6 research outputs found

    Clarifying the Controversial Catalytic Performance of Co(OH)<sub>2</sub> and Co<sub>3</sub>O<sub>4</sub> for Oxygen Reduction/Evolution Reactions toward Efficient Zn–Air Batteries

    No full text
    Cobalt-based nanomaterials have been widely studied as catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) due to their remarkable bifunctional catalytic activity, low cost, and easy availability. However, controversial results concerning OER/ORR performance exist between different types of cobalt-based catalysts, especially for Co­(OH)<sub>2</sub> and Co<sub>3</sub>O<sub>4</sub>. To address this issue, we develop a facile electrochemical deposition method to grow Co­(OH)<sub>2</sub> directly on the skeleton of carbon cloth, and further Co<sub>3</sub>O<sub>4</sub> was obtained by post thermal treatment. The entire synthesis strategy removes the use of any binders and also avoids the additional preparation process (e.g., transfer and slurry coating) of final electrodes. This leads to a true comparison of the ORR/OER catalytic performance between Co­(OH)<sub>2</sub> and Co<sub>3</sub>O<sub>4</sub>, eliminating uncertainties arising from the electrode preparation procedures. The surface morphologies, microstructures, and electrochemical behaviors of prepared Co­(OH)<sub>2</sub> and Co<sub>3</sub>O<sub>4</sub> catalysts were systemically investigated by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and electrochemical characterization methods. The results revealed that the electrochemically deposited Co­(OH)<sub>2</sub> was in the form of vertically aligned nanosheets with average thickness of about 4.5 nm. After the thermal treatment in an air atmosphere, Co­(OH)<sub>2</sub> nanosheets were converted into mesoporous Co<sub>3</sub>O<sub>4</sub> nanosheets with remarkably increased electrochemical active surface area (ECSA). Although the ORR/OER activity normalized by the geometric surface area of mesoporous Co<sub>3</sub>O<sub>4</sub> nanosheets is higher than that of Co­(OH)<sub>2</sub> nanosheets, the performance normalized by the ECSA of the former is lower than that of the latter. Considering the superior apparent overall activity and durability, the Co<sub>3</sub>O<sub>4</sub> catalyst has been further evaluated by integrating it into a Zn–air battery prototype. The Co<sub>3</sub>O<sub>4</sub> nanosheets <i>in situ</i> supported on carbon cloth cathode enable the assembled Zn–air cells with large peak power density of 106.6 mW cm<sup>–2</sup>, low charge and discharge overpotentials (0.67 V), high discharge rate capability (1.18 V at 20 mA cm<sup>–2</sup>), and long cycling stability (400 cycles), which are comparable or even superior to the mixture of state-of-the-art Pt/C and RuO<sub>2</sub> cathode

    Self-Assembly of Graphene-Encapsulated Cu Composites for Nonenzymatic Glucose Sensing

    No full text
    Cu has recently received great interest as a potential candidate for glucose sensing to overcome the problems with noble metals. In this work, reduced graphene oxide-encapsulated Cu nanoparticles (Cu@RGO) have been prepared via an electrostatic self-assembly method. This core/shell composites were found to be more stable than conventional Cu-decorated graphene composites and bare copper nanoparticles in an air atmosphere because the graphene shell can effectively protect the Cu nanoparticles from oxidation. In addition, the obtained Cu@RGO composites also showed an outstanding electrocatalytic activity toward glucose oxidation with a wide linear detection range of 1 μM to 2 mM, low detection limit of 0.34 μM (S/N = 3), and a sensitivity of 150 μA mM<sup>–1</sup> cm<sup>–2</sup>. Moreover, Cu@RGO composites exhibited a satisfactory reproducibility, selectivity, and long effective performance. These excellent properties indicated that Cu@RGO nanoparticles have great potential application in glucose detection

    Sub‑3 nm Co<sub>3</sub>O<sub>4</sub> Nanofilms with Enhanced Supercapacitor Properties

    No full text
    Two-dimensional materials often show a range of intriguing electronic, catalytic, and optical properties that differ greatly from conventional nanoparticles. Herein, we demonstrate the large-scale preparation of sub-3 nm atomic layers Co<sub>3</sub>O<sub>4</sub> nanofilms with a nonsurfactant and substrate-free hydrothermal method. This successful preparation of ultrathin nanofilms highlighted the reconstruction of cobalt–ammonia complexes and synergistic effect of free ammonia and nitrate on film growth control. Subsequent performance tests uncovered that these sub-3 nm atomic layer Co<sub>3</sub>O<sub>4</sub> nanofilms exhibited an ultrahigh specific capacitance of 1400 F/g in the first galvanostatic charge/discharge test. The specific capacitance of Co<sub>3</sub>O<sub>4</sub> nanofilms only slightly decayed less than 3% after 1500 cycling tests. With some parameter adjustments, similar Co(OH)<sub>2</sub> nanofilms with a thickness of 3.70 ± 0.10 nm were also prepared. The Co(OH)<sub>2</sub> nanofilms possessed maximum specific capacitance of 1076 F/g and peak performance attenuation of about 2% after a cycle stability test

    Controllable Synthesis of Ni<sub><i>x</i></sub>Se (0.5 ≤ <i>x</i> ≤ 1) Nanocrystals for Efficient Rechargeable Zinc–Air Batteries and Water Splitting

    No full text
    The development of earth-abundant, highly active, and corrosion-resistant electrocatalysts to promote the oxygen reduction reaction (ORR) and oxygen and hydrogen evolution reactions (OER/HER) for rechargeable metal–air batteries and water-splitting devices is urgently needed. In this work, Ni<sub><i>x</i></sub>Se (0.5 ≤ <i>x</i> ≤ 1) nanocrystals with different crystal structures and compositions have been controllably synthesized and investigated as potential electrocatalysts for multifunctional ORR, OER, and HER in alkaline conditions. A novel hot-injection process at ambient pressure was developed to control the phase and composition of a series of Ni<sub><i>x</i></sub>Se by simply adjusting the added molar ratio of the nickel resource to triethylenetetramine. Electrochemical analysis reveals that Ni<sub>0.5</sub>Se nanocrystalline exhibits superior OER activity compared to its counterparts and is comparable to RuO<sub>2</sub> in terms of the low overpotential required to reach a current density of 10 mA cm<sup>–2</sup> (330 mV), which may benefit from the pyrite-type crystal structure and Se enrichment in Ni<sub>0.5</sub>Se. For the ORR and HER, Ni<sub>0.75</sub>Se nanoparticles achieve the best performance including lower overpotentials and larger apparent current densities. Further investigations demonstrate that Ni<sub>0.75</sub>Se could not only provide an enhanced electrochemical active area but also facilitate electron transfer during the electrocatalytic process, thus contributing to the remarkable catalytic activity. As a practical application, the Ni<sub>0.75</sub>Se electrode enables rechargeable Zn–air battery with a considerable performance including a long cycling lifetime (200 cycles), high specific capacity (609 mA h g<sup>–1</sup> based on the consumed Zn), and low overpotential (0.75 V) at 10 mA cm<sup>–2</sup>. Meanwhile, the water-splitting cell setup with an anode of Ni<sub>0.5</sub>Se for the HER and a cathode of Ni<sub>0.75</sub>Se for the OER exhibits a considerable performance with low decay in activity of 12.9% under continuous polarization for 10 h. These results suggest the promising potential of nickel selenide nanocrystals as earth-abundant and high-performance electrocatalysts for metal–air batteries and alkaline water splitting

    Electrochemical Oxidation of Chlorine-Doped Co(OH)<sub>2</sub> Nanosheet Arrays on Carbon Cloth as a Bifunctional Oxygen Electrode

    No full text
    The primary challenge of developing clean energy conversion/storage systems is to exploit an efficient bifunctional electrocatalyst both for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with low cost and good durability. Here, we synthesized chlorine-doped Co­(OH)<sub>2</sub> in situ grown on carbon cloth (Cl-doped Co­(OH)<sub>2</sub>) as an integrated electrode by a facial electrodeposition method. The anodic potential was then applied to the Cl-doped Co­(OH)<sub>2</sub> in an alkaline solution to remove chlorine atoms (electro-oxidation (EO)/Cl-doped Co­(OH)<sub>2</sub>), which can further enhance the electrocatalytic activity without any thermal treatment. EO/Cl-doped Co­(OH)<sub>2</sub> exhibits a better performance both for ORR and OER in terms of activity and durability because of the formation of a defective structure with a larger electrochemically active surface area after the electrochemical oxidation. This approach provides a new idea for introducing defects and developing active electrocatalyst
    corecore