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    28 August 2022, Volume 28 Issue 8
    Facile One-Step Solid-State Synthesis of Ni-Rich Layered Oxide Cathodes for Lithium-Ion Batteries
    Wang Jing-Yue, Wang Rui, Wang Shi-Qi, Wang Li-Fan, Zhan Chun
    2022, 28(8):  2112131.  doi:10.13208/j.electrochem.211213
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    Nickel-rich layered oxide is one of the dominate cathode materials in the lithium ion batteries, due to its high specific energy density meeting the range requirement of the electric vehicles. Typically, the commercial Ni-rich layered oxides are synthesized from co-precipitated precursors, while precision control is required in the co-precipitation process to ensure the atomic level mixing of the cations such as Ni, Co and Mn, et.al. In this work, a one-step solid-state method was successfully applied to synthesize the Ni-rich layered oxide materials with ultra-high Ni content. By choosing the nickel hydroxides as the precursor with layered structure similar to the targeting product, we successfully synthesized LiNiO2 (LNO) and LiNixCoyO2(x = 0.85, 0.9, 0.95; x + y = 1) with the electrochemical performance comparable to NCM prepared from precipitated precursors. It was confirmed by XRD and XPS that Co is doped into LNO and suppresses the Li+/Ni2+ mixing in Ni-rich oxides. The Co dopant exhibits a noticeable advantage in improving the discharge capacity, rate performance and cycle performance. This work provides some perspective that the one-step solid-state method is a promising approach to prepare high-energy ultrahigh-Ni layered oxide cathodes.

    Quantitative Lithium Composite as 3D Lithium Foam Anode for Lithium Metal Battery
    Li Hu-Dong, Jia Wei-Shang, Yan Xin-Xiu, Yang Yao-Yue
    2022, 28(8):  2202051.  doi:10.13208/j.electrochem.2202051
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    Lithium (Li) metal as an anode material for batteries has extremely high specific capacity and extremely low redox potential, which can significantly improve the energy density of the battery. However, the main problems faced by the use of Li metal anodes are Li dendrite growth, interfacial side reaction and volumetric change of electrode. Herein, a strategy to prepare the three-dimensional (3D) Li foam by combining 3D scaffold with quantitative Li was proposed to suppress Li dendrites growth and alleviate electrode volumetric change. The 3D Li foam facilitated the efficient utilization of Li metal by suppressing the Li dendrite growth, mitigating the volumetric change, and improving the rate performance. Therefore, the cycling lifetime and rate performance of the symmetric cells using the 3D Li foam were improved. The EIS results showed that the 3D Li foam reduced the charge transfer resistance of the symmetric cells. And the average discharge specific capacity of the LTO cell during 1000 cycles was enhanced from 65 mAh·g-1 to 121 mAh·g-1 by using the 3D Li foam.

    Optimized Electrochemical Performance of Si@C Prepared by Hydrothermal Reaction and Glucose Carbon Source
    Chen Si, Zheng Song-Sheng, Zheng Lei-Ming, Zhang Ye-Han, Wang Zhao-Lin
    2022, 28(8):  2112221.  doi:10.13208/j.electrochem.211222
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    Silicon (Si) has been considered as the potential material for the next-generation lithium-ion batteries (LIBs) for its high capacity (4200 mAh·g-1, Li22Si5) and suitable working voltage (about 0.25 V vs. Li/Li+). However, the cycling stability and electrochemical performance of Si anode become significant challenges because of low intrinsic conductivity and huge volume variation (about 400%) during cycling processes. In addition, the repeated formation and destruction of surface solid electrolyte interphase (SEI) film will continuously consume the electrolyte and cause damage to LIBs. Carbon (C) materials, such as graphite, carbon spheres and tubes, have been widely applied to ameliorate the conductivity and restrict the volume change of Si anode, which guarantees electrical performance. Especially, a Si@C core-shell structure is preferred to perform a high capacity and relatively good cycle stability. The hydrothermal process has been commonly used to prepare Si@C anodes for LIBs, therefore, it is significant to optimize the preparing conditions to achieve ideal electrochemical performance. In this study, glucose was taken as the carbon source, using the Si waste from the photovoltaic industry as raw materials to prepare Si@C core-shell structure by hydrothermal process. The preparing parameters have been evaluated and optimized, including temperature, reaction time, raw material composition, and mass ratio.

    The optimal preparing process was proceeded in the solution with a glucose concentration of 0.5 mol·L-1 and a Si/glucose mass ratio of 0.3. Then, it was treated in a hydrothermal reactor at 190 oC for 9 h. The obtained Si@C anode candidate (Sample CS190-3) was tested with a coin half-cell. The specific capacity after the first cycle reached 3369.5 mAh·g-1, and the remaining capacity after 500 cycles 1405.0 mAh·g-1 in a current density of 655 mAh·g-1. Moreover, for the rate testing, it retained the discharge capacities of 2328.7 mAh·g-1, 2209.8 mAh·g-1, 2007.1 mAh·g-1, 1769.2 mAh·g-1, 1307.7 mAh·g-1 and 937.1 mAh·g-1 at the charge rates of 655 mA·g-1, 1310 mA·g-1, 2620 mA·g-1, 3930 mA·g-1, 5240 mA·g-1, and 6550 mA·g-1, respectively. And it was recovered to 1683.0 mAh·g-1 when the current density was restored to 655 mA·g-1. In addition, the EIS data revealed that the half-circle radius of the sample obtained by using the optimal conditions (Sample CS190-3) in the low-frequency region was greatly reduced, and the Warburg impedance became the smallest. This work can provide an important approach, and make a significant impact in the preparation of Si/C anode material for LIBs.

    Low-Crystallinity and Heterostructured AuPt-Ru@CNTs as Highly Efficient Multifunctional Electrocatalyst
    Gan Tuan-Jie, Wu Jian-Ping, Liu Shi, Ou Wen-Jun, Bin Ling, Kang Xiong-Wu
    2022, 28(8):  2201241.  doi:10.13208/j.electrochem.2201241
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    The catalytic activity of the catalysts is strongly dependent on the structure of the catalysts, and the exploration of their correlation and structure-controlled synthesis of the high-performance catalysts are always at the central. Currently, platinum (Pt) is the optimum catalyst for hydrogen evolution reaction (HER), oxygen reduction reaction (ORR) and alcohol oxidation reaction, while ruthenium (Ru) behaves as the champion catalyst for oxygen evolution reaction (OER) during water splitting. Preparing alloy catalysts with these precious metals can modulate the catalytic activity of these catalysts from the perspective of strain effect, ensemble effect and ligand effect. Here, we developed a strategy to deposit AuPt alloy as a solid solution phase on amorphous Ru supported on CNTs, thus forming AuPt-Ru heterostructures. The well-defined AuPt-Ru heterostructured catalysts were examined by X-ray diffraction and elemental mapping in high-angle annular dark-field scanning transition electron spectroscopy (HAADF-STEM). As compared to the high crystallinity AuPt alloy, AuPt alloy in AuPt-Ru heterostructure became amorphous, and AuPt-Ru showed superior catalytic activity toward ethanol oxidation reaction (EOR), achieving the mass activity of Pt as high as 21.44 A·mg-1 due to the high tolerance toward the poisoning species. The intermediates species of the EOR were also examined by in-situ FTIR spectroscopy. The stability of the catalysts toward EOR was also excellent and the degradation in the activity of the catalysts was strongly related to the loss of Ru content during the stability test. The heterostructured AuPt-Ru catalysts also exhibited the excellent alkaline HER and OER performances, superior to those of commercial Pt/C and RuO2 catalysts, ascribing to the amorphous state of AuPt-Ru heterostructure, and the modulation by strain and ensemble effects. This work highlights the importance in the design of the multicomponent heterostructures for the synthesis of high-performance and multifunctional electrocatalysts.

    A Novel Electrochemical Sensor Based on Au/rGO/FeOOH for One-Step Detection of Nitrite
    Luo Da-Juan, Liu Bing-Qian, Qin Meng-Yan, Gao Rong, Su Li-Xia, Su Yong-Huan
    2022, 28(8):  2110191.  doi:10.13208/j.electrochem.211019
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    Nitrite, a widespread raw material, is harmful to human health for long-term consumption. At present, the detection methods of nitrite mainly include chemical analysis, fluorescence, ultraviolet spectrophotometry and chromatography. These methods have ideal sensitivity and selectivity, but also have some characteristics: cumbersome operation, expensive equipment and professional personnel. Therefore, the development of a simple and sensitive nitrite assay is of great significance. In this paper, the Au/rGO/FeOOH composite materials, which revealed good synergistic catalytic performance among the three elements in the composite, were prepared by simple hydrothermal method and reduction method for the first time with large specific surface area and good electrical conductivity. A one-step electrochemical sensor was constructed by using a traditional three-electrode system for detecting NO2-. Of course, the Au/rGO/FeOOH composite modified FTO was regarded as the working electrode. When the target NO2- existed, the current increased because the material on the electrode could electro-catalyze NO2- to NO3-. When the NO2- was oxidized, the electron was transferred from NO2- to the Au/rGO/FeOOH composite. And the rGO with a large specific surface area and good conductivity in the composite would rapidly transfer electrons to the FTO electrode, thus, enhancing the current signal. Quantitative analysis of NO2- could be obtained according to the current intensity which is positively correlated with the concentration of the target. Under the optimal experimental conditions, nitrite was quantitatively detected by differential pulse voltammetry with a linear range of 0.001 ~ 5 mmol·L-1 and a detection limit of 0.8 μmol·L-1 (S/N = 3), and the response time was less than 2s. Moreover, the sensor exhibited good selectivity and reproducibility, and could be applied to actual samples. The excellent sensitivity for rapid detection of NO2- may be derived from two aspects: 1. the unique structure of rGO FeOOH expands the surface area of the electrode, and further speeds up electron transfer during electrochemical reactions; 2. the composite material has synergistic electrocatalytic oxidation performance among Au, rGO and FeOOH. More importantly, the one-step determination of NO2- could be realized accompanying with the simple fabrication of electrode and quick response (~ 2s). It also provides a new idea for the application of metal-organic framework materials in electrochemical field.