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Surface states of bismuth vanadate are manipulated by an electrochemical surface engineering strategy to achieve an efficient PEC water oxidation.

Co/CoP crystalline-amorphous hetero-phase electrocatalysts with superior alkaline HER performance are successfully synthesized by a facile and environmentally friendly one-step electrochemical approach.

Mn-Based metal oxides have shown promising performance in catalytic oxidation of toluene due to the mixed Mn3+ and Mn4+ valences and in large numbers of oxygen vacancy clusters on the surface.

Understanding the phase regulation mechanism of BaTiO3 synthesized by a hydrothermal method is a complicated and challenging task. Here, we successfully prepared cubic and tetragonal BaTiO3 single nanocrystals by changing the ratio of water and ethanol in the solvent. We confirm that the BaTiO3 phase is mainly affected by the hydroxylation process due to the reaction with solvent. In particular, ethanol can be catalytically oxidized by titanium atoms, cause BaTiO3 hydroxylation and promote the formation of a cubic phase. In the mixed solution of ethanol and water, the hydroxylation process is suppressed, which facilitates the formation of the tetragonal phase. The relationship framework between the solvent ratio, phase structure and hydroxyl defects of BaTiO3 is established. Tetragonal BaTiO3 with fewer hydroxyl defects can promote charge transfer and surface reaction after polarization, thereby enhancing their photoelectric catalytic performance. This work provides references for the controllable synthesis of ferroelectric nanocrystals by hydrothermal methods and new insight for the utilization of polarization in photoelectrocatalysis applications.

Room-temperature cyclic voltammetry (CV) electrodynamic deposition is proposed for the first time to deposit Co9−xMnxS8 nanosheet arrays.

Construction of heterostructured electrocatalyst with interface effect is an effective strategy for enhancing the alkaline hydrogen evolution efficiency, whereas this process often requires complex treatments. Herein, we proposed a one-step electrodeposition method to obtain heterostructured CoNi-LDH@NiCo alloy on Ni foam (NF) through a competition reduction between NO3− group and metal cations in the electrolyte. The HER performance for the CoNi-LDH@NiCo alloy achieved the current density of 10 mA cm−2 at overpotential of 69 mV in 1 M KOH solution, improved 60% for η10 by comparing with the pristine NiCo alloy. Utilizing the specialized adsorption of CoNi-LDH for H2O and the featured attractiveness of NiCo alloy for H atom, the interface effect of the heterostructure electrocatalyst accelerated the dissociation of water molecules and elevated the catalytic kinetics dramatically. This work points out a potential approach towards the easy construction of inexpensive heterostructured electrocatalysts for HER activity in alkaline medium.

Prussian blue analogs (PBAs) with unique structure show great potential for aqueous potassium-ion batteries (AKIBs). Herein, K2Co[Fe(CN)6] and KNi[Co(CN)6] architectures are developed as the cathode candidates for AKIBs. Moreover, the reaction kinetics detection and DFT calculations are employed to analyse the battery performances.

The synthesis of some complex polyoxometalates (POMs) is critical to develop potential photocatalysts with high catalytic activity and selectivity. Here, we address this challenge by a hydrothermal self-assembly route to obtain a novel POM-based Co4W6O21(OH)2·4H2O with a hierarchical microsphere structure. The Co4W6O21(OH)2·4H2O crystallizes in the cubic space group Im3 with cell parameters: a = b = c = 12.878 A, α = β = γ = 90°, and Z = 4. The structure is further characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis spectroscopy, thermogravimetric analysis, and Fourier transform infrared spectra. After depositing Ag2O nanoparticles on the 3D Co4W6O21(OH)2·4H2O microsphere by photochemical synthesis, the Co4W6O21(OH)2·4H2O/Ag2O heterojunction presents enhanced photocatalytic activity for RhB compared with P25 and pristine Ag2O. Moreover, we confirm the key role of holes for the Co4W6O21(OH)2·4H2O/Ag2O and put forward a possible mechanism for the photocatalytic degradation reaction.

Industrial parks have a very important impact on regional economic development, but the extremely complex and relatively concentrated volatile organic compound (VOC) emissions from industrial parks also result in it being difficult to control VOCs. In this study, we took a large integrated industrial park in the upper reaches of the Yangtze River as an example, conducted a 1-year monitoring campaign of ambient air VOCs, and established a speciated VOC emission inventory based on the measured chemical profiles of the key industries. The comprehensive control index (CCI) of 125 VOCs was evaluated using the entropy weighting method based on comprehensive consideration of three aspects, namely, emission behavior, environmental effects, and health risks of VOCs, to identify priority VOC species and their key sources for VOC control in industrial parks. The total estimated VOC emissions in the industrial park in 2019 were 6446.96 t. Steel production, sewage treatment, natural gas chemical industry, pharmaceuticals, and industrial boilers were the main sources of VOC emissions. In terms of VOC components, halocarbons, aromatics, and OVOCs were the largest groups of VOCs emitted from the industrial park, accounting for 73.75 % of the total VOC emissions. Using the entropy weighting method, we evaluated the index weights of five parameters: emissions, ozone formation potential, secondary organic aerosol formation potential, hazard quotient, and lifetime cancer risk. Based on the CCI, five control levels for VOC species were further established. The VOC species in Level I and Level II, which contain species such as naphthalene, 2-chlorotoluene, benzene, acrolein, and chloroform, should be considered as extremely important priority control species. These results serve as a reference for the development of precise control strategies for VOCs in industrial parks.

Efficient methods are urgently required for developing electrocatalysts with superior activities and practical applications. In this work, a novel pure ternary CoFeCr hydroxide was synthesized on carbon paper using a low-temperature (60 °C) hydrothermal approach. The OER performances of the CoFeCr hydroxides with different atomic ratios were systematically investigated. Intriguingly, the optimized trimetallic CoFeCr-6:2:1 electrocatalyst exhibited significantly improved OER performance with a small overpotential of 260 mV at 10 mA cm−2 and a low Tafel slope of 40.1 mV dec−1 under alkaline conditions. Combined experimental and DFT+U computational studies revealed that Fe was the active site and the excellent OER activity could be attributed to the electronic structure regulation effect via the introduction of Cr, which on the one hand improved the d-band center position of the Fe sites and on the other hand decreased the band gap of the sample. This regulation effect optimized the adsorption of oxygen species and efficiently accelerated the oxygen evolution kinetics and charge transfer kinetics, thus enhancing the OER performance of CoFeCr-6:2:1. Our results provide both experimental and theoretical basis for the further exploration of efficient hydroxide electrocatalysts for energy-related applications.

Aqueous potassium-ion hybrid supercapacitors (APHSs) are among the promising technologies for energy storage because it combines the advantages of potassium-ion batteries and supercapacitors, which can provide high energy density and power density. However, the biggest obstacle to APHS is finding suitable positive electrode materials that can facilitate rapid transport for K+ intercalation/deintercalation and industrial preparation. Herein, a commercially valuable electrode material, K0.296Mn0.926O2, is developed via a simple method, which can be fabricated on a large scale. The crystal structure and atomic arrangement of the as-prepared K0.296Mn0.926O2 were identified by the Rietveld-refined XRD and high-angle annular dark-field STEM. Importantly, the upper potential of K0.296Mn0.926O2 can extend to 1.2 V with a specific capacitance of 313 F g−1 at 1 A g−1, which is larger than that of commercial MnO2 electrode material. Density functional theory (DFT) results show that the diffusion barrier of the potassium ion in K0.296Mn0.926O2 (0.06 eV) is lower than that of MnO2 (0.25 eV), and K0.296Mn0.926O2 exhibits improved interfacial K+ adsorption ability. Moreover, an APHS was assembled by using K0.296Mn0.926O2 as the positive electrode and the commercial active carbon (AC) as the negative electrode. The K0.296Mn0.926O2//AC exhibits a “double high device” characteristic with a high energy density of 70 W h kg−1 and a high power density of 6000 W kg−1, and the voltage window extends to 2.4 V. This work represents a significant step forward in the exploitation of K-ion storage and accelerates the development of APHS.

The combination of transition metal-based cocatalysts with semiconductors is a promising route to improve the photoelectrochemical performance in solar water splitting. However, it is difficult to evaluate the catalytic ability for cocatalysts quantitatively. Herein, we use kelvin probe force microscopy technique, combining with Mott-Schottky method, to investigate the cocatalysts from the point of surface potential and Femi level. Through synthesis the nickel/cobalt oxide nanoparticles and nanoporous bismuth vanadate (BiVO4), the result indicates the surface potential of NiCoO2 coated BiVO4 is lower than pristine BiVO4 and BiVO4 coated by NiO and CoO cocatalysts respectively. The lower surface potential means a more upward band bending structure at the interface of electrode and electrolyte, which can promote the separation of electron-hole pairs and enhance the charge transfer kinetics. Thus, the NiCoO2/BiVO4 photoanode achieve a remarkable photocurrent density of 2.34 mA/cm2 for water oxidation, and the charge separation and oxidation kinetics efficiencies are 61.9% and 72.7% respectively. In all, our studies provide a new mechanistic insight into cocatalysts for solar energy conversion.

Octahedral CuWO4 microstructurals were successfully obtained via a simple self-assembly solvothermal synthesis pathway for the first time. The effect of organic solvents on the morphology of copper tungstate (CuWO4) was systematically investigated here. In addition, some other parameters, such as the reaction time, sodium salts and a possible mechanism for the formation of CuWO4 with varied morphologies were discussed. We succeed in fabricating and characterizing an octahedral CuWO4 and the results demonstrate that the amount of ethylene glycol (EG) and Cl− plays a critical effect on the formation of unique morphology of CuWO4. According to our investigation, samples obtained show better photocatalytic activity toward the degradation of RhB. Our research provides some new perspective of the morphology control of CuWO4 and is conducive to understand the relationship between the morphology of other wolframite-type microcrystals and their properties.

As a key building block to power flexible electronics, there is need for the development of flexible current collectors. Bombyx mori silk, a traditional textile, attracts increasing attention for its potential application in flexible electronics and is a promising raw material for flexible carbon electrodes in current collector fabrication. In this work, molybdenum dioxide nanoparticles (MoO2 NPs), which possess chemical stability and high mass specific capacitance, was used as a feed additive and combined with mulberry leaves to raise silkworms. It was found that the MoO2 NPs were embedded within the silk fibers, which endowed the resulting silk with favorable features for electrochemical energy storage in flexible electronics. After carbonization, the specific capacitance of electrodes prepared with silk from the MoO2 NPs feeding group, with a mass/volume ratio of 5 g/L, was enhanced from 100 F/g to 245 F/g at a current density of 0.2 A/g. Impressively, the electrodes show high coulombic efficiency with excellent stability. This work demonstrates the possibility of producing carbonized silk with superior properties for developing silk-based flexible electrodes for use in energy storage devices in a large-scale, green, low-cost way.

High efficient catalysts for hydrogen evolution reaction are crucial for hydrogen production. As potential catalysts for hydrogen evolution reaction, NimMon (m + n = 5) clusters have been studied i...

A successful strategy for reducing the content of Pt without compromising the activity of a Pt-based catalyst is to deposit Pt as an ultrathin overlayer on the surface of another metal. Here, we report a facile one-pot synthesis of Pd@Pt1L (1L: one atomic layer) core–shell octahedra using a solution-phase method. The success of this method relies on the use of metal precursors with markedly different reduction kinetics. In a typical synthesis, the ratio between the initial reduction rates of the Pd(II) and Pt(II) precursors differed by almost 100 times, favoring the formation of Pd–Pt bimetallic octahedra with a core–shell structure. The reduction of the Pt(II) precursor at a very slow rate and the use of a high temperature allowed the deposited Pt atoms to spread and cover the entire surface of Pd octahedral seeds formed in the initial stage. More importantly, we were able to scale up this synthesis using continuous-flow reactors without compromising product quality. Compared to a commercial Pt/C catalys...

We have successfully developed a MOF-based (Co3[Fe(CN)6]2·10H2O) strategy to synthesize Co-Fe mixed metal oxide (Co3O4/Fe2O3) nanocubes (denoted as CFNC). The obtained CFNC is applied as both anode and cathode for high-performance symmetric supercapacitors, exhibiting high energy density of 35.15 W h kg−1 at a power density of 1125 W kg−1 as well as excellent stability. Meanwhile, when CFNC is used as electrocatalyst for oxygen evolution reaction (OER), it requires a low overpotential of 310 mV to achieve a current density of 10 mA cm−2 and exhibited excellent stability.

Carbon-incorporated NiO/Co3O4 concave surface microcubes (denoted as NCMC) are successfully developed from a precursor of Ni3[Co(CN)6]2 for the first time. The NCMC exhibits excellent electrocatalytic activity for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in potassium hydroxide solution, affording a current density of 10 mA cm-2 at 169.5 mV for the HER and 290 mV for the OER, respectively. This communication describes a rational design of MOF-derived mixed metal oxides as electrocatalysts for overall water splitting, promoting the further development of MOF materials in the field of energy conversion.

Shape-controlled synthesis of non-noble metal nanocrystals (NCs) is vital to their catalysis applications due to their different exposed surfaces and atomic coordination environments. Here, we report a facile synthesis of Ni nanocubes and cuboctahedra with controlled shapes and high yields via a wet-chemistry strategy. The key to success relies on the use of cetyltrimethyl ammonium bromide (CTAB), formaldehyde (HCHO) and a specific reaction temperature, which could effectively cap the desired surface and tune their growth rate. Specifically, nanocubes switched to cuboctahedra and octahedra with an increased reaction temperature due to gradual CO desorption from the surfaces of NCs. Meanwhile, it should be worth noting that CTAB and the generated CO molecules through HCHO decomposition would co-adsorb on the {100} facets of Ni NCs. As a proof-of-application, the obtained Ni NCs exhibited high activity in the oxygen evolution reaction (OER) with over-potentials of 383 mV and 402 mV for nanocubes and cuboctahedra at a current density of 10 mA cm−2, respectively, demonstrating that the {100} facets are more favorable toward OER. These results suggested that their performance is strongly shape dependent and is derived from different surface energies and active sites.

Layered NbS2, a member of group-V transition metal dichalcogenides, was synthesized via a colloidal synthesis method and employed as a negative material for a supercapacitor. The morphologies of NbS2 can be tuned from ultrathin nanosheets to hierarchical structures through dynamics controls based on growth mechanisms. Electrochemical energy storage measurements present that the ultrathin NbS2 electrode exhibits the highest rate capability due to having the largest electrochemical surface area and its efficient ion diffusion. Meanwhile, the hierarchical NbS2 shows the highest specific capacitance at low current densities for small charge transfer resistance, displays 221.4 F g−1 at 1 A g−1 and 117.1 F g−1 at 10 A g−1, and cycling stability with 78.9% of the initial specific capacitance after 10,000 cycles. The aggregate or stacking of nanosheets can be suppressed effectively by constructing hierarchical structure NbS2 nanosheets.

To improve photoelectrochemical properties of Si nanowires (SiNWs), MoS2/SiNWs is prepared via two-step method. SiNWs is synthesized by metal−catalyzed electroless etching (MCEE) method and MoS2 is subsequently deposited onto SiNWs through the direct thermal decomposition method. MoS2 is introduced as both light absorber and catalyst for hydrogen evolution reaction (HER). Moreover, it forms a heterojunction with SiNWs that contribute to the charge separation. Herein, MoS2/SiNWs attains excellent hydrogen evolution reaction (HER) catalysis with onset potential of 55 mV. A photocurrent density of 25 mA cm− 2 at −1.0 VRHE were achieved under simulated solar illumination, which is about 6 times higher than that of SiNWs, and the carrier concentration is increased by 100−fold. The enhanced photocatalytic activity of MoS2/SiNWs toward HER is attributed to the Schottky junction at the interface, which enhances the photo−generation of electron−hole pairs and suppresses the charge recombination, making them promising earth−abundant alternatives to noble metal−based photocathode for HER.

Suitable semiconductor and its efficient coupling with catalysts is vital to hydrogen evolution reaction (HER). Herein, Ternary heterostructured MoS2/Ag/p-type silicon nanowires (SiNWs) array photocathode are constructed by a simple two-step method, where Ag is self-reduced on SiNWs via Galvanic Displacement method and MoS2 is subsequently loaded by direct thermal decomposition. Ag interfacial layer is introduced between Si and MoS2 to facilitate the charge transfer and suppress the recombination of photo-generated electron-hole pairs. MoS2/Ag/SiNWs exhibits an onset potential of 62 mV and photocurrent density of 50 mA cm−2 at −1.0 VRHE, as well as good stability. Besides, MoS2/Ag/SiNWs is capable of generating 325.9 μL hydrogen per minute. The superior HER catalytic activity of MoS2/Ag/SiNWs is contributed to the improved charge transport at the solid–solid interfaces by virtue of Ag layer, allowing more electrons flow from SiNWs to MoS2 and thus effectively separating the photoelectrons and holes. This work demonstrates the potential of novel heterostructure for robust and efficient photoelectrochemical HER.

Hematite (Fe2O3) can be suitable when used in a solar energy conversion system, but the short charge diffusion lengths limit its applications. Here, we report the studies of charge transfer ability with a 40 nm Fe2O3 nanorod decorated by a 5 nm iron phosphide (FeP) core–shell structure. By selecting the optimized time of phosphorization (20 min), the photocurrent of FeP@Fe2O3-20 photoanode reached 0.86 mA/cm2, enhanced by 4.10-fold compared with pristine Fe2O3 (0.21 mA/cm2) for water oxidation. Further, the charge transport time reduced by 30% due to the FeP shell that served as the hole transport layer. Compared with Fe2O3, FeP@Fe2O3 has a higher Fermi level, which guides the electron’s transfer from FeP to Fe2O3 to create a space charge layer. The charge balance induces an upward bending of band structure at the FeP and Fe2O3 interface and accelerates the separation of photogenerated electron–holes ascribed to the built-in electric field at the interface. Our studies provide a detailed understanding of ...

Aqueous asymmetric supercapacitors (ASCs) with a wide voltage window can effectively improve energy storage capacity of energy storage devices. Zeolitic imidazolate framework-67 (ZIF-67) was used as a precursor to prepare nanoporous carbon (NC), and K0.5 Mn2 O4 nanosheets were subsequently grown on the NC surface through a facile in situ redox process (denoted as NCMO). The electrode potential window of NCMO was extended to 1.2 V in a three-electrode system and the value of the potential window was higher than that of most reported manganese oxides. To assemble the asymmetric supercapacitor with a high voltage range, the as-prepared NCMO and NC (with a potential window of -1.2-0 V) were used as the positive and negative electrode, respectively. A 2.4 V NCMO//NC aqueous ASC was constructed and displayed a large energy density of 60 Wh kg-1 at a power density of 1200 W kg-1 and excellent rate performance (41 Wh kg-1 even at a specific power density of 12.3 kW kg-1 ) as well as good cycling stability (92.6 % capacitance retention over 10 000 cycles at 10 A g-1 ). This work provides new opportunities for the development of high voltage ASCs with a high energy density for further practical application.

Efficient and stable bifunctional electrocatalysts composed of Earth-abundant elements are crucial to the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Herein, FeCo2S4 ...

Pseudocapacitors are promising energy storage devices combining the merit of fast charging ability and high energy density. Constructing electrode materials for pseudocapacitors with two-dimensional (2D) materials has become a trending topic. However, it is still a challenge to address the restacking propensity of the 2D materials and to broaden the operational potential window of pseudocapacitors. We herein demonstrate a facile hydrothermal reaction of synthesizing a three-dimensional V2O3 tubes (assembled with ultrathin nanosheets) coated with MoS2 nanosheets and explore their electrochemical properties for pseudocapacitors. The V2O3 tubes prevent the restacking of MoS2 nanosheets and serve as conductive scaffold for fast electron transport. Owing to the multi-valence of both Mo and V, the potential window of composite is able to straddle between negative and positive potentials. Therefore, the V2O3@MoS2 composite electrode exhibits a broad operational potential range between −1.0 V and +1.0 V, and a high reversible capacitance of 655 F g−1 at 20 mV s−1. Moreover, an asymmetric pseudocapacitor with our composite as a positive electrode achieves a high specific capacitance (108.7 F g−1 at 0.5 A g−1), high energy density (31.8 W h kg-1) and excellent cycling stability (no capacitance decay after 35000 cycles).

In this work, hollow CoS nanobox (noted as HCSN) have been successfully synthesized via annealing and hydrothermal process from zeolitic imidazolate framework (ZIF-67) template. When tested as positive electrode materials in alkaline aqueous electrolyte, it shows high specific capacitance of 720 F g−1 at a current density of 1 A g−1, good rate capability (82.1%) and good cycling stability with 86.4% capacitance retention over 10,000 cycles at 10 A g−1. To further demonstrate the advantages of our ZIF-67 derived materials, asymmetric energy storage device was assembled (HCSN//NC), where the as-prepared HCSN was employed as the anode and ZIF-67-derived nanoporous carbon (noted as NC) as the cathode. This device achieves high energy density (80 Wh kg−1 at a specific power density of 882 W kg−1), good rate capability (53.3 Wh kg−1 even at a specific power density of 7.9 kW kg−1) and long-term stability up to 10,000 cycles. More importantly, it could simultaneously light up 12 LEDs in parallel, demonstrating its potential in practical applications.

Bimetallic nickel–cobalt (Ni-Co) alloy has been regarded as an emerging class of material for the electrochemical hydrogen evolution reaction (HER). However, it operates at an overpotential significantly above the thermodynamic requirement. Here we present a facile one-step electrochemical reduction approach to incorporate fcc NiCo alloy with ⅥB group transition metals (M−NiCo, M = chromium (Cr), molybdenum (Mo), or tungsten (W)). This method enables to control the induction time of protrusion growth (τ) to produce hierarchical structure by imposing high current density (-0.6 A cm−2) and strong electric field on the cathode. Herein, W-NiCo holey nanotower arrays show tremendously enhanced HER activity compared with pristine NiCo alloy, which provides an overpotential of 109.2 mV (reduced by 58.7%) to achieve a current density of −10 mA cm−2, with a Tafel slope of 110.3 mV dec-1 in alkaline medium. The same law applies to the acid electrolyte with an overpotential of 78.5 mV (reduced by 66.1%) and low Tafel slop of 56.6 mV dec-1. Based on the experimental and theory analysis, We find W-doping can promote more active sites exposed, tune the electron configuration, moderate the gibbs free energy of the H intermediate, and accelerate the desorption of H2. It makes the rate-determining step change from Volmer to Heyrovsky reaction and finally surmount the limit of sluggish dynamics. The novel route provides an efficient doping control on Ni-based hierarchical alloys via 4f-orbital electronic and geometric structure engineering, which suggests an environmentally friendly method for energy-related process in practical applications.

Development of highly active and robust earth-abundant electrocatalysts for the hydrogen evolution reaction (HER) is of great significance for the broad utilization of alkaline electrolyzers. Herein, cobalt molybdenum suboxides (Co2Mo3O8) supported on Ni foam are reduced from their corresponding oxide precursors and first used as efficient electrocatalysts for the HER in alkaline electrolyte. The catalytic activity is further improved through the construction of a unique hierarchical Co2Mo3O8/Co/NF nanostructure. With a very low onset overpotential (∼9 mV), this electrocatalyst only requires overpotentials of 50 mV and 137 mV to drive current densities of 10 mA cm−2 and 100 mA cm−2, respectively. After 5000 cycles, a slight increase of ∼6 mV in the overpotential to drive a current density of 10 mA cm−2 verifies the excellent stability of Co2Mo3O8/Co/NF during the alkaline HER process.

The direct Z-scheme heterojunction structure benefits separation and migration of photoinduced carriers while maintaining original redox ability of each component. Nowadays, most Z-scheme structures are fabricated by g-C3N4 with other narrow band photocatalysts due to its low conduction band (CB). In this paper, SiC, another kind of photoelectric semiconductor with low CB, was employed to prepare direct Z-scheme photocatalyst with 2D WO3 by simple water oxidation precipitation method. The component and interface band structure of Z-scheme heterojunction WO3/SiC (WS) were verified by XPS, KPFM, Mott-Schottky method. The photodegradation efficiency and rate constant values of WS-1 for degrading RhB enhanced 2.5 and 5.3 times respectively compared with pristine WO3. Radical capture experiments and ESR tests affirmed that WS-1 photocatalyst produced •OH and •O2－active species, which further confirmed the photogenerated carriers were transmitted through the Z-scheme mode in principle. Band structure investigation showed that the direct Z-scheme structure assembled by WO3 with high valence band (VB) and SiC with low CB could maintain the high photocatalytic activity of active species. Therefore, this study offers a feasible method for construction of a novel and efficient direct Z-scheme photocatalyst.

Spontaneous polarization field in ferroelectric can improve the oxidation kinetics and photocurrent of a photoanode in photoelectrochemical water splitting. But the impact of ferroelectric polarization field on the migration of different charge carriers which have different mobility and diffusion length is still unknown. In this work, we synthesized tetragonal BaTiO3 nanoparticles by solvothermal method successfully and fabricated the hybrid photoanode composed by monoclinic WO3 and BaTiO3 for solar water oxidation. Density functional theory calculations showed that the mobility of electron was faster than that of the hole in WO3, and had a longer diffusion length. We demonstrated that the polarization field of ferroelectric had a greatly impact upon holes migration compared with electrons, thus the thin hybrid photoanode after poling by bias presented a significant improvement of photocurrent (210.5%) under the back-side illumination, and a remarkable augment of charge separation efficiency (94%) and oxidation kinetics (69%) at 1.23 V. Our work provided a deeper understanding of how ferroelectric polarization field affected the photoelectrochemical water oxidation and a general pathway towards enhancing minority carrier collection in photoanode.

Monoclinic bismuth vanadate (BiVO 4 ) has been widely applied as a promising n-type semiconductor for photoelectrochemical (PEC) water splitting because of its low cost, environmentally friendly, and relatively narrow band gap of ∼2.4 eV. Here, we developed a facile fabrication of Mo doped BiVO 4 photoanode on the fluorine-doped tin oxide substrate by electrodeposition method and used these samples to better understand the doping effect for charge separation and charge oxidation kinetics. Compared with the undoped BiVO 4 photoanode, the optimized Mo doped BiVO 4 (3AMo:BV) produced a much higher photocurrent of 1.91 mA/cm 2 at 1.23 V vs. RHE under AM 1.5G illumination for water oxidation. The results of the photoelectric conversion kinetics for various samples revealed that the charge separation and oxidation kinetics efficiencies for 3AMo:BV sample are 74.42% and 49.25% at 1.23 V vs. RHE, while the values for undoped BiVO 4 are 48.04% and 32.98%, respectively. The improved PEC performance for Mo doped BiVO 4 is mainly ascribed to the crystal deformation caused by larger tetrahedral ionic VO 4 and higher photovoltage generated by the interface of photoanode and electrolyte.

Architecturally assembling primary building blocks into the expected geometric heterostructure is a tremendous challenge due to the interfaces dislocation and stretch resulting from the lattice-mismatch between heterogeneous building blocks. Although different dimensional nanomaterials have been synthesized, the branched acanthosphere-like hierarchical architecture is needed to be developed and the growth mechanism should be investigated. Here we design and fabricate an acanthosphere-like NiCo 2 O 4 @α-MnO 2 heterostructures architecture by an “in situ growth” technique of two-steps hydrothermal method. The as-prepared acanthosphere-like NiCo 2 O 4 @α-MnO 2 microspheres (denoted as AM-NCM) have a diameter of 5 ∼ 7 um with a highly open and interstitial three dimensional (3D) architecture formed by α-MnO 2 ultrathin nanosheets leading to faster ion diffusion and improved charge transfer kinetics. Therefore, the hybrid electrodes exhibits exceptional specific capacitances of 695 F g −1 (2.17 F cm −2 ) at the current densities of 3.2 A g −1 (10 mA cm −2 ) and good cycling electrochemical stability with only 2.4% capacitance loss after 1000 cycles and still maintains 92% of its initial value after 6000 cycles. The outstanding performance of the branched AM-NCM reveals its potential to be a promising material for energy storage, and also inspires continued research on the formation of branched hierarchical architecture as energy storage materials.

In this paper, hierarchical NiCo2S4@MnMoO4 core-shell structure composites are first designed and fabricated via three-steps hydrothermal process. NiCo2S4 microspheres consisting of nanotubes are utilized as ideal conductive scaffolds, while ultrathin MnMoO4 nanosheets are controllably deposited. The particular structure is beneficial to the migration and diffusion of ions, making the redox reactions of the active materials can be carried out quickly and completely. The NiCo2S4@MnMoO4 hybrid electrode shows an ultrahigh specific capacitance of 1186.44 F g-1 at a current density of 1 A g-1 (3.6 F cm-2 at 3 mA cm-2). It exhibits good cycling stability with 90.1% capacitance retention over 5000 cycles at 10 A g-1. Moreover, an electrochemical energy storage device is fabricated where the as-prepared NiCo2S4@MnMoO4 are employed as cathode and anode respectively. The device achieves a high energy density of 47.8 Wh kg-1 at a power density of 699.9 W kg-1, as well as excellent cycling stability (88.3% capacitance retention over 5000 cycles at 10A g-1). The outstanding performance demonstrates that the NiCo2S4@MnMoO4 core-shell composite are a kind of promising electrode material for electrochemical energy storage, which inspire researchers continued devote themselves to the hetero-structured materials as energy storage materials.

Lithium ion capacitors (LICs) are considered to be high-performance energy storage devices that have stimulated intense attention to bridge the gap between lithium ion battery and supercapacitor. Currently, the major challenge for LICs has been to improve the energy density without sacrificing the high rate of power output performance. Herein, we designed a three-dimensional (3D) hierarchical porous nanostructure of hydrogen-treated TiO2 nanoparticles wrapped conducting polymer polypyrrole (PPy) framework with single-walled carbon nanotubes (SWCNTs) hybrid (denoted as, H-TiO2/PPy/SWCNTs) anode material for LICs through a conventional and green approach. Such a unique network can offer continuous electron transport and reduce the diffusion length of lithium ions. A greatly lithium storage specific capacity is achieved with reversible discharge capacity ∼213 mA h g−1 (based on the mass of TiO2) over 50 cycles (@ 0.1 A g−1), which is almostly three times compared with raw TiO2 (a commercial TiO2 nanoparticles powder). In addition, coupled with commercial activated carbon (AC) cathode, the fully assembled H-TiO2/PPy/SWCNTs//AC LICs delivers a maximum energy and power densities of 31.3 Wh kg−1 and 4 kW kg−1, a reasonably good cycling stability (∼77.8% retention after 3000 cycles) within the voltage range of 1.0–3.0 V.

First-row (3d) transition-metal catalysts, such as bimetallic Ni–Co, represent an emerging class of electrocatalysts for HER, but they usually suffer from a large overpotential significantly above thermodynamic demands. Here, we doped NiCo catalyst with non3d metals molybdenum (Mo) for improvement in catalyzing the hydrogen evolution reaction. The ternary catalyst was readily obtained by a one-pot process via the sequential electrodeposition of Ni, Co, and Mo precursors on titanium (Ti) support. By tailing the deposition conditions, we fabricated NiCoMo catalysts with three-dimensional dendritic structures, exhibiting large amounts of electrochemically active sites. To attain the benchmark HER current density of −10 mA cm–2, an overpotential of ∼132 mV is required in 0.1 M KOH for the Mo-doped NiCo (5 atom % Mo in bath), and they produced the decreasing in Tafel slope of ∼108 mV decade–1 exceeding those of binary NiCo alloy catalysts and other contents of Mo doping. In a synergistic effect, dopant incorpo...