Xifeng Shi

1D Ni–Co oxide and sulfide nanoarray/carbon aerogel hybrid nanostructures for asymmetric supercapacitors with high energy density and excellent cycling stability

The fabrication of supercapacitor electrodes with high energy density and excellent cycling stability is still a great challenge. A carbon aerogel, possessing a hierarchical porous structure, high specific surface area and electrical conductivity, is an ideal backbone to support transition metal oxides and bring hope to prepare electrodes with high energy density and excellent cycling stability. Therefore, NiCo2S4 nanotube array/carbon aerogel and NiCo2O4 nanoneedle array/carbon aerogel hybrid supercapacitor electrode materials were synthesized by assembling Ni-Co precursor needle arrays on the surface of the channel walls of hierarchical porous carbon aerogels derived from chitosan in this study. The 1D nanostructures grow on the channel surface of the carbon aerogel vertically and tightly, contributing to the enhanced electrochemical performance with ultrahigh energy density. The energy density of NiCo2S4 nanotube array/carbon aerogel and NiCo2O4 nanoneedle array/carbon aerogel hybrid asymmetric supercapacitors can reach up to 55.3 Wh kg-1 and 47.5 Wh kg-1 at a power density of 400 W kg-1, respectively. These asymmetric devices also displayed excellent cycling stability with a capacitance retention of about 96.6% and 92% over 5000 cycles.

IR-Driven Photocatalytic Water Splitting with WO2–NaxWO3 Hybrid Conductor Material

An IR-driven photocatalytic water splitting system based on WO2-NaxWO3 (x > 0.25) hybrid conductor materials was established for the first time; this system can be directly applied in seawater. The WO2-NaxWO3 (x > 0.25) hybrid conductor material was readily prepared by a high-temperature reduction process of semiconductor NaxWO3 (x < 0.25) nanowire bundles. A novel ladder-type carrier transfer process is suggested for the established IR-driven photocatalytic water splitting system.

Rational design of carbon and TiO2 assembly materials: covered or strewn, which is better for photocatalysis?

The rational design of carbonaceous hybrid nanostructures is very important for obtaining high photoactivity. TiO2 particles strewn with an optimal quantity of carbon nanodots have a much higher photoactivity than that of TiO2 covered with a carbon layer, showing the importance of carbon morphology in the photocatalysis of carbonaceous hybrid nanostructures.

Electrochemical Ammonia Synthesis via Nitrogen Reduction Reaction on a MoS2 Catalyst: Theoretical and Experimental Studies

The discovery of stable and noble-metal-free catalysts toward efficient electrochemical reduction of nitrogen (N2 ) to ammonia (NH3 ) is highly desired and significantly critical for the earth nitrogen cycle. Here, based on the theoretical predictions, MoS2 is first utilized to catalyze the N2 reduction reaction (NRR) under room temperature and atmospheric pressure. Electrochemical tests reveal that such catalyst achieves a high Faradaic efficiency (1.17%) and NH3 yield (8.08 × 10-11 mol s-1 cm-1 ) at -0.5 V versus reversible hydrogen electrode in 0.1 m Na2 SO4 . Even in acidic conditions, where strong hydrogen evolution reaction occurs, MoS2 is still active for the NRR. This work represents an important addition to the growing family of transition-metal-based catalysts with advanced performance in NRR.

Highly efficient photocatalytic degradation of methylene blue by P2ABSA-modified TiO2 nanocomposite due to the photosensitization synergetic effect of TiO2 and P2ABSA

To enhance the photocatalytic activity of TiO2, poly-2-aminobenzene sulfonic acid (P2ABSA)-modified TiO2 nanocomposites were successfully synthesized using an in situ oxidative polymerization method. The modified nanocomposites were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, and a photocurrent test. The photocatalytic degradation of methylene blue was chosen as a model reaction to evaluate the photocatalytic activities of TiO2 and P2ABSA/TiO2 nanocomposites, with results indicating that P2ABSA/TiO2 exhibited the higher activity. The apparent first-order rate constant, kapp, of P/T(2/1) was 0.0138 min−1, which was six times higher than that of TiO2 (0.0021 min−1). Meanwhile, the P2ABSA/TiO2 nanocomposites showed excellent photocatalytic stability, which was dependent on structural stability. A photocatalytic activity enhanced mechanism has been proposed, accounting for the photosensitization effect and synergetic effect of TiO2 with P2ABSA. Mass spectroscopy analysis showed that there were two possible degradation pathways for MB, via degradation of the chromophoric group or the auxochrome group.

Efficient oxygen evolution electrocatalyzed by a Cu nanoparticle-embedded N-doped carbon nanowire array

Development of efficient and durable catalysts based on earth-abundant elements for oxygen evolution reactions (OER) is important for renewable energy storage and conversion technologies. Herein, we report the development of a Cu nanoparticle-embedded N-doped carbon nanowire array on copper foam (Cu–N–C NA/CF) via carbonization of a Cu(TCNQ) (TCNQ = 7,7,8,8-tetracyanoquinodimethane) nanoarray. As a 3D OER electrode, this Cu–N–C NA/CF shows high catalytic activity, needing an overpotential of 314 mV to drive a geometrical current density of 20 mA cm−2 in 1.0 M KOH. It also shows strong long-term electrochemical durability. This suggested that CuO nanoparticles as active species were in situ electrochemically converted from Cu nanoparticles and stably dispersed in the carbon matrix during electrocatalysis.

A platinum oxide decorated amorphous cobalt oxide hydroxide nanosheet array towards alkaline hydrogen evolution

We report the design of an amorphous cobalt oxide hydroxide nanosheet array with anchored platinum oxide. This electrocatalyst can efficiently catalyze the hydrogen evolution reaction with outstanding activity due to the strong synergetic effect derived from its favorable composition and structure. Density functional theory calculations further demonstrate that it can greatly reduce water dissociation barriers and tune the free energy of H* adsorption close to the optimized value.

Flow Injection Catalytic Kinetic Spectrofluorimetric Determination of Trace Amount of Ruthenium

Abstract A novel fluorescence reagent 2-pyridine carboxaldehyde benzoylhydrazone (PCBH) was synthesized. A flow injection (FI) kinetic spectrofluorimetric method was developed for the determination of trace amounts of ruthenium. The method was based on the fluorescence-enhancing reaction of PCBH with potassium bromate, which was catalyzed by Ru 3+ in aqueous medium at pH 6.70 and 55 °C. Under these conditions, the oxidized product of PCBH had excitation and emission maxima wavelengths at 284 and 377 nm, respectively. The linear range of this method was 2.0–400 ng ml −1 with a relative standard deviation of 1.8% from a series of 11 standards each containing 50 ng ml −1 of ruthenium. The detection limit was 0.60 ng ml −1 of ruthenium. A high analysis rate of 18 samples per hour was obtained by the FI method. The proposed method was successfully applied to determine ruthenium in synthetic mixtures and mineral samples.

Superior alkaline hydrogen evolution electrocatalysis enabled by an ultrafine PtNi nanoparticle-decorated Ni nanoarray with ultralow Pt loading

The development of efficient hydrogen evolution reaction (HER) catalysts is of great importance for electrolytic hydrogen production in alkaline media. In this communication, we report the development of an ultrafine PtNi nanoparticle-decorated Ni nanosheet array with ultralow Pt loading (7.7 wt%) as a superior electrocatalyst for the alkaline HER. Such a nanoarray drives a geometrical current density of 10 mA cm−2 at an overpotential as low as 38 mV in 0.1 M KOH, outperforming commercial 20 wt% Pt/C and all reported HER electrocatalysts. Remarkably, it also shows outstanding long-term electrochemical durability with a faradaic efficiency close to 100%. This work provides us with an attractive ultralow-Pt-content catalyst material in water-splitting devices toward high-performance and durable electrochemical production of hydrogen fuels.

An Fe-MOF nanosheet array with superior activity towards the alkaline oxygen evolution reaction

It is highly desired to develop high-performance non-noble-metal electrocatalysts for the oxygen evolution reaction (OER) in alkaline solutions. In this communication, we report the hydrothermal synthesis of an Fe-MOF nanosheet array on nickel foam (Fe-MOF/NF) using aqueous Fe3+ and terephthalic acid as precursors. Such an Fe-MOF/NF shows superior electrocatalytic performance towards the OER in 1.0 M KOH with a low overpotential of 240 mV at 50 mA cm−2 and a small Tafel slope of 72 mV dec−1. Notably, this catalyst also exhibits high long-term electrochemical durability to maintain its activity for at least 30 h. Moreover, this catalyst electrode achieves a high turnover frequency of 0.74 mol O2 per s at an overpotential of 300 mV.