Activation of MoS2 Basal Planes for Hydrogen Evolution by Zinc.

Molybdenum disulfide (MoS2 ) has been widely studied as a potential earth-abundant electrocatalyst for the hydrogen-evolution reaction (HER). Defect engineering and heteroelemental doping are effective methods to enhance the catalytic activity in the HER, so exploring an efficient route to simultaneously achieve in-plane vacancy engineering and elemental doping of MoS2 is necessary. In this study, Zinc, a low-cost and moderately active metal, has been used to realize this strategy by generation of sulfur vacancies and zinc doping on MoS2 in one step. Density functional theory calculations reveal that the zinc atoms not only lower the formation energy of S vacancies, but also help to decrease ΔGH of S-vacancy sites near the Zn atoms. At an optimal zinc-reduced MoS2 (Zn@MoS2 ) example, the activated basal planes contribute to the HER activity with an overpotential of -194 mV at 10 mA cm-2 and a low Tafel slope of 78 mV/dec.

Understanding H2 Evolution Electrochemistry to Minimize Solvated Water Impact on Zinc-Anode Performance.

H2 evolution is the reason for poor reversibility and limited cycle stability with Zn-metal anodes, and impedes practical application in aqueous zinc-ion batteries (AZIBs). Here, using a combined gas chromatography experiment and computation, it is demonstrated that H2 evolution primarily originates from solvated water, rather than free water without interaction with Zn2+ . Using linear sweep voltammetry (LSV) in salt electrolytes, H2 evolution is evidenced to occur at a more negative potential than zinc reduction because of the high overpotential against H2 evolution on Zn metal. The hypothesis is tested and, using a glycine additive to reduce solvated water, it is confirmed that H2 evolution and "parasitic" side reactions are suppressed on the Zn anode. This electrolyte additive is evidenced to suppress H2 evolution, reduce corrosion, and give a uniform Zn deposition in Zn|Zn and Zn|Cu cells. It is demonstrated that Zn|PANI (highly conductive polyaniline) full cells exhibit boosted electrochemical performance in 1 M ZnSO4 -3 M glycine electrolyte. It is concluded that this new understanding of electrochemistry of H2 evolution can be used for design of relatively low-cost and safe AZIBs for practical large-scale energy storage.

Determination of Selected Pyrrolizidine Alkaloids in Honey by Dispersive Liquid-Liquid Microextraction and Ultrahigh-Performance Liquid Chromatography-Tandem Mass Spectrometry.

The contamination of honey with hepatotoxic pyrrolizidine alkaloids (PAs) is an actual concern for food safety. This study reports the first application of dispersive liquid-liquid microextraction (DLLME) in the determination of five relevant PAs, and the relative N-oxide derivatives (PANOs), in honey. The effects of different experimental parameters (pH, ionic strength, type and volume of DLLME solvents) affecting the extraction efficiency were carefully investigated and optimized. PAs were extracted from honey (diluted solution 10% w/v at pH 9.5) by injecting a mixture of chloroform and isopropyl alcohol. A reduction step (zinc powder in acidic aqueous solution) before DLLME was performed to convert PANOs in PAs and to obtain the total PA levels. Both sample preparation protocols (DLLME and Zn-DLLME) showed negligible matrix effects on PA signal intensity in honeys of different botanical origins. The overall recoveries of DLLME and Zn-DLLME ranged from 71 to 102% and from 63 to 103%, respectively, with a good precision (standard deviations in the range from 1 to 12%). The attained method quantification limits stayed between 0.03 and 0.06 µg kg-1, and the linear response range extended to 25 µg kg-1. Additionally, the proposed method provides results comparable to those of the SPE protocol in the analysis of real samples. An analysis of retail honeys revealed PA residues in all analyzed samples, with a maximum level of 17.5 µg kg-1 (total PAs). Globally, the proposed method provides a sensitive and accurate determination of analytes and offers numerous advantages, such as simplicity, low cost, and a high sample throughput, which make it suitable for screening and quality control programs in food chain and occurrence studies.

Microliter Operation for Determination of Nitrate-Nitrogen via Simple Zinc Reduction and Color Formation in a Well Plate with a Smartphone.

We propose a simple greener colorimetric method for the determination of nitrate-nitrogen by operating on a 96-well microplate and using a smartphone camera as a simple detector. A slurry containing 0.3 mg zinc was used for reduction of nitrate to nitrite, the reduction solution was transferred to a 96-well microplate to react with Griess reagent to form a pink azo dye product. The color product image was captured and processed by a smartphone camera and ImageJ software, respectively. The limit of detection and limit of quantitation were 0.04 and 0.10 mg/L nitrate-nitrogen, respectively, for the smartphone camera. Application to real samples was demonstrated. The proposed method results showed no significant difference (at 95% confidence) with the hydrazine reduction method. The proposed method could be used as an alternative method for on-site analysis due to the advantages of portability and rapidity; duplicate run of 20 samples could be carried out simultaneously in 12 min.

Zinc-Reduced Mesoporous TiOx Li-Ion Battery Anodes with Exceptional Rate Capability and Cycling Stability.

We demonstrate a unique synthetic route for oxygen-deficient mesoporous TiOx by a redox-transmetalation process by using Zn metal as the reducing agent. The as-obtained materials have significantly enhanced electronic conductivity; 20 times higher than that of as-synthesized TiO2 material. Moreover, electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) measurements are performed to validate the low charge carrier resistance of the oxygen-deficient TiOx . The resulting oxygen-deficient TiOx battery anode exhibits a high reversible capacity (∼180 mA h g-1 at a discharge/charge rate of 1 C/1 C after 400 cycles) and an excellent rate capability (∼90 mA h g-1 even at a rate of 10 C). Also, the full cell, which is coupled with a LiCoO2 cathode material, exhibits an outstanding rate capability (>75 mA h g-1 at a rate of 3.0 C) and maintains a reversible capacity of over 100 mA h g-1 at a discharge/charge of 1 C/1 C for 300 cycles.