Spatially Separating Redox Centers on Z‐Scheme ZnIn2S4/BiVO4 Hierarchical Heterostructure for Highly Efficient Photocatalytic Hydrogen Evolution

Photocatalysis technology using solar energy for hydrogen (H₂) production still faces great challenges to design and synthesize highly efficient photocatalysts, which should realize the precise regulation of reactive sites, rapid migration of photoinduced carriers and strong visible light harvest. Here, a facile hierarchical Z‐scheme system with ZnIn₂S₄/BiVO₄ heterojunction is proposed, which can precisely regulate redox centers at the ZnIn₂S₄/BiVO₄ hetero‐interface by accelerating the separation and migration of photoinduced charges, and then enhance the oxidation and reduction ability of holes and electrons, respectively. Therefore, the ZnIn₂S₄/BiVO₄ heterojunction exhibits excellent photocatalytic performance with a much higher H₂‐evolution rate of 5.944 mmol g^?1 h^?1, which is about five times higher than that of pure ZnIn₂S₄. Moreover, this heterojunction shows good stability and recycle ability, providing a promising photocatalyst for efficient H₂ production and a new strategy for the manufacture of remarkable photocatalytic materials.     

Polyaniline Derived N‐Doped Carbon‐Coated Cobalt Phosphide Nanoparticles Deposited on N‐Doped Graphene as an Efficient Electrocatalyst for Hydrogen Evolution Reaction

The development of highly efficient and durable non‐noble metal electrocatalysts for the hydrogen evolution reaction (HER) is significant for clean and renewable energy research. This work reports the synthesis of N‐doped graphene nanosheets supported N‐doped carbon coated cobalt phosphide (CoP) nanoparticles via a pyrolysis and a subsequent phosphating process by using polyaniline. The obtained electrocatalyst exhibits excellent electrochemical activity for HER with a small overpotential of ?135 mV at 10 mA cm^?2 and a low Tafel slope of 59.3 mV dec^?1 in 0.5 m H₂SO₄. Additionally, the encapsulation of N‐doped carbon shell prevents CoP nanoparticles from corrosion, exhibiting good stability after 14 h operation. Moreover, the as‐prepared electrocatalyst also shows outstanding activity and stability in basic and neutral electrolytes.     

Hierarchical NiO@N‐Doped Carbon Microspheres with Ultrathin Nanosheet Subunits as Excellent Photocatalysts for Hydrogen Evolution

Achieving highly efficient hierarchical photocatalysts for hydrogen evolution is always challenging. Herein, hierarchical mesoporous NiO@N‐doped carbon microspheres (HNINC) are successfully fabricated with ultrathin nanosheet subunits as high‐performance photocatalysts for hydrogen evolution. The unique architecture of N‐doped carbon layers and hierarchical mesoporous structures from HNINC could effectively facilitate the separation and transfer of photo‐induced electron–hole pairs and afford rich active sites for photocatalytic reactions, leading to a significantly higher H₂ production rate than NiO deposited with platinum. Density functional theory calculations reveal that the migration path of the photo‐generated electron transfer is from Ni 3d and O 2p hybrid states of NiO to the C 2p state of graphite, while the photo‐generated holes locate at Ni 4s and Ni 4p hybrid states of NiO, which is beneficial to improve the separation of photo‐generated electron–hole pairs. Gibbs free energy of the intermediate state for hydrogen evolution reaction is calculated to provide a fundamental understanding of the high H₂ production rate of HNINC. This research sheds light on developing novel photocatalysts for efficient hydrogen evolution.     

Core–Shell Nitrogen‐Doped Carbon Hollow Spheres/Co3O4 Nanosheets as Advanced Electrode for High‐Performance Supercapacitor

Co₃O₄/nitrogen‐doped carbon hollow spheres (Co₃O₄/NHCSs) with hierarchical structures are synthesized by virtue of a hydrothermal method and subsequent calcination treatment. NHCSs, as a hard template, can aid the generation of Co₃O₄ nanosheets on its surface; while SiO₂ spheres, as a sacrificed‐template, can be dissolved in the process. The prepared Co₃O₄/NHCS composites are investigated as the electrode active material. This composite exhibits an enhanced performance than Co₃O₄ itself. A higher specific capacitance of 581 F g^?1 at 1 A g^?1 and a higher rate performance of 91.6% retention at 20 A g^?1 are achieved, better than Co₃O₄ nanorods (318 F g^?1 at 1 A g^?1 and 67.1% retention at 20 A g^?1). In addition, the composite is employed as a positive electrode to fabricate an asymmetric supercapacitor. The device can deliver a high energy density of 34.5 Wh kg^?1 at the power density of 753 W kg^?1 and display a desirable cycling stability. All of these attractive results make the unique hierarchical Co₃O₄/NHCS core–shell structure a promising electrode material for high‐performance supercapacitors.     

Ultrathin Visible‐Light‐Driven Mo Incorporating In2O3–ZnIn2Se4 Z‐Scheme Nanosheet Photocatalysts

Inspired by natural photosynthesis, the design of new Z‐scheme photocatalytic systems is very promising for boosting the photocatalytic performance of H₂ production and CO₂ reduction; however, until now, the direct synthesis of efficient Z‐scheme photocatalysts remains a grand challenge. Herein, it is demonstrated that an interesting Z‐scheme photocatalyst can be constructed by coupling In₂O₃ and ZnIn₂Se₄ semiconductors based on theoretical calculations. Experimentally, a class of ultrathin In₂O₃–ZnIn₂Se₄ (denoted as In₂O₃–ZISe) spontaneous Z‐scheme nanosheet photocatalysts for greatly enhancing photocatalytic H₂ production is made. Furthermore, Mo atoms are incorporated in the Z‐scheme In₂O₃–ZISe nanosheet photocatalyst by forming the Mo? Se bond, confirmed by X‐ray photoelectron spectroscopy, in which the formed MoSe₂ works as cocatalyst of the Z‐scheme photocatalyst. As a consequence, such a unique structure of In₂O₃–ZISe–Mo makes it exhibit 21.7 and 232.6 times higher photocatalytic H₂ evolution activity than those of In₂O₃–ZnIn₂Se₄ and In₂O₃ nanosheets, respectively. Moreover, In₂O₃–ZISe–Mo is also very stable for photocatalytic H₂ production by showing almost no activity decay for 16 h test. Ultraviolet–visible diffuse reflectance spectra, photoluminescence spectroscopy, transient photocurrent spectra, and electrochemical impedance spectroscopy reveal that the enhanced photocatalytic performance of In₂O₃–ZISe–Mo is mainly attributed to its widened photoresponse range and effective carrier separation because of its special structure.     

SnS2/Co3S4 Hollow Nanocubes Anchored on S‐Doped Graphene for Ultrafast and Stable Na‐Ion Storage

SnS₂ has been widely studied as an anode material for sodium‐ion batteries (SIBs) based on the high theoretical capacity and layered structure. Unfortunately, rapid capacity decay associated with volume variation during cycling limits practical application. Herein, SnS₂/Co₃S₄ hollow nanocubes anchored on S‐doped graphene are synthesized for the first time via coprecipitation and hydrothermal methods. When applied as the anode for SIBs, the sample delivers a distinguished charge specific capacity of 1141.8 mAh g^?1 and there is no significant capacity decay (0.1 A g^?1 for 50 cycles). When the rate is increased to 0.5 A g^?1, it presents 845.7 mAh g^?1 after cycling 100 times. Furthermore, the composite also exhibits an ultrafast sodium storage capability where 392.9 mAh g^?1 can be obtained at 10 A g^?1 and the charging time is less than 3 min. The outstanding electrochemical properties can be ascribed to the enhancement of conductivity for the addition of S‐doped graphene and the existence of p–n junctions in the SnS₂/Co₃S₄ heterostructure. Moreover, the presence of mesopores between nanosheets can alleviate volume expansion during cycling as well as being beneficial for the migration of Na⁺.     

Pseudocapacitive Ni‐Co‐Fe Hydroxides/N‐Doped Carbon Nanoplates‐Based Electrocatalyst for Efficient Oxygen Evolution

The oxygen evolution reaction (OER) catalytic activity of a transition metal oxides/hydroxides based electrocatalyst is related to its pseudocapacitance at potentials lower than the OER standard potential. Thus, a well‐defined pseudocapacitance could be a great supplement to boost OER. Herein, a highly pseudocapacitive Ni‐Fe‐Co hydroxides/N‐doped carbon nanoplates (NiCoFe‐NC)‐based electrocatalyst is synthesized using a facile one‐pot solvothermal approach. The NiCoFe‐NC has a great pseudocapacitive performance with 1849 F g^?1 specific capacitance and 31.5 Wh kg^?1 energy density. This material also exhibits an excellent OER catalytic activity comparable to the benchmark RuO₂ catalysts (an initiating overpotential of 160 mV and delivering 10 mA cm^?2 current density at 250 mV, with a Tafel slope of 31 mV dec^?1). The catalytic performance of the optimized NiCoFe‐NC catalyst could keep 24 h. X‐ray photoelectron spectroscopy, electrochemically active surface area, and other physicochemical and electrochemical analyses reveal that its great OER catalytic activity is ascribed to the Ni‐Co hydroxides with modular 2‐Dimensional layered structure, the synergistic interactions among the Fe(III) species and Ni, Co metal centers, and the improved hydrophily endowed by the incorporation of N‐doped carbon hydrogel. This work might provide a useful and general strategy to design and synthesize high‐performance metal (hydr)oxides OER electrocatalysts.     

Nickel@Nitrogen‐Doped Carbon@MoS2 Nanosheets: An Efficient Electrocatalyst for Hydrogen Evolution Reaction

Developing cheap, abundant, and easily available electrocatalysts to drive the hydrogen evolution reaction (HER) at small overpotentials is an urgent demand of hydrogen production from water splitting. Molybdenum disulfide (MoS₂) based composites have emerged as competitive electrocatalysts for HER in recent years. Herein, nickel@nitrogen‐doped carbon@MoS₂ nanosheets (Ni@NC@MoS₂) hybrid sub‐microspheres are presented as HER catalyst. MoS₂ nanosheets with expanded interlayer spacings are vertically grown on nickel@nitrogen‐doped carbon (Ni@NC) substrate to form Ni@NC@MoS₂ hierarchical sub‐microspheres by a simple hydrothermal process. The formed Ni@NC@MoS₂ composites display excellent electrocatalytic activity for HER with an onset overpotential of 18 mV, a low overpotential of 82 mV at 10 mA cm^?2, a small Tafel slope of 47.5 mV dec^?1, and high durability in 0.5 H₂SO₄ solution. The outstanding HER performance of the Ni@NC@MoS₂ catalyst can be ascribed to the synergistic effect of dense catalytic sites on MoS₂ nanosheets with exposed edges and expanded interlayer spacings, and the rapid electron transfer from Ni@NC substrate to MoS₂ nanosheets. The excellent Ni@NC@MoS₂ electrocatalyst promises potential application in practical hydrogen production, and the strategy reported here can also be extended to grow MoS₂ on other nitrogen‐doped carbon encapsulated metal species for various applications.     

Reversible Stacking of 2D ZnIn2S4 Atomic Layers for Enhanced Photocatalytic Hydrogen Evolution

It is technically challenging to reversibly tune the layer number of 2D materials in the solution. Herein, a facile concentration modulation strategy is demonstrated to reversibly tailor the aggregation state of 2D ZnIn₂S₄ (ZIS) atomic layers, and they are implemented for effective photocatalytic hydrogen (H₂) evolution. By adjusting the colloidal concentration of ZIS (ZIS-X, X = 0.09, 0.25, or 3.0 mg mL⁻¹), ZIS atomic layers exhibit the significant aggregation of (006) facet stacking in the solution, leading to the bandgap shift from 3.21 to 2.66 eV. The colloidal stacked layers are further assembled into hollow microsphere after freeze-drying the solution into solid powders, which can be redispersed into colloidal solution with reversibility. The photocatalytic hydrogen evolution of ZIS-X colloids is evaluated, and the slightly aggregated ZIS-0.25 displays the enhanced photocatalytic H₂ evolution rates (1.11 µmol m⁻² h⁻¹). The charge-transfer/recombination dynamics are characterized by time-resolved photoluminescence (TRPL) spectroscopy, and ZIS-0.25 displays the longest lifetime (5.55 µs), consistent with the best photocatalytic performance. This work provides a facile, consecutive, and reversible strategy for regulating the photo-electrochemical properties of 2D ZIS, which is beneficial for efficient solar energy conversion.     

Construction of ZnIn2S4/CdS/PdS S-Scheme Heterostructure for Efficient Photocatalytic H2 Production

It is facing a tremendous challenge to develop the desirable hybrids for photocatalytic H₂ generation by integrating the advantages of a single semiconductor. Herein, an all-sulfide ZnIn₂S₄/CdS/PdS heterojunction is constructed for the first time, where CdS and PdS nanoparticles anchor in the spaces of ZnIn₂S₄ micro-flowers due to the confinement effects. The morphology engineering can guarantee rapid charge transfer owing to the short carrier migration distances and the luxuriant reactive sites provided by ZnIn₂S₄. The S-scheme mechanism between ZnIn₂S₄ and CdS assisted by PdS cocatalyst is testified by in situ irradiated X-ray photoelectron spectroscopy and electron paramagnetic resonance (EPR), where the electrons and holes move in reverse driven by work function difference and built-in electric field at the interfaces. The optimal ZnIn₂S₄/CdS/PdS performs a glaring photocatalytic activity of 191.9 µmol h⁻¹ (10 mg of catalyst), and the largest AQE (apparent quantum efficiency) can reach a high value of 26.26%. This work may afford progressive tactics to design multifunctional photocatalysts.     

Ultrafine Dual‐Phased Carbide Nanocrystals Confined in Porous Nitrogen‐Doped Carbon Dodecahedrons for Efficient Hydrogen Evolution Reaction

Designing novel non‐noble electrocatalysts with controlled structures and composition remains a great challenge for efficient hydrogen evolution reaction (HER). Herein, a rational synthesis of ultrafine carbide nanocrystals confined in porous nitrogen‐doped carbon dodecahedrons (PNCDs) by annealing functional zeolitic imidazolate framework (ZIF‐8) with molybdate or tungstate is reported. By controlling the substitution amount of MO₄ units (M = Mo or W) in the ZIF‐8 framework, dual‐phase carbide nanocrystals confined in PNCDs (denoted as MC‐M₂C/PNCDs) can be obtained, which exhibit superior activity toward the HER to the single‐phased MC/PNCDs and M₂C/PNCDs. The evenly distributed ultrafine nanocrystals favor the exposure of active sites. PNCDs as the support facilitate charge transfer and protect the nanocrystals from aggregation during the HER process. Moreover, the strong coupling interactions between MC and M₂C provide beneficial sites for both water dissociation and hydrogen desorption. This work highlights a new feasible strategy to explore efficient electrocatalysts via engineering on nanostructure and composition.     

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.     

石墨烯-ZnIn2S4纳米复合微球的制备及光催化产氢活性

采用光催化还原法制备了石墨烯-ZnIn₂S₄纳米复合微球。采用XRD、SEM、TEM、FT-IR、XPS和DRS等手段对样品进行表征, 结果表明, 经过光催化还原处理后氧化石墨被还原成石墨烯, ZnIn₂S₄纳米微球负载在石墨烯表面。光催化产氢的实验结果表明, 当石墨烯含量为2.0wt%、光催化还原时间为24 h时, 石墨烯-ZnIn₂S₄纳米复合微球在模拟太阳光下产氢量达到1540.8 μmol, 是纯ZnIn₂S₄纳米微球的9.8倍。增强光催化性能的原因归结为石墨烯在复合光催化剂中起到了电子快速传输作用, 同时还对纳米复合微球光催化产氢反应机理进行了分析讨论。     

Single Tungsten Atoms Supported on MOF‐Derived N‐Doped Carbon for Robust Electrochemical Hydrogen Evolution

Tungsten‐based catalysts are promising candidates to generate hydrogen effectively. In this work, a single‐W‐atom catalyst supported on metal–organic framework (MOF)‐derived N‐doped carbon (W‐SAC) for efficient electrochemical hydrogen evolution reaction (HER), with high activity and excellent stability is reported. High‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) and X‐ray absorption fine structure (XAFS) spectroscopy analysis indicate the atomic dispersion of the W species, and reveal that the W₁N₁C₃ moiety may be the favored local structure for the W species. The W‐SAC exhibits a low overpotential of 85 mV at a current density of 10 mA cm^?2 and a small Tafel slope of 53 mV dec^?1, in 0.1 m KOH solution. The HER activity of the W‐SAC is almost equal to that of commercial Pt/C. Density functional theory (DFT) calculation suggests that the unique structure of the W₁N₁C₃ moiety plays an important role in enhancing the HER performance. This work gives new insights into the investigation of efficient and practical W‐based HER catalysts.     

Preparation of Carbon‐Rich g‐C3N4 Nanosheets with Enhanced Visible Light Utilization for Efficient Photocatalytic Hydrogen Production

Exfoliation of layered bulk g‐C₃N₄ (CNB) to thin g‐C₃N₄ sheets in nanodomains has attracted much attention in photocatalysis because of the intriguing properties of nanoscaled g‐C₃N₄. This study shows that carbon‐rich g‐C₃N₄ nanosheets (CNSC) can be easily prepared by self‐modification of polymeric melon units through successively thermally treating bulk g‐C₃N₄ in an air and N₂ atmosphere. The prepared CNSC not only retain the outstanding properties of nanosheets, such as large surface area, high aspect ratios, and short charges diffusion distance, but also overcome the drawback of enlarged bandgap caused by the quantum size effect, resulting in an enhanced utilization of visible light and photoinduced electron delocalization ability. Therefore, the as‐prepared CNSC show a high hydrogen evolution rate of 39.6 µmol h^?1 with a turnover number of 24.98 in 1 h at λ > 400 nm. Under irradiation by longer wavelength of light (λ > 420 nm), CNSC still exhibit a superior hydrogen evolution rate, which is 72.9 and 5.4 times higher than that of bulk g‐C₃N₄ and g‐C₃N₄ nanosheets, respectively.     

Co–Fe Alloy/N‐Doped Carbon Hollow Spheres Derived from Dual Metal–Organic Frameworks for Enhanced Electrocatalytic Oxygen Reduction

Metal–organic framework (MOF) composites have recently been considered as promising precursors to derive advanced metal/carbon‐based materials for various energy‐related applications. Here, a dual‐MOF‐assisted pyrolysis approach is developed to synthesize Co–Fe alloy@N‐doped carbon hollow spheres. Novel core–shell architectures consisting of polystyrene cores and Co‐based MOF composite shells encapsulated with discrete Fe‐based MOF nanocrystallites are first synthesized, followed by a thermal treatment to prepare hollow composite materials composed of Co–Fe alloy nanoparticles homogeneously distributed in porous N‐doped carbon nanoshells. Benefitting from the unique structure and composition, the as‐derived Co–Fe alloy@N‐doped carbon hollow spheres exhibit enhanced electrocatalytic performance for oxygen reduction reaction. The present approach expands the toolbox for design and preparation of advanced MOF‐derived functional materials for diverse applications.     

Constructing Built‐in Electric Field in Ultrathin Graphitic Carbon Nitride Nanosheets by N and O Codoping for Enhanced Photocatalytic Hydrogen Evolution Activity

Codoping of N and O in ultrathin graphitic carbon nitride (g‐C₃N₄) nanosheets leads to an inner electric field. This field restrains the recombination of photogenerated carriers and, thus, enhances hydrogen evolution. The layered structure of codoped g‐C₃N₄ nanosheets (N‐O‐CNNS) not only provides abundant sites of contact with the reaction medium, but also decreases the distance over which the photogenerated electron–hole pairs are transported to the reaction interface. Quantum confinement in the ultrathin structure results in an increased bandgap and makes the photocatalytic reaction more favorable than bulk g‐C₃N₄. Under visible light irradiation, N‐O‐CNNS with 3 wt% Pt achieves a hydrogen evolution rate of 9.2 mmol g^?1 h^?1 and a value of 46.9 mmol g^?1 h^?1 under AM1.5 with 5 wt% Pt. Thus, this work paves the way for designing efficient nanostructures with increased separation/transfer efficiency of photogenerated carriers and, hence, increased photocatalytic activities.