Rapid solvent-evaporation strategy for three-dimensional cobalt-based complex hierarchical architectures as catalysts for water oxidation.

It is a challenging task to seek a highly-efficient electrocatalyst for oxygen evolution reaction (OER) of water splitting. Non-noble Co-based nanomaterials are considered as earth-abundant and effective catalysts to lower overpotential and increase polarization current density of OER. In this work, we reported, for the first time, a "rapid solvent-evaporation" strategy for the synthesis of three-dimensional (3D) cobalt complex hierarchical architectures constructed by two-dimensional (2D) nanosheets. The 3D structured cobalt complexes have excellent performances in catalyzing OER with lower onset potential, overpotential, Tafel slope and better stability than commercial IrO2. Superior electrochemical performances would be beneficial from the unique 3D structure. This extremely simple method for 3D Co complex with good OER activities makes the complex be promising commercial OER catalyst to replace earth-rare and expensive IrO2.

Tube-in-tube tin dioxide superstructures with enhanced lithium storage performance.

Novel tube-in-tube tin dioxide superstructures (TTS) were synthesized with α-Fe2O3 hollow prisms as templates. Due to the special tube-in-tube structure, the SnO2 TTS possess brilliant lithium storage properties.

In situ construction of hierarchical Co/MnO@graphite carbon composites for highly supercapacitive and OER electrocatalytic performances.

The development of new electrode materials with high specific capacity for excellent supercapacitive storage and energy conversion is highly desirable. The combination of metal and metal oxide with carbon is an effective strategy to achieve active bimetallic nanocatalysts. Herein, we developed a facile method to synthesize CoxMn1-xO@GC and Co/MnO@GC nanocomposites by an in situ conversion of Co-Mn PBAs. The as-prepared carbon hybrids, especially the resulting Co/MnO@GC carbonized under 700 °C (Co/MnO@GC-700), preserve the nanocubic morphology of Co-Mn PBAs and show excellent supercapacitance and OER performance. Specifically, an outstanding specific capacitance of 2275 F g-1 can be obtained with Co/MnO@GC-700 as the electrode material at a current density of 4 A g-1. When used as OER catalysts, Co/MnO@GC-700 shows a low overpotential of only 358 mV at 10 mA cm-2 in 1 M KOH. Moreover, a fabricated asymmetric supercapacitor device (ASC device), in combination with active carbon, shows a high cell voltage of 1.7 V and a considerably high specific capacitance of 246 F g-1 at 2 A g-1. Our nanoarchitecture design derived from PBAs provides a new opportunity for future applications in high-performance energy storage and transformation systems.

Quantum Effects Allow the Construction of Two-Dimensional Co3 O4 -Embedded Nitrogen-Doped Porous Carbon Nanosheet Arrays from Bimetallic MOFs as Bifunctional Oxygen Electrocatalysts.

In terms of promising candidates for high-performance fuel cells and water splitting electrocatalysts, two-dimensional (2D) materials refer to a class of materials with high electrical conductivity along 2D conducting channels and possessing abundant active sites in the form of surface atoms and edge sites. Herein, we report an ammonia-modulated method for the synthesis of nanosized bimetallic ZnCo-ZIF, and owing to quantum effects, the nanosized ZnCo-ZIF can be transformed into novel 2D nanosheet arrays, which can be used as a bifunctional electrocatalyst. The size of the ZnCo-ZIF crystals can be controlled to less than 10 nm by increasing the ammonia amount. The products from the nanosized particles through calcination have a distinct structure from the microsized nanoparticles owing to quantum effects and appear to be well-aligned 2D mono-crystalline Co3 O4 -embedded nitrogen-doped porous carbon nanosheet arrays (2D-MCo3 O4 -NCNAs). These novel 2D nanosheet arrays lead to large active surface areas, enhanced mass/charge transport capability, numerous active sites, and strong structure stability. When used as bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), the 2D-MCo3 O4 -NCNAs exhibit superior ORR activity as well as efficient OER activity in alkaline electrolyte, in comparison to the state-of-the-art precious metal catalysts.

Enhanced photocatalytic efficiency of C3N4/BiFeO3 heterojunctions: the synergistic effects of band alignment and ferroelectricity.

As one of the most promising photocatalysts, graphitic carbon nitride (g-C3N4) shows a visible light response and great chemical stability. However, its relatively low photocatalytic efficiency is a major obstacle to actual applications. Here an effective and feasible method to dramatically increase the visible light photocatalytic efficiency by forming C3N4/BiFeO3 ferroelectric heterojunctions is reported, wherein the band alignment and piezo-/ferroelectricity have synergistic positive effects in accelerating the separation of the photogenerated carriers. At the optimum composition of 10 wt% BiFeO3, the heterojunction shows 1.4 times improved photocatalytic efficiency than that of the pure C3N4. Most importantly, mechanical pressing and electrical poling can also improve the photocatalytic efficiencies by 1.3 times and 1.8 times, respectively. The optimized photocatalytic efficiency is even comparable with that of some noble metal based compounds. These results not only prove the improved photocatalytic activity of the C3N4-ferroelectric heterojunctions, but also provide a new approach for designing high-performance photocatalysts by taking advantage of ferroelectricity.

Delicate Control of Multishelled Zn-Mn-O Hollow Microspheres as a High-Performance Anode for Lithium-Ion Batteries.

Mixed/composite oxides of transition metals with hollow structures, especially multishelled hollow architecture, have promising potential for different applications, but their syntheses still remain a big challenge. Herein, a facile coordination polymer precursor method was developed to construct various multishelled Zn-Mn-O hollow microspheres, including ZnMnO3, ZnMn2O4, and ZnMn2O4/Mn2O3. The composition of the hollow structures can be adjusted by controlling the composition of the coordination polymer precursors, which are easily obtained with Zn2+, Mn2+, and salicylic acid under solvothermal conditions. With a simple programmable heating process, the shell of the hollow structures can be adjusted and double-/triple-shelled ZnMnO3, ZnMn2O4, and ZnMn2O4/Mn2O3 hollow microspheres have been controllably obtained. When the triple-shelled ZnMn2O4 hollow microspheres are used as anode materials for lithium-ion batteries, excellent activity and enhanced stability can be achieved. The triple-shelled hollow ZnMn2O4 exhibits a reversible capacity of 537 mA·h·g-1 at 400 mA·g-1 and a nearly 100% capacity retention after 150 cycles. This strategy is facile and scalable for the production of high-quality complex hollow nanostructures, with the possibility of extension to the preparation of other mixed metal oxides with complex structures.

In Situ Antisolvent Approach to Hydrangea-like HCo3 O4 -NC@CoNi-LDH Core@Shell Superstructures for Highly Efficient Water Electrolysis.

Highly active, durable, and cost-effective electrocatalysts for water oxidation are at the center of renewable energy technologies. However, the development of water oxidation catalysts with high activity at low cost remains a great challenge. Herein, an in situ antisolvent approach is reported for synthesizing ultrathin Co-Ni layered double hydroxide (CoNi-LDH) nanosheets wrapped on hollow Co3 O4 nanoparticle-embedded nitrogen-doped carbon (HCo3 O4 -NC) as a high-performance catalyst for the oxygen evolution reaction (OER). Although HCo3 O4 -NC or NiCo-LDH alone has little OER activity, their hybrid exhibits low overpotential and Tafel slope as well as high stability, due to the synergistic effect of Co3 O4 and LDH. Furthermore, the hydrangea-like HCo3 O4 -NC@NiCo-LDH core@shell composite exhibits higher catalytic activity and stability than commercial IrO2 , which makes it a high-performance nonprecious-metal-based catalyst for OER.

One-step synthesis of novel Cu@polymer nanocomposites through a self-activated route and their application as nonenzymatic glucose sensors.

In this study, we developed a one-step self-activated route for synthesizing novel core-shell Cu@polymer nanocomposites. Under solvothermal conditions, Cu2+ was reduced to metal copper by formaldehyde and salicylaldehyde and the newly generated copper crystals acted as the catalysts to activate the condensation polymerization between formaldehyde and salicylaldehyde, resulting in the formation of core-shell Cu@polymer nanocomposites with Cu nanoparticles as the cores and polymer as the shells. The Cu@polymer nanocomposites can be applied as a nonenzymatic sensor for glucose detection. The as-prepared Cu@polymer nanocomposite modified electrode shows good linear dependence in a wide range from 0.01 mM to 1 mM, a low detection limit, high sensitivity up to 1417.1 µA cm-2 mM-1 and great selectivity to glucose concentration change.