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[en] Graphical Abstract: Display Omitted - Abstract: Non-precious metal electrodes, Ni and Co hydroxides and oxides, have been recently found active towards electro-oxidation of methanol in alkaline. In this article, we present a first and complete study on composition dependence of Ni–Co hydroxides and oxides for methanol electro-oxidation. Ni–Co hydroxide electrodes were prepared by co-electrodeposition on stainless steel mesh (SSM). The atomic ratio of Ni/Ni + Co in Ni–Co hydroxides was controlled by adjusting the ratio of precursor concentration. Ni–Co oxide electrodes were further obtained by annealing the Ni–Co hydroxides. The morphology factors of Ni–Co hydroxides and oxides were revealed by measuring double layer capacitance using cyclic voltammetry (CV). Methanol oxidation reaction (MOR) performance of these Ni–Co hydroxides and oxide electrodes was investigated by CV, and electrochemical impedance spectroscopy (EIS) techniques at room temperature (RT, ∼25 °C). It is found that the MOR performance of Ni–Co hydroxides increased with the increase of Ni content, while the performance of Ni–Co oxide electrodes presented a volcano plot. The highest MOR performance, the smallest charge transfer resistance and Tafel slope were found at the atomic composition of 46% Ni. Such an enhancement probably was due to the synergistic effect of co-existing Ni and Co in the spinel structure. In contrast, the electrode with the mixture of Ni oxide and Co oxide was unable to reach such a high activity. The function of Ni in Ni–Co hydroxides and oxides was attributed to facilitating the methanol oxidation, and in low potential it presented high absorption of intermediate products
[en] Highlights: • Engineering graphene films was achieved by steamed water regulation techniques. • Gravimetric specific capacitance of tailored graphene films can reach 340 F/g. • A highest specific capacitance of 326 F/cm3 or 915 mF/cm2 can be achieved. • Assembly of high-performance flexible solid-state supercapacitor was achieved. Developing versatile methods to fabricate flexible graphene film electrodes with favorable mechanical strength and desirably tailored areal and volumetric capacitances are very challenging for high-performance capacitive energy storages. Here, we present a simple yet versatile method to regulate the structures of scalable free-standing reduced graphene oxide (rGO) films for high-performance flexible supercapacitors. Steamed water with a high pressure and a moderately high temperature in closed vessels was used to prepare reduced graphene oxide with regulated structures, and the resultant rGO films exhibited favorable mechanical robustness (with modulus and tensile strength higher than 0.28 GPa and 5.9 MPa respectively) as well as excellently controllable areal and volumetric capacitances (with a highest gravimetric specific capacitance, a highest areal specific capacitance, and a highest volumetric capacitance up to 340 F/g, 915 mF/cm2, and 326 F/cm3, respectively), revealing the versatile behavior of this regulation technique for high-performance flexible energy storage. In addition, a typical assembled all-solid-state supercapacitor based on as-fabricated graphene films shows large gravimetric and areal specific capacitances, high energy density and power density, as well as excellent capacitance stability, highlighting its great potential for high-performance flexible energy storage devices.
[en] Highlights: • Nano-HA has been demonstrated as an efficient polysulfide absorbent. • The shuttle effect of polysulfide in Li-S battery has been confined by the nano-HA. • Nano-HA used as additive improved electrochemical performance of Li-S battery. - Abstract: Lithium-sulfur (Li-S) battery is regarded as one of the most promising candidates for developing advanced energy storage system, but the polysulfide shuttle effect remains the biggest obstacle for its practical application. In this work, nano-hydroxyapatite (Ca5(PO4)3(OH)) was used as an additive in the sulfur cathode and carbon-coated separator to prevent the polysulfide shuttle effect and thus to achieve the high performance. The sulfur cathode with nano-hydroxyapatite exhibited a higher reversible capacity and a more stable cycling performance than that of the pristine sulfur cathode. The improved capacity retention from 58% (100th) to 73% (200th) after introducing nano-hydroxyapatite into the sulfur cathode confirmed its strong polysulfide absorption ability. Furthermore, a nano-hydroxyapatite modified separator was developed to suppress the polysulfide shuttle effect and to facilitate the reutilization of sulfur species. The nano-hydroxyapatite particles served as polysulfide absorbents to bind polysulfides and suppress their diffusion to the anode. The batteries assembled with this separator exhibited a high reversible capacity of 886 mAhg−1 at 0.1C and 718 mAh g−1 at 0.5C after 200 cycles, with a low capacity fading of ∼0.10-0.11% per-cycle. At the highest sulfur loading of 4.5 mg cm−2 used for practical applications, the reversible areal capacity was much higher than the areal capacity (4 mAh cm−2) of commercial lithium-ion batteries. Therefore, the strategy using nano-hydroxyapatite as polysulfide absorbent shows great potential for solving the polysulfide shuttle problem and developing high performance Li-S batteries.
[en] This article reports a composite electrode of Fe_2O_3 nanoparticles/SWCNTs for hydroquinone electrochemical sensing. The synthesis includes the wet-chemical synthesis of Fe_3O_4 nanoparticles and the assembly of Fe_3O_4 nanoparticles onto single walled carbon nanotubes. Fe_3O_4/NH_2-CNTs composite is formed via the electrostatic attraction between positively-charged ammonia-terminated CNTs and negatively-charged Fe_3O_4 nanoparticles. Subsequent heat treatment oxidizes Fe_3O_4 to Fe_2O_3. The composite can be applied onto FTO glass to form Fe_2O_3/CNTs/FTO electrode and the electrode shows good performance in electrochemical sensing of hydroquinone as compared to Fe_2O_3/FTO and CNTs/FTO electrodes. SEM and TEM results show the iron oxide NPs were uniformly dispersed onto the surface of SWCNTs. The iron oxide NPs which uniformly anchored on the SWCNTs could accelerate the electron transfer rate which was evidenced by electrochemical impedance spectroscopy. The enhancement of electrochemical response further confirms the synergy between Fe_2O_3 NPs and SWCNTs. Differential pulse voltammetry was successfully used to quantify hydroquinone within the concentration range of 1.0∼80.0 μM under optimal conditions. The detection limit of Fe_2O_3/CNTs/FTO electrode for hydroquinone was 0.50 μM (S/N = 3). The electrode was further applied to test for hydroquinone in tap water and the Fe_2O_3/CNTs/FTO electrode also presents good stability and high reproducibility, proofing the potential of Fe_2O_3/CNTs electrode as a promising electrochemical sensor. This work presents an electrode using FTO substrate for the first time. It shows that FTO can be a potential alternative to glassy carbon electrode with lower cost, but without compromising too much on the sensitivity.
[en] Highlights: •A simple and scalable process to concomitant downsizing to nanoscale, carbon coating, inclusion of voids and conductive network of graphite. •Using tungsten carbide milling media and 80:1 ball to powder ratio, micron SnO2 particles are comminuted to nanosized SnO2 crystallites. •Hierarchical structure of carbon-coated SnO2 nanoclusters anchored on thin graphite sheets are prepared. •Impressive reversible capacity of 725 mAh g−1 is achieved by ball milling a mixture of SnO2 with 20 wt. % graphite for 20 h. •Synthesis parameters such as graphite content and milling time are systematically examined. -- Abstract: Development of novel electrode materials with unique architectural designs is necessary to attain high power and energy density lithium-ion batteries (LIBs). SnO2, with high theoretical capacity of 1494 mAh g−1, is a promising candidate anode material, which has been explored with various strategies, such as dimensional reduction, morphological modifications and composite formation. Unfortunately, most of the SnO2-based electrodes are prepared by using complex chemical synthesis methods, which are not feasible to scale up for practical applications. In addition, concomitant irrecoverable initial capacity loss and consequently poor initial Coulombic efficiency still persistently plagued these SnO2-based anodes. To overcome hitherto conceived irreversible formation of Li2O by conversion reaction, to fully harness its theoretical capacity, this work demonstrates that a hierarchical structured SnO2-C nanocomposite with 68.5% initial Coulombic efficiency and reversible capacity of 725 mAh g−1 can be derived from the mixtures of SnO2 and graphite, by using low cost industrial compatible high energy ball milling activation.