Nanostructured Li2S Cathodes for Silicon-Sulfur Batteries.

Lithium-sulfur batteries are regarded as an advantageous option for meeting the growing demand for high-energy-density storage, but their commercialization relies on solving the current limitations of both sulfur cathodes and lithium metal anodes. In this scenario, the implementation of lithium sulfide (Li2S) cathodes compatible with alternative anode materials such as silicon has the potential to alleviate the safety concerns associated with lithium metal. In this direction, here, we report a sulfur cathode based on Li2S nanocrystals grown on a catalytic host consisting of CoFeP nanoparticles supported on tubular carbon nitride. Nanosized Li2S is incorporated into the host by a scalable liquid infiltration-evaporation method. Theoretical calculations and experimental results demonstrate that the CoFeP-CN composite can boost the polysulfide adsorption/conversion reaction kinetics and strongly reduce the initial overpotential activation barrier by stretching the Li-S bonds of Li2S. Besides, the ultrasmall size of the Li2S particles in the Li2S-CoFeP-CN composite cathode facilitates the initial activation. Overall, the Li2S-CoFeP-CN electrodes exhibit a low activation barrier of 2.56 V, a high initial capacity of 991 mA h gLi2S-1, and outstanding cyclability with a small fading rate of 0.029% per cycle over 800 cycles. Moreover, Si/Li2S full cells are assembled using the nanostructured Li2S-CoFeP-CN cathode and a prelithiated anode based on graphite-supported silicon nanowires. These Si/Li2S cells demonstrate high initial discharge capacities above 900 mA h gLi2S-1 and good cyclability with a capacity fading rate of 0.28% per cycle over 150 cycles.

Sulfate-Decorated Amorphous-Crystalline Cobalt-Iron Oxide Nanosheets to Enhance O-O Coupling in the Oxygen Evolution Reaction.

The electrochemical oxygen evolution reaction (OER) plays a fundamental role in several energy technologies, which performance and cost-effectiveness are in large part related to the used OER electrocatalyst. Herein, we detail the synthesis of cobalt-iron oxide nanosheets containing controlled amounts of well-anchored SO42- anionic groups (CoFexOy-SO4). We use a cobalt-based zeolitic imidazolate framework (ZIF-67) as the structural template and a cobalt source and Mohr's salt ((NH4)2Fe(SO4)2·6H2O) as the source of iron and sulfate. When combining the ZIF-67 with ammonium iron sulfate, the protons produced by the ammonium ion hydrolysis (NH4+ + H2O = NH3·H2O + H+) etch the ZIF-67, dissociating its polyhedron structure, and form porous assemblies of two-dimensional nanostructures through a diffusion-controlled process. At the same time, iron ions partially replace cobalt within the structure, and SO42- ions are anchored on the material surface by exchange with organic ligands. As a result, ultrathin CoFexOy-SO4 nanosheets are obtained. The proposed synthetic procedure enables controlling the amount of Fe and SO4 ions and analyzing the effect of each element on the electrocatalytic activity. The optimized CoFexOy-SO4 material displays outstanding OER activity with a 10 mA cm-2 overpotential of 268 mV, a Tafel slope of 46.5 mV dec-1, and excellent stability during 62 h. This excellent performance is correlated to the material's structural and chemical parameters. The assembled nanosheet structure is characterized by a large electrochemically active surface area, a high density of reaction sites, and fast electron transportation. Meanwhile, the introduction of iron increases the electrical conductivity of the catalysts and provides fast reaction sites with optimum bond energy and spin state for the adsorption of OER intermediates. The presence of sulfate ions at the catalyst surface modifies the electronic energy level of active sites, regulates the adsorption of intermediates to reduce the OER overpotential, and promotes the surface charge transfer, which accelerates the formation of oxygenated intermediates. Overall, the present work details the synthesis of a high-efficiency OER electrocatalyst and demonstrates the introduction of nonmetallic anionic groups as an excellent strategy to promote electrocatalytic activity in energy conversion technologies.

Cobalt Molybdenum Nitride-Based Nanosheets for Seawater Splitting.

The development of cost-effective bifunctional catalysts for water electrolysis is both a crucial necessity and an exciting scientific challenge. Herein, a simple approach based on a metal-organic framework sacrificial template to preparing cobalt molybdenum nitride supported on nitrogen-doped carbon nanosheets is reported. The porous structure of produced composite enables fast reaction kinetics, enhanced stability, and high corrosion resistance in critical seawater conditions. The cobalt molybdenum nitride-based electrocatalyst is tested toward both oxygen evolution reaction and hydrogen evolution reaction half-reactions using the seawater electrolyte, providing excellent performances that are rationalized using density functional theory. Subsequently, the nitride composite is tested as a bifunctional catalyst for the overall splitting of KOH-treated seawater from the Mediterranean Sea. The assembled system requires overpotentials of just 1.70 V to achieve a current density of 100 mA cm-2 in 1 M KOH seawater and continuously works for over 62 h. This work demonstrates the potential of transition-metal nitrides for seawater splitting and represents a step forward toward the cost-effective implementation of this technology.

2D/2D Heterojunction of TiO2 Nanoparticles and Ultrathin G-C3N4 Nanosheets for Efficient Photocatalytic Hydrogen Evolution.

Photocatalytic hydrogen evolution is considered one of the promising routes to solve the energy and environmental crises. However, developing efficient and low-cost photocatalysts remains an unsolved challenge. In this work, ultrathin 2D g-C3N4 nanosheets are coupled with flat TiO2 nanoparticles as face-to-face 2D/2D heterojunction photocatalysts through a simple electrostatic self-assembly method. Compared with g-C3N4 and pure TiO2 nanosheets, 2D/2D TiO2/g-C3N4 heterojunctions exhibit effective charge separation and transport properties that translate into outstanding photocatalytic performances. With the optimized heterostructure composition, stable hydrogen evolution activities are threefold and fourfold higher than those of pure TiO2, and g-C3N4 are consistently obtained. Benefiting from the favorable 2D/2D heterojunction structure, the TiO2/g-C3N4 photocatalyst yields H2 evolution rates up to 3875 µmol·g-1·h-1 with an AQE of 7.16% at 380 nm.

MOF-Derived Ultrathin Cobalt Molybdenum Phosphide Nanosheets for Efficient Electrochemical Overall Water Splitting.

The development of high-performance and cost-effective earth-abundant transition metal-based electrocatalysts is of major interest for several key energy technologies, including water splitting. Herein, we report the synthesis of ultrathin CoMoP nanosheets through a simple ion etching and phosphorization method. The obtained catalyst exhibits outstanding electrocatalytic activity and stability towards oxygen and hydrogen evolution reactions (OER and HER), with overpotentials down to 273 and 89 mV at 10 mA cm-2, respectively. The produced CoMoP nanosheets are also characterized by very small Tafel slopes, 54.9 and 69.7 mV dec-1 for OER and HER, respectively. When used as both cathode and anode electrocatalyst in the overall water splitting reaction, CoMoP-based cells require just 1.56 V to reach 10 mA cm-2 in alkaline media. This outstanding performance is attributed to the proper composition, weak crystallinity and two-dimensional nanosheet structure of the electrocatalyst.

δ-MoN Yolk Microspheres with Ultrathin Nanosheets for a Wide-Spectrum, Sensitive, and Durable Surface-Enhanced Raman Scattering Substrate.

Facing the complex environment of on-site detection, the development of active substrates with wide-spectrum surface-enhanced Raman scattering (SERS) activity is essential. Herein, we report on the low temperature and reproducible synthesis of plasmonic δ-MoN yolk microspheres by in situ-nitriding amorphous MoO2 microspheres at 500 °C and 1 atm. The yolk-structured δ-MoN exhibits strong and wide-spectrum surface plasmon resonance and SERS effects and can perform highly selective detection for probes with different absorption wavelengths under excitation of 532, 633, and 785 nm lasers, with a limitation of 10-11 M and an enhanced factor of 3.6 × 107. Moreover, the plasmonic δ-MoN yolk microspheres have high environmental durability, which can maintain high sensitivity in strong acid and alkaline solutions.

ZnSe/N-Doped Carbon Nanoreactor with Multiple Adsorption Sites for Stable Lithium-Sulfur Batteries.

To commercially realize the enormous potential of lithium-sulfur batteries (LSBs) several challenges remain to be overcome. At the cathode, the lithium polysulfide (LiPS) shuttle effect must be inhibited and the redox reaction kinetics need to be substantially promoted. In this direction, this work proposes a cathode material based on a transition-metal selenide (TMSe) as both adsorber and catalyst and a hollow nanoreactor architecture: ZnSe/N-doped hollow carbon (ZnSe/NHC). It is here demonstrated both experimentally and by means of density functional theory that this composite provides three key benefits to the LSBs cathode: (i) A highly effective trapping of LiPS due to the combination of sulfiphilic sites of ZnSe, lithiophilic sites of NHC, and the confinement effect of the cage-based structure; (ii) a redox kinetic improvement in part associated with the multiple adsorption sites that facilitate the Li+ diffusion; and (iii) an easier accommodation of the volume expansion preventing the cathode damage due to the hollow design. As a result, LSB cathodes based on S@ZnSe/NHC are characterized by high initial capacities, superior rate capability, and an excellent stability. Overall, this work not only demonstrates the large potential of TMSe as cathode materials in LSBs but also probes the nanoreactor design to be a highly suitable architecture to enhance cycle stability.

Quasi-metal Microwave Route to MoN and Mo2C Ultrafine Nanocrystalline Hollow Spheres as Surface-Enhanced Raman Scattering Substrates.

MoN and Mo2C are important functional materials; however, due to the high activation energy barrier in their nucleation, their synthesis generally requires harsh conditions such as high temperature (>1000 °C) and high pressure (several GPa). The extreme conditions also hinder the acquisition of their ultrafine nanostructures. Herein, we report that MoN and Mo2C hollow spheres with large surface area (108.7-125.6 m2 g-1) and ultrafine nanoparticles (2-5 nm) are prepared by a quasi-metal-based microwave route under mild conditions. MoO2 hollow spheres are used as a quasi-metallic microwave absorbing medium as well as a molybdenum source and template simultaneously. The MoN and Mo2C ultrafine nanocrystalline hollow spheres exhibit strong localized surface plasmon resonance, high photothermal conversion efficiency, and strong surface-enhanced Raman scattering effects. Highly crystalline MoS2 nanosheet hollow spheres can also be obtained by this method, indicating its universality. The present work provides an effective strategy for the rapid and mild preparation of ultrafine nanocrystalline transition metal nitrides and carbides with ultrahigh activation energy.

Metallic Ti3O5 hierarchical porous microspheres with an enhanced photothermal property.

γ-Ti3O5 is one kind of prominent non-stoichiometric metal oxide due to its intriguing ability in electric and electrochemical behaviors. This work reports another attractive property of γ-Ti3O5 hierarchical porous microspheres, the extremely effective photothermal property with a high photothermal conversion efficiency. Theory and experimental results indicate that γ-Ti3O5 hierarchical porous microspheres possess metallic features and display very strong localized surface plasma resonance effects over the visible and near-infrared region. Under simulated sunlight or near infrared light, the metallic γ-Ti3O5 exhibits a photothermal conversion efficiency of up to 65.29%. Under irradiation by a near-infrared laser with a wavelength of 808 nm, the γ-Ti3O5 hierarchical porous microspheres can significantly inhibit cancer cell viability in vitro and disrupt tumor tissue growth in vivo in a short period. In vitro and in vivo toxicity experiments demonstrate that it has good biocompatibility. The ultrahigh photothermal conversion efficiency and biocompatibility make the γ-Ti3O5 very attractive for technological uses in photothermal therapy, solar energy utilization, and infrared light detection and so on.

Preparation, Characterization and Intermediate-Temperature Electrochemical Properties of Er3+-Doped Barium Cerate-Sulphate Composite Electrolyte.

In this study, BaCe0.9Er0.1O3-α was synthesized by a microemulsion method. Then, a BaCe0.9Er0.1O3-α-K2SO4-BaSO4 composite electrolyte was obtained by compounding it with a K2SO4-Li2SO4 solid solution. BaCe0.9Er0.1O3-α and BaCe0.9Er0.1O3-α-K2SO4-BaSO4 were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectrometry. AC impedance spectroscopy was measured in a nitrogen atmosphere at 400-700 °C. The logσ~log (pO2) curves and fuel cell performances of BaCe0.9Er0.1O3-α and BaCe0.9Er0.1O3-α-K2SO4-BaSO4 were tested at 700 °C. The maximum output power density of BaCe0.9Er0.1O3-α-K2SO4-BaSO4 was 115.9 mW·cm-2 at 700 °C, which is ten times higher than that of BaCe0.9Er0.1O3-α.

Solution-Processed Ultrathin SnS2-Pt Nanoplates for Photoelectrochemical Water Oxidation.

Tin disulfide (SnS2) is attracting significant interest because of the abundance of its elements and its excellent optoelectronic properties in part related to its layered structure. In this work, we specify the preparation of ultrathin SnS2 nanoplates (NPLs) through a hot-injection solution-based process. Subsequently, Pt was grown on their surface via in situ reduction of a Pt salt. The photoelectrochemical (PEC) performance of such nanoheterostructures as photoanode toward water oxidation was tested afterwards. Optimized SnS2-Pt photoanodes provided significantly higher photocurrent densities than bare SnS2 and SnS2-based photoanodes of previously reported study. Mott-Schottky analysis and PEC impedance spectroscopy (PEIS) were used to analyze in more detail the effect of Pt on the PEC performance. From these analyses, we attribute the enhanced activity of SnS2-Pt photoanodes reported here to a combination of the very thin SnS2 NPLs and the proper electronic contact between Pt nanoparticles (NPs) and SnS2.

Novel Composite Electrolytes of Zr0.92Y0.08O2-α(8YSZ)-Low Melting Point Glass Powder for Intermediate Temperature Solid Oxide Fuel Cells.

In this study, Zr0.92Y0.08O2-α(8YSZ) powders were synthesized by the sol-gel method. The chemical physics changes and phase formation temperature of 8YSZ crystal were determined by thermogravimetry analysis and differential scanning calorimetry (TGA-DSC). 8YSZ-low melting point glass powder (8YSZ-glass) composite electrolytes with various weight ratios were prepared and calcined at different temperatures. The X-ray diffraction (XRD) patterns of the composite electrolytes were tested. The effects of synthesis temperature, weight ratio, test temperature, and oxygen partial pressure on the conductivities of 8YSZ-glass composite electrolytes, were also investigated at 400⁻800 °C. The result of the logσ ~ log(pO2) plot indicates that the 8YSZ-20% glass (700 °C) is almost a pure ionic conductor. The oxygen concentration discharge cell illustrates that the 8YSZ-20% glass (700 °C) composite electrolyte is a good oxygen ion conductor.

Metal Oxide Aerogels with Controlled Crystallinity and Faceting from the Epoxide-Driven Cross-Linking of Colloidal Nanocrystals.

We present a novel method to produce crystalline oxide aerogels which is based on the cross-linking of preformed colloidal nanocrystals (NCs) triggered by propylene oxide (PO). Ceria and titania were used to illustrate this new approach. Ceria and titania colloidal NCs with tuned geometry and crystal facets were produced in solution from the decomposition of a suitable salt in the presence of oleylamine (OAm). The native surface ligands were replaced by amino acids, rendering the NCs colloidally stable in polar solvents. The NC colloidal solution was then gelled by adding PO, which gradually stripped the ligands from the NC surface, triggering a slow NC aggregation. NC-based metal oxide aerogels displayed both high surface areas and excellent crystallinity associated with the crystalline nature of the constituent building blocks, even without any annealing step. Such NC-based metal oxide aerogels showed higher thermal stability compared with aerogels directly produced from ionic precursors using conventional sol-gel chemistry strategies.

Controllable synthesis of Co3O4 nanocrystals as efficient catalysts for oxygen reduction reaction.

The electrochemical oxygen reduction reaction (ORR) has received great attention due to its importance in fuel cells and metal-air batteries. Here, we present a simple approach to prepare non-noble metal catalyst-Co3O4 nanocrystals (NCs). The particle size and shape were simply controlled by different types and concentrations of metal precursor. Furthermore, different sizes and shapes of Co3O4 NCs are explored as electrocatalysts for ORR, and it has been observed that particles with a similar shape, and smaller particle size led to greater catalytic current densities because of the greater surface area. For particles with a comparable size, the shape or crystalline structure governed the activity of the electrocatalytic reactions. Most importantly, the 9 nm-Co3O4 were demonstrated to act as low-cost catalysts for the ORR with a similar performance to that of Pt catalysts.

An ultrasensitive electrochemical immunosensor based on the synergistic effect of quaternary Cu2SnZnS4 NCs and cyclodextrin-functionalized graphene.

In this study, highly monodispersed Cu2SnZnS4 NCs with a quasi-spherical structure were prepared to construct a sandwich-type electrochemical immunosensor for alpha-fetoprotein detection. Quaternary Cu2SnZnS4 NCs as novel biomimetic catalysts show an efficient intrinsic peroxidase-like activity for H2O2 reduction. This excellent catalytic activity is ascribed to the higher electroconductivity than those of the binary Cu2S and ternary Cu2SnS3 NCs. Moreover, ß-cyclodextrin-functionalized graphene sheets are used as substrate materials that can capture large amounts of primary antibodies due to host-guest interaction and high surface area. Under the optimized conditions, the electrochemical immunosensor exhibites a wide working range from 0.5 pg mL-1 to 10 ng mL-1 and a detection limit of 0.16 pg mL-1 at a signal-to-noise ratio of 3. Good sensitivity, reproducibility, and stability demonstrate its potential application in clinical diagnostics.

Synthesis of Bi2S3-Au Dumbbell Heteronanostructures with Enhanced Photocatalytic and Photoresponse Properties.

In this article, novel types of Bi2S3-Au heterostructures are fabricated through rationally controlling the growth atmosphere. Under argon, Au nanoparticles are preferentially deposited onto the tips of Bi2S3 nanorods to form Bi2S3-Au dumbbell heterostructures. In contrast, because of the etching effect by amine, Au nanoparticles are randomly anchored onto the surface of nanorods to form Bi2S3-Au nanocorns in the presence of oxygen. Furthermore, the size of gold nanoparticles can be controlled through adjusting the concentration of reaction precursors. Bi2S3-Au dumbbells show superior activity for the photodegradation of organic pollutants and an enhanced photoresponse compared to the Bi2S3-Au nanocorns. The significantly improved photocatalytic performance of Bi2S3-Au dumbbells is ascribed to the more efficient charge separation compared to that of Bi2S3-Au nanocorns. These heterostructures composed of environmentally friendly elements are expected to be promising for applications in the field of clean energy.

Biomolecule-assisted synthesis of defect-mediated Cd1-xZnxS/MoS2/graphene hollow spheres for highly efficient hydrogen evolution.

Moderate efficiency and the utilization of noble metal cocatalysts are the key factors that restrict the large-scale application of photocatalytic hydrogen production. To develop more efficient photocatalysts based on earth abundant elements, either a new material strategy or a fundamental understanding of the semiconductor/cocatalyst interfaces is highly desirable. In this paper, we studied the feasibility of in situ formation of defect-rich cocatalysts on graphene-based photocatalysts. A facile biomolecule-assisted strategy was used to self-assmble Cd1-xZnxS/MoS2/graphene hollow spheres. The defect-mediated cocatalyst and synergetic charge transfer around heterostructured interfaces exhibit a significant impact on the visible-light-driven photocatalytic activity of multicomponent solid solutions. With engineered interfacial defects, Cd0.8Zn0.2S/MoS2/graphene hollow spheres exhibited a 63-fold improved H2 production rate, which was even 2 and 3.8 times higher than those of CdS/MoS2/graphene hollow spheres and Cd0.8Zn0.2S/Pt. Therefore, our research provides a promising approach for the rational design of high-efficiency and low-cost photocatalysts for solar fuel production.