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Hierarchical porous iron and nitrogen co-doped carbon (Fe-N/C) materials have been considered as an appealing non-noble metal-based catalyst in oxygen reduction reactions (ORR). However, the conductivity loss caused by the scattering of electrons on pores and defects markedly limits their catalytic activity, which attracted seldom attention in this area. Herein, a novel crystalline carbon modified hierarchical porous Fe-N/C electrocatalyst with enhanced electronic conductivity is designed and prepared via a two-step calcination-catalysis process. The resistivity of hierarchical porous Fe-N/C is decreased from 2.123 Ω cm to 0.479 Ω cm after crystalline carbon introduction. The electrocatalyst annealed at 800 °C (Fe-N/C-800) exhibits a superior activity with the half-wave potential (E1/2) of 0.89 V, which outperforms the commercial carbon-supported platinum (Pt/C) catalyst (0.85 V). The strategy of crystalline carbon modification provides a fresh approach to improve the electronic conductivity of porous carbon-based materials.

The rational design of oxygen evolution reaction (OER) catalysts from the perspective of electronic structure is highly desirable to optimize electrocatalytic activity. Monometallic phosphides such...

Developing oxygen evolution reaction (OER) catalysts with high activity and long-term stability is critical to achieving efficient hydrogen production from water electrolysis. Herein, a porous bimetallic cobalt-iron phosphide (CoFe-P) nanofoam is synthesized via a novel one-pot glucose-blowing followed by oxidization and then phosphidization process. The CoFe-P nanofoam presents a porous nanostructure which contributes to contact with electrolytes and release of generated gas during electrocatalytic reactions. As OER catalysts in alkaline, the bimetallic porous CoFe-P nanofoam exhibit a lower overpotential (258 mV@10 mA cm

Multi-walled carbon nanotubes (MWCNTs) with one-dimensional nanostructure are an ideal support for oxygen reduction reaction (ORR) catalysts thanks to their intrinsic outstanding electrical conductivity and high specific surface area. Iron and nitrogen doping could alter the local electronic structure and therefore enhance the ORR activity of MWCNTs, but the preparation process always includes complicated growth conditions and post-treatment. Herein, an iron and nitrogen co-modified multi-walled carbon nanotubes (Fe–N-MWCNTs) with hierarchical nanostructure is engineered and synthesized via a simple two-step pyrolysis approach. Large specific surface area, low resistivity, and intensified charge density near the Fermi level synergistically endow the Fe–N-MWCNTs with outstanding ORR activity. The optimal Fe–N-MWCNTs exhibit a higher onset potential value of 0.92 V (versus RHE) and half-wave potential (E 1/2) of 0.85 V (versus RHE) in 0.1 M KOH medium, which exceeds the benchmark Pt/C electrocatalyst (E 1/2 = 0.84 V). This strategy of modifying MWCNTs support by a simple calcination process provides a feasible method to prepare cost-efficient ORR electrocatalysts.

Metal–organic frameworks (MOFs) are a preferred electrode material choice due to their open crystalline framework and potential redox sites. However, their random crystal orientations and low condu...

Lithium-ion batteries (LIBs) are widely regarded as a promising electrochemical energy storage device, due to their high energy density and good cycling stability. To date, the development of anode materials for LIBs is still confronted with many serious problems, and much effort is required for constructing more ideal anode materials. Herein, starting with metal–organic frameworks (MOFs), an amorphous VOx coated Fe3O4/C hierarchical nanospindle has been successfully synthesized. The obtained Fe3O4/C@VOx nanospindle has a uniform particle size of ∼100 nm in diameter and ∼400 nm in length and consists of ultrafine Fe3O4 nanoparticles (∼5 nm) embedded in a porous carbon matrix as the core and an amorphous VOx layer as the shell. Notably, as the anode material for LIBs, Fe3O4/C@VOx delivers a high coulombic efficiency (74.2%) and a large capacity of 845 mA h g−1 after 500 cycles at 1000 mA g−1. A prominent discharge reversible capacity of 340 mA h g−1 is also still retained at 5000 mA g−1. More importantly, the presented facile MOF-derived route could be easily extended to other functional materials for widespread applications.

The integration of structural design and compositional modulation has been a hotspot for the optimization of electrocatalytic properties due to their synergistic effect. However, the details of this synergistic effect still lacks deep study. Herein, we fabricated an Ni2P/Ni5P4 electrocatalyst with a Janus nanostructure embedded in N-doped carbon through a controllable phosphidation approach. The as-obtained hybrid catalyst realized an overpotential of 104 mV and Tafel slope of 38.5 mV dec−1, which were smaller than that of the single Ni2P and Ni5P4, at a current density of −10 mA cm−2 in 0.5 M H2SO4 electrolyte. To reveal the reasons for the promotion of electrocatalytic properties, the synergistic effect was analyzed with the difference charge density (DCD), density of state (DOS), ΔGH*, and strength of the internal electric field (IEF) on the interface between Ni5P4 and Ni2P. The results indicated that the composite structures could optimize the ΔGH* due to the change in the DOS instead of DCD. Further calculations indicated that the composite structure could modify the effective electric field, which is often overlooked and may be the reason for the change in the DOS. This study provides new insight for designing multi-component catalysts and deeply illuminating a part of the synergistic effect for high-efficiently electrocatalytic activities.

Developing highly efficient, stable, and inexpensive electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is the premise of achieving large-scale water splitting. Here, NixFe1−xB prepared by a facile borothermal reduction in molten salt is a robust bifunctional electrocatalyst for overall water splitting. The NixFe1−xB electrocatalyst achieves a current density of 10 mA cm−2 at overpotentials of 63.5 mV for the HER and 282 mV for the OER in 1 M KOH electrolyte, respectively. Density functional theory (DFT) calculations suggest that the NixFe1−xB possesses a lower absolute value of H* adsorption free energy (|ΔGH*|) than the primitive FeB and NiB, which is beneficial to improve the HER activity. Two identical NixFe1−xB electrodes are combined to form an alkaline electrolyzer, which achieves a current density of 10 mA cm−2 at 1.57 V for overall water splitting. This work provides a strategy to develop highly efficient transition metal boride catalysts for overall water splitting.

Developing highly active and inexpensive electrocatalysts for oxygen evolution reaction (OER) is critical to large-scale applications of electrochemical water splitting. In the present work, a novel porous NiO/NiCo2O4 heterostructure is constructed by two-stage calcination of nickel-cobalt bimetallic hydroxide precursors prepared using a microwave-assisted hydrothermal method, in which abundant interfaces are constituted. The NiO phase stabilized in NiCo2O4 matrix is the nanometer scale (ca. 13 nm). The porous nanoscale NiO/NiCo2O4 heterostructure shows a 10 mA cm−2 current density under the overpotential of 264 mV which outperforms the noble catalyst RuO2. It is demonstrated that the highly active Ni3+ species generated by the oxidation of nanometer scale NiO surface are responsible for enhanced OER. Additionally, DFT calculations certify that the heterostructure interfaces promote the chemisorption of OH intermediates. This strategy of increasing the intrinsic activity and improving the chemisorption abilities for oxygen-containing intermediates by constructing nanoscale heterostructure electrocatalysts provides a feasible method to accelerate the reaction rate of OER.

Graphene promoted triphasic N/Ti3+-TiO2 (GNTT) heterostructures with different weight addition ratios of graphene have been assembled by a facile in-situ hydrothermal treatment of TiN and graphene oxide. The obtained GNTT photocatalysts are characterized by a collection of techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, and photoluminescence (PL), etc. It is demonstrated that graphene modified N/Ti3+ codoped TiO2 with ternary phases mixture of brookite, anatase and rutile can be obtained. Furthermore, the GNTT heterostructure photocatalysts exhibit an enhanced photoactivity for photocatalytic degradation of methyl blue, levofloxacin, and rhodamine B as compared with TiO2, N-doped TiO2, and N/Ti3+ codoped TiO2 (NTT). The reason for the improved photoactivity can be listed as follows: i) N and Ti3+ doping can severally form N2p impurity level above valance band (VB) and local states below the conduction band (CB) of TiO2, which contribute to the visible light response of TiO2; ii) the ternary heterophase junction can efficiently transfer and separate photogenerated electron-hole pairs; iii) graphene acts as an electron reservoir to trap and transport the electrons photogenerated from TiO2. The synergistic effect of these factors accounts for the photoactivity advancement of GNTT photocatalysts. This study develops a novel approach to improve the visible light utilization of TiO2 and facilitates their applications in the environment and energy issues.

Lithium-ion batteries (LIBs) are widely regarded as a promising electrochemical energy storage device, due to their high energy density and good cycling stability. To date, the development of anode materials for LIBs is still confronted with many serious problems, and much effort is required for constructing more ideal anode materials. Herein, starting with metal-organic frameworks (MOFs), an amorphous VO

NiCo-layered double hydroxides (LDHs) have recently emerged as potential oxygen evolution reaction (OER) catalysts in alkaline solutions. However, their preferred active sites have been ill-defined until now. In this work, hierarchical hollow nanopolyhedra assembled by NiCo-LDH nanosheets with adjustable composition and nanostructure are prepared via a facile self-templated strategy. DFT calculations indicate that Co3+ hollow sites are the preferred adsorption and active sites. The resultant hierarchical NiCo-LDH hollow nanopolyhedra realize superior OER activity by optimizing the composition of NiCo-LDH, which achieves a 10 mA cm–2 current density at an overpotential of 314 mV. This work not only presents deeper insights into the intrinsic OER electrocatalytic activity for NiCo-LDH but also elucidates on the further optimization of the OER properties of other bimetallic electrocatalysts.

There has been considerable progress in the field of semiconductor photocatalysis; nevertheless, developing low-cost and high-activity photocatalysts are still a challenge at the present. Here, a series of graphene/MoS2/Fe2O3 ternary composites (MG/Fe2O3) were prepared via a two-step simple hydrothermal process using H2MoO4, CH4N2S, graphene oxide, and Fe(NO3)3·9H2O as the starting materials, respectively. Various techniques such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectra, and UV–Vis diffuse reflectance spectroscopy were adopted to characterize the as-prepared samples. The results suggested that MoS2/graphene hybrids were successfully composited with Fe2O3. A redshift of absorption edge in the light region and more absorption in the visible light region were confirmed for the prepared ternary composites. The highest photocatalytic activity of MG/Fe2O3 composites (3.01 × 10−3 min−1) was observed, which was 1.5 times higher than that of pure Fe2O3 (1.97 × 10−3 min−1). The effect of ultrasound on photocatalytic reactions was investigated, and its photodegradation rate was improved 2.2 times than the photoreactor system without sonication. The results indicated that the positive synergetic effect of the MoS2 and graphene components in this hybrid cocatalyst, which extended the light response and acted as a charges transfer medium, respectively, is the key to improve photocatalytic performance of Fe2O3. This research may provide new concepts for the design of high-efficiency photocatalysts and broaden the potential of application of Fe2O3 in photocatalytic fields. MoS2/graphene/Fe2O3 nanocomposites were successfully fabricated via a simple two-step hydrothermal process and a considerably enhanced activity of visible light-induced photodecomposition of MB was demonstrated.

Carbon-incorporated TiO 2 microspheres (CTMs), produced by a flame assisted hydrolysis method, were successfully decorated with Cu 2 O nanoparticles via a chemical bath deposition process. A red shift of absorption edge and enhanced visible light absorption were observed for the resulted Cu 2 O/CTMs composites compared with bare TiO 2 and CTMs. Their effective visible-light-driven photocatalytic activity and the effect of deposition amount of Cu 2 O on the photocatalytic properties were determined by the degradation of methylene blue. The highest degradation rate was achieved for Cu 2 O/CTMs composite (29.2%) compared to CTMs (18.5%) and bare TiO 2 (7.3%) under visible light illumination for 80 min. The improved photoactivity can be ascribed to the integrative synergistic effect of carbon and Cu 2 O on TiO 2 . This work develops a rapid and facile approach for the fabrication of Cu 2 O decorated carbon-incorporated TiO 2 microspheres composites and demonstrates it is an efficient route to improve the photocatalytic activity of TiO 2 .

A series of composites, based on graphitic carbon nitride and nitrogen-doped titanium dioxide (g-C3N4/N-TiO2), were prepared by a solid-phase calcination process, in which a homogenous mixture containing melamine and TiN was calcined at 550 °C for 3 h in air. Various techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectroscopy (UV-vis DRS) characterized the as-prepared composites. The results suggested that nitrogen was incorporated into the TiO2 lattice that formed the N–Ti bonds, which was followed by the successful combination of g-C3N4 with N-TiO2. A red-shift of absorption edge in the light region and more absorption in the visible light region were observed for the prepared composites. The synthesized composites exhibited excellent photocatalytic activities, which were evaluated by the degradation of methylene blue (MB) after irradiation with visible light. Especially, g-C3N4/N-TiO2 composites, prepared using melamine and TiN with a mass ratio of 1 : 1, showed the highest photocatalytic activity, and the corresponding rate of MB degradation was 0.028 min−1, which was 1.9 times greater than that of N-TiO2 (0.015 min−1). Furthermore, the photoelectrochemical performances of the samples on illumination with UV-visible light were evaluated. Remarkable enhancement of photoelectrochemical response of g-C3N4/N-TiO2 composites in UV-visible light, compared to pristine N-TiO2, was noticed. The co-modifications of TiO2 with N doping and g-C3N4 coupling resulted in an enhancement in the capacity of light absorption and an improvement in the transfer of charge carriers, which predominantly contributed to the improvement of photoactivity. This study develops a new and facile fabrication procedure for g-C3N4/N-TiO2 hybrids and represents an important step in the improvement of solar energy conversion using cost-effective materials.

Herein, we report the successful formation of graphitic carbon nitride coated titanium oxide nanotube array thin films (g-C3N4/TiO2) via the facile thermal treatment of anodized Ti sheets over melamine. The proportion of C3N4 and TiO2 in the composite can be adjusted by changing the initial addition mass of melamine. The as-prepared samples are characterized by several techniques in order to understand the morphological, structural, compositional and optical properties. UV-vis absorption studies exhibit a remarkable red shift for the g-C3N4/TiO2 thin films as compared to the pristine TiO2 nanotubes. Importantly, the prepared composites exhibit an enhanced photocurrent and photo-potential under both UV-vis and visible light irradiation. Moreover, the observed maximum photo-conversion efficiency of the prepared composites is 1.59 times higher than that of the pristine TiO2 nanotubes. The optical and electrochemical impedance spectra analysis reveals that the better photo-electrochemical performance of the g-C3N4/TiO2 nanotubes is mainly due to the wider light absorption and reduced impedance compared to the bare TiO2 nanotube electrode. The presented work demonstrates a facile and simple method to fabricate g-C3N4/TiO2 nanotubes and clearly revealed that the introduction of g-C3N4 is a new and innovative approach to improve the photocurrent and photo-potential efficiencies of TiO2.

A composite of N-doped TiO2 with Ag loading (Ag/N-TiO2) was successfully synthesized by a facile in situ calcination process using titanium nitride (TiN) and silver nitrate (AgNO3) as the starting materials. The effects of Ag loading and N doping on the structure and properties of TiO2 were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectroscopy (UV-visible DRS). XPS results indicated that the loading content of Ag in Ag/N-TiO2 nanomaterials can be adjusted by varying the amount of AgNO3 in the starting materials. There is an enhanced light absorption and a red shift of the optical edge for the resulting Ag/N-TiO2 compared with bare TiO2 and N-doped TiO2. The photocatalytic activities of the samples were evaluated for the degradation of methylene blue in aqueous solutions under visible light (λ > 420 nm). The superior visible light photodegradation of Ag/N-TiO2 composites was confirmed compared to N-doped TiO2 nanoparticles. In addition, an enhanced visible light photoelectrochemical performance was demonstrated. The photocurrent and photovoltage of Ag/N-TiO2 were about 1.5 and 1.4 times larger than those of N-TiO2, respectively. The technique proposed in this paper can also be applied to fabricate other N-TiO2 based composites.

A ternary composite of Cu2O, graphene and rutile TiO2 nanorods was prepared using Cu(CH3COO)2·H2O, graphene oxide and TiCl4 as the starting materials and its enhanced photocatalytic performance was demonstrated. Graphene/TiO2 nanorod composites (GT) were obtained by a simple hydrothermal method and then, Cu2O was coupled onto the surface of graphene/rutile TiO2 to form Cu2O/graphene/rutile TiO2 nanorod (CGT) composites via a chemical bath deposition process. The as-prepared sample was characterized by X-ray diffraction (XRD), emission field scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), specific surface area analyzer (BET), Raman spectroscopy and ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS). It is found that the introduction of graphene and Cu2O has little effect on the morphology of TiO2 nanorods with average dimensions of 140 nm (length) × 30 nm (diameter) (L/D ratio ≈5). A red shift of light absorption edge and more absorption in the visible light region were observed for the resulted ternary samples compared with TiO2 and graphene/TiO2 composites. The photocatalytic activity was evaluated by the photodegradation of methylene blue under visible light irradiation, which showed 2.8 times corresponding enhancement of the degradation efficiency for the ternary composites compared with TiO2. This work provides a new strategy to improve the visible light response of TiO2 and facilitate its application in environmental remediation.

CdS photocatalysts loaded with Ag2S and MoS2 as dual co-catalysts were prepared via a one-step in situ hydrothermal method using CdCl2·2.5H2O, H2MoO4, AgNO3·9H2O, and CS(NH2)2 as the raw materials. The as-prepared photocatalysts were characterized by X-ray diffraction, scanning electron microscopy, transmission electron micrograph, X-ray photoelectron spectroscopy, photoluminescence spectra, and Ultraviolet–Visible diffuse reflectance spectroscopy (UV–Vis DRS). The highest photocatalytic degradation rate was achieved for Ag2S/MoS2/CdS composites (87 %) compared to MoS2/CdS composites (66 %) and CdS (62 %) under visible light illumination for 60 min. The recycled photocatalytic experiments showed that the photocatalytic stability of CdS was improved with the introduction of Ag2S and MoS2. The improved photocatalytic performance of Ag2S/MoS2/CdS composites can be ascribed to the red shift of absorption edge, enhanced light absorption intensity, and the increased separation of the photoinduced electron–hole pairs, which was attributed to the synergetic effect of MoS2 and Ag2S on CdS. It was proven that Ag2S and MoS2 can act as effective dual co-catalysts to enhance the photocatalytic degradation activity of CdS.

Chemically bonded graphene/TiO2 nanorod hybrid composites with superior dispersity were synthesized by a one-step in situ hydrothermal method using graphene oxide (GO) and TiO2 (P25) as the starting materials. The as-prepared samples were characterized by XRD, XPS, TEM, FE-SEM, EDX, Raman, N2 adsorption, and UV–vis DRS techniques. Enhanced light absorption and a red shift of absorption edge were observed for the composites in the ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS). Their effective photocatalytic activity was evaluated by the photodegradation of methylene blue under visible light irradiation. An enhancement of photocatalytic performance was observed over graphene/TiO2 nanorod hybrid composite photocatalysts, as 3.7 times larger than that of pristine TiO2 nanorods. This work demonstrated that the synthesis of TiO2 nanorods and simultaneous conversion of GO to graphene “without using reducing agents” had shown to be a rapid, direct and clean approach to fabricate chemically bonded graphene/TiO2 nanorod hybrid composites with enhanced photocatalytic performance.

The insufficient separation of photogenerated charge carriers and faint CO2 capture remains the major obstacles for photocatalytic conversion of CO2 into solar fuel. Rational design of semiconductor photocatalysts with unique structures may be promising to break this bottleneck. Herein, bismuth rich Bi4O5B2 hollow microspheres are designed as a robust photocatalyst for efficient CO2 reduction. Thanks to the bismuth rich strategy, the highly dispersed band structure and the elevated conduction band (CB) potential facilitate the charge transfer and photoreduction ability. Meanwhile, hollow structure provides the large specific area and creates a resonance in its interior to enhance the CO2 adsorption and activation. Benefiting from the collaborative promotion effect, the local charge arrangement and electronic structure are tuned so as to an exceptional efficiency of photocatalytic CO2 conversion into CO (3.16 μmol g−1 h−1) and CH4 (0.5 μmol g−1 h−1) is attained over hollow Bi4O5Br2, which is superior to that of solid Bi4O5Br2 and BiOBr, as well as other reported Bi-based photocatalysts. This work paves new opportunities for exploring high-efficiency CO2 photoreduction catalysts.

MoS 2 /CdS/TiO 2 nanocomposites were synthesized via one-step in situ solvothermal method and characterized by X-ray diffraction, scanning electron microscopy, transmission electron micrograph, X-ray photoelectron spectroscopy, photoluminescence spectra, Ultraviolet–Visible diffuse reflectance spectroscopy, and photocatalytic measurement. Enhanced visible light photoresponse, higher efficiency of charge carriers separation, and improved photocatalytic degradation of methylene blue were confirmed for MoS 2 /CdS/TiO 2 nanocomposites. It was observed that the highest degradation ratio was achieved for MoS 2 /CdS/TiO 2 nanoparticles (72%) prepared at 180 °C when exposed to visible light illumination for 160 min relative to CdS/TiO 2 (59%) and TiO 2 (29%). Furthermore, the improved photocatalytic performance of MoS 2 /CdS/TiO 2 nanoparticles was also demonstrated by the degradation of colorless resorcinol under UV–vis light irradiation. This work demonstrates that synergetic effect of MoS 2 and CdS in which it proves to be a good choice for improving the utilization of visible light of TiO 2 -based materials.