Lithium-rich manganese-based cathode materials have become one of promising cathode materials due to their low cost and large discharge specific capacity exceeding 250 mAh·g^-1. However, their problems such as low coulombic efficiency of first cycle and apparent voltage decay influence commercialization process. The high charging voltage will cause instability of structure and increase the hidden danger of the battery. Therefore, structural evolution of first cycle at higher voltage needs to be further studied. In this work, the precursor was synthesized by the co-precipitation method, and the lithium-rich manganese-based layered cathode materials were prepared by lithium-mixed and high-temperature sintering, and the effects of coulombic efficiency and cycle performance were studied at different charge cut-off voltages. Results have shown that high charging voltage would increase the capacity, but reduce the coulombic efficiency greatly in the first cycle, leading to the decayed specific capacity of long cycle. Cyclic voltammetric investigation proves that when the charge cut-off voltage was 5.0 V, part of the bulk lattice oxygen underwent a reversible oxidation reaction, which lead to the increase of capacity. TEM, XRD and SEM characterization results show that the electrode not only went deep into the bulk phase structural changes, including a large number of stacking faults and spinel phases MnO_x and NiO_x, and other irreversible phase changes, but also reacted with the electrolyte. Mapping and XPS results show that when the charging voltage became higher, more bulk lattice oxygen participated during redox reaction, which causes stronger oxidizing peroxygen and superoxide ions to undergo side reactions with the electrolyte and accelerates the structural collapse of the electrode, ultimately, becomes not conducive to long cycle performance of the battery accompanied by the dissolution of the transition metal.

Low-cost and high-safety aqueous sodium-ion batteries have received widespread attention in the field of large-scale energy storage, but the narrow electrochemical stability window (1.23 V) of water limits the energy density of aqueous sodium-ion batteries. The “water-in-salt” strategy which uses the interaction between cations and water molecules in the solution can inhibit water decomposition and broaden the electrochemical stability window of water. In this work, two types of low-cost salts, namely, ammonium acetate (NH₄CH₃COOH) and sodium acetate (NaCH₃COOH), were used to configure a mixed aqueous electrolyte for aqueous sodium-ion batteries. The solution consisted of 25 mol·L ^-1 NH₄CH₃COOH and 5 mol·L^-1 NaCH₃COOH, used as an aqueous electrolyte, exhibited a wide electrochemical stability window of 3.9 V and high ionic conductivity of 28.2 mS·cm^-1. The composite of layered manganese dioxide and multi-wall carbon nanotubes (MnO₂/CNTs) was used as a positive electrode material, while the carbon-coated NaTi₂(PO₄)₃ with NASICON structure was used as a negative electrode material. Both of these electrode materials had excellent electrochemical performances in the aqueous electrolyte. A full cell achieved an average working voltage of about 1.3 V and a discharge capacity of 74.1 mAh·g^-1 at a current density of 0.1 A·g^-1. This aqueous sodium-ion battery displayed excellent cycling stability with negligible capacity losses (0.062% per cycle) for 500 cycles. The safe and environmentally friendly aqueous acetate electrolyte, with a wide electrochemical stability window, showed the potential to be matched with positive materials having higher potential and negative materials having lower potential for further improving the voltage of aqueous sodium-ion batteries and promoting the development of aqueous batteries for large-scale energy storage technology.

Establishment of an ozone-based advanced oxidation process (AOPs-O₃) for effective treatment of acid wastewater is an important and difficult task. The process of ozonation coupled with electrolysis (electrolysis-ozonation, E-O₃) has been reported to effectively degrade pollutants in neutral solution. We studied the efficiency of E-O₃ for degradation of acetic acid (HAc, an ozone inert chemical) in acid solution and found that E-O₃ had high oxidative efficiency at pH less than 3. For example, 52.2% of 100 mg·L^-1 HAc could be removed by E-O₃ in 120 min at pH 1.0, but only 2.2% and 3.5% by electrolysis and ozonation, respectively. Although the efficiency of E-O₃ decreased with the increase of acidity of solution, it still remained relatively high even at pH 0. An aromatic compound of acetophenone could also be effectively degraded by E-O₃ at pH 1.0. The results indicate that electrons can transfer from cathode to dissolved ozone or oxygen in acidic solution, thus resulting in generation of reactive species, e.g. hydroxyl radicals. A real acidic wastewater was also effectively pretreated by E-O₃. This study provides a promising AOPs-O₃ for treatment of acid wastewaters.

Three-dimensional (3D) nanostructural Flower-like cobalt sulfide (CoS) on flexible self-supporting graphene tape electrode (GTE) with remarkably electrocatalytic activity toward glucose was successfully prepared by electrodeposition. Structural characterizations revealed that the electrodeposited CoS was highly dispersed on GTE as an active material. The fabricated binder-free and self-standing CoS/GTE shows a good linear response in the range of 0.025 ~ 1.0 mmol·L^-1, reaching a high glucose sensitivity value of 323.3 μA·(mmol·L ^-1)^-1·cm^-2 and a low detection limit of 8.5 μmol·L ^-1 (S/N = 3). Moreover, the as-prepared sensor was well applied for glucose determination in human serum. Thus, the self-supporting, binder-free, low-cost sensor has good potential as a promising device for practical quantitative analysis of glucose in human serum.

The electrochemical carbon dioxide reduction reaction (CO₂RR) is a promising approach to produce liquid fuels and industrial chemicals by utilizing intermittent renewable electricity for mitigating environmental problems. However, the traditional H-type reactor seriously limits the electrochemical performance of CO₂RR due to the low CO₂ solubility in electrolyte, and high ohmic resistance caused by the large distance between two electrodes, which is unbeneficial for industrial application. Herein, we demonstrated a high-performance continuous flow membranes electrode assembly (MEA) reactor based on a self-growing Cu/Sn bimetallic electrocatalyst in 0.5 mol·L^-1 KHCO₃ for converting CO₂ to formate. Compared with an H-type cell, the MEA reactor not only shows the excellent current density (66.41 mA·cm^-2 at -1.11 V_RHE), but also maintains high Faraday efficiency of formate (89.56%) with the steady work around 20 h. Notably, we also designed the new CO₂RR system to effectively separate the gaseous/liquid production. Surprisingly, the production rate of formate reached 163 μmol·h^-1·cm^-2 at -0.91 V_RHE with the cell voltage of 3.17 V. This study provides a promising path to overcome mass transport limitations of the electrochemical CO₂RR and to separate liquid from gas products.

Transition metal phosphide (TMP), as an ideal catalytic promoter in methanol fuel oxidation, has received increased attention because of its multifunctional active sites, tunable structure and composition, as well as unique physical and chemical properties and efficient multi-composition synergistic effect. Some advances have been made for this catalyst system recently. In the current review, the research progresses of transition metal phosphides (TMPs) in the assisted electrooxidation of methanol including the catalysts fabrication and their performance evaluation for methanol oxidation are reviewed. The promotion effect of TMPs has been firstly presented and the catalyst systems based on the different metal centers of TMPs are then mainly discussed. It is concluded that the TMPs can greatly promote methanol oxidation through the electronic effect and the oxyphilic property based on the bifunctional catalytic mechanism. The problems and challenges in methanol fuel oxidation by using TMPs are also described at the end with the attention being paid to the precise catalyst design. The catalytic mechanism probing and application of the fuel cells device are proposed. The current effort might be helpful to the community for novel catalyst system design and fabrication.

Fuel cells are energy conversion devices that convert chemical energy directly into electricity. It has the advantages of high energy density, high utilization efficiency of fuel, clean and noiseless during working. Among all kinds of fuel cells, proton exchange membrane fuel cells (PEMFCs) are most popular since PEMFCs function at near ambient temperature, while their power densities are higher than those of other fuel cells. Currently, Pt-based nanomaterials are still the unreplaceable catalysts in commercialized PEMFCs. The lack of low-cost and high-performance cathode catalysts is still one of key factors that hampers the commercialization of PEMFCs. In this review, the structurally controlled syntheses of catalysts and their influences on the performances of oxygen reduction reaction (ORR) and membrane electrode assembly (MEA) are summarized. The performance of membrane electrode assembly (MEA) can also be adjusted by regulating the structure of catalyst layer. Special attention has been paid with a focus on the achievement of enhanced utilization of noble metal, and thus, lowering the loading of noble metals in MEA.