Yanluo Lu

Monodisperse cobalt sulfides embedded within nitrogen-doped carbon nanoflakes: an efficient and stable electrocatalyst for the oxygen reduction reaction

Unique hollow hybrid structures composed of well-dispersed catalyst nanoparticles embedded in a carbon matrix offer great advantages for constructing advanced supported catalysts. Herein, we report the designed synthesis of Co9S8 and nitrogen doped hollow carbon sphere (Co9S8/NHCS) composites by carbonization of metanilic anions within the confinement of two-dimensional galleries of hollow spherical cobalt–aluminum layered double hydroxides. The Co9S8/NHCS composites are composed of numerous porous carbon nanoflakes, and monodisperse Co9S8 nanoparticles are embedded within the carbon nanoflakes. Electrochemical measurements show that the Co9S8/NHCS catalysts prepared at 900 °C exhibit superior oxygen reduction reaction (ORR) activity, resulting in the highest ORR performance to date among all transition metal sulfide-based ORR catalysts in both alkaline and acidic electrolytes. This interlayer confined reaction approach may provide an efficient platform for the synthesis of other functional materials for alternative applications.

Chemical power source based on layered double hydroxides

Layered double hydroxides (LDHs) have been widely investigated in the past years because of their unique physicochemical properties and promising applications in chemical power sources. In this article, we review the current work on applications in areas such as supercapacitors, fuel cells, metal-air batteries, Li-ion batteries based on various LDH materials, such as LDH powder, LDH nanosheet, LDH film, or their composites, and offer some perspectives for the future application and development direction of LDHs.

Self-Assembled Peptide Hydrogel as a Smart Biointerface for Enzyme-Based Electrochemical Biosensing and Cell Monitoring

A self-assembled peptide nanofibrous hydrogel composed of N-fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF) was used to construct a smart biointerface. This biointerface was then used for enzyme-based electrochemical biosensing and cell monitoring. The Fmoc-FF hydrogel had two functions. One was as a matrix to embed an enzyme model, horseradish peroxidase (HRP), during the self-assembly of Fmoc-FF peptides. The other was use as a robust substrate for cell adhesion. Experimental data demonstrated that HRP was immobilized in a stable manner within the peptide hydrogel, and that HRP retained its inherent bioactivity toward H2O2. The HRP also can realize direct electron transfer in the Fmoc-FF hydrogel. The resulting third-generation electrochemical H2O2 biosensor exhibited good analytical performance, including a low limit of detection of 18 nM, satisfactory reproducibility, and high stability and selectivity. HeLa cells were then adhered to the HRP/Fmoc-FF hydrogel-modified electrode. The sensitive in situ monitoring of H2O2 released from HeLa cells was realized. This biointerface based on the Fmoc-FF hydrogel was easily prepared, environmentally friendly, and also versatile for integration of other cells and recognized molecules for the monitoring of various cellular biomolecules. The smart biointerface has potential application in broad physiological and pathological investigations.

A Co-N/C hollow-sphere electrocatalyst derived from a metanilic CoAl layered double hydroxide for the oxygen reduction reaction, and its active sites in various pH media

Transition-metal-coordinating nitrogen-doped carbon catalysts (M-N/C, M = Co, Fe, Mn, Ni, etc.) are considered one of the most promising nonprecious-metal electrocatalysts for the oxygen reduction reaction (ORR). However, they suffer from low ORR catalytic activity, and their active sites have not been fully identified. Herein, we report the synthesis of a porous Co-N/C hollow-sphere electrocatalyst by carbonization of metanilic anions between the layers of a Co-Al layered double hydroxide. The as-prepared Co-N/C catalyst exhibited excellent ORR catalytic activity with a high half-wave potential and a large diffusion-limited current in alkaline and neutral solutions. The performance of the catalyst was comparable to those of commercial Pt/C electrocatalysts. Through investigating the effects of mask ions (SCN− and F−) on the ORR activity of the Co-N/C catalyst, and comparing the ORR activity before and after the destruction of Co-Nx sites in different pH media, we concluded that the Co-Nx sites act directly as the ORR active sites in acidic and neutral solutions, but have a negligible effect on the ORR activity in alkaline conditions.

Single-crystalline organic-inorganic layered cobalt hydroxide nanofibers: facile synthesis, characterization, and reversible water-induced structural conversion.

New pink organic-inorganic layered cobalt hydroxide nanofibers intercalated with benzoate ions [Co(OH)(C6H5COO)·H2O] have been synthesized by using cobalt nitrate and sodium benzoate as reactants in water with no addition of organic solvent or surfactant. The high-purity nanofibers are single-crystalline in nature and very uniform in size with a diameter of about 100 nm and variable lengths over a wide range from 200 μm down to 2 μm by simply adjusting reactant concentrations. The as-synthesized products are well-characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), fast Fourier transforms (FFT), X-ray diffraction (XRD), energy dispersive X-ray spectra (EDX), X-ray photoelectron spectra (XPS), elemental analysis (EA), Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), and UV-vis diffuse reflectance spectra (UV-vis). Our results demonstrate that the structure consists of octahedral cobalt layers and the benzoate anions, which are arranged in a bilayer due to the π-π stacking of small aromatics. The carboxylate groups of benzoate anions are coordinated to Co(II) ions in a strong bridging mode, which is the driving force for the anisotropic growth of nanofibers. When NaOH is added during the synthesis, green irregular shaped platelets are obtained, in which the carboxylate groups of benzoate anions are coordinated to the Co(II) ions in a unidentate fashion. Interestingly, the nanofibers exhibit a reversible transformation of the coordination geometry of the Co(II) ions between octahedral and pseudotetrahedral with a concomitant color change between pink and blue, which involves the loss and reuptake of unusual weakly coordinated water molecules without destroying the structure. This work offers a facile, cost-effective, and green strategy to rationally design and synthesize functional nanomaterials for future applications in catalysis, magnetism, gas storage or separation, and sensing technology.

Intercalated Co(OH)2-derived flower-like hybrids composed of cobalt sulfide nanoparticles partially embedded in nitrogen-doped carbon nanosheets with superior lithium storage

Cobalt sulfides are considered as one of the most promising alternative anode materials for high-performance lithium-ion batteries by virtue of their remarkable electrical conductivity and high theoretical capacity. However, the volume expansion of cobalt sulfides and polysulfide shuttling effect during the discharge/charge process result in a poor cycling stability and low rate capability. Herein, we report the designed synthesis of a flower-like structure, including cobalt sulfide nanoparticles with a small particle size partially embedded within the nitrogen-doped carbon nanosheets and few-layer graphene covering the external surface of cobalt sulfides (Co9S8/Co1−xS@NC), by simultaneous decomposition and sulfidation of a metanilic anion intercalated Co(OH)2 precursor. Through adjusting the annealed temperature and the mass ratio of the precursor and S powders, the composition of cobalt sulfides could be easily controlled. Co9S8/Co1−xS@NC prepared under optimized conditions exhibits a high reversible capacity of 1230 mA h g−1 after 110 cycles, excellent rate capability (≈1016, 979, 931, 813 mA h g−1 at the current densities of 200, 500, 1000, and 2000 mA g−1, respectively), and stable cycling performance (≈98.4% capacity retention after 110 cycles). Significantly, this intercalated Co(OH)2-derived strategy can be expanded to the preparation of other metal sulfides and carbon composites for application in other energy conversion and storage devices.

Layered Li–Mn oxides with the O2 structure: preparation of Li2/3[Mn1−xMx]O2 (M=Li, Cr, Mg, Al) by ion exchange

Abstract Layered sodium manganese bronzes, Na 2/3 [Mn 1− x M x ]O 2 (M=Li, Cr, Mg, Al) with the P2 structure have been investigated. In the case of M=Li, the location of the dopant was identified on the basis of ion-exchange properties and chemical analysis. With the increase doped Cr content, the P2-structure Na 2/3 [Mn 1− x Cr x ]O 2 gradually underwent a transformation to orthorhombic Na 4 [Mn 9− y Cr y ]O 18 . X-ray photoelectron spectroscopy (XPS) was used to measure the oxidation state and the composition near the surface. The compositions near the surface and in the bulk were found to vary with the identity of the doped element. The O2-structure lithium manganese oxides were prepared from Na-bronzes by ion exchange, but the crystallinity decreased after the ion exchange as a result of stacking faults.

Encapsulation of enzyme into mesoporous cages of metal–organic frameworks for the development of highly stable electrochemical biosensors

A water-stable metal–organic framework (MOF) [PCN-333(Fe)] with ultra-large cavities and ultra-high porosity was synthesized and employed to encapsulate horseradish peroxidases (HRP) for the fabrication of electrochemical biosensors. Due to the size-match of a HRP and large cage of PCN-333(Fe), encapsulation of enzyme into the PCN-333(Fe) was achieved. The prepared HRP@PCN-333(Fe) was characterized by XRD, SEM, confocal microscopy, N2 adsorption isotherms, UV-vis spectroscopy and circular dichroism. The analytical performance of the electrochemical biosensor based on the HRP@PCN-333(Fe) for the detection of H2O2 was investigated by cyclic voltammetry and amperometry. Encapsulation of HRP in PCN-333(Fe) presented a high enzyme loading and excellent electrocatalytic activity toward H2O2 reduction. An extended linear range from 0.5 μM to 1.5 mM with a low detection limit of 0.09 μM (S/N = 3) was obtained based on the biosensor. More importantly, the operational acid and thermal stabilities of the biosensor were significantly improved due to the HRP adsorbed on the surface of the support. These good properties are mainly attributed to the confinement of HRP in the cage of PCN-333(Fe), which not only essentially eliminates enzyme aggregation and leaching, and improves the catalytic efficiency, but also effectively hinders the conformational change of immobilized HRP when continuously used, or heated under acidic condition. As a result, the encapsulation of enzymes in the mesopore PCN-333(Fe) provides a new and excellent platform for the development of highly stable and sensitive electrochemical biosensors.