ultrafast Hydrogen‐Evolving Electrocatalysis

The development of cost‐effective and high‐performance electrocatalysts for the hydrogen evolution reaction (HER) is one critical step toward successful transition into a sustainable green energy era. Different from previous design strategies based on single parameter, here the necessary and sufficient conditions are proposed to develop bulk non‐noble metal oxides which are generally considered inactive toward HER in alkaline solutions: i) multiple active sites for different reaction intermediates and ii) a short reaction path created by ordered distribution and appropriate numbers of these active sites. Computational studies predict that a synergistic interplay between the ordered oxygen vacancies (at pyramidal high‐spin Co³⁺ sites) and the O 2p ligand holes (OLH; at metallic octahedral intermediate‐spin Co⁴⁺ sites) in RBaCo₂O_5.5+δ (δ = 1/4; R = lanthanides) can produce a near‐ideal HER reaction path to adsorb H₂O and release H₂, respectively. Experimentally, the as‐synthesized (Gd_0.5La_0.5)BaCo₂O_5.75 outperforms the state‐of‐the‐art Pt/C catalyst in many aspects. The proof‐of‐concept results reveal that the simultaneous possession of ordered oxygen vacancies and an appropriate number of OLH can realize a near‐optimal synergistic catalytic effect, which is pivotal for rational design of oxygen‐containing materials.     

An O2 Self‐Supplementing and Reactive‐Oxygen‐Species‐Circulating Amplified Nanoplatform via H2O/H2O2 Splitting for Tumor Imaging and Photodynamic Therapy

Conventional photodynamic therapy (PDT) has limited applications in clinical cancer therapy due to the insufficient O₂ supply, inefficient reactive oxygen species (ROS) generation, and low penetration depth of light. In this work, a multifunctional nanoplatform, upconversion nanoparticles (UCNPs)@TiO₂@MnO₂ core/shell/sheet nanocomposites (UTMs), is designed and constructed to overcome these drawbacks by generating O₂ in situ, amplifying the content of singlet oxygen (¹O₂) and hydroxyl radical (?OH) via water‐splitting, and utilizing 980 nm near‐infrared (NIR) light to increase penetration depth. Once UTMs are accumulated at tumor site, intracellular H₂O₂ is catalyzed by MnO₂ nanosheets to generate O₂ for improving oxygen‐dependent PDT. Simultaneously, with the decomposition of MnO₂ nanosheets and 980 nm NIR irradiation, UCNPs can efficiently convert NIR to ultraviolet light to activate TiO₂ and generate toxic ROS for deep tumor therapy. In addition, UCNPs and decomposed Mn²⁺ can be used for further upconversion luminescence and magnetic resonance imaging in tumor site. Both in vitro and in vivo experiments demonstrate that this nanoplatform can significantly improve PDT efficiency with tumor imaging capability, which will find great potential in the fight against tumor.     

Generalized Synthetic Strategy for Amorphous Transition Metal Oxides-Based 2D Heterojunctions with Superb Photocatalytic Hydrogen and Oxygen Evolution

2D amorphous transition metal oxides (a-TMOs) heterojunctions that have the synergistic effects of interface (efficiently promoting the separation of electron−hole pairs) and amorphous nature (abundant defects and dangling bonds) have attracted substantial interest as compelling photocatalysts for solar energy conversion. Strategies to facilely construct a-TMOs-based 2D/2D heterojunctions is still a big challenge due to the difficulty of preparing individual amorphous counterparts. A generalized synthesis strategy based on supramolecular self-assembly for bottom–up growth of a-TMOs-based 2D heterojunctions is reported, by taking 2D/2D g-C₃N₄ (CN)/a-TMOs heterojunction as a proof-of-concept. This strategy primarily depends on controlling the cooperation of the growth of supramolecular precursor and the coordinated covalent bonds arising from the tendency of metal ions to attain the stable configuration of electrons, which is independent on the intrinsic character of individual metal ion, indicating it is universally applicable. As a demonstration, the structure, physical properties, and photocatalytic water-splitting performance of CN/a-ZnO heterojunction are systematically studied. The optimized 2D/2D CN/a-ZnO exhibits enhanced photocatalytic performance, the hydrogen (432.6 µmol h⁻¹ g⁻¹) and oxygen (532.4 µmol h⁻¹ g⁻¹) evolution rate are 15.5 and 12.2 times than bulk CN, respectively. This synthetic strategy is useful to construct 2D a-TMOs nanomaterials for applications in energy-related areas and beyond.     

Engineering Facets and Oxygen Vacancies over Hematite Single Crystal for Intensified Electrocatalytic H2O2 Production

Hydrogen peroxide is a highly valuable chemical, and electrocatalytic oxygen reduction towards H₂O₂ offers an alternative method for safe on‐site applications. Generally, low‐cost hematite (α‐Fe₂O₃) is not recognized as an efficient electrocatalyst because of its inert nature, but it is herein reported that α‐Fe₂O₃ can be endowed with high catalytic activity and selectivity via the engineering of facets and oxygen vacancies. Density‐functional theory (DFT)calculations predict that the {001} facet is intrinsically selective for H₂O₂ production, and that oxygen vacancies can trigger the high activity, providing sites for O₂ adsorption and protonation, stabilizing the *OOH intermediate, and preventing cleavage of the O? O bond. The synthesized oxygen‐defective α‐Fe₂O₃ single crystals with exposed {001} facets achieve high selectivities for H₂O₂ of >90%, >88%, and >95% in weakly acidic, neutral, and alkaline electrolytes, respectively, and the H₂O₂ production rate reaches 454 mmol g^?1_cat h^?1 at 0.1 V versus RHE under alkaline conditions. In an anion exchange membrane fuel cell, a maximum H₂O₂ production of 546.8 mmol L^?1 with a high Faradaic efficiency of 80.5% is achieved. Thus, this work details a low‐cost catalyst feasible for H₂O₂ synthesis, and highlights the feasibility of theoretical catalyst design for practical applications.     

Tuning Anionic Redox Activity and Reversibility for a High‐Capacity Li‐Rich Mn‐Based Oxide Cathode via an Integrated Strategy

When fabricating Li‐rich layered oxide cathode materials, anionic redox chemistry plays a critical role in achieving a large specific capacity. Unfortunately, the release of lattice oxygen at the surface impedes the reversibility of the anionic redox reaction, which induces a large irreversible capacity loss, inferior thermal stability, and voltage decay. Therefore, methods for improving the anionic redox constitute a major challenge for the application of high‐energy‐density Li‐rich Mn‐based cathode materials. Herein, to enhance the oxygen redox activity and reversibility in Co‐free Li‐rich Mn‐based Li_1.2Mn_0.6Ni_0.2O₂ cathode materials by using an integrated strategy of Li₂SnO₃ coating‐induced Sn doping and spinel phase formation during synchronous lithiation is proposed. As an Li⁺ conductor, a Li₂SnO₃ nanocoating layer protects the lattice oxygen from exposure at the surface, thereby avoiding irreversible oxidation. The synergy of the formed spinel phase and Sn dopant not only improves the anionic redox activity, reversibility, and Li⁺ migration rate but also decreases Li/Ni mixing. The 1% Li₂SnO₃‐coated Li_1.2Mn_0.6Ni_0.2O₂ delivers a capacity of more than 300 mAh g^?1 with 92% Coulombic efficiency. Moreover, improved thermal stability and voltage retention are also observed. This synergic strategy may provide insights for understanding and designing new high‐performance materials with enhanced reversible anionic redox and stabilized surface lattice oxygen.     

Tuning Bifunctional Oxygen Electrocatalysts by Changing the A‐Site Rare‐Earth Element in Perovskite Nickelates

Perovskite‐structured (ABO₃) transition metal oxides are promising bifunctional electrocatalysts for efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In this paper, a set of epitaxial rare‐earth nickelates (RNiO₃) thin films is investigated with controlled A‐site isovalent substitution to correlate their structure and physical properties with ORR/OER activities, examined by using a three‐electrode system in O₂‐saturated 0.1 m KOH electrolyte. The ORR activity decreases monotonically with decreasing the A‐site element ionic radius which lowers the conductivity of RNiO₃ (R = La, La_0.5Nd_0.5, La_0.2Nd_0.8, Nd, Nd_0.5Sm_0.5, Sm, and Gd) films, with LaNiO₃ being the most conductive and active. On the other hand, the OER activity initially increases upon substituting La with Nd and is maximal at La_0.2Nd_0.8NiO₃. Moreover, the OER activity remains comparable within error through Sm‐doped NdNiO₃. Beyond that, the activity cannot be measured due to the potential voltage drop across the film. The improved OER activity is ascribed to the partial reduction of Ni³⁺ to Ni²⁺ as a result of oxygen vacancies, which increases the average occupancy of the e_g antibonding orbital to more than one. The work highlights the importance of tuning A‐site elements as an effective strategy for balancing ORR and OER activities of bifunctional electrocatalysts.     

Hydrogenated V2O5 Nanosheets for Superior Lithium Storage Properties

V₂O₅ is a promising cathode material for lithium ion batteries boasting a large energy density due to its high capacity as well as abundant source and low cost. However, the poor chemical diffusion of Li⁺, low conductivity, and poor cycling stability limit its practical application. Herein, oxygen‐deficient V₂O₅ nanosheets prepared by hydrogenation at 200 °C with superior lithium storage properties are described. The hydrogenated V₂O₅ (H‐V₂O₅) nanosheets deliver an initial discharge capacity as high as 259 mAh g^?1 and it remains 55% when the current density is increased 20 times from 0.1 to 2 A g^?1. The H‐V₂O₅ electrode has excellent cycling stability with only 0.05% capacity decay per cycle after stabilization. The effects of oxygen defects mainly at bridging O(II) sites on Li⁺ diffusion and overall electrochemical lithium storage performance are revealed. The results reveal here a simple and effective strategy to improve the capacity, rate capability, and cycling stability of V₂O₅ materials which have large potential in energy storage and conversion applications.     

Oxygen‐Deficient Bismuth Oxide/Graphene of Ultrahigh Capacitance as Advanced Flexible Anode for Asymmetric Supercapacitors

Oxygen‐deficient bismuth oxide (r‐Bi₂O₃)/graphene (GN) is designed, fabricated, and demonstrated via a facile solvothermal and subsequent solution reduction method. The ultrafine network bacterial cellulose (BC) as substrate for r‐Bi₂O₃/GN exhibits high flexibility, remarkable tensile strength (55.1 MPa), and large mass loading of 9.8 mg cm^?2. The flexible r‐Bi₂O₃/GN/BC anode delivers appreciable areal capacitance (6675 mF cm^?2 at 1 mA cm^?2) coupled with good rate capability (3750 mF cm^?2 at 50 mA cm^?2). In addition, oxygen vacancies have great influence on the capacitive performance of Bi₂O₃, delivering significantly improved capacitive values than the untreated Bi₂O₃ flexible electrode, and ultrahigh gravimetric capacitance of 1137 F g^?1 (based on the mass of r‐Bi₂O₃) can be obtained, achieving 83% of the theoretical value (1370 F g^?1). Flexible asymmetric supercapacitor is fabricated with r‐Bi₂O₃/GN/BC and Co₃O₄/GN/BC paper as the negative and positive electrodes, respectively. The operation voltage is expanded to 1.6 V, revealing a maximum areal energy density of 0.449 mWh cm^?2 (7.74 mWh cm^?3) and an areal power density of 40 mW cm^?2 (690 mW cm^?3). Therefore, this flexible anode with excellent electrochemical performance and high mechanical properties shows great potential in the field of flexible energy storage devices.