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)2 and Co3O4. To address this issue, we develop a facile electrochemical deposition method to grow Co(OH)2 directly on the skeleton of carbon cloth, and further Co3O4 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)2 and Co3O4, eliminating uncertainties arising from the electrode preparation procedures. The surface morphologies, microstructures, and electrochemical behaviors of prepared Co(OH)2 and Co3O4 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)2 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)2 nanosheets were converted into mesoporous Co3O4 nanosheets with remarkably increased electrochemical active surface area (ECSA). Although the ORR/OER activity normalized by the geometric surface area of mesoporous Co3O4 nanosheets is higher than that of Co(OH)2 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 Co3O4 catalyst has been further evaluated by integrating it into a Zn-air battery prototype. The Co3O4 nanosheets in situ supported on carbon cloth cathode enable the assembled Zn-air cells with large peak power density of 106.6 mW cm-2, low charge and discharge overpotentials (0.67 V), high discharge rate capability (1.18 V at 20 mA cm-2), and long cycling stability (400 cycles), which are comparable or even superior to the mixture of state-of-the-art Pt/C and RuO2 cathode.
Abstract The fabrication of metal‐supported hybrid structures with enhanced properties typically requires external energy input, such as pyrolysis, photolysis, and electrodeposition. In this study, silver‐nanoparticle‐decorated transition‐metal hydroxide (TMH) composites were synthesized by an approach based on a spontaneous redox reaction (SRR) at room temperature. The SRR between silver ions and TMH provides a simple and facile route to establish effective and stable heterostructures that can enhance the oxygen evolution reaction (OER) activity. Ag@Co(OH) x grown on carbon cloth exhibits outstanding OER activity and durability, even superior to IrO 2 and many previously reported OER electrocatalysts. Experimental and theoretical analysis demonstrates that the strong electronic interaction between Ag and Co(OH) 2 activates the silver clusters as catalytically OER active sites, effectively optimizing the binding energies with reacted intermediates and facilitating the OER kinetics.
Abstract In this work, the core‐shelled Sb@Sb 2 O 3 heterostructure encapsulated in 3D N‐doped carbon hollow‐spheres is fabricated by spray‐drying combined with heat treatment. The novel core‐shelled heterostructures of Sb@Sb 2 O 3 possess a mass of heterointerfaces, which formed spontaneously at the core‐shell contact via annealing oxidation and can promote the rapid Na + /K + transfer. The density functional theory calculations revealed the mechanism and significance of Na/K‐storage for the core‐shelled Sb@Sb 2 O 3 heterostructure, which validated that the coupling between the high‐conductivity of Sb and the stability of Sb 2 O 3 can relieve the shortcomings of the individual building blocks, thereby enhancing the Na/K‐storage capacity. Furthermore, the core‐shell structure embedded in the 3D carbon framework with robust structure can further increase the electrode mechanical strength and thus buffer the severe volume changes upon cycling. As a result, such composite architecture exhibited a high specific capacity of ≈573 mA h g −1 for sodium‐ion battery (SIB) anode and ≈474 mA h g −1 for potassium‐ion battery (PIB) anode at 100 mA g −1 , and superior rate performance (302 mA h g −1 at 30 A g −1 for SIB anode, while 239 mA h g −1 at 5 A g −1 for PIB anode).
Surface decoration with metal atoms is an efficient way to improve the hydrogen storage capacity of graphene. The hydrogen adsorption behavior on Al-decorated graphene is studied based on first-principles calculations. The dissociation of hydrogen molecule adsorbed on Al-decorated graphene is revealed, and its effect on the hydrogen storage capacity is investigated. Moreover, the effects of B-dopant on the dispersion of Al atoms on graphene and the dissociation behavior of hydrogen molecules are also studied. Our results indicate that hydrogen dissociation behavior has a significant effect on the hydrogen storage capacity of metal-decorated graphene and must be considered in the investigation of hydrogen storage behavior of metal-decorated carbon nanomaterials. Furthermore, through a comparison study on the hydrogen adsorption behavior on Li-, Ca-, and Al-decorated graphene, the factors relating to the hydrogen molecule dissociation are revealed.
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