Chunyu Du

Nanoporous PdNi Alloy Nanowires As Highly Active Catalysts for the Electro-Oxidation of Formic Acid

Highly active and durable catalysts for formic acid oxidation are crucial to the development of direct formic acid fuel cell. In this letter, we report the synthesis, characterization, and electrochemical testing of nanoporous Pd(57)Ni(43) alloy nanowires for use as the electrocatalyst towards formic acid oxidation (FAO). These nanowires are prepared by chemically dealloying of Ni from Ni-rich PdNi alloy nanowires, and have high surface area. X-ray diffraction data show that the Pd(57)Ni(43) nanowires have the face-centered cubic crystalline structure of pure Pd, whereas X-ray photoelectron spectroscopy confirm the modification of electronic structure of Pd by electron transfer from Ni to Pd. Electrocatalytic activity of the nanowires towards FAO exceeds that of the state-of-the-art Pd/C. More importantly, the nanowires are highly resistant to deactivation. It is proposed that the high active surface area and modulated surface properties by Ni are responsible for the improvement of activity and durability. Dealloyed nanoporous Pd(57)Ni(43) alloy nanowires are thus proposed as a promising catalyst towards FAO.

Facile fabrication of a nanoporous silicon electrode with superior stability for lithium ion batteries

In this paper, we demonstrate that a novel silicon electrode with a large amount of nanopores can be fabricated by an in-situ thermal generating approach using triethanolamine as a sacrificing template. The fabrication process is simple, green, low cost, and easy to be scaled up. This electrode achieves high reversible capacities (2500 mAh g−1) with excellent cycling stability (∼90% capacity retention after 100 charge–discharge cycles), showing great potential as a high-performance anode for lithium-ion batteries. It is revealed that the high void volume with pore size of <200 nm can both enlarge the interface between active silicon particles and the electrolyte, and accommodate the severe volume change of silicon, thus leading to remarkably improved reversible capacity and cycling stability. The design concept and the fabrication approach used in the nanoporous silicon electrode may also be extended to other electrodes for electrochemical applications.

An Li-rich oxide cathode material with mosaic spinel grain and a surface coating for high performance Li-ion batteries

Lithium-rich layered oxides are considered to be one of the most promising cathode materials for lithium ion batteries due to their extremely high reversible capacity. Here, we report the design of a novel heterostructured Li1.2Ni0.13Co0.13Mn0.54O2 material with mosaic spinel nanograins and a surface coating, which is synthesized by a facile and green one-step solid-phase surface-modification process. We propose that the chemical Li leaching from Li2MnO3 simultaneously induces the formation of a fluorite coating and the layer-to-spinel phase transformation at high temperatures. The fluorite coating protects the lithium-rich oxides from direct exposure to the highly active electrolyte. The spinel phase provides an efficient path for Li+ mobility and also facilitates the suppression of the initial irreversible capacity loss. This unique heterostructured Li1.2Ni0.13Co0.13Mn0.54O2 material thus exhibits an outstanding initial Coulombic efficiency, superior rate capability and excellent cyclability. The design concept and facile synthetic strategy can be applied to both advanced lithium ion batteries and other high-performance energy storage devices.

Lithium-rich Li1.2Ni0.13Co0.13Mn0.54O2 oxide coated by Li3PO4 and carbon nanocomposite layers as high performance cathode materials for lithium ion batteries

Lithium-rich layered oxide Li1.2Ni0.13Co0.13Mn0.54O2 (LNCMO) coated with a nanocomposite layer of Li3PO4 and carbon (LNCMO@Li3PO4/C) is designed and facilely prepared as the cathode material for rechargeable lithium ion batteries. The structure and morphology of the LNCMO@Li3PO4/C material are characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, and its electrochemical performance is measured by the constant current charge and discharge, electrochemical impedance spectroscopy and cyclic voltammetry. It is clearly revealed that the LNCMO surface is uniformly coated by the Li3PO4/C nanocomposite layer. Moreover, the coating process induces the layer-to-spinel phase transformation, leading to the formation of a spinel nanophase in the LNCMO@Li3PO4/C material. The presence of Li3PO4/C composite coating with high ionic and electronic conductivity and the spinel nanophase synergistically contribute to the electrochemical properties. Therefore, the LNCMO@Li3PO4/C material shows a high discharge capacity of 124.4 mA h g−1 even at a current density of 1000 mA g−1, a remarkable capacity retention of 87.3% after 200 cycles, and a desirable initial coulombic efficiency of 87.0%. The LNCMO@Li3PO4/C material represents an attractive alternative to high-rate and long-life electrode materials for lithium-ion batteries.

Covalently-functionalizing synthesis of Si@C core–shell nanocomposites as high-capacity anode materials for lithium-ion batteries

This paper reports the facile fabrication of Si@C core–shell nanocomposites by covalently grafting aniline monomer onto the surface of silicon nanoparticles, followed by a carbonizing process. Our covalently-functionalizing approach can lead to a uniform carbon coating with a tunable thickness and is low cost, environmentally friendly and easily scaled up. The Si@C nanocomposite was employed as an anode material for lithium-ion batteries (LIBs), showing a high initial reversible capacity of >1300 mA h g−1 as well as a good cycling stability. The enhanced performance is attributed to the fact that the uniform and elastic carbon coating can efficiently increase the electronic conductivity and accommodate severe volume changes of the Si particles. This Si@C nanocomposite exhibits great potential as an anode material in LIBs, and the fabrication strategy can be extended to prepare other carbon-coated core–shell nanocomposites.

Understanding undesirable anode lithium plating issues in lithium-ion batteries

Lithium-ion batteries (LIBs) are attractive candidates as power sources for various applications, such as electric vehicles and large-scale energy storage devices. However, safety and life issues are still great challenges for the practical applications of LIBs. Metallic lithium plating on the negative electrode under critical charging conditions accelerates performance degradation and poses safety hazards for LIBs. Therefore, anode lithium plating in LIBs has recently drawn increased attention. This article reviews the recent research and progress regarding anode lithium plating of LIBs. Firstly, the adverse effects of anode lithium plating on the electrochemical performance of LIBs are presented. Various in situ and ex situ techniques for characterizing and detecting anode lithium plating are then summarized. Also, this review discusses the influencing factors that induce anode lithium plating and approaches to mitigating or preventing anode lithium plating. Finally, remaining challenges and future developments related to anode lithium plating are proposed in the conclusion.

Facile synthesis of nanostructured TiNb2O7 anode materials with superior performance for high-rate lithium ion batteries

One-dimensional nanostructured TiNb2O7 was prepared by a simple solution-based process and subsequent thermal annealing. The obtained anode materials exhibited excellent electrochemical performance with superior reversible capacity, rate capability and cyclic stability.

Pd-around-CeO2−x hybrid nanostructure catalyst: three-phase-transfer synthesis, electrocatalytic properties and dual promoting mechanism

In this work, we report a Pd-around-CeO2−x hybrid nanostructure catalyst for direct ethanol fuel cells, which is synthesized via a facile three-phase-transfer approach. The obtained nanostructure catalyst is characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. In this nanostructure, Pd nanoparticles (NPs) are closely attached onto the surface of the CeO2−x NPs, leading to an intense interfacial interaction between Pd and CeO2−x. The electrocatalytic properties of the Pd-around-CeO2−x hybrid nanostructure catalyst for ethanol electrooxidation is investigated by cyclic voltammetry and chronoamperometry. This Pd-around-CeO2−x hybrid nanostructure catalyst shows a superior catalytic performance for ethanol electrooxidation, which can be attributed to a novel dual promoting mechanism.

Improved electrochemical performance and capacity fading mechanism of nano-sized LiMn0.9Fe0.1PO4 cathode modified by polyacene coating

Nano-sized LiMn1−xFexPO4 (x = 0 and 0.1) was prepared by a solvothermal method in a mixed solvent of water and ethanol. LiMn0.9Fe0.1PO4–polyacene (PAS) composite exhibits a high conductivity (0.15 S cm−1), resulting in an excellent rate performance and good cycle life. The LiMn0.9Fe0.1PO4–PAS composite delivers a discharge capacity of 161, 141, and 107 mA h g−1 at 0.1 C, 1 C and 10 C, respectively. The well-distributed conductive polyacene surrounding the LiMn0.9Fe0.1PO4 nanoplates enhances the electronic contact of the nanosized crystalline particles and suppresses the manganese dissolution related to the structure evolution during cycling. Specifically, the manganese dissolution, electrolyte decomposition and the antisite defects are the most significant factors that impact the capacity degradation of olivine iron-doped lithium manganese phosphate cathode materials.

Electrochemical performance degeneration mechanism of LiCoO2 with high state of charge during long-term charge/discharge cycling

Electrochemical performance degeneration of LiCoO2 electrodes under high state of charge (SOC) during long-term cycling was studied using LiCoO2/MCMB batteries. The batteries were charged/discharged at 0.6C with 30% depth of discharge (DOD) for 100, 400, 800, 1600, 2000 and 2400 cycles, respectively, and then disassembled to analyze the evolution of morphology, element content, microstructure and electrochemical performance. Through energy dispersive spectrometer (EDS), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM) characterization, it was confirmed that the formation of discontinuous solid electrolyte interface (SEI) layer consisting of Li2CO3, RCOOLi and LiF led to the increase of electrochemical charge transfer resistance (Rct). Although the X-ray diffraction (XRD) refined results showed that there was no new phases were formed during the long-term cycling, the actually increased Li/Co exchange ratio of LiCoO2 from 1.6% at 800th to 2.1% at 2400th resulted in the decrease of lithium ion diffusion coefficient and deterioration of the rate performance.