Controllable synthesis of mesostructures from TiO2 hollow to porous nanospheres with superior rate performance for lithium ion batteries

Uniform TiO2 nanospheres from hollow, core-shell and mesoporous structures have been synthesized using quasi-nano-sized carbonaceous spheres as templates. The TiO2 nanospheres formed after calcination at 400 °C are composed of ∼7 nm nanoparticles and the shells of the hollow TiO2 nanospheres are as thin as a single layer of nanoparticles. The ultrafine nanoparticles endow the hollow and mesoporous TiO2 nanospheres with short lithium ion diffusion paths leading to high discharge specific capacities of 211.9 and 196.0 mA h g-1 at a current rate of 1 C (167.5 mA g-1) after 100 cycles, and especially superior discharge specific capacities of 125.9 and 113.4 mA h g-1 at a high current rate of up to 20 C. The hollow and mesoporous TiO2 nanospheres also show superior cycling stability with long-term discharge capacities of 103.0 and 110.2 mA h g-1, respectively, even after 3000 cycles at a current rate of 20 C

Bottom-Up Enhancement of g-C 3

Disordered intermolecular interaction carbon nitride precursor prepared by water-assisted grinding of dicyandiamide was used for synthesis of g-C3N4. The final sample possesses much looser structure and provides a broadening optical window for effective light harvesting and charge separation efficiency, which exhibits significantly improved H2 evolution by photocatalytic water splitting. The bottom-up mechanochemistry method opens new vistas towards the potential applications of weak interactions in the photocatalysis field and may also stimulate novel ideas completely different from traditional ones for the design and optimization of photocatalysts

An efficient and low-cost TiO2 compact layer for performance improvement of dye-sensitized solar cells

A TiO2 org. sol was synthesized for the prepn. of a compact TiO2 layer on fluorine-doped tin oxide (FTO) glass by a dip-coating technique. The resultant thin film was used for the fabrication of dye-sensitized solar cells (DSSCs). The compact layer typically has a thickness of ca. 110 nm as indicated by its SEM, and consists of anatase as confirmed by the XRD pattern. Compared with the traditional DSSCs without this compact layer, the solar energy-to-electricity conversion efficiency, short-circuit current and open-circuit potential of the DSSCs with the compact layer were improved by 33.3%, 20.3%, and 10.2%, resp. This can be attributed to the merits brought by the compact layer. It can effectively improve adherence of TiO2 to FTO surface, provide a larger TiO2/FTO contact area, and reduce the electron recombination by blocking the direct contact between the redox electrolyte and the conductive FTO surface.Griffith Sciences, Griffith School of EnvironmentFull Tex

TMN4 complex embedded graphene as efficient and selective electrocatalysts for chlorine evolution reactions

In the industrial large-scale chlor-alkali process, the electrocatalytic chlorine evolution reaction (CER) is a crucial half anodic reaction. However, the concomitant oxygen evolution reaction (OER) is unavoidable by using the noble metal-based dimensionally stable anodes (DSAs) as CER benchmark catalysts. Through purposely screening six TMN4 complexes embedded graphene with the demonstrated low performance of OER, our density functional theory (DFT) results predict that NiN4 complex embedded graphene (NiN4@G) can efficiently catalyse the CER. This single-atom catalyst (SAC) shows superior CER activity with the ultralow thermodynamic overpotential of 0.014 V via the Cl* intermediate instead of the formation of the ClO*. Moreover, its high theoretical overpotential of OER inherently promotes the selectivity of chlorine evolution. The analyses of the bonding mechanism between TM and Cl atoms reveal that their electrostatic attraction forces can be a good descriptor for the discovery of high-performance CER electrocatalysts. Our findings may broaden the scope of CER catalysts design beyond DSAs with the maximized metal atom utilization.</p

Low-Dimensional Metal-Organic Frameworks with High Activity and Selectivity toward Electrocatalytic Chlorine Evolution Reactions

Chlorine gas plays a paramount role in modern industrial chemistry and is one of the most basic chemicals produced by the electrolysis of brine solution. In the past decades, the dimensionally stable anode (DSA) made of RuO2is the benchmark catalyst for the chlorine evolution reaction (CER) with high activity. However, the drawbacks of the DSA, such as high cost and inferior selectivity, demand the development of low-cost and efficient electrocatalysts for CER. Herein, three low-dimensional Fe/Co/Ni-dithiolene metal-organic frameworks (MOFs) were systematically investigated using the density functional theory. Our calculation results predict that Ni-based dithiolene MOF can efficiently catalyze the CER with a low thermodynamic overpotential of 0.049 V via the Cl∗ intermediate. The electronic resonance structure of [Ni2+(L•-)(L2-)]-in the Ni-based dithiolene MOF leads to the electron transfer first from S atoms in ligands to Ni cations to achieve a stable electronic configuration, which leads to the most desirable Ni-Cl interaction strength for CER. Moreover, the selectivity to Cl2generation is due to its high thermodynamic overpotential of oxygen evolution reaction. Our findings may, therefore, accelerate CER catalyst discoveries beyond DSAs with the optimized electronic structures.</p

β-Arsenene Monolayer : A Promising Electrocatalyst for Anodic Chlorine Evolution Reaction

Materials innovation plays an essential role to address the increasing demands of gaseous chlorine from anodic chlorine evolution reaction (CER) in chlor-alkali electrolysis. In this study, two-dimensional (2D) semiconducting group-VA monolayers were theoretically screened for the electrochemical CER by means of the density functional theory (DFT) method. Our results reveal the monolayered β-arsenene has the ultralow thermodynamic overpotential of 0.068 V for CER, which is close to that of the commercial Ru/Ir-based dimensionally stable anode (DSA) of 0.08 V @ 10 mA cm−2 and 0.13 V from experiments and theory, respectively. The change of CER pathways via Cl* intermediate on 2D β-arsenene also efficiently suppresses the parasitical oxygen gas production because of a high theoretical oxygen evolution reaction (OER) overpotential of 1.95 V. Our findings may therefore expand the scope of the electrocatalysts design for CER by using emerging 2D materials.</p

Real-time on-site monitoring of soil ammonia emissions using membrane permeation-based sensing probe

An ability to real-time, continuously monitor soil ammonia emission profiles under diverse meteorological conditions with high temporal resolution in a simple and maintenance-free fashion can provide the urgently needed scientific insights to mitigate ammonia emission to the atmosphere and improve agricultural fertilization practice. Here, we report an open-chamber deployment unit embedded a gas-permeable membrane-based conductometric sensing probe (OC-GPMCP) capable of on-site continuously monitoring soil ammonia emission flux (JNH3) –time (t) profiles without the need for ongoing calibration. The developed OC-GPMCPs were deployed to a sugarcane field and a cattle farm under different fertilization/meteorological conditions to exemplify their real-world applicability for monitoring soil ammonia emission from agricultural land and livestock farm, respectively. The obtained JNH3– t profiles from the sugarcane field unveil that the ammonia emission rate is largely determined by fertilization methods and meteorological conditions. While the JNH3– t profiles from the cattle farm can be decisively correlated to various meteorological conditions. The reported OC-GPMCP is cheap to fabricate, easy to deploy, and maintenance-free to operate. These advantageous features make OC-GPMCP an effective analytical tool for large-scale soil ammonia emission assessment under diverse meteorological conditions, providing critically important scientific insights to mitigate ammonia emission into the atmosphere and improve agricultural fertilization practice

Theoretical Understanding of Electrocatalytic Hydrogen Production Performance by Low-Dimensional Metal-Organic Frameworks on the Basis of Resonant Charge-Transfer Mechanisms

The exploration of low-cost and efficient electrocatalysts for the hydrogen evolution reaction (HER) is a prerequisite for large-scale hydrogen fuel generation. The understanding of the electronic properties of electrocatalysts plays a key role in this exploration process. In this study, our first-principles results demonstrate that the catalytic performance of the 1D metal-organic frameworks (MOFs) can be significantly influenced by engineering the composite of the metal node. Using the Gibbs free energy of the adsorption of hydrogen atoms as a key descriptor, we found that Ni- and Cr-based dithiolene MOFs possess better hydrogen evolution performance, and the much different efficiencies can be ascribed to their electronic resonance structures [TM3+(L2-)(L2-)]- → [TM2+(L•-)(L2-)]-. The [TM2+(L•-)(L2-)]- structure is preferred due to the higher activity of the catalytic site L with more radical features, and the stabilized [TM2+(L•-)(L2-)]- structure of the Cr- and Ni-based MOFs can be ascribed to the electronic configurations of their TM2+ cations with half-occupied and fully occupied valence orbitals. Our results therefore reveal a novel strategy for optimizing the electronic structures of materials on the basis of the resonant charge-transfer mechanism for their practical applications.</p