Faliang Cheng

Co 3 O 4 supported on N, P-doped carbon as a bifunctional electrocatalyst for oxygen reduction and evolution reactions

Noble metals, such as platinum, ruthenium and iridium-group metals, are often used as oxygen reduction or evolution reaction (ORR/OER) electrocatalysts. To reduce the cost and provide an application of bifunctional catalysis, in this work, cobalt oxide supported on nitrogen and phosphorus co-doped carbon (Co 3 O 4 /NPC) was fabricated and examined as a bifunctional electrocatalyst for OER and ORR. To prepare Co 3 O 4 /NPC, NPC was pyrolyzed from melamine and phytic acid supported on carbon, followed by the solvothermal synthesis of Co 3 O 4 on NPC. Linear sweep voltammetry was used to evaluate the activity for OER and ORR. For OER, Co 3 O 4 /NPC showed an onset potential of 0.54 V (versus the saturated calomel electrode) and a current density of 21.95 mA/cm 2 at 0.80 V, which was better than both Co 3 O 4 /C and NPC. The high activity of Co 3 O 4 /NPC was attributed to a synergistic effect of the N, P co-dopants and Co 3 O 4 . For ORR, Co 3 O 4 /NPC exhibited an activity close to commercial Pt/C in terms of the diffusion limited current density (-4.49 vs -4.76 mA/cm 2 at -0.80 V), and Co 3 O 4 played the key role for the catalysis. Chronoamperometry (current versus time) was used to evaluate the stability, which showed that Co 3 O 4 /NPC maintained 46% current after the chronoamperometry test for OER and 95% current for ORR. Overall, Co 3 O 4 /NPC exhibited high activity and improved stability for both OER and ORR.

Binder-free WS2 nanosheets with enhanced crystallinity as a stable negative electrode for flexible asymmetric supercapacitors

Tungsten disulfide (WS2) has been emerging as an attractive electrode material for supercapacitors because of its intrinsically layered structure and high capacitance. Unfortunately, most of the currently developed WS2-based electrodes suffer from poor conductivity and fast capacitance fading. In this work, we demonstrated that the durability of WS2 nanosheets can be remarkably boosted via improving their crystallinity and the first example of using these WS2 nanosheets as a high-energy and stable negative electrode for flexible asymmetric supercapacitors (ASCs). Electrochemical results reveal the WS2 nanosheets with enhanced crystallinity were able to deliver an excellent durability with more than 82% capacitance retention after 10 000 cycles and an areal capacitance of 0.93 F cm−2 at 4 mA cm−2. Importantly, when using the as-prepared WS2 nanosheets as a negative electrode, a flexible and stable ASC device with an extraordinary volumetric energy density of 0.97 mW h cm−3 is obtained. This work affords new opportunities to use WS2 nanostructures and other 2D TMDs in constructing high-performance energy-storage devices.

High sensitivity chlorogenic acid detection based on multiple layer-by-layer self-assembly films of chitosan and multi-walled carbon nanotubes on a glassy carbon electrode

A chlorogenic acid sensor based on a chitosan (CS) and multi-walled carbon nanotubes (MWCNTs) modified glassy carbon electrode (GCE) was fabricated via a layer-by-layer (LBL) self-assembly method. The prepared electrode exhibited excellent catalytic performance for chlorogenic redox reactions compared to the bare GCE. The effects of the number assembly layers, scan rate, pH of the supporting electrolyte and accumulation time on chlorogenic acid detection were optimized. Under the optimal conditions, the proposed sensor was significantly sensitive for the detection of chlorogenic acid and showed wide linear detection ranges at low concentrations from 2 × 10−8 to 1 × 10−7 mol dm−3 and at high concentrations from 1 × 10−7 to 2.25 × 10−4 mol dm−3. The detection limit was estimated to be 1.16 × 10−8 mol dm−3 (S/N = 3). Furthermore, the chlorogenic acid sensor exhibited excellent selectivity and stability and was utilized in practical applications, in particular, for the determination of human real samples.

Cuprous oxide template synthesis of hollow-cubic Cu2O@PdxRuy nanoparticles for ethanol electrooxidation in alkaline media

Surfactant-free and low Pd loading Cu2O@PdxRuy hollow-cubes were facilely prepared via a galvanic replacement reaction with electrodeposited Cu2O cubes as sacrificed templates. The morphology and composition of the as-synthesized nanoparticles were characterized, through which the Pd : Ru atomic ratio, metal loading, surface composition and structure of several Cu2O@PdxRuy nanoparticles were determined. The promotional role of Ru on electrooxidation of ethanol in alkaline media over Cu2O@PdxRuy was investigated. By comparison, the following electrocatalytic activity order of the catalysts was obtained: Pd/C < Cu2O@Pd < Cu2O@Pd1Ru3 < Cu2O@Pd3.5Ru1 < Cu2O@Pd2.1Ru1 < Cu2O@Pd1Ru1.6 < Cu2O@Pd1Ru1. Combined with the stability study, the hollow-cubic Cu2O@Pd1Ru1 nanoparticles show superior catalytic activity and stability toward electrooxidation of ethanol in alkaline media compared to the other catalysts studied in this work which is attributed to the appropriate Pd : Ru ratio and the hollow-cubic structure.

A highly sensitive morin sensor based on PEDT–Au/rGO nanocomposites modified glassy carbon electrode

In this work, we fabricated a sensitive electrochemical sensor based on a PEDT–Au/reduced graphene oxide nanocomposites (PEDT–Au/rGO) modified glassy carbon electrode (PEDT–Au/rGO/GCE) for electrochemical determination of morin. A facile, effective and high-efficiency one-pot method was employed to synthesize the PEDT–Au/rGO nanocomposites. The morphology and structure of as-prepared PEDT–Au/rGO nanocomposites were characterized by using a scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray spectroscopy (EDS), and its electrochemical characteristics were studied by EIS, CV and SWV. The PEDT–Au/rGO nanocomposites modified electrode exhibited excellent catalytic activities for morin oxidation, which was attributed to the synergistic catalytic effect that occurred at the interface of PEDT–Au and rGO layers. The effects of square wave voltammetry (SWV) parameters, accumulation time, accumulation potential and pH of the supporting electrolyte for morin were optimized. At the optimal experimental conditions, the PEDT–Au/rGO/GCE presented a high sensitivity of 0.0083 μmol dm−3 and a wide linear range from 1 to 150 μmol dm−3 toward morin oxidation with satisfactory selectivity and stability.

Enhanced Photoelectrochemical Activity by Autologous Cd/CdO/CdS Heterojunction Photoanodes with High Conductivity and Separation Efficiency

The development for hydrogen from solar energy has attracted great attention due to the global demand for clean, environmentally friendly energy. Herein, autologous Cd/CdO/CdS heterojunctions were prepared in a carefully controlled process with metallic Cd as the inner layer and CdO as the interlayer. Further research revealed that the transportation and separation of photogenerated pairs were enhanced due to low resistance of the Cd inner layer and the type II CdO/CdS heterojunction. As a result, the optimized Cd/CdO/CdS heterojunction photoanode showed outstanding and long-term photoelectrochemical activity for water splitting, with a current density of 3.52 mA cm-2 , or a benchmark specific hydrogen production rate of 1.65 μmol cm-2  min-1 at -0.3 V versus Ag/AgCl, by using the environmental pollutants of sulfide and sulfite as sacrificial agents.

Highly Ordered Pd Nanowire Array by Template Fabrication for Propanol Electrooxidation

Highly ordered Pd nanowire arrays (NWAs) prepared by electrodeposition method using the fresh prepared anodic aluminum oxide (AAO) as the template have been characterized by X-ray diffraction pattern (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), scanning electron microscopy (SEM), and electrochemical measurements. SEM results revealed that the brush-shaped Pd NWAs are dispersed uniformly. The diameter and length of the obtained Pd NWAs are about 50 nm and 850 nm, respectively. Furthermore, the electrocatalytic activity of Pd NWAs electrode for propanol oxidation in alkaline media has also been studied. It is found that the obtained nanostructurs exhibit excellent electrocatalytic activity toward the oxidation of propanol, demonstrating the potential application in portable direct alcohol fuel cells (DAFCs).

Vertical bismuth oxide nanosheets with enhanced crystallinity: promising stable anodes for rechargeable alkaline batteries

Aqueous alkaline batteries represent an emerging kind of energy storage device, which hold great promise to power electronics with both high energy density and power density. However, their development is severely limited by their anodes which have unsatisfying cycling stability. Herein, we report the facile synthesis of Bi2O3 nanosheets vertically aligned on carbon paper, which achieve good electrochemical properties as anodes for alkaline batteries. It is also demonstrated that the crystallinity plays an important role in adjusting the energy storage ability. High crystallinity can efficiently promote the ion diffusion rate within Bi2O3, the reversible phase transition and the accommodation of structural strain, which significantly boost the capacity and cycling stability. The as-obtained highly crystalline Bi2O3 electrode reached a high specific capacity of 0.14 mA h cm−2 at 4 mA cm−2 and achieved outstanding electrochemical stability, with a high capacity retention of 71.4% after 5000 cycles. These findings will provide additional insight into the construction of high-performance anodes for alkaline batteries.

Mechanism studies of addition reactions between the pyrimidine type radicals and their 3′/5′ neighboring deoxyguanosines

To clarify the biologically significant sequence effect existing in the formation of the pyrimidine-type radicals induced DNA intrastrand cross-links, addition mechanisms between the uridine-5-methyl (˙UCH2), 6-hydroxy-5,6-dihydrothymidine-5-yl (˙T6OH), and 6-hydroxy-5,6-dihydrocytidine-5-yl (˙C6OH) radicals and their 3′/5′ neighboring deoxyguanosines (dG) are explored in the present study employing the model 5′-G(˙UCH2)-3′, 5′-(˙UCH2)G-3′, 5′-G(˙T6OH)-3′, 5′-(˙T6OH)G-3′, 5′-G(˙C6OH)-3′, and 5′-(˙C6OH)G-3′ sequences. It is found that the 5′ G/C8 additions of the three radicals are all simple direct one-step reactions inducing only relatively small structural changes, while a conformational adjustment involving orientation transitions of both nucleobase moieties and twisting of the DNA backbone is indispensable for each 3′ G/C8 addition. Furthermore, markedly positive reaction free energy requirements are estimated for these conformational transformations making the 3′ G/C8 additions of the three radicals thermodynamically much more unfavorable than the corresponding 5′ G/C8 additions. Such essential conformational adjustments along the 3′ G/C8 addition paths that structurally greatly influence the local DNA structures and thermodynamically substantially reduce the addition efficiencies may be the reasons responsible for the differences in the formation yields and biological consequences of the pyrimidine-type radicals induced DNA intrastrand cross-link lesions.

Direct determination of oxalic acid by a bare platinum electrode contrasting a platinum nanoparticles-modified glassy carbon electrode

ABSTRACT A bare platinum disk electrode without further decoration was directly used to determine oxalic acid (OA), showing good linear ranges of 0.57–104.01 μM and 104.01–228.75 μM with a low detection limit of 0.38 μM (S/N = 3). In contrast, platinum nanoparticles (PtNPs) dispersed on a glassy carbon electrode were successfully achieved by an one-step electrochemical deposition method, possessing relatively wider linear detection ranges of 1.14–342.80 μM and 342.80–548.92 μM for OA with a lower detection limit of 0.28 μM (S/N = 3). Both the proposed electrochemical sensors exhibit great reproducibility, stability and selectivity. In particular, they have been applied to the determination of OA in real spinach samples, showing excellent analytical performance.