Yida Deng

Sub-3 nm Co3O4 Nanofilms with Enhanced Supercapacitor Properties

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 Co3O4 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 Co3O4 nanofilms exhibited an ultrahigh specific capacitance of 1400 F/g in the first galvanostatic charge/discharge test. The specific capacitance of Co3O4 nanofilms only slightly decayed less than 3% after 1500 cycling tests. With some parameter adjustments, similar Co(OH)2 nanofilms with a thickness of 3.70 ± 0.10 nm were also prepared. The Co(OH)2 nanofilms possessed maximum specific capacitance of 1076 F/g and peak performance attenuation of about 2% after a cycle stability test.

Pt-Decorated highly porous flower-like Ni particles with high mass activity for ammonia electro-oxidation

Pt-Decorated Ni particles with different surface morphologies were directly prepared on a conducting substrate for use as electrocatalysts for ammonia electro-oxidation. The whole preparation process avoided the use of surfactants, binders, and reducing and capping agents. Flower-like Ni particles consisting of interconnected thin nanosheets and featureless Ni particles with a relatively smooth surface were obtained by controlling the electrodeposition potential. Pt-Decorated Ni particles were prepared by the galvanic replacement reaction between Ni particles and Pt2+ ions. The surface morphology and chemical composition of Pt-decorated Ni particles were characterized by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The Pt loading was determined by an inductively coupled plasma method, and the electrocatalytic activity of the prepared electrocatalysts was characterized by cyclic voltammetry. The results showed that there is a significant effect of the surface morphology of Ni particles and the Pt replacement time on the electrocatalytic activity. In particular, Pt-decorated flower-like Ni particles with a highly porous structure exhibited a high mass activity of 75.32 mA mg−1, which was 2 times higher than that of commercial Pt/C catalysts. The improved activity is attributed not only to the highly porous flower-like morphology, but also to the presence of nanopores and small 2–3 nm sized Pt grains with good dispersion on the petals of flower-like particles.

Atomically Thin Mesoporous Co3O4 Layers Strongly Coupled with N‐rGO Nanosheets as High‐Performance Bifunctional Catalysts for 1D Knittable Zinc–Air Batteries

Under development for next-generation wearable electronics are flexible, knittable, and wearable energy-storage devices with high energy density that can be integrated into textiles. Herein, knittable fiber-shaped zinc-air batteries with high volumetric energy density (36.1 mWh cm-3 ) are fabricated via a facile and continuous method with low-cost materials. Furthermore, a high-yield method is developed to prepare the key component of the fiber-shaped zinc-air battery, i.e., a bifunctional catalyst composed of atomically thin layer-by-layer mesoporous Co3 O4 /nitrogen-doped reduced graphene oxide (N-rGO) nanosheets. Benefiting from the high surface area, mesoporous structure, and strong synergetic effect between the Co3 O4 and N-rGO nanosheets, the bifunctional catalyst exhibits high activity and superior durability for oxygen reduction and evolution reactions. Compared to a fiber-shaped zinc-air battery using state-of-the-art Pt/C + RuO2 catalysts, the battery based on these Co3 O4 /N-rGO nanosheets demonstrates enhanced and stable electrochemical performance, even under severe deformation. Such batteries, for the first time, can be successfully knitted into clothes without short circuits under external forces and can power various electronic devices and even charge a cellphone.

Shape-controlled synthesis of Pt-Ir nanocubes with preferential (100) orientation and their unusual enhanced electrocatalytic activities

Pt-Ir nanocubes with (100)-terminated facets were synthesized for the first time and their unusual high electrocatalytic activity for a model reaction (i.e., ammonia oxidation) was reported. The key parameters in controlling the shape of the Pt-Ir nanocubes were systematically investigated by transmission electron microscopy (TEM). The electrocatalytic activities of the prepared Pt-Ir and pure Pt nanoparticles (NPs) were characterized by cyclic voltammetry (CV). The results showed that the amount of W(CO)6 and the volume ratio of oleylamine and oleic acid play a significant role in the development of well-defined Pt-Ir nanocubes. The resultant Pt-Ir nanocubes exhibit (100) orientation, which has been confirmed by not only the structural characterization results from high-resolution TEM (HRTEM) and X-ray diffraction (XRD) but also hydrogen desorption profiles obtained from the CV measurements in H2SO4 solution. Lattice contraction of the Pt-Ir nanocubes were suggested by HRTEM and XRD measurements, and the electronic interactions between Pt and Ir in the Pt-Ir nanocubes were demonstrated by X-ray photoelectron spectroscopy. The Pt-Ir nanocubes show higher specific activity than pure Pt nanocubes and much higher specific activity than the polycrystalline Pt-Ir NPs. The much improved specific activity of the Pt-Ir nanocubes could be attributed to the reason that the introduction of Ir in the Pt-Ir nanocubes largely maintains the highly active Pt (100) sites and thus a positive synergistic effect through the addition of Ir to Pt could be achieved due to the possible bifunctional mechanism and the electronic effect.摘要同时控制纳米贵金属颗粒的形状(表面原子结构)和成分对进一步提升其性能具有重要意义. 针对铂铱合金纳米颗粒, 已有研究发现铱原子的引入会降低铂基合金纳米颗粒在一些体系中的催化活性. 本文首次制备了具有(100)择优晶面的铂铱立方体纳米颗粒, 并在一(100)敏感的模型反应(即氨的电催化氧化反应)中, 发现其特殊的高催化活性. 所制备的铂铱立方体纳米颗粒具有规则的(100)晶面特征, 并伴随有晶格收缩现象, 此外铂和铱存在电子交互作用. 铂铱立方体纳米颗粒的特定催化活性高于纯铂纳米颗粒, 并远高于普通多晶铂铱纳米颗粒. 该现象一方面可归因于具有高催化活性的铂(100)活性点, 另一方面可归因于铱和铂的协同效应. 以上研究结果表明, 在铂基合金纳米颗粒形状可控的前提下, 引入铱原子可进一步提升其催化活性, 这对于发展具有高催化活性的贵金属纳米颗粒具有一定的指导意义.

Morphology-Controllable Synthesis of Zn–Co-Mixed Sulfide Nanostructures on Carbon Fiber Paper Toward Efficient Rechargeable Zinc–Air Batteries and Water Electrolysis

It remains an ongoing challenge to develop cheap, highly active, and stable electrocatalysts to promote the sluggish electrocatalytic oxygen evolution, oxygen reduction, and hydrogen evolution reactions for rechargeable metal-air batteries and water-splitting systems. In this work, we report the morphology-controllable synthesis of zinc cobalt mixed sulfide (Zn-Co-S) nanoarchitectures, including nanosheets, nanoplates, and nanoneedles, grown on conductive carbon fiber paper (CFP) and the micronanostructure dependent electrochemical efficacy for catalyzing hydrogen and oxygen in zinc-air batteries and water electrolysis. The formation of different Zn-Co-S morphologies was attributed to the synergistic effect of decomposed urea products and the corrosion of NH4F. Among synthesized Zn-Co-S nanostructures, the nanoneedle arrays supported on CFP exhibit superior trifunctional activity for oxygen reduction, oxygen evolution, and hydrogen evolution reactions than its nanosheet and nanoplate counterparts through half reaction testing. It also exhibited better catalytic durability than Pt/C and RuO2. Furthermore, the Zn-Co-S nanoneedle/CFP electrode enables rechargeable Zn-air batteries with low overpotential (0.85 V), high efficiency (58.1%), and long cycling lifetimes (200 cycles) at 10 mA cm-2 as well as considerable performance for water splitting. The superior performance is contributed to the integrated nanoneedle/CFP nanostructure, which not only provides enhanced electrochemical active area, but also facilitates ion and gas transfer between the catalyst surface and electrolyte, thus maintaining an effective solid-liquid-gas interface necessary for electrocatalysis. These results indicate that the Zn-Co-S nanoneedle/CFP system is a low cost, highly active, and durable electrode for highly efficient rechargeable zinc-air batteries and water electrolysis in alkaline solution.

Clarifying the Controversial Catalytic Performance of Co(OH)2 and Co3O4 for Oxygen Reduction/Evolution Reactions toward Efficient Zn–Air Batteries

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.

Hollow Co3O4 microspheres with nano-sized shells: one-step large-scale synthesis, growth mechanism and supercapacitor properties

Hollow Co3O4 microspheres with thin spherical shells were produced using a one-step method at a low hydrothermal temperature (120 °C), and could be obtained without the use of a solid template, organic reagent or subsequent calcination. These hollow Co3O4 microspheres possess a diameter of ca. 500 nm and a thin shell thickness of ca. 50 nm. The samples were characterized by field emission scanning electron microscope (SEM), transmission electron microscope (TEM) and powder X-ray diffraction (PXRD). A multistep-splitting growth mechanism was proposed to reveal the formation of hollow Co3O4 microspheres. The successful fabrication of the hollow spherical morphology of these microspheres highlighted the importance of H2O2 dosage and the nitrate concentration. Electrochemical performance tests of the as-prepared samples indicated that the hollow Co3O4 microspheres exhibited ultrahigh specific capacitances of 1227, 1169, 1116, 1035 F g−1 at current densities of 1, 2, 4, 8 A g−1, respectively. After 1000 cycles, the specific capacitance of hollow Co3O4 microspheres showed high charge–discharge reversibility and only a slight decay of less than 3% at a current density of 2 A g−1.

Synthesis of Cubic-Shaped Pt Particles with (100) Preferential Orientation by a Quick, One-Step and Clean Electrochemical Method

A new approach has been developed for in situ preparing cubic-shaped Pt particles with (100) preferential orientation on the surface of the conductive support by using a quick, one-step, and clean electrochemical method with periodic square-wave potential. The whole electrochemical deposition process is very quick (only 6 min is required to produce cubic Pt particles), without the use of particular capping agents. The shape and the surface structure of deposited Pt particles can be controlled by the lower and upper potential limits of the square-wave potential. For a frequency of 5 Hz and an upper potential limit of 1.0 V (vs saturated calomel electrode), as the lower potential limit decreases to the H adsorption potential region, the Pt deposits are changed from nearly spherical particles to cubic-shaped (100)-oriented Pt particles. High-resolution transmission electron microscopy and selected-area electron diffraction reveal that the formed cubic Pt particles are single-crystalline and enclosed by (100) facets. Cubic Pt particles exhibit characteristic H adsorption/desorption peaks corresponding to the (100) preferential orientation. Ge irreversible adsorption indicates that the fraction of wide Pt(100) surface domains is 47.8%. The electrocatalytic activities of different Pt particles are investigated by ammonia electro-oxidation, which is particularly sensitive to the amount of Pt(100) sites, especially larger (100) domains. The specific activity of cubic Pt particles is 3.6 times as high as that of polycrystalline spherical Pt particles, again confirming the (100) preferential orientation of Pt cubes. The formation of cubic-shaped Pt particles is related with the preferential electrochemical deposition and dissolution processes of Pt, which are coupled with the periodic desorption and adsorption processes of O-containing species and H adatoms.

Preparation, characterization and microwave absorbing properties of nano-sized yolk-in-shell Ni–P nanospheres

In this work, preparation of novel yolk-in-shell Ni–P nanospheres (YNNs) can be fulfilled through a facile method. Via adding sufficient amount of sodium dodecyl benzene sulfonate (SDBS) as a surfactant, stable and uniform Ni(OH)2 colloids were prepared firstly as precursors. Meanwhile, with adding a moderate amount of PVP, PdCl2 and NaH2PO2, yolk-in-shell and well-dispersed nanoparticles have been successfully fabricated. A string of means of characterizations were exploited to analyse their contents, structures and physical properties. In the present situation where the electro-magnetic interference (EMI) is ubiquitous, the YNNs have shown remarkable microwave-absorbing properties, with a minimum reflection loss () −39.9 dB at 1.7 mm of sample thickness. Besides, the of a sample is closely related to its thickness, which makes YNNs a potential EM absorber for the future.

Fabrication and microwave absorbing properties of NixPy nanotubes

Materials possessing microwave absorbing properties have been a researching hotspot for their important applications amid a high frequency electromagnetic waves environment. This paper focuses on the preparation of a series of NixPy(x:y = 2.65–2.73) nanotubes (NTs) and their corresponding microwave absorbing properties. After being heat-treated, different NixPy phases would appear, without damaging their initial hollow morphologies. These processes were accompanied with the alteration of related physical properties. Low enough minimum reflection loss (RL) has been achieved in all of these samples, with −48.63 dB as the lowest one being obtained at the non-heat-treated sample. Besides, a large proportion of the microwave frequency band could be covered on the 450 °C heat-treated sample (over a 4.5 GHz bandwidth). These are indicative of the superior microwave absorbing nature of NixPy NTs.