Peng Dong

Facile electrochemical preparation of self-supported porous Ni–Mo alloy microsphere films as efficient bifunctional electrocatalysts for water splitting

The exploration of low-cost, stable, and robust electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is urgently needed for developing renewable-energy storage and conversion techniques. In this study, we report a facile one-step electrodeposition route to prepare self-supported porous Ni–Mo alloy microsphere (Ni–Mo MS) films directly grown on copper foils from a deep eutectic solvent, ethaline (mixture of choline chloride and ethylene glycol), as a highly efficient and durable catalyst for both the HER and OER in 1.0 M KOH. The prepared Ni–Mo MS/Cu, as a hydrogen-evolving cathode, shows remarkable catalytic performance toward the HER with a small Tafel slope of 49 mV dec−1 and a low HER overpotential of −63 mV to deliver 20 mA cm−2. Serving as an oxygen-evolving anode, the catalyst also offers excellent OER catalytic activity with a moderate Tafel slope of 108 mV dec−1, and reaches 20 mA cm−2 at an OER overpotential of 335 mV. Utilized as both the cathode and anode in a symmetric two-electrode water electrolysis system, the bifunctional catalyst requires a cell voltage of 1.59 V to reach an overall water splitting current density of 10 mA cm−2 with robust durability, which could be potentially used in water splitting devices for practical applications.

TiO2–MoS2 hybrid nano composites with 3D network architecture as binder-free flexible electrodes for lithium ion batteries

TiO2 hybrid nano composites are encouraging electrode materials for lithium-ion batteries due to the increased specific capacity and excellent electrochemical performance. In this work, the TiO2–MoS2 hybrid binder free electrodes have been successfully synthesized by using a facile hydrothermal process. Encouragingly, when being assessed as an anode electrode for LIBs, the MoS2–TiO2 electrode after the calcination treatment could retain a capacity of 361.5 mAh g−1 with high capacity retention of 88.0% after 300 cycles at a high current density of 800xa0mAxa0g−1. Such good performance may be derived from the special 3D network architecture, well-dispersed MoS2 nanoparticles and the close connection between TiO2 and MoS2 after the calcination treatment.

Expanded biomass-derived hard carbon with ultra-stable performance in sodium-ion batteries

A hard carbon sheet-like structure has been successfully prepared with a short flow process by simply using cherry petals (CPs) as the raw materials. The sodium storage mechanism in CPs was detected with cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). Encouragingly, when being assessed as an anode electrode for sodium-ion batteries (SIBs), the CP electrode can provide a high initial reversible capacity of 310.2xa0mA h g−1 with a favorable initial Coulomb efficiency of 67.3%, delivering a high retention rate of 99.3% at 20 mA g−1 after 100 cycles. Even at a high current density of 500 mA g−1, the reversible capacity can reach 146.5 mA h g−1, indicating that the high rate performance is excellent as well. Such a preferable performance may be derived from the prepared structures with sufficient mesopores, the presence of nitrogen/oxygen functional groups on the surface and the expanded interlayer distances (∼0.44 nm), which enable reversible sodium-ion storage through surface adsorption and sodium intercalation.

A combined process for cobalt recovering and cathode material regeneration from spent LiCoO 2 batteries: Process optimization and kinetics aspects

A combined process has been developed for recovering cobalt and regenerating cathode material from leach liquor of spent LiCoO2 batteries. Cobalt of 98% can be selectively separated from leach liquor using ammonium oxalate of 1.15 (mole ratio) at pH of 2.0, 55u202f°C, and 40 min. Kinetics analysis indicates that precipitation of cobalt is controlled by a combination of surface chemical reaction and diffusion. The Ea value of precipitation is 19.68 kJ/mol obtained from the second-order model of (1u202f-u202fa)-1u202f=u202fktu202f+u202fc. Based on the TG/DSC curves of oxidation of cobalt oxalate, it is found that formation of Co3O4 oxidized from cobalt oxalate is in according with the model of randomly nucleating followed by nucleus growth. The Ea value is 84.93 kJ/mol that is provided by the suitable model of g(α)u202f=u202f[-ln(1u202f-u202fα)]1/3. Then, lithium is recovered from the filtrate as Li2CO3 with the purity of 99.5% by precipitation method. Finally, new cathode material with a good electrochemical performance is regenerated using obtained Co3O4 and lithium carbonate through solid phase method.

Combustion combined with ball milling to produce nanoscale La 2 O 3 coated on LiMn 2 O 4 for optimized Li-ion storage performance at high temperature

In this study, La2O3 is synthesized by combustion method and then subjected to ultrafine ball milling to obtain La2O3 nanoparticles. In neopentyl glycol, La2O3 nanoparticles are coated on the surface of spinel LiMn2O4 ultimately obtaining La2O3 coating contents of 1.5, 3, 4.5, and 6xa0wt%. XRD characterization reveals that the nano La2O3 exhibits a favorable crystalline intensity, without impurities and the crystalline peak of La2O3 can be observed when the coating content is of up to 6xa0wt%. Successful deposition of a thin layer of La2O3 on the LiMn2O4 surface is confirmed by scanning electron microscopy, transmission electron microscopy, X-ray spectrum elemental plane scanning, and line scanning. Furthermore, inductively coupled plasma emission spectrography and electrochemical impedance spectroscopy analyses show that the nano-La2O3 coating significantly relieves the dissolution of Mn in LiMn2O4 materials, and also improves the electro-conductivity. The electrochemical performances of the coated LiMn2O4 samples are also investigated in this work. Compared with the pristine LiMn2O4, the LiMn2O4 coated with 3xa0wt% La2O3 exhibits a higher rate capability and better reversibility, exhibiting 103.5 and 90.6xa0mAhxa0g−1 at 5 and 10xa0°C, respectively. After 100 cycles at 60 and 1xa0°C, the 3xa0wt% nano-La2O3-coated sample still exhibits a high-capacity retention of 91.68%.Graphical Abstract

Non-haloaluminate ionic liquids for low-temperature electrodeposition of rare-earth metals—A review

Abstract The inherent advantages of ionic liquids (ILs) in electrochemistry have received extensive attention in recent two decades. As a new generation of ILs, non-haloaluminate ILs exhibit better benefits and fewer drawbacks compared to haloaluminate based ILs, which are more qualified for metal electrodeposition, especially reactive metals. In this brief review, the recent developments regarding the application of non-haloaluminate ILs as solvents for low-temperature electrodeposition of rare-earth (RE) metals are outlined. In addition, the current problems and an outlook on future research are presented.

A ternary oxide precursor with trigonal structure for synthesis of LiNi0.80Co0.15Al0.05O2 cathode material

A Ni-Co-Al ternary oxide precursor with a trigonal structure, which can be used to synthesize LiNi0.8Co0.15Al0.05O2 cathode material, was prepared by calcining Ni-Co-Al composite oxalates formed by using a facile chemical approach. The LiNi0.8Co0.15Al0.05O2 cathode material calcined at a temperature as low as 650xa0°C had acceptable electrochemical performance with an initial discharge capacity of 183.9xa0mAhxa0g−1. The sample prepared at 750xa0°C possessed the highest initial discharge capacity of 196.0xa0mAhxa0g−1, while the sample calcined at 700xa0°C showed the optimal capacity retention (89.9%) after 100 cycles under 1 C. To prepare a pure LiNi0.8Co0.15Al0.05O2 phase by a conventional solid-state reaction, the calcination temperature should exceed 750xa0°C, and the highest initial discharge capacity was only 185.4xa0mAhxa0g−1. We suggest that the ternary oxide precursor with trigonal structure accelerates lithiation and, therefore, promotes the generation of LiNi0.8Co0.15Al0.05O2 with high crystallinity at a lower temperature. This study provides a facile way to synthesize layered cathode material with good electrochemical performance at a lower calcination temperature.

Enhanced electrokinetic remediation of lead- and cadmium-contaminated paddy soil by composite electrolyte of sodium chloride and citric acid

PurposeThe aim of this study was to inquire about the removal efficiencies of lead and cadmium in paddy soil by a composite electrolyte of sodium chloride and citric acid under electrokinetic remediation.Materials and methodsThe experiment was operated in a plexiglass tank, which was divided into one soil column (lengthxa0×xa0widthxa0×xa0heightu2009=u200920xa0cmu2009×u20095xa0cmu2009×u20095xa0cm) and two electrode chambers (lengthxa0×xa0widthxa0×xa0heightu2009=u20096xa0cmu2009×u20095xa0cmu2009×u20095xa0cm).Results and discussionIn this paper, the composite electrolyte (sodium chloridexa0+xa0citric acid) which combined the merits of two different chemicals was investigated for electrokinetic remediation of lead- and cadmium-contaminated paddy soil under a voltage gradient of 1.5xa0V/cm during a 20-day treatment. The total concentrations of lead and cadmium in the initial soil were 940.83 and 4.51xa0mg/kg, respectively. As sodium chloride was solubilized in solution, a number of Na+, Cl−, OH−, and H+ ions were generated that could dissolve some of Pb and Cd in soil to form Cd–Cl and Pb–Cl. When the lead- and cadmium-contaminated paddy soil was implemented with 0.1xa0M sodium chloride, the total removal efficiencies of lead and cadmium were 23.10 and 27.94%, respectively, which were little higher than those implemented with deionized water. Citric acid was not only used to control pH, but it can also combine with metals to form soluble M-citrate. When sodium chloride was mixed with citric acid in electrokinetic (EK) remediation, high redox potential was obtained that forced most of the metals to migrate out from soil. The overall removal efficiencies of lead and cadmium were increased from 56.85 and 62.26% with single citric acid electrolyte to 80.37 and 90.86% with composite electrolyte of sodium chloride and citric acid, respectively. Eventually, the residual concentrations of lead and cadmium in the soil were only 184.70 and 0.41mg/kg, respectively, which met the demand of agricultural production and human health requirements.ConclusionsCitric acidxa0+xa0sodium chloride treatment poses less environmental risk than inorganic acid (HCl, HNO3, and H2SO4). There is good synergistic effect of sodium chloride and citric acid during the EK remediation process. Thus, citric acidxa0+xa0sodium chloride is considered as an effective electrolyte to remove lead and cadmium from paddy soil.

One-pot synthesis of PdM/RGO (M=Co, Ni, or Cu) catalysts under the existence of PEG for electro-oxidation of methanol

The binary PdM (M=Co, Ni, Cu) catalysts were synthesized with one-pot on reduced graphene oxide (RGO) using the sodium borohydride reduction method under the existence of the polyethylene glycol (PEG). And the catalysts were used for the electro-oxidation of methanol in alkaline media. Cyclic voltammetry (CV) and chronoamperometry (i-t) tests indicated that the Pd-based binary systems significantly enhanced electrochemical activities and improved stability compared with the monometallic Pd/RGO and commercial Pd/C (JM) catalysts. The lower onset potentials of PdM/RGO indicated that the prepared PdM/RGO catalysts had the better electrochemical performance than Pd/RGO and Pd/C (JM). Physicochemical properties of the PdM/RGO catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman. These results show that the better electrochemical performance of PdM/RGO can be ascribed to the addition of the second metal and PEG, because M successfully modified the morphology and electronic structure of Pd, and improved dispersibility of PdM on the reduced graphene oxide. And these modifications can be easily carried out under the presence of PEG.

CeVO 4 -coated LiNi 0.6 Co 0.2 Mn 0.2 O 2 as positive material: towards the excellent electrochemical performance at normal and high temperature

The CeVO4-coated LiNi0.6Co0.2Mn0.2O2 (NCM 622) cathode materials are successfully synthesized by hydrothermal method. The structure, morphology and electrochemical properties of the surface modified NCM 622 materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and constant current charge and discharge test. The SEM images and XPS patterns show that nanosized CeVO4 layer is uniformly coated on the surface of NCM 622 active material. Furthermore, the electrochemical performance of all the CeVO4-coated NCM 622 samples are improved significantly. 3xa0wt% of CeVO4-coated NCM 622 cathode material exhibits specific capacity of 146.1 mAh g-1 and excellent capacity retention (89.63%) between 2.8 and 4.3xa0V after 100 cycles at elevated temperature (60xa0°C). The alternating current impedance and cyclic voltammetry tests show that the CeVO4 coating can reduce the electrode polarization and enhance the electrochemical activity of cathode materials.