Nanosized CoWO 4 and NiWO 4 as efficient oxygen-evolving electrocatalysts

Low Pt Loading on Wolframite-Type NiWO4 to Excel the Electrocatalytic Water Splitting and Ammonia Oxidation Reaction

Hydrogen production via water-splitting or ammonia electrolysis using transition metal-based electrodes is one of the most cost-effective approaches. Herein, ca. 1-4% of Pt atoms are stuffed into a wolframite-type NiWO4 lattice to improve the electrocatalytic efficiency. The co-existence of atomically dilute quantities of Pt0 and PtIV atoms in the NiWO4 without altering the lattice structure is established via powder X-ray diffraction, inductively coupled plasma mass spectrometry (ICP-MS), core-level X-ray photoelectron spectroscopy, and other spectroscopic studies. While the undoped NiWO4 and a physical mixture of Pt0 (2 wt %) and NiWO4 exhibit poor oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and ammonia oxidation reaction (AOR) activities, 3-4% Pt-enriched NiWO4 depict improved electrocatalytic performances with at least 50 mV overpotential drop for both the OER and HER. The 3%Pt/NiWO4 electrode showcases a long-term (for 110 h) chronoamperometric/chronopotentiometric OER and HER performance, delivering high current at a low working potential. The bifunctional behavior of the material leads to the development of a water-splitting electrolyzer, 3%Pt/NiW/NF(-)/(+)3%Pt/NiW/NF, achieving >90% Faradaic efficiency for H2 production. The onset potential for the AOR is also cathodically shifted for 3%Pt/NiW and 4%Pt/NiW compared to the NiWO4 itself. Electrokinetic study through a rotating ring-disk electrode (RRDE) experiment and the Koutecký-Levich study provides an observed rate constant (kobs) of 1.68 × 10-3 cm s-1 of AOR with a 6e- count from the kinetic current region, highlighting [NO2]- as the major product. The electrolysis of 1 M NH3 using 4%Pt/NiW/NF as a working electrode produces predominantly [NO2]- (FE: 53%) and [NO3]- (FE: 30%). The improved electrocatalytic activity of 3-4% Pt-enriched NiWO4 can be due to the low Tafel slope and charge transfer resistance (Rct). Pt0 being electron-rich induces facile electronic conduction during electrocatalysis and enhances a better binding of the analytes such as H2O, [OH]-, and NH3. At the same time, the PtIV centers present adjacent to the NiII sites can polarize the electron density to stabilize NiIII species and enhance the possibility of OER and AOR. This study demonstrates the effect of hetero-metal doping to tune the electronic structure to improve the electrochemical activity. The low-Pt-doped NiWO4 material is presented here as a multimodal electrocatalyst that can efficiently electrolyze water or ammonia to produce hydrogen.

A sensitive electrochemical sensor based on CoWO4/multi-walled carbon nanotubes for the selective determination of chlorpromazine hydrochloride

In this work, a novel electrochemical sensor based on cobalt tungstate/multi-walled carbon nanotube (CoWO4/MWCNT) nanocomposites has been used to detect chlorpromazine hydrochloride (CPZ). The CoWO4/MWCNT nanocomposite was obtained by solvothermal technology and ultrasonic method and analyzed using different characterization techniques such as scanning electron microscopy (SEM), X-ray diffractometry (XRD), energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The electrochemical behavior of CoWO4/MWCNT/GCE was explored using cyclic voltammetry (CV). Electrochemical experiments confirm that CoWO4/MWCNT/GCE exhibits excellent electrocatalytic activity towards CPZ with good selectivity, reproducibility and stability. The linear dynamic range of CPZ was observed to be 1-2000 μM with a detection limit of 0.33 μM. Moreover, the actual sample was analyzed using lake water with satisfactory results, portraying the sensor as a potential candidate for the detection of CPZ.

Stability of Multivalent Ruthenium on CoWO4 Nanosheets for Improved Electrochemical Water Splitting with Alkaline Electrolyte

Engineering low-cost electrocatalysts with desired features is vital to decrease the energy consumption but challenging for superior water splitting. Herein, we development a facile strategy by the addition of multivalence ruthenium (Ru) into the CoWO4/CC system. During the synthesis process, the most of Ru3+ ions were insinuated into the lattice of CoWO4, while the residual Ru3+ ions were reduced to metallic Ru and further attached to the interface between carbon cloth and CoWO4 sheets. The optimal Ru2(M)-CoWO4/CC exhibited superior performance for the HER with an overpotential of 85 mV@10 mA cm-2, which was much better than most of reported electrocatalysts, regarding OER, a low overpotential of 240 mV@10 mA cm-2 was sufficient. In comparison to Ru2(0)-CoWO4/CC with the same Ru mass loading, multivalence Ru2(M)-CoWO4/CC required a lower overpotential for OER and HER, respectively. The Ru2(M)-CoWO4/CC couple showed excellent overall water splitting performance at a cell voltage of 1.48 V@10 mA cm-2 for used as both anodic and cathodic electrocatalysts. Results of the study showed that the electrocatalytic activity of Ru2(M)-CoWO4/CC was attributed to the in-situ transformation of Ru/Co sites, the multivalent Ru ions and the synergistic effect of different metal species stimulated the intrinsic activity of CoWO4/CC.

Silver nanoparticle-decorated NiFe2O4/CuWO4 heterostructure electrocatalyst for oxygen evolution reactions

In this work, Ag nanoparticles decorated with NiFe2O4/CuWO4 heterostructure were synthesized using the step-wise precipitation method. The influence of varying Ag loading on the NiFe2O4/CuWO4 heterostructure and its electrochemical OER performance was extensively studied in 1 M KOH electrolyte. The obtained LSV profile was analyzed to determine the overpotential, Tafel slope, and onset potential. The heterostructure with an optimal Ag loading of 5 wt% required the least overpotential (1.60 V vs. RHE) for generating a current density of 10 mA cm-2 with a lower Tafel slope of 44.5 mV dec-1, indicating its faster OER kinetics. Furthermore, the composite remained stable over a period of 24 hours with a minimum rise in the overpotential after the stability test. The enhanced OER performance of the as-prepared catalyst can be attributed to the presence of multiple metallic elements in the Ag-loaded NiFe2O4/CuWO4 composite, which created a diverse array of oxygen-vacant sites with varying reactivity, enhancing the charge-transfer kinetics; and thus contributing to the overall efficiency of OER. Therefore, optimizing the Ag concentration and engineering a microstructure represents an encouraging strategy for developing cost-effective catalysts for next-generation energy-conversion applications.

Nanoparticulated WO3/NiWO4 Using Cellulose as a Template and Its Application as an Auxiliary Co-Catalyst to Pt for Ethanol and Glycerol Electro-Oxidation

This work reports the use of cellulose as a template to prepare nanosized WO3 or NiWO4 and its application as a co-catalyst in the electro-oxidation of ethanol and glycerol. Microcrystalline cellulose was hydrolyzed with phosphotungstic acid (H3PW12O40) to prepare the nanocrystalline cellulose template. The latter was air-calcinated to remove the template and obtain nanometric WO3. Tungsten oxide was impregnated with Ni(NO3)2, which was subsequently air-calcinated to obtain the nanometric NiWO4. Elemental analysis confirmed the coexistence of nickel and tungsten, whereas thermal analysis evidenced a high thermal stability for these materials. The X-ray diffractograms displayed crystal facets of WO3 and, when Ni(II) was added, NiWO4. The transmission electron micrographs corroborated the formation of nanosized particles with average particle sizes in the range of 30 to 50 nm. Finally, to apply this material, Pt/WO3-C and Pt/WO3-NiWO4-C were prepared and used in ethanol and glycerol electro-oxidation in an alkaline medium, observing a promotional effect of the oxide and tungstate by reducing the onset potential and increasing the current density. These materials show great potential to produce clean electricity or green hydrogen, contributing to energetic transition.

Neodymium-Doped Novel Barium Tungstate Nanospindles for the Enhanced Oxygen Evolution Reaction

In this work, pristine, 0.02, 0.04, and 0.06 M neodymium (Nd)-doped barium tungstate nanostructures were synthesized via a simple co-precipitation method for the water oxidation process. The obtained X-ray diffraction high-intensity peak at a 2θ value of 26.4° corresponding to the (112) lattice plane confirmed the formation of a tetragonal structure of BaWO₄. Moreover, the BaWO₄ morphology was examined by scanning electron microscopy, which showed the existence of nanospindles. An energy-dispersive X-ray spectrum confirmed the subsistence of the produced materials, for example, barium (Ba), tungsten (W), oxide (O), and neodymium (Nd), with weight percentages of 28.58, 46.63, 16.64, and 8.16%, respectively. The 0.04 M Nd-doped BaWO₄ product was explored to attain a high surface area of 18.18 m²/g, a pore volume of 0.079 cm³/g, and a pore diameter of 2.215 nm. Compared to the other prepared electrodes, the 0.04 M Nd-doped BaWO₄ product exhibited low overpotential values of 330 mV and 450 mV to deliver current densities of 10 mA/cm² and 50 mA/cm², respectively. In addition, the optimized electrode achieved a small Tafel slope value of 158 mV dec^-1 and followed the Volmer-Heyrovsky mechanism. Moreover, the electrical conductivity of BaWO₄ was tuned due to the addition of a rare-earth metal dopant, and it exhibited the charge-transfer resistance and solution resistance values of 0.98 and 1.01 Ω, respectively. The prepared electrocatalyst was further studied by using cyclic voltammetry, and it exhibited a high double-layer capacitance value of 29.3 mF/cm² and high electrochemically active surface areas of 1.465 cm². The electrochemical performance was greatly improved depending on the concentration of the doping agent, and it was well consistent with the obtained results. The best electrocatalyst was subjected to a chronoamperometry test, which exhibited excellent stability even after 20 h. Hence, this work suggests that alkaline metal tungstates have a cost-effective, efficient, and promising electrocatalyst, and it is a new approach for the water oxidation process.

Hierarchical Hollow CoWO4-Co(OH)2 Heterostructured Nanoboxes Enabling Efficient Water Oxidation Electrocatalysis

Rational design and construction of well-defined hollow heterostructured nanomaterials assembled by ultrathin nanosheets overtakes crucial role in developing high-efficiency oxygen evolution reaction (OER) electrocatalysts. Herein, a reliable metal-organic framework-mediated and cation-exchange strategy to tune the geometric structure and multicomponent heterostructures has been proposed for the fabrication of hollow CoWO₄-Co(OH)₂ hierarchical nanoboxes assembled by rich ultrathin nanosheets. Benefiting from the hierarchical hollow nanostructure, the CoWO₄-Co(OH)₂ nanoboxes offer plenty of metal active centers available for reaction intermediates. Moreover, the well-defined nanointerfaces between CoWO₄ and Co(OH)₂ can function as the bridge for boosting the efficient electron transfer from CoWO₄ to Co(OH)₂. As a consequence, the optimized CoWO₄-Co(OH)₂ nanoboxes can exhibit outstanding electrocatalytic performance toward OER by delivering 10 mA cm^-2 with a low overpotential of 280 mV and a small Tafel slope of 70.6 mV dec^-1 as well as outstanding electrochemical stability. More importantly, this CoWO₄-Co(OH)₂ heterostructured nanocatalyst can couple with Pt/C to drive overall water splitting to achieve 10 mA cm^-2 with a voltage of 1.57 V.

Intrinsic Lability of NiMoO4 to Excel the Oxygen Evolution Reaction

Nickel-based bimetallic oxides such as NiMoO₄ and NiWO₄, when deposited on the electrode substrate, show remarkable activity toward the electrocatalytic oxygen evolution reaction (OER). The stability of such nanostructures is nevertheless speculative, and catalytically active species have been less explored. Herein, NiMoO₄ nanorods and NiWO₄ nanoparticles are prepared via a solvothermal route and deposited on nickel foam (NF) (NiMoO₄/NF and NiWO₄/NF). After ensuring the chemical and structural integrity of the catalysts on electrodes, an OER study has been performed in the alkaline medium. After a few cyclic voltammetry (CV) cycles within the potential window of 1.0-1.9 V (vs reversible hydrogen electrode (RHE)), ex situ Raman analysis of the electrodes infers the formation of NiO(OH)_ED (ED: electrochemically derived) from NiMoO₄ precatalyst, while NiWO₄ remains stable. A controlled study, stirring of NiMoO₄/NF in 1 M KOH without applied potential, confirms that NiMoO₄ hydrolyzes to the isolable NiO, which under a potential bias converts into NiO(OH)_ED. Perhaps the more ionic character of the Ni-O-Mo bond in the NiMoO₄ compared to the Ni-O-W bond in NiWO₄ causes the transformation of NiMoO₄ into NiO(OH)_ED. A comparison of the OER performance of electrochemically derived NiO(OH)_ED, NiWO₄, ex-situ-prepared Ni(OH)₂, and NiO(OH) confirmed that in-situ-prepared NiO(OH)_ED remained superior with a substantial potential of 238 (±6) mV at 20 mA cm^-2. The notable electrochemical performance of NiO(OH)_ED can be attributed to its low Tafel slope value (26 mV dec^-1), high double-layer capacitance (C_dl, 1.21 mF cm^-2), and a low charge-transfer resistance (R_ct, 1.76 Ω). The NiO(OH)_ED/NF can further be fabricated as a durable OER anode to deliver a high current density of 25-100 mA cm^-2. Post-characterization of the anode proves the structural integrity of NiO(OH)_ED even after 12 h of chronoamperometry at 1.595 V (vs reversible hydrogen electrode (RHE)). The NiO(OH)_ED/NF can be a compatible anode to construct an overall water splitting (OWS) electrolyzer that can operate at a cell potential of 1.64 V to reach a current density of 10 mA cm^-2. Similar to that on NF, NiMoO₄ deposited on iron foam (IF) and carbon cloth (CC) also electrochemically converts into NiO(OH) to perform a similar OER activity. This work understandably demonstrates monoclinic NiMoO₄ to be an inherently unstable electro(pre)catalyst, and its structural evolution to polycrystalline NiO(OH)_ED succeeding the NiO phase is intrinsic to its superior activity.

Investigation of enhanced electro-catalytic HER/OER performances of copper tungsten oxide@reduced graphene oxide nanocomposites in alkaline and acidic media

In this paper, we investigate the electro-catalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) of synthesized copper tungsten oxide@reduced graphene oxide (CuWO4@rGO) nanocomposites.

γ-FeO(OH) with Multi-surface Terminations Intrinsically Active for Electrocatalytic Oxygen Evolution Reaction

Due to poor conductivity, electrocatalytic performance of independently prepared iron oxy-hydroxide (FeO(OH)) is inferior whereas in-situ derived FeO(OH) from the iron based electro(pre)catalyst shows superior oxygen evolution reaction (OER). Use...

Development of efficient bi-functional g-C3N4@MOF heterojunctions for water splitting

Highly efficient heterojunctions by combining n-type g-C3N4 and MOFs as bi-functional photoelectrocatalysts towards the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER).

Rapid Surface Reconstruction of Amorphous Co(OH)2 /WOx with Rich Oxygen Vacancies to Promote Oxygen Evolution

Herein, a transition metal dissolution-oxygen vacancy strategy, based on dissolution of highly oxidized transition metal species in alkaline electrolyte, was suggested to construct a high-performance amorphous Co(OH)₂ /WO_x (a-CoW) catalyst for the oxygen evolution reaction (OER). The surface reconstruction of a-CoW and its evolution were described by regulating oxygen vacancies. With continuous dissolution of W species, oxygen vacancies on the surface were generated rapidly, the surface reconstruction was promoted, and the OER performance was improved significantly. During the surface reconstruction, W species also played a role in electronic modulation for Co. Due to its rapid surface reconstruction, a-CoW exhibited excellent OER performance in alkaline electrolyte with an overpotential of 208 mV at 10 mA cm^-2 and had long-term stability for at least 120 h. This work shows that the transition metal dissolution-oxygen vacancy strategy is effective for preparation of high-performance catalysts.

Amorphous nickel tungstate films prepared by SILAR method for electrocatalytic oxygen evolution reaction

Development of electrocatalyst using facile way from non-noble metal compounds with high efficiency for effective water electrolysis is highly demanding for production of hydrogen energy. Nickel based electrocatalysts were currently developed for electrochemical water oxidation in alkaline pH. Herein, amorphous nickel tungstate (NiWO₄) was synthesized using the facile successive ionic layer adsorption and reaction method. The films were characterized by X-ray diffraction, Raman spectroscopy, Fourier transfer infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy techniques. The electrochemical analysis showed 315 mV of overpotential at 100 mA cm^-2 with lowest Tafel slope of 32 mV dec^-1 for oxygen evolution reaction (OER) making films of NiWO₄ compatible towards electrocatalysis of water in alkaline media. The chronopotentiometry measurements at 100 mA cm^-2 over 24 h showed 97% retention of OER activity. The electrochemical active surface area (ECSA) of NW120 film was 25.5 cm^-2.

Iron and Manganese Codoped Cobalt Tungstates Co1-(x+y)Fe x Mn y WO4 as Efficient Photoelectrocatalysts for Oxygen Evolution Reaction

Photoelectrocatalysts are robust materials for the production of energy through different ways such as water splitting. Narrow optical band gaps and high overpotentials are limiting the development of photoelectrocatalysts. In this study, a series of Co_1-(x+y)Fe _x Mn _y WO₄ solid solutions of cobalt tungstate codoped with iron and manganese have been synthesized hydrothermally. The synthesized solid solutions have been characterized by powder XRD, UV-visible spectra, cyclic voltammetry (CV), and linear sweep voltammetry (LSV). They all crystallize in a wolframite-type monoclinic crystal system with space group P2/c. Doping of iron and manganese leads to narrowing of the optical band gap of Co_1-(x+y)Fe _x Mn _y WO₄ from 2.60 to 2.04 eV. The electrocatalytic activity toward oxygen evolution reaction of all of the samples has been evaluated through LSV measurements. It is found that the sample named C5, which is codoped with manganese and iron, has the lowest onset potential and needs the lowest overpotential to attain the targeted 5 mA cm^-2 and standard 10 mA cm^-2 current densities as compared with all other synthesized samples. This study shows that the synthesized tungstates can be good candidates for the photoelectrocatalytic oxygen evolution reaction.

Co/Ni-polyoxotungstate photocatalysts as precursor materials for electrocatalytic water oxidation

An open-core cobalt polyoxometalate (POM) [(A-α-SiW9O34)Co4(OH)3(CH3COO)3]8-Co(1) and its isostructural Co/Ni-analogue [(A-α-SiW9O34)Co1.5Ni2.5(OH)3(CH3COO)3]8-CoNi(2) were synthesized and investigated for their photocatalytic and electrocatalytic performance. Co(1) shows high photocatalytic O2 yields, which are competitive with leading POM water oxidation catalysts (WOCs). Furthermore, Co(1) and CoNi(2) were employed as well-defined precursors for heterogeneous WOCs. Annealing at various temperatures afforded amorphous and crystalline CoWO4- and Co1.5Ni2.5WO4-related nanoparticles. CoWO4-related particles formed at 300 °C showed substantial electrocatalytic improvements and were superior to reference materials obtained from co-precipitation/annealing routes. Interestingly, no synergistic interactions between cobalt and nickel centers were observed for the mixed-metal POM precursor and the resulting tungstate catalysts. This stands in sharp contrast to a wide range of studies on various heterogeneous catalyst types which were notably improved through Co/Ni substitution. The results clearly demonstrate that readily accessible POMs are promising precursors for the convenient and low-temperature synthesis of amorphous heterogeneous water oxidation catalysts with enhanced performance compared to conventional approaches. This paves the way to tailoring polyoxometalates as molecular precursors with tuneable transition metal cores for high performance heterogeneous electrocatalysts. Our results furthermore illustrate the key influence of the synthetic history on the performance of oxide catalysts and highlight the dependence of synergistic metal interactions on the structural environment.

CoWO4-x -Based Photothermal Membranes for Solar-Driven Water Evaporation and Eutrophic Lake Water Purification

Solar-driven water evaporation has been proven to be a promising and efficient method for the energy crisis and clean water shortage issues. Herein, we strategically design and fabricate a novel nonstoichiometric CoWO_4-x -deposited foam nickel (NF) membrane (CoWO_4-x @NF) that possesses all the desirable optical, thermal, and wetting properties for efficient water evaporation and purification. The broadband absorption of CoWO_4-x nanoparticles (NPs) obtained by hydrogen reduction contributes to light-to-heat conversion, while NF with a three-dimensional porous structure can support CoWO_4-x NPs and ensure the rapid flow of water molecules during the water evaporation process. We systematically explore and compare the outdoor water evaporation performance of the pure water group, NF group, and CoWO_4-x @NF group, and the results show that CoWO_4-x @NF performs well under natural sunlight irradiation (water evaporation: 2.91 kg m^-2). Significantly, under solar irradiation, the remarkable reduction of Cyanophyta and Euglenophyta in lake water is achieved in the CoWO_4-x @NF membrane-administered group, and these two algae are the main factors for eutrophication of the lake water. Our work highlights the great potentials of the CoWO_4-x @NF membrane as a device for realizing outdoor solar energy-driven water evaporation and proposes a new strategy for purifying the eutrophication of the lake water.

Cooperative Catalytic Behavior of SnO2 and NiWO4 over BiVO4 Photoanodes for Enhanced Photoelectrochemical Water Splitting Performance

n-BiVO4 is a favorable photoelectrode candidate for a photoelectrochemical (PEC) water splitting reaction owing to its suitable energy level edge locations for an oxygen evolution reaction. On the other hand, the sluggish water oxidation kinetics of BiVO4 photoanodes when used individually make it necessary to use a hole blocking layer as well as water oxidation catalysts to overcome the high kinetic barrier for the PEC water oxidation reaction. Here, we describe a very simple synthetic strategy to fabricate nanocomposite photoanodes that synergistically address both of these critical limitations. In particular, we examine the effect of a SnO2 buffer layer over BiVO4 films and further modify the photoanode surface with a crystalline nickel tungstate (NiWO4) nanoparticle film to boost PEC water oxidation. When NiWO4 is incorporated over BiVO4/SnO2 films, the PEC performance of the resultant triple-layer NiWO4/BiVO4/SnO2 films for the oxygen evolution reaction (OER) is further improved. The enhanced performance for the PEC OER is credited to the synergetic effect of the individual layers and the introduction of a SnO2 buffer layer over the BiVO4 film. The optimized NiWO4/BiVO4/SnO2 electrode demonstrated both enriched visible light absorption and achieves charge separation and transfer efficiencies of 23% and 30%, respectively. The photoanodic current density for the OER on optimized NiWO4/BiVO4/SnO2 photoanode shows a maximum photocurrent of 0.93 mA/cm2 at 1.23 V vs. RHE in a phosphate buffer solution (pH~7.5) under an AM1.5G solar simulator, which is an incredible five-fold and two-fold enhancement compared to its parent BiVO4 photoanode and BiVO4/SnO2 photoanodes, respectively. Further, the incorporation of the NiWO4 co-catalyst over the BiVO4/SnO2 film increases the interfacial electron transfer rate across the composite/solution interface.

Hierarchical CuAl-layered double hydroxide/CoWO4 nanocomposites with enhanced efficiency for use in supercapacitors with long cycling stability

A CuAl-LDH/CoWO₄ nanocomposite was used in an asymmetric supercapacitor, providing 35.87 W h kg⁻¹ energy density and 10 188 W kg⁻¹ power density.

Solvothermal synthesis of NiWO4 nanostructure and its application as a cathode material for asymmetric supercapacitors

This study proposes a facile solvothermal synthesis of nickel tungstate (NiWO4) nanowires for application as a novel cathode material for supercapacitors. The structure, morphology, surface area and pore distribution were characterized and their capacitive performances were investigated. The results showed that the NiWO4 nanowires synthesized in ethylene glycol solvent could offer a high specific capacitance of 1190 F g-1 at a current density of 0.5 A g-1 and a capacitance retaining ratio of 61.5% within 0.5-10 A g-1. When used as a cathodic electrode of an asymmetric supercapacitor (ASC), the NiWO4 nanowire based device can be cycled reversibly in a high-voltage region of 0-1.7 V with a high specific capacitance of 160 F g-1 at 0.5 A g-1, which therefore contributed to an energy density of 64.2 W h kg-1 at a power density of 425 W kg-1. Moreover, 92.8% of its initial specific capacitance can be maintained after 5000 consecutive cycles (5 A g-1). These excellent capacitive properties make NiWO4 a credible electrode material for high-performance supercapacitors.

3D-Structured Polyoxometalate Microcrystals with Enhanced Rate Capability and Cycle Stability for Lithium-Ion Storage

The unsatisfactory rate capability and poor cycle stability are two major obstacles for polyoxometalates (POMs) in lithium-ion storage. On the other hand, how to endow POMs with 3D macrostructures for further practice is a challenge. To this end, a facile hydrothermal strategy was practiced to fabricate Co₈W₁₂O₄₂(OH)₄(H₂O)₈ microcrystals or CoWO₄ aggregates onto the foamed substrate (denoted as CoW-POM and CoW-Salt, respectively). Integrating the extraordinary redox stability and lattice deformability of POMs with the excellent volume accommodation, the as-prepared CoW-POM presents an extraordinary better electrochemical performance (specific capacity, rate capability, and cycle life) than that of CoW-Salt. In detail, the CoW-POM can deliver a reversible capacity of 737.8 mA h g^-1 at the current density of 0.1 A g^-1 and provide a capacity retention of 90.1% even after 100 cycles. This work not only promotes the application of POMs in energy storage and conversion but also guides an effect methodology to endow POMs with 3D structures.

MnWO4 nanoparticles as advanced anodes for lithium-ion batteries: F-doped enhanced lithiation/delithiation reversibility and Li-storage properties

F-Doped MnWO4 nano-particles were synthesized by a one-pot hydrothermal reaction. When evaluated as an electrode material for a Li ion battery, the F-doped nano-MnWO4 delivers a theoretical capacity of 708 mA h g-1 and a long cycle life, as demonstrated by more than 85% capacity retention when cycled for 150 cycles.

Bifunctional electro-catalytic performances of CoWO4 nanocubes for water redox reactions (OER/ORR)

In this paper, we report the synthesis of cube shaped nanoparticles of CoWO₄ (∼30 nm) by molten salts and their bifunctional electro-catalytic activities in water redox reactions for oxygen evolution and oxygen reduction reactions (OER and ORR).

Synthesis, characterization, and enhanced photocatalytic properties of NiWO4 nanobricks

NiWO₄ nanobricks were used as photocatalysts in the degradation of organic pollutants in neutral and basic media.