Adsorbing and Activating N2 on Heterogeneous Au–Fe3O4 Nanoparticles for N2 Fixation

Electrochemical nitrogen reduction reaction (NRR) is a promising approach to convert earth‐adundant N₂ into highly value‐added NH₃. Herein, it is demonstrated that the heterogeneous Au–Fe₃O₄ nanoparticles (NPs) can be adopted as highly efficient catalysts for NRR. Due to the synergistic effect of the strong N₂ fixation ability of Fe₃O₄ and the charge transfer capability of Au, the Au–Fe₃O₄ NPs show excellent performance with a high yield (NH₃: 21.42 µg mg_cat^?1 h^?1) and a favorable faradaic efficiency (NH₃: 10.54%) at ?0.2 V (vs reversible hydrogen electrode), both of which are much better than those of the Au NPs, Fe₃O₄ NPs, as well as core@shell Au@Fe₃O₄ NPs. It also exhibits good stability with largely maintained performance after six cycles. The N₂ temperature‐programmed desorption, surface valance band spectra, and X‐ray photoelectron spectroscopy collectively confirm that Au–Fe₃O₄ NPs have a strong adsorption capacity for the reaction species and suitable surface structure for electronic transfer. The theoretical calculations reveal that Fe provides the active site to fix N₂ into *N₂H while introducing Au optimizes the adsorption of NRR intermediates, making the NRR pathway on Au–Fe₃O₄ along an energetic‐favorable process and enhancing the NRR.     

Nanowire Structural Evolution from Fe3O4 to ϵ‐Fe2O3

The ?‐Fe₂O₃ phase is commonly considered an intermediate phase during thermal treatment of maghemite (γ‐Fe₂O₃) to hematite (α‐Fe₂O₃). The routine method of synthesis for ?‐Fe₂O₃ crystals uses γ‐Fe₂O₃ as the source material and requires dispersion of γ‐Fe₂O₃ into silica, and the obtained ?‐Fe₂O₃ particle size is rather limited, typically under 200 nm. In this paper, by using a pulsed laser deposition method and Fe₃O₄ powder as a source material, the synthesis of not only one‐dimensional Fe₃O₄ nanowires but also high‐yield ?‐Fe₂O₃ nanowires is reported for the first time. A detailed transmission electron microscopy (TEM) study shows that the nanowires of pure magnetite grow along [111] and <211> directions, although some stacking faults and twins exist. However, magnetite nanowires growing along the <110> direction are found in every instance to accompany a new phase, ?‐Fe₂O₃, with some micrometer‐sized wires even fully transferring to ?‐Fe₂O₃ along the fixed structural orientation relationship, (001) ∥ (111), [010] ∥ <110>. Contrary to generally accepted ideas regarding epsilon phase formation, there is no indication of γ‐Fe₂O₃ formation during the synthesis process; the phase transition may be described as being from Fe₃O₄ to ?‐Fe₂O₃, then to α‐Fe₂O₃. The detailed structural evolution process has been revealed by using TEM. 120° rotation domain boundaries and antiphase boundaries are also frequently observed in the ?‐Fe₂O₃ nanowires. The observed ?‐Fe₂O₃ is fundamentally important for understanding the magnetic properties of the nanowires.     

The β‐to‐γ Transition in BiFeO3: A Powder Neutron Diffraction Study

High‐temperature powder neutron diffraction experiments are conducted around the reported β–γ phase transition (～930 °C) in BiFeO₃. The results demonstrate that while a small volume contraction is observed at the transition temperature, consistent with an insulator–metal transition, both the β‐ and γ‐phase of BiFeO₃ exhibit orthorhombic symmetry; i.e., no further increase of symmetry occurs during this transition. The γ‐orthorhombic phase is observed to persist up to a temperature of approximately 950 °C before complete decomposition into Bi₂Fe₄O₉ (and liquid Bi₂O₃), which subsequently begins to decompose at approximately 960 °C.     

High‐Content,Well‐Dispersed γ‐Fe2O3 Nanoparticles Encapsulated in Macroporous Silica with Superior Arsenic Removal Performance

Novel composites of iron oxide encapsulated in macroporous silica with excellent arsenic adsorption performance have been successfully developed. Macroporous silica foams with large pore sizes of ≈100 nm and a high pore volume of 1.6 cm³ g^?1 are chosen as the porous matrix. Electron tomography technique confirms that γ‐Fe₂O₃ nanoparticles with an average particle size of ≈6 nm are spatially well‐dispersed and anchored on the pore walls at even a high γ‐Fe₂O₃ content of 34.8 wt%, rather than forming aggregates inside the pores or on the external surface. The open large‐pore structure, high loading amount, and the non‐aggregated nature of γ‐Fe₂O₃ nanoparticles lead to increased adsorption sites and thus high adsorption capacities of both As (V) and As (III) without pre‐treatment (248 and 320 mg g^?1, respectively). Moreover, the composites can reduce the concentration of both As (V) and As (III) from 100 to 2 μg L^?1. It is also demonstrated that the composites can be applied in a household drinking water treatment device, which can continuously treat 20 L of wastewater containing As (V) with the effluent concentration lower than the World Health Organization standard.     

Template‐Assisted Synthesis of Mesoporous Magnetic Nanocomposite Particles

A new concept is proposed to synthesize mesoporous magnetic nanocomposite particles of great scientific and technological importance. Mesoporous silica coatings were created on micrometer‐sized magnetite (Fe₃O₄) particles using cetyltrimethylammonium chloride micelles as molecular templates. The characterization by transmission electron microscopy (TEM), nitrogen adsorption–desorption, diffuse‐reflectance Fourier‐transform infrared spectroscopy, and zeta‐potential measurements confirmed the deposition of mesoporous silica thin layers on the magnetite particles. The synthesized particles showed a drastic increase in specific surface area with an average pore size of 2.5 nm. The coating material showed a negligible effect on the saturation magnetization of the original particles that were fully protected by silica coatings. The synthesized mesoporous magnetic nanocomposite particles have a wide range of applications in toxin removal, waste remediation, catalysis, reactive sorbents, and biological cell separations.     

Fabrication and Size‐Selective Bioseparation of Magnetic Silica Nanospheres with Highly Ordered Periodic Mesostructure

In this paper, we report a novel synthesis and selective bioseparation of the composite of Fe₃O₄ magnetic nanocrystals and highly ordered MCM‐41 type periodic mesoporous silica nanospheres. Monodisperse superparamagnetic Fe₃O₄ nanocrystals were synthesized by thermal decomposition of iron stearate in diol in an autoclave at low temperature. The synthesized nanocrystals were encapsulated in mesoporous silica nanospheres through the packing and self‐assembly of composite nanocrystal–surfactant micelles and surfactant/silica complex. Different from previous studies, the produced magnetic silica nanospheres (MSNs) possess not only uniform nanosize (90 ～ 140 nm) but also a highly ordered mesostructure. More importantly, the pore size and the saturation magnetization values can be controlled by using different alkyltrimethylammonium bromide surfactants and changing the amount of Fe₃O₄ magnetic nanocrystals encapsulated, respectively. Binary adsorption and desorption of proteins cytochrome c (cyt c) and bovine serum albumin (BSA) demonstrate that MSNs are an effective and highly selective adsorbent for proteins with different molecular sizes. Small particle size, high surface area, narrow pore size distribution, and straight pores of MSNs are responsible for the high selective adsorption capacity and fast adsorption rates. High magnetization values and superparamagnetic property of MSNs provide a convenient means to remove nanoparticles from solution and make the re‐dispersion in solution quick following the withdrawal of an external magnetic field.     

Nanoengineered Polypyrrole‐Coated Fe2O3@C Multifunctional Composites with an Improved Cycle Stability as Lithium‐Ion Anodes

Novel multifunctional composites composed of highly dispersed nanosized Fe₂O₃ particles, a tubular mesoporous carbon host, and a conductive polypyrrole (PPy) sealing layer are hierarchically assembled via two facile processes, including bottom‐up introduction of Fe₂O₃ nanoparticles in tubular mesoporous carbons, followed by in situ surface sealing with the PPy coating. Fe₂O₃ particles are well‐dispersed within the carbon matrix and PPy is spatially and selectively coated onto the external surface and the pore entrances of the Fe₂O₃@C composite, thereby bridging the composite particles together into a larger unit. As an anode material for Li‐ion batteries (LIBs), the PPy‐coated Fe₂O₃@C composite exhibits stable cycle performance. Additionally, the PPy‐coated Fe₂O₃@C composite also possesses fast electrode reaction kinetics, high Fe₂O₃ use efficiency, and large volumetric capacity. The excellent electrochemical performance is associated with a synergistic effect of the highly porous carbon matrix and the conducting PPy sealing layer. Such multifunctional configuration prevents the aggregation of NPs and maintains the structural integrity of active materials, in addition to effectively enhancing the electronic conductivity and warranting the stability of as‐formed solid electrolyte interface (SEI) films. This nanoengineering strategy might open new avenues for the design of other multifunctional composite architectures as electrode materials in order to achieve high‐performance LIBs.     

Uniform Rattle‐type Hollow Magnetic Mesoporous Spheres as Drug Delivery Carriers and their Sustained‐Release Property

A novel kind of rattle‐type hollow magnetic mesoporous sphere (HMMS) with Fe₃O₄ particles encapsulated in the cores of mesoporous silica microspheres has been successfully fabricated by sol–gel reactions on hematite particles followed by cavity generation with hydrothermal treatment and H₂ reduction. Such a structure has the merits of both enhanced drug‐loading capacity and a significant magnetization strength. The prepared HMMSs realize a relatively high storage capacity up to 302 mg g^?1 when ibuprofen is used as a model drug, and the IBU–HMMS system has a sustained‐release property, which follows a Fick's law.     

Novel Composites of α‐Fe2O3 Tetrakaidecahedron and Graphene Oxide as an Effective Photoelectrode with Enhanced Photocurrent Performances

Novel composites composed of α‐Fe₂O₃ tetrakaidecahedrons and graphene oxide have been easily fabricated and demonstrated to be efficient photoelectrodes for photoelectrochemical water splitting reaction with superior photocurrent response. α‐Fe₂O₃ tetrakaidecahedrons are facilely synthesized in a green manner without any organic additives and then modified with graphene oxide. The morphological and structural properties of α‐Fe₂O₃/graphene composite are intensively investigated by several means, such as X‐ray diffraction, field‐emission scanning electron microscope, transmission electron microscope, X‐ray photoelectron spectroscopy, Fourier Transform infrared spectroscopy, and Raman spectroscopy. The tetrakaidecahedronal hematite particles have been indicated to be successfully coupled with graphene oxide. Systematical photoelectrochemical and impedance spectroscopy measurements have been carried out to investigate the favorable performance of α‐Fe₂O₃/graphene composites, which are found to be effective photoanodes with rapid, steady, and reproducible feature. The coupling of graphene with α‐Fe₂O₃ particles has greatly enhanced the photoelectrochemical performance, resulting in higher photocurrent and lower onset potential than that of pure α‐Fe₂O₃. This investigation has provided a feasible method to synthesize α‐Fe₂O₃ tetrakaidecahedron and fabricate an efficient α‐Fe₂O₃/graphene photoelectrode for photoelectrochemical water oxidation, suggesting a promising route to design noble metal free semiconductor/graphene photocatalysts.     

Large Upconversion Enhancement in the “Islands” Au–Ag Alloy/NaYF4: Yb3+, Tm3+/Er3+ Composite Films,and Fingerprint Identification

The surface plasmon (SP) modulation is a promised way to highly improve the strength of upconversion luminescence (UCL) and expand its applications. In this work, the “islands” Au–Ag alloy film is prepared by an organic removal template method and explored to improve the UCL of NaYF₄: Yb3+, Tm³⁺/Er³⁺. After the optimization of Au–Ag molar ratio (Au_1.25–Ag_0.625) and the size of NaYF₄ nanoparticles (NPs, ≈7 nm), an optimum enhancement as high as 180 folds is obtained (by reflection measurement) for the overall UCL intensity of Tm³⁺. Systematic studies indicate that the UCL enhancement factor (EF) increases with the increased size of metal NPs and the increase of diffuse reflection, with the decreased size of NaYF₄ NPs, with the decreased power density of excitation light and with improving order of multiphoton populating. The total decay rate varies only ranging of about 20% while EF changes significantly. All the facts above indicate that the UCL enhancement mainly originates from coupling of SP with the excitation electromagnetic field. Furthermore, the fingerprint identification based on SP‐enhanced UCL is realized in the metal/UC system, which provides a novel insight for the application of the metal/UC device.     

Synthesis of Self‐Supported Ordered Mesoporous Cobalt and Chromium Nitrides

Herein, we demonstrate an ammonia nitridation approach to synthesize self‐supported ordered mesoporous metal nitrides (CoN and CrN) from mesostructured metal oxide replicas (Co₃O₄ and Cr₂O₃), which were nanocastly prepared by using mesoporous silica SBA‐15 as a hard template. Two synthetic routes are adopted. One route is the direct nitridation of mesoporous metal oxide nanowire replicas templated from SBA‐15 to metal nitrides. By this method, highly ordered mesoporous cobalt nitrides (CoN) can be obtained by the transformation of Co₃O₄ nanowire replica under ammonia atmosphere from 275 to 350 °C, without a distinct lose of the mesostructural regularity. Treating the samples above 375 °C leads to the formation of metallic cobalt and the collapse of the mesostructure due to large volume shrinkage. The other route is to transform mesostructured metal oxides/silica composites to nitrides/silica composites at 750–1000 °C under ammonia. Ordered mesoporous CrN nanowire arrays can be obtained after the silica template removal by NaOH erosion. A slowly temperature‐program‐decrease process can reduce the influence of silica nitridation and improve the purity of final CrN product. Small‐angle XRD patterns and TEM images showed the 2‐D ordered hexagonal structure of the obtained mesoporous CoN and CrN nanowires. Wide‐angle XRD patterns, HRTEM images, and SAED patterns revealed the formation of crystallized metal nitrides. Nitrogen sorption analyses showed that the obtained materials possessed high surface areas (70–90 m² g^?1) and large pore volumes (about 0.2 cm³ g^?1).     

Novel Au–SiO2–WO3 Core–Shell Composite Nanoparticles for Surface‐Enhanced Raman Spectroscopy with Potential Application in Cancer Cell Imaging

With the rapid development of nanotechnology during the last decades, the ability to detect and control individual objects at the nanoscale has enabled us to deal with complex biomedical challenges. In cancer imaging, novel nanoparticles (NPs) offer promising potential to identify single cancer cells and precisely label larger areas of cancer tissues. Herein, a new class of size tunable core–shell composite (Au–SiO₂–WO₃) nanoparticles is reported. These nanoparticles display an easily improvable ≈10³ surface‐enhanced Raman scattering (SERS) enhancement factor with a double Au shell for dried samples over Si wafers and several orders of magnitude for liquid samples. WO₃ core nanoparticles measuring 20–50 nm in diameter are sheathed by an intermediate 10–60 nm silica layer, produced by following the Stöber‐based process and Turkevich method, followed by a 5–20 nm thick Au outer shell. By attaching 4‐mercaptobenzoic acid (4‐MBA) molecules as Raman reporters to the Au, high‐resolution Raman maps that pinpoint the nanoparticles' location are obtained. The preliminary results confirm their advantageous SERS properties for single‐molecule detection, significant cell viability after 24 h and in vitro cell imaging using coherent anti‐stokes Raman scattering. The long‐term objective is to measure SERS nanoparticles in vivo using near‐infrared light.     

The Effects of Multiphase Formation on Strain Relaxation and Magnetization in Multiferroic BiFeO3 Thin Films

Multiferroic epitaxial Bi‐Fe‐O thin films of different thicknesses (15–500 nm) were grown on SrTiO₃ (001) substrates by pulsed laser deposition under various oxygen partial pressures to investigate the microstructural evolution in the Bi‐Fe‐O system and its effect on misfit strain relaxation and on the magnetic properties of the films. Films grown at low oxygen partial pressure show the canted antiferromagnetic phase α‐Fe₂O₃ embedded in a matrix of BiFeO₃. The ferromagnetic phase, γ‐Fe₂O₃ is found to precipitate inside the α‐Fe₂O₃ grains. The formation of these phases changes the magnetic properties of the films and the misfit strain relaxation mechanism. The multiphase films exhibit both highly strained and fully relaxed BiFeO₃ regions in the same film. The magnetization in the multiphase Bi‐Fe‐O films is controlled by the presence of the γ‐Fe₂O₃ phase rather than heteroepitaxial strain as it is the case in pure single phase BiFeO₃. Also, our results show that this unique accommodation of misfit strain by the formation of α‐Fe₂O₃ gives rise to significant enhancement of the piezo electric properties of BiFeO_3.     

Single Molecular Wells–Dawson‐Like Heterometallic Cluster for the In Situ Functionalization of Ordered Mesoporous Carbon: A T 1‐ and T 2‐Weighted Dual‐Mode Magnetic Resonance Imaging Agent and Drug Delivery System

Developing a feasible way to prepare highly dispersed heterometallic nanoparticles incorporated in porous carbon composites is of significant importance for multifunctional materials. In this work, heterometallic γ‐Fe₂O₃ and GdPO₄ nanoparticles that are incorporated in ordered mesoporous carbon composites are facilely prepared by a one‐pot in situ method using a Wells–Dawson‐like cluster of [Fe₆Gd₆(μ₃‐O)₂(CO₃)(O₃PPh)₆(O₂C ^t Bu)₁₈] ({Fe₆Gd₆P₆} for short) as the precursor. It is verified that the γ‐Fe₂O₃ and GdPO₄ nanoparticles are highly dispersed and embedded into the carbon matrix with a particle size smaller than 5 nm, even when the carbon matrix is changed from 2D hexagonal P6mm to 3D body‐centered cubic Im‐3m symmetry. Additionally, a formation mechanism is proposed. Furthermore, dual‐mode magnetic resonance (MR) imaging and drug carrier properties are evaluated by in vitro experiments, which show a satisfactory T ₁‐ and T ₂‐weighted MR imaging effect with r ₁ and r ₂ relaxivity values of 2.7 and 183.7 mM^?1 s^?1, respectively, and doxorubicin hydrochloride carrier amount of 102 mg g^?1, identifying a combined function for potential diagnostic and therapy.     

Systematic Study of the Growth of Aligned Arrays of α‐Fe2O3 and Fe3O4 Nanowires by a Vapor–Solid Process

Growth of aligned and uniform α‐Fe₂O₃ nanowire (NW) arrays has been achieved by a vapor–solid process. The experimental conditions, such as type of substrate, local growth and geometrical environment, gas‐flow rate, and growth temperature, under which the high density α‐Fe₂O₃ NW arrays can be grown by a vapor–solid route via the tip‐growth mechanism have been systematically investigated. The density of the α‐Fe₂O₃ NWs can be enhanced by increasing the concentration of Ni atoms inside the alloy substrate. The synthesized temperature can be as low as 400 °C. Fe₃O₄ NWs can be produced by converting α‐Fe₂O₃ NWs in a reducing atmosphere at 450 °C. The transformation of phase and structure have been observed by in situ transmission electron microscopy. The magnetic and field‐emission properties of the NWs indicate their potential applications in nanodevices.     

One‐Step Hydrothermal Synthesis of 2D Hexagonal Nanoplates of α‐Fe2O3/Graphene Composites with Enhanced Photocatalytic Activity

There has been significant progress in the field of semiconductor photocatalysis, but it is still a challenge to fabricate low‐cost and high‐activity photocatalysts because of safety issues and non‐secondary pollution to the environment. Here, 2D hexagonal nanoplates of α‐Fe₂O₃/graphene composites with relatively good distribution are synthesized for the first time using a simple, one‐step, template‐free, hydrothermal method that achieves the effective reduction of the graphene oxide (GO) to graphene and intimate and large contact interfaces of the α‐Fe₂O₃ nanoplates with graphene. The α‐Fe₂O₃/graphene composites showed significantly enhancement in the photocatalytic activity compared with the pure α‐Fe₂O₃ nanoplates. At an optimal ratio of 5 wt% graphene, 98% of Rhodamine (RhB) is decomposed with 20 min of irradiation, and the rate constant of the composites is almost four times higher than that of pure α‐Fe₂O₃ nanoplates. The decisive factors in improving the photocatalytic performance are the intimate and large contact interfaces between 2D hexagonal α‐Fe₂O₃ nanoplates and graphene, in addition to the high electron withdrawing/storing ability and the highconductivity of reduced graphene oxide (RGO) formed during the hydrothermal reaction. The effective charge transfer from α‐Fe₂O₃ nanoplates to graphene sheets is demonstrated by the significant weakening of photoluminescence in α‐Fe₂O₃/graphene composites.     

Supramolecular Photonic Elastomers with Brilliant Structural Colors and Broad‐Spectrum Responsiveness

Photonic elastomers (PEs) that can tune their colors through adjusting the lattice spacing of incorporated colloidal particles during mechanical deformation have shown great promise in visualized strain/stress sensors. However, the unsatisfactory structural color and narrow‐spectrum responsiveness limit their broad applications. Herein, carbon‐coated Fe₃O₄ nanoparticles (Fe₃O₄@C NPs) with a high refractive index (RI) and broad light absorption are employed for the construction of PEs with brilliant colors and broad‐spectrum responsiveness by incorporating the Fe₃O₄@C NPs into amino‐terminated poly(dimethylsiloxane) (amino‐PDMS) polymer through supramolecular interactions. The inherent light‐absorbing property, high RI, and supramolecular‐induced short‐range ordered arrangement of Fe₃O₄@C NPs imparts the PEs with brilliant and angle‐independent structural color. By optimizing the content of Fe₃O₄@C NPs in the PEs, broad‐spectrum responsiveness (stopband shifting ≈223 nm) and excellent recovery properties under a large strain can be achieved. The dynamic and reversible interaction endows the PEs with a healable capability. More interestingly, the incorporated Fe₃O₄@C NPs with photothermal capability can effectively absorb light and convert it into heat under light irradiation (solar light or near‐infrared laser), accelerating healing of the damaged PEs. This study provides a new strategy for bioinspired construction of PEs for applications in the fields of sensing, colorful coating, and display.     

Epitaxial Growth of Branched α‐Fe2O3/SnO2 Nano‐Heterostructures with Improved Lithium‐Ion Battery Performance

We report the synthesis of a novel branched nano‐heterostructure composed of SnO₂ nanowire stem and α‐Fe₂O₃ nanorod branches by combining a vapour transport deposition and a facile hydrothermal method. The epitaxial relationship between the branch and stem is investigated by high resolution transmission electron microscopy (HRTEM). The SnO₂ nanowire is determined to grow along the [101] direction, enclosed by four side surfaces. The results indicate that distinct crystallographic planes of SnO₂ stem can induce different preferential growth directions of secondary nanorod branches, leading to six‐fold symmetry rather than four‐fold symmetry. Moreover, as a proof‐of‐concept demonstration of the function, such α‐Fe₂O₃/SnO₂ composite material is used as a lithium‐ion batteries (LIBs) anode material. Low initial irreversible loss and high reversible capacity are demonstrated, in comparison to both single components. The synergetic effect exerted by SnO₂ and α‐Fe₂O₃ as well as the unique branched structure are probably responsible for the enhanced performance.     

α‐Fe2O3 Nanoflakes as an Anode Material for Li‐Ion Batteries

Nanoflakes of α‐Fe₂O₃ were prepared on Cu foil by using a thermal treatment method. The nanoflakes were characterized by X‐ray diffraction, scanning electron microscopy, high‐resolution transmission electron microscopy, and Raman spectroscopy. The reversible Li‐cycling properties of the α‐Fe₂O₃ nanoflakes have been evaluated by cyclic voltammery, galvanostatic discharge–charge cycling, and impedance spectral measurements on cells with Li metal as the counter and reference electrodes, at ambient temperature. Results show that Fe₂O₃ nanoflakes exhibit a stable capacity of (680 ± 20) mA h g^–1, corresponding to (4.05 ± 0.05) moles of Li per mole of Fe₂O₃ with no noticeable capacity fading up to 80 cycles when cycled in the voltage range 0.005–3.0 V at 65 mA g^–1 (0.1 C rate), and with a coulombic efficiency of > 98 % during cycling (after the 15th cycle). The average discharge and charge voltages are 1.2 and 2.1 V, respectively. The observed cyclic voltammograms and impedance spectra have been analyzed and interpreted in terms of the ‘conversion reaction' involving nanophase Fe⁰–Li₂O. The superior performance of Fe₂O₃ nanoflakes is clearly established by a comparison of the results with those for Fe₂O₃ nanoparticles and nanotubes reported in the literature.     

Highly Efficient Photoelectrochemical Water Splitting: Surface Modification of Cobalt‐Phosphate‐Loaded Co3O4/Fe2O3 p–n Heterojunction Nanorod Arrays

Hematite (α‐Fe₂O₃) as a photoanode material for photoelectrochemical (PEC) water splitting suffers from the two problems of poor charge separation and slow water oxidation kinetics. The construction of p–n junction nanostructures by coupling of highly stable Co₃O₄ in aqueous alkaline environment to Fe₂O₃ nanorod arrays with delicate energy band positions may be a challenging strategy for efficient PEC water oxidation. It is demonstrated that the designed p‐Co₃O₄/n‐Fe₂O₃ junction exhibits superior photocurrent density, fast water oxidation kinetics, and remarkable charge injection and bulk separation efficiency (η_inj and η_sep), attributing to the high catalytic behavior of Co₃O₄ for the oxygen evolution reaction as well as the induced interfacial electric field that facilitates separation and transportation of charge carriers. In addition, a cocatalyst of cobalt phosphate (Co‐Pi) is introduced, which brings the PEC performance to a high level. The resultant Co‐Pi/Co₃O₄/Ti:Fe₂O₃ photoanode shows a photocurrent density of 2.7 mA cm^?2 at 1.23 V_RHE (V vs reversible hydrogen electrode), 125% higher than that of the Ti:Fe₂O₃ photoanode. The optimized η_inj and η_sep of 91.6 and 23.0% at 1.23 V_RHE are achieved on Co‐Pi/Co₃O₄/Ti:Fe₂O₃, respectively, corresponding to the 70 and 43% improvements compared with those of Ti:Fe₂O₃. Furthermore, Co‐Pi/Co₃O₄/Ti:Fe₂O₃ shows a low onset potential of 0.64 V_RHE and long‐time PEC stability.