Large area, one step synthesis of NiSe2 films on cellulose paper for glucose monitoring in bio-mimicking samples for clinical diagnostics

There is an urgent need to develop low cost electrochemical sensors wherein the sensor can be disposed after recording data, thereby eliminating the issue of inaccuracy arising from repeated sensing measurements, which plagues most conventional electrochemical sensors. This work is the first demonstration of a NiSe₂ based disposable, one time use electrochemical glucose sensor in bio-mimicking real samples wherein NiSe₂ was hydrothermally grown NiSe₂ on a biodegradable cellulose paper. Both physicochemical (x-ray diffraction, x-ray photoelectron spectroscopy, field emission scanning electron microscope) and electrochemical (impedance spectroscopy and cyclic voltammetry (CV)) characterization techniques confirmed the growth and presence of NiSe₂ on a cellulose paper. Electrochemical techniques like CV and amperometric (i-t) were utilized for the selective and sensitive oxidation of glucose. The results suggests that the proposed NiSe₂ sensor is effective in a linear range of 0.1-1 mM with fast response time (3.9 s), low detection limit (24.8 ± 0.1 μM) and high sensitivity (0.25 A M^-1 cm^-2) at a potential applied (E _app = 0.55 V versus Ag∣AgCl). Prior to the real sample analyses i.e. glucose detection in human urine, the fabricated NiSe₂ sensor was tested for selectivity towards glucose in co-existing interferences (dopamine, ascorbic acid, uric acid, urea, sodium chloride, fructose, lactose and cysteine). Finally, glucose in artificial blood serum and urine samples was demonstrated with the fabricated NiSe₂ sensor and the results are comparable to the conventional laboratory methods. The present methodology presents a novel possibility towards the design of next generation, affordable point-of-care devices for a broad range of clinical diagnostics.

Changing the Blood Test: Accurate Determination of Mercury(II) in One Microliter of Blood Using Oriented ZnO Nanobelt Array Film Solution-Gated Transistor Chips

The measurement of ultralow concentrations of heavy metal ions (HMIs) in blood is challenging. A new strategy for the determination of mercury ions (Hg²⁺ ) based on an oriented ZnO nanobelt (ZnO-NB) film solution-gated field-effect transistor (FET) chip is adopted. The FET chips are fabricated with ZnO-NB film channels with different orientations utilizing the Langmuir-Blodgett (L-B) assembly technique. The combined simulation and I-V behavior results show that the nanodevice with ZnO-NBs parallel to the channel has exceptional performance. The sensing capability of the oriented ZnO-NB film FET chips corresponds to an ultralow minimum detectable level (MDL) of 100 × 10^-12 m in deionized water due to the change in the electrical double layer (EDL) arising from the synergism of the field-induced effect and the specific binding of Hg²⁺ to the thiol groups (-SH) on the film surface. Moreover, the prepared FET chips present excellent selectivity toward Hg²⁺ , excellent repeatability, and a rapid response time (less than 1 s) for various Hg²⁺ concentrations. The sensing performance corresponds to a low MDL of 10 × 10^-9 m in real samples of a drop of blood.

Scheelite type Sr1-xBaxWO4 (x = 0.1, 0.2, 0.3) for possible application in Solid Oxide Fuel Cell electrolytes

Polycrystalline scheelite type Sr_1−xBa_xWO₄ (x = 0.1, 0.2 & 0.3) materials were synthesized by the solid state sintering method and studied with respect to phase stability and ionic conductivity under condition of technological relevance for SOFC applications. All compounds crystallized in the single phase of tetragonal scheelite structure with the space group of I4₁/a. Room temperature X-ray diffraction and subsequent Rietveld analysis confirms its symmetry, space group and structural parameters. SEM illustrates the highly dense compounds. Significant mass change was observed to prove the proton uptake at higher temperature by TG-DSC. All compound shows lower conductivity compared to the traditional BCZY perovskite structured materials. SBW with x = 0.3 exhibit the highest ionic conductivity among all compounds under wet argon condition which is 1.9 × 10⁻⁶ S cm⁻¹ at 1000 °C. Since this scheelite type compounds show significant conductivity, the new series of SBW could serve in IT-SOFC as proton conducting electrolyte.

Interconnected Vertically Stacked 2D-MoS2 for Ultrastable Cycling of Rechargeable Li-Ion Battery

A two-dimensional (2D) layer-structured material is often a high-capacity ionic storage material with fast ionic transport within the layers. This appears to be the case for nonconversion layer structure, such as graphite. However, this is not the case for conversion-type layered structure such as transition-metal sulfide, in which localized congestion of ionic species adjacent to the surface will induce localized conversion, leading to the blocking of the fast diffusion channels and fast capacity fading, which therefore constitutes one of the critical barriers for the application of transition-metal sulfide layered structure. In this work, we report the tackling of this critical barrier through nanoscale engineering. We discover that interconnected vertically stacked two-dimensional-molybdenum disulfide can dramatically enhance the cycling stability. Atomic-level in situ transmission electron microscopy observation reveals that the molybdenum disulfide (MoS₂) nanocakes assembled with tangling {100}-terminated nanosheets offer abundant open channels for Li⁺ insertion through the {100} surface, featuring an exceptional cyclability performance for over 200 cycles with a capacity retention of 90%. In contrast, (002)-terminated MoS₂ nanoflowers only retain 10% of original capacity after 50 cycles. The present work demonstrates a general principle and opens a new route of crystallographic design to enhance electrochemical performance for assembling 2D materials for energy storage.

Spinel Cobalt Titanium Binary Oxide as an All-Non-Precious Water Oxidation Electrocatalyst in Acid

Replacing precious water oxidation electrocatalysts used in proton exchange membrane (PEM) water electrolyzers with the nonprecious and abundant electrocatalysts is still a poorly addressed issue in the field of hydrogen generation in acidic medium through water electrolysis. Herein we report such an all-nonprecious binary spinel metal oxide the "cobalt titanate" (Co₂TiO₄) as an efficient alternate to expensive IrO₂ and RuO₂ for PEM water electrolyzer. The synthesized Co₂TiO₄ octahedral nanocrystals of size 50 to 210 nm showed excellent oxygen evolution reaction (OER) activity in 0.5 M H₂SO₄, which was comparable to IrO₂ and better than spinel Co₃O₄ when examined under identical experimental conditions. Overpotential of just 513 mV was sufficient enough to drive a kinetic current density of 10 mA cm^-2, which is a significant figure of merit as far as acidic water oxidation electrocatalysis is concerned.

Synthesis Process of CoSeO3 Microspheres for Unordinary Li-ion Storage Performances and Mechanism of Their Conversion Reaction with Li ions

Multicomponent materials with various double cations have been studied as anode materials of lithium-ion batteries (LIBs). Heterostructures formed by coupling different-bandgap nanocrystals enhance the surface reaction kinetics and facilitate charge transport because of the internal electric field at the heterointerface. Accordingly, metal selenites can be considered efficient anode materials of LIBs because they transform into metal selenide and oxide nanocrystals in the first cycle. However, few studies have reported synthesis of uniquely structured metal selenite microspheres. Herein, synthesis of high-porosity CoSeO₃ microspheres is reported. Through one-pot oxidation at 400 °C, CoSe_x -C microspheres formed by spray pyrolysis transform into CoSeO₃ microspheres showing unordinary cycling and rate performances. The conversion mechanism of CoSeO₃ microspheres for lithium-ion storage is systematically studied by cyclic voltammetry, in situ X-ray diffraction and electrochemical impedance spectroscopy, and transmission electron microscopy. The reversible reaction mechanism of the CoSeO₃ phase from the second cycle onward is evaluated as CoO + xSeO₂ + (1 - x)Se + 4(x + 1)Li⁺ + 4( x + 1)e^- ↔ Co + (2x + 1)Li₂ O + Li₂ Se. The CoSeO₃ microspheres show a high reversible capacity of 709 mA h g^-1 for the 1400th cycle at a current density of 3 A g^-1 and a high reversible capacity of 526 mA h g^-1 even at an extremely high current density of 30 A g^-1 .

Thermodynamics, Electronic Structure, and Vibrational Properties of Sn n (S1-x Se x ) m Solid Solutions for Energy Applications

The tin sulfides and selenides have a range of applications spanning photovoltaics and thermoelectrics to photocatalysts and photodetectors. However, significant challenges remain to widespread use, including electrical and chemical incompatibilities between SnS and device contact materials and the environmental toxicity of selenium. Solid solutions of isostructural sulfide and selenide phases could provide scope for optimizing physical properties against sustainability requirements, but this has not been comprehensively explored. This work presents a detailed modeling study of the Pnma and rocksalt Sn(S_1-x Se _x ), Sn(S_1-x Se _x )₂, and Sn₂(S_1-x Se _x )₃ solid solutions. All four show an energetically favorable and homogenous mixing at all compositions, but rocksalt Sn(S_1-x Se _x ) and Sn₂(S_1-x Se _x )₃ are predicted to be metastable and accessible only under certain synthesis conditions. Alloying leads to a predictable variation of the bandgap, density of states, and optical properties with composition, allowing SnS₂ to be "tuned down" to the ideal Shockley-Queisser bandgap of 1.34 eV. The impact of forming the solid solutions on the lattice dynamics is also investigated, providing insight into the enhanced performance of Sn(S_1-x Se _x ) solid solutions for thermoelectric applications. These results demonstrate that alloying affords facile and precise control over the electronic, optical, and vibrational properties, allowing material performance for optoelectronic applications to be optimized alongside a variety of practical considerations.

The rational design of hierarchical MoS2 nanosheet hollow spheres sandwiched between carbon and TiO2@graphite as an improved anode for lithium-ion batteries

Molybdenum disulfide (MoS₂) shows high capacity but suffers from poor rate capability and rapid capacity decay, which greatly limit its practical applications in lithium-ion batteries. Herein, we successfully prepared MoS₂ nanosheet hollow spheres encapsulated into carbon and titanium dioxide@graphite, denoted as TiO₂@G@MoS₂@C, via hydrothermal and polymerization approaches. In this hierarchical architecture, the MoS₂ hollow sphere was sandwiched by graphite and an amorphous carbon shell; thus, TiO₂@G@MoS₂@C exhibited effectively enhanced electrical conductivity and withstood the volume changes; moreover, the aggregation and diffusion of the MoS₂ nanosheets were restricted; this advanced TiO₂@G@MoS₂@C fully combined the advantages of a three-dimensional architecture, hollow structure, carbon coating, and a mechanically robust TiO₂@graphite support, achieving improved specific capacity and long-term cycling stability. In addition, it exhibited the high reversible specific capacity of 823 mA h g^-1 at the current density of 0.1 A g^-1 after 100 cycles, retaining almost 88% of the initial reversible capacity with the high coulombic efficiency of 99%.

2D Single Crystal WSe2 and MoSe2 Nanomeshes with Quantifiable High Exposure of Layer Edges from 3D Mesoporous Silica Template

The design and fabrication of layered transition metal chalcogenides with high exposure of crystal layer edges is one of the key paths to achieve distinctive performances in their catalysis and electrochemistry applications. Two-dimensional WSe₂ and MoSe₂ nanomeshes with orderly arranged nanoholes were synthesized by using a mesoporous silica material KIT-6 with three-dimensional mesoporous structure as a hard template via a nanocasting strategy. Each piece of the nanomesh is a single crystal, and its c axis is always perpendicular to the nanomesh plane. The highly porous structure brings these nanomeshes extremely high exposure of layer edges, and the well-defined nanostructure provides an opportunity to quantitatively estimate the specific length of the crystal layer edges for the WSe₂ and MoSe₂ nanomeshes synthesized in this work, which are estimated to be 3.8 × 10¹⁰ and 6.0 × 10¹⁰ m g^-1, respectively. The formation of a 2D sheet-like nanomesh structure inside a 3D confined pore space should be attributed to the synergistic effect from the crystal self-limitation growth that is caused by their layered crystal structures and the space-limitation effect coming from the unique pore structure of the KIT-6 template. The catalytic activities of the nanomeshes in an electrocatalytic hydrogen evolution reaction were also investigated.

Vanadium-based nanowires for sodium-ion batteries

Sodium-ion batteries (SIBs) have received great attention because of the abundance source and low cost. To date, some Na⁺ storage materials have achieved great performance, but the larger Na⁺ radius and more complex Na⁺ storage mechanism compared with Li⁺ still limit the energy density and power density. This review systematically summarizes emerging synthetic technologies of vanadium-based materials from simple nanowires to complicated modified/optimized structures. In addition, vanadium-based nanowire materials are reviewed at both the cathode and anode side, and advantages and drawbacks are proposed to explain the challenges facing application of novel materials. Furthermore, a vanadium-based single-nanowire device is reported to reveal the Na⁺ storage mechanism, which contributes to the understanding of the reaction in SIBs. Finally, this review summarizes the current development challenges of SIBs and looks forward to the future development prospects of vanadium-based nanowires, providing a new direction for further applications of SIBs.

Tuning the coupling interface of ultrathin Ni3S2@NiV-LDH heterogeneous nanosheet electrocatalysts for improved overall water splitting

Tuning the coupling interface of a heterostructured catalyst is an effective approach to achieve abundant surface catalytic active sites and strong electronic interactions among active materials for improving electrocatalytic water splitting performance. Herein, we report a novel heterogeneous catalyst comprising Ni3S2 nanoparticles embedded in ultrathin NiV-layered double hydroxide nanosheet arrays supported on nickel foam, denoted as Ni3S2@NiV-LDH/NF. We demonstrate that the active edge-state length and the surface chemical state of such NiV-LDH-based heterostructures are well modulated by tailoring the coupling interfaces, resulting in the exposure of more catalytic reaction sites and enhancement of the electronic interactions between NiV-LDH and Ni3S2, thus greatly promoting the water dissociation kinetics. As expected, the optimized Ni3S2@NiV-LDH/NF heterostructures exhibit outstanding electrocatalytic activity for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), with an extremely low overpotential of 126 mV and 190 mV to deliver 10 mA cm-2 for the HER and OER without iR compensation in alkaline media, respectively. More importantly, Ni3S2@NiV-LDH/NF simultaneously functioned as both the anode and cathode for water splitting to yield a current density of 10 mA cm-2 at a cell voltage of only 1.53 V with an outstanding durability for 160 h. This work provides a new insight into the regulation of the coupling interface for obtaining highly active heterostructured catalysts for overall water splitting.

Bimetallic NiCo2S4 Nanoneedles Anchored on Mesocarbon Microbeads as Advanced Electrodes for Asymmetric Supercapacitors

Bimetallic Ni-Co sulfides are outstanding pseudocapacitive materials with high electrochemical activity and excellent energy storage performance as electrodes for high-performance supercapacitors. In this study, a novel urchin-like NiCo₂S₄@mesocarbon microbead (NCS@MCMB) composite with a core-shell structure was prepared by a facile two-step hydrothermal method. The highly conductive MCMBs offered abundant adsorption sites for the growth of NCS nanoneedles, which allowed each nanoneedle to fully unfold without aggregation, resulting in improved NCS utilization and efficient electron/ion transfer in the electrolyte. When applied as an electrode material for supercapacitors, the composite exhibited a maximum specific capacitance of 936 F g^-1 at 1 A g^-1 and a capacitance retention of 94% after 3000 cycles at 5 A g^-1, because of the synergistic effect of MCMB and NCS. Moreover, we fabricated an asymmetric supercapacitor based on the NCS@MCMB composite, which exhibited enlarged voltage windows and could power a light-emitting diode device for several minutes, further demonstrating the exceptional electrochemical performance of the NCS@MCMB composite.

Solution-Based Synthesis and Processing of Metal Chalcogenides for Thermoelectric Applications

Metal chalcogenide materials are current mainstream thermoelectric materials with high conversion efficiency. This review provides an overview of the scalable solution-based methods for controllable synthesis of various nanostructured and thin-film metal chalcogenides, as well as their properties for thermoelectric applications. Furthermore, the state-of-art ink-based processing method for fabrication of thermoelectric generators based on metal chalcogenides is briefly introduced. Finally, the perspective on this field with regard to material production and device development is also commented upon.

Nitrogen-plasma treated hafnium oxyhydroxide as an efficient acid-stable electrocatalyst for hydrogen evolution and oxidation reactions

Development of earth-abundant electrocatalysts for hydrogen evolution and oxidation reactions in strong acids represents a great challenge for developing high efficiency, durable, and cost effective electrolyzers and fuel cells. We report herein that hafnium oxyhydroxide with incorporated nitrogen by treatment using an atmospheric nitrogen plasma demonstrates high catalytic activity and stability for both hydrogen evolution and oxidation reactions in strong acidic media using earth-abundant materials. The observed properties are especially important for unitized regenerative fuel cells using polymer electrolyte membranes. Our results indicate that nitrogen-modified hafnium oxyhydroxide could be a true alternative for platinum as an active and stable electrocatalyst, and furthermore that nitrogen plasma treatment may be useful in activating other non-conductive materials to form new active electrocatalysts.

Renewable hydrogen technologies are promising for alternative energy, but are encumbered by the kinetics of electrochemical reactions in harsh conditions. Here, authors report nitrogen-modified hafnium oxyhydroxide for electrocatalysis of hydrogen evolution and oxidation reactions in acidic media.

Retracted Article: Fabrication of hollow CoS1.097 prisms toward supercapactior performance

The controlled synthesis of a variety of microstructures is valuable for understanding the relationship between morphology and properties and exploring potential applications. In this paper, hollow CoS_1.097 prisms were prepared by prismatic Co-precursors using thioacetamide (TAA) as a sulfidation treatment reagent. A plausible mechanism was proposed for the formation of the hollow prism structure. S^2- comes from TAA to displace the anions in Co-precursors by adjusting temperature and pressure. The original prism morphology of the Co-precursor was maintained and a hollow prismatic structure was formed by an anion exchanging process. Interestingly, the composition of samples after sulfidation treatment can be controlled by changing the diffusion to obtain Co₃O₄/CoS_1.097 and CoS_1.097 materials. As electrode materials for supercapacitors, hollow CoS_1.097 prisms revealed ideal electrochemical performance.

Morphology-Controlled Metal Sulfides and Phosphides for Electrochemical Water Splitting

Because H₂ is considered a promising clean energy source, water electrolysis has attracted great interest in related research and technology. Noble-metal-based catalysts are used as electrode materials in water electrolyzers, but their high cost and low abundance have impeded them from being used in practical areas. Recently, metal sulfides and phosphides based on earth-abundant transition metals have emerged as promising candidates for efficient water-splitting catalysts. Most studies have focused on adjusting the composition of the metal sulfides and phosphides to enhance the catalytic performance. However, morphology control of catalysts, including faceted and hollow structures, is much less explored for these systems because of difficulties in the synthesis, which requires a deep understanding of the nanocrystal growth process. Herein, representative synthetic methods for morphology-controlled metal sulfides and phosphides are introduced to provide insights into these methodologies. The electrolytic performance of morphology-controlled metal sulfide- and phosphide-based nanocatalysts with enhanced surface area and intrinsically high catalytic activity is also summarized and the future research directions for this promising catalyst group is discussed.

Rational construction of self-supported triangle-like MOF-derived hollow (Ni,Co)Se2 arrays for electrocatalysis and supercapacitors

In this work, we have adopted a facile three-step method for constructing an intriguing bifunctional electrode of self-supported hollow (Ni,Co)Se2 arrays with a metal-organic framework (MOF) precursor. The triangle-like cobalt-based MOF arrays are first grown on a carbon cloth at room temperature, which is followed by an ion exchange/etching process with Ni(NO3)2 to form a critical hollow nanostructure with an incorporated hetero-metal element. The intermediate is then transformed into the final product through solvothermal selenization treatment. Taking advantages of the structural and compositional merits as well as the self-supporting nature, the resultant (Ni,Co)Se2 electrode exhibits excellent electrochemical activity and stability. When tested as an electrocatalyst for the oxygen evolution reaction (OER), the (Ni,Co)Se2 array electrode displayed a low onset overpotential of 226 mV and a small overpotential of 256 mV to afford a current density of 10 mA cm-2. The (Ni,Co)Se2 electrode is also utilized in a supercapacitor, which delivers a high specific capacitance of 2.85 F cm-2 at 2 mA cm-2 and exhibits excellent cycling stability with a capacitance retention of 80.8% after 2000 charge-discharge cycles at 20 mA cm-2. These results demonstrate the significance of the rational design of electrode materials and disclose the potential of our MOF-derived hollow (Ni,Co)Se2 array electrode for a variety of practical applications in energy conversion and storage.

Facile fabrication of Ni0.85Se nanowires by the composite alkali salt method as a novel cathode material for asymmetric supercapacitors

The search for Earth-abundant and efficient electrode materials is significant for advanced supercapacitors. Here we introduce a facile strategy for one-step synthesis of Ni0.85Se nanowires via a composite alkali salt method. When used as an electrode material in supercapacitors, the as-prepared Ni0.85Se nanowires exhibit a high specific capacitance of 1354 F g-1 at a current density of 1 A g-1, and still retain 671 F g-1 at 30 A g-1. The superior electrochemical performance of the Ni0.85Se electrode can be attributed to the metallic conductivity of nickel selenides and fast electrical transport along the axial direction due to the nanowire morphology. For practical applications, an asymmetric supercapacitor was assembled by using Ni0.85Se and activated carbon, which delivered a high energy density of 40.7 W h kg-1 at a power density of 800 W kg-1 and 12.1 W h kg-1 at 16 kW kg-1. Moreover, the device retained 92.4% specific capacitance after 20 000 cycles at a high current density of 5 A g-1, showing its promising application prospects.

Electrocatalytic and Enhanced Photocatalytic Applications of Sodium Niobate Nanoparticles Developed by Citrate Precursor Route

Development of cost effective and efficient electrocatalysts is crucial to generate H2 as an alternative source of energy. However, expensive noble metal based electrocatalysts show best electrocatalytic performances which acts as main bottle-neck for commercial application. Therefore, non-precious electrocatalysts have become important for hydrogen and oxygen evolution reactions. Herein, we report the synthesis of high surface area (35 m2/g) sodium niobate nanoparticles by citrate precursor method. These nanoparticles were characterized by different techniques like X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Electrocatalytic properties of cost-effective sodium niobate nanoparticles were investigated for HER and OER in 0.5 M KOH electrolyte using Ag/AgCl as reference electrode. The sodium niobate electrode showed significant current density for both OER (≈2.7 mA/cm2) and HER (≈0.7 mA/cm2) with onset potential of 0.9 V for OER and 0.6 V for HER. As-prepared sodium niobate nanoparticles show enhanced photocatalytic property (86% removal) towards the degradation of rose Bengal dye. Dielectric behaviour at different sintering temperatures was explained by Koop's theory and Maxwell-Wagner mechanism. The dielectric constants of 41 and 38.5 and the dielectric losses of 0.04 and 0.025 were observed for the samples sintered at 500 °C and 700 °C, respectively at 500 kHz. Conductivity of the samples was understood by using power law fit.

W2C nanodot-decorated CNT networks as a highly efficient and stable electrocatalyst for hydrogen evolution in acidic and alkaline media

Although tungsten carbide (W2C) has long been reported as an excellent platinum-like catalyst, it is still a challenge to synthesize W2C as an electrocatalyst for a highly efficient hydrogen evolution reaction (HER) due to its high onset overpotential, inevitable aggregation, and lack of a scalable and controllable synthesis method. Herein, we synthesized W2C nanodot-decorated CNT networks (W2C@CNT-S) via a facile and scalable spray drying method followed by a carbonization process. It is demonstrated that this unique nanoarchitecture, constructed by ultrafine W2C nanodots homogeneously decorated on a three-dimensional and conductive CNT skeleton, leads to the exposure of abundant catalytic sites and promotes highly efficient electron transfer and ion diffusion during the HER process. As a result, in acidic and alkaline media, the optimized W2C@CNT-S hybrid exhibited excellent HER performance with very low onset overpotentials of only 60 and 40 mV (vs. RHE) and very small Tafel slopes of 57.4 and 56.2 mV dec-1, and only needed 176 and 148 mV (vs. RHE) to obtain a current density of 10 mA cm-2, respectively; it also showed outstanding long-term durability even after a 30-hour test in both acidic and alkaline media. This study presents an overview of a low-cost and scalable spray-drying strategy to synthesize a high-performance carbide-based electrocatalyst for hydrogen evolution.

Electrocatalytic and Enhanced Photocatalytic Applications of Sodium Niobate Nanoparticles Developed by Citrate Precursor Route

Development of cost effective and efficient electrocatalysts is crucial to generate H₂ as an alternative source of energy. However, expensive noble metal based electrocatalysts show best electrocatalytic performances which acts as main bottle-neck for commercial application. Therefore, non-precious electrocatalysts have become important for hydrogen and oxygen evolution reactions. Herein, we report the synthesis of high surface area (35 m²/g) sodium niobate nanoparticles by citrate precursor method. These nanoparticles were characterized by different techniques like X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Electrocatalytic properties of cost-effective sodium niobate nanoparticles were investigated for HER and OER in 0.5 M KOH electrolyte using Ag/AgCl as reference electrode. The sodium niobate electrode showed significant current density for both OER (≈2.7 mA/cm²) and HER (≈0.7 mA/cm²) with onset potential of 0.9 V for OER and 0.6 V for HER. As-prepared sodium niobate nanoparticles show enhanced photocatalytic property (86% removal) towards the degradation of rose Bengal dye. Dielectric behaviour at different sintering temperatures was explained by Koop's theory and Maxwell-Wagner mechanism. The dielectric constants of 41 and 38.5 and the dielectric losses of 0.04 and 0.025 were observed for the samples sintered at 500 °C and 700 °C, respectively at 500 kHz. Conductivity of the samples was understood by using power law fit.

Coaxial-cable hierarchical tubular MnO2@Fe3O4@C heterostructures as advanced anodes for lithium-ion batteries

Nanostructured manganese oxides have been regarded as promising anodes for lithium-ion batteries (LIBs) due to their high specific capacity, environmental friendliness and low cost. However, as conversion-type electrodes, their scalable utilization is hindered by intrinsically low reaction kinetics, large volume variation and high polarization. Herein, a coaxial-cable tubular heterostructure composed of a hollow carbon skeleton, Fe₃O₄ nanoparticles and ultrathin MnO₂ nanosheets from inside out, donated as MnO₂@Fe₃O₄@C, is synthesized via a facile two-step hydrothermal process. The unique design integrates conductive carbon and nanostructured MnO₂ and Fe₃O₄ into a one-dimensional (1D) hierarchically open architecture, which provides abundant electrode-electrolyte contact areas, favorable heterointerfaces and ultrafast electron/ion pathways. Benefiting from these features, the MnO₂@Fe₃O₄@C anode exhibits a high reversible capacity of 946 mAh g^-1 at 200 mA g^-1 after 160 cycles, and excellent cyclability with a specific capacity of 845 mAh g^-1 at 500 mA g^-1 after 600 cycles. This work might provide an insightful guideline for the design of novel electrode materials.

Facile efficient earth abundant NiO/C composite electrocatalyst for the oxygen evolution reaction

Due to the increasing energy consumption, designing efficient electrocatalysts for electrochemical water splitting is highly demanded. In this study, we provide a facile approach for the design and fabrication of efficient and stable electrocatalysts through wet chemical methods. The carbon material, obtained by the dehydration of sucrose sugar, provides high surface area for the deposition of NiO nanostructures and the resulting NiO/C catalysts show higher activity towards the OER in alkaline media. During the OER, a composite of NiO with 200 mg C can produce current densities of 10 and 20 mA cm-2 at a bias of 1.45 V and 1.47 V vs. RHE, respectively. Electrochemical impedance spectroscopy experiments showed the lowest charge transfer resistance and the highest double layer capacitance in the case of the NiO/C composite with 200 mg C. The presence of C for the deposition of NiO nanostructures increases the active centers and consequently a robust electrocatalytic activity is achieved. The obtained results in terms of the low overpotential and small Tafel slope of 55 mV dec-1 for non-precious catalysts are clear indications for the significant advancement in the field of electrocatalyst design for water splitting. This composite material based on NiO/C is simple and scalable for widespread use in various applications, especially in supercapacitors and lithium-ion batteries.

Selective electroreduction of carbon dioxide to methanol on copper selenide nanocatalysts

Production of methanol from electrochemical reduction of carbon dioxide is very attractive. However, achieving high Faradaic efficiency with high current density using facile prepared catalysts remains to be a challenge. Herein we report that copper selenide nanocatalysts have outstanding performance for electrochemical reduction of carbon dioxide to methanol, and the current density can be as high as 41.5 mA cm⁻² with a Faradaic efficiency of 77.6% at a low overpotential of 285 mV. The copper and selenium in the catalysts cooperate very well for the formation of methanol. The current density is higher than those reported up to date with very high Faradaic efficiency for producing methanol. As far as we know, this is the first work for electrochemical reduction of carbon dioxide using copper selenide as the catalyst.

While the conversion of CO₂ to valuable, storable chemicals is attractive, there are few inexpensive and abundant catalysts that are also active and selective for liquid fuels. Here, the authors study copper selenide as a high-performing and efficient electrocatalyst for CO₂ conversion to methanol.

Free-Standing Three-Dimensional CuCo2S4 Nanosheet Array with High Catalytic Activity as an Efficient Oxygen Electrode for Lithium-Oxygen Batteries

In this work, a novel free-standing CuCo₂S₄ nanosheet cathode (CuCo₂S₄@Ni) with high catalytic activity is fabricated for aprotic lithium-oxygen (Li-O₂) battery. This deliberately designed oxygen electrode is found to yield lower overpotential (0.82 V), improved specific capacity (9673 mA h g^-1 at 100 mA g^-1), and enhanced cycle life (164 cycles) as compared to the traditional carbonaceous electrode. The improved performance can be ascribed to the superb spinel structure of CuCo₂S₄, in which both Cu and Co exhibit more abundant redox properties, improving oxygen reduction reaction and oxygen evolution reaction kinetics effectively and boosting the electrochemical reactions. Furthermore, the well-designed architecture also plays a critical role in the improved performance. Encouraged by the excellent catalytic activity of this free-standing cathode, large-scale pouch-type Li-O₂ cell based on CuCo₂S₄@Ni cathode is fabricated and can work under different bending and twisting conditions. This free-standing electrode provides a new strategy for developing Li-O₂ batteries with excellent performance and flexible wearable devices.

Tuning and mechanistic insights of metal chalcogenide molecular catalysts for the hydrogen-evolution reaction

The production of hydrogen through water splitting using earth-abundant metal catalysts is a promising pathway for converting solar energy into chemical fuels. However, existing approaches for fine stoichiometric control, structural and catalytic modification of materials by appropriate choice of earth abundant elements are either limited or challenging. Here we explore the tuning of redox active immobilised molecular metal-chalcoxide electrocatalysts by controlling the chalcogen or metal stoichiometry and explore critical aspects of the hydrogen evolution reaction (HER). Linear sweep voltammetry (LSV) shows that stoichiometric and structural control leads to the evolution of hydrogen at low overpotential with no catalyst degradation over 1000 cycles. Density functional calculations reveal the effect of the electronic and structural features and confer plausibility to the existence of a unimolecular mechanism in the HER process based on the tested hypotheses. We anticipate these findings to be a starting point for further exploration of molecular catalytic systems.

Hollow core–shell NiCo2S4@MoS2 dodecahedrons with enhanced performance for supercapacitors and hydrogen evolution reaction

Hollow core–shell NiCo₂S₄@MoS₂ heterostructures were fabricated using zeolitic imidazolate frameworks as templates and exhibited enhanced electrochemical performance for supercapacitors and hydrogen evolution reaction.

In Operando analysis of the charge storage mechanism in a conversion ZnCo2O4 anode and the application in flexible Li-ion batteries

Intermediate phases of LiCo₂O₃, CoO and ZnO are evidenced during the 1^st lithiation of a ZnCo₂O₄ anode.

Electrochemically chopped WS2 quantum dots as an efficient and stable electrocatalyst for water reduction

A single-step electrochemical disintegration of bulk WS₂ led to a highly active WS₂ QDs electrocatalyst for HER.

Mesoporous nickel cobalt manganese sulfide yolk–shell hollow spheres for high-performance electrochemical energy storage

Mesoporous Ni–Co–Mn sulfide yolk–shell hollow spheres have been prepared via a self-template route and show excellent electrochemical performance in supercapacitors.

S. V, C. S. PK, Kandaiah S. Anodic fabrication of nanostructured CuxS and CuNiSx thin films and their hydrogen evolution activities in acidic electrolytes

The electrochemical anodization method is advantageous for direct growth of highly ordered and large surface area hybrid nanostructures.

Applications of 2D MXenes in energy conversion and storage systems

This article provides a comprehensive review of MXene materials and their energy-related applications.