In this study, a novel Co3O4/Co(OH)2 heterostructure is obtained via electrodeposition on nickel (Ni) foam, forming sandwich‐like structure and freestanding electrode. The outer Co(OH)2 with layered ...structure can provide sufficient absorption sites and enable facile ion intercalation, meanwhile the presence of a conductive and robust interfacial Co3O4 layer between Ni foam and Co(OH)2 is found effectively minimizes the charge transfer resistance and stabilizes the interface, thus improving the electrode's rate and cycling performance with high capacity preserved synergistically. Furthermore, the structural evolution of Co(OH)2 and Co3O4 upon cycling are elucidated systematically using a series of in situ and ex situ techniques. The Co(OH)2 is found irreversibly changed to CoOOH upon first charge, which is then reversibly converted to CoO2 during the subsequent charge–discharge cycles. The Co3O4 exhibits negligible phase changes of the bulk upon cycling, indicating its good structural integrity that contributes to the significantly improved cyclability. In general, this work not only offers an ease and effective approach to optimize the charge storage properties of Co3O4/Co(OH)2 heterostructure via interfacial layer control, but also provides valuable insights in understanding their charge storage mechanisms, which may inspire the development of more heterostructures or extend to other applications.
Interfacial layer control of freestanding sandwich‐like Co3O4/Co(OH)2 heterostructure is reported as a generalized and effective approach to optimize the electrode's charge storage properties, leading to improved rate and cycle performance. This work also provides valuable insights in understanding the charge storage mechanisms of Co3O4 and Co(OH)2, which will promote the rational design of more heterostructures with excellent electrochemical performance.
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Efficient and reliable energy storage systems are crucial for our modern society. Lithium-ion batteries (LIBs) with excellent performance are widely used in portable electronics and ...electric vehicles (EVs), but frequent fires and explosions limit their further and more widespread applications. This review summarizes aspects of LIB safety and discusses the related issues, strategies, and testing standards. Specifically, it begins with a brief introduction to LIB working principles and cell structures, and then provides an overview of the notorious thermal runaway, with an emphasis on the effects of mechanical, electrical, and thermal abuse. The following sections examine strategies for improving cell safety, including approaches through cell chemistry, cooling, and balancing, afterwards describing current safety standards and corresponding tests. The review concludes with insights into potential future developments and the prospects for safer LIBs.
In this work, we report the fabrication of a new 3D graphene foam (GF)/carbon nanotube (CNT) hybrid film with high flexibility and robustness as the ideal support for deposition of large amounts of ...electrochemically active materials per unit area. To demonstrate the concept, we have deposited MnO sub(2) and polypyrrole (Ppy) on the GF/CNT films and successfully fabricated lightweight and flexible asymmetric supercapacitors (ASCs). These ASCs assembled from GF/CNT/MnO sub(2) and GF/CNT/Ppy hybrid films with high loading of electroactive materials in an aqueous electrolyte are able to function with an output voltage of 1.6 V, and deliver high energy/power density (22.8 W h kg super(-1) at 860 W kg super(-1) and 2.7 kW kg super(-1) at 6.2 W h kg super(-1)). The rate performance can be further improved with less loading of electroactive materials (10.3 kW kg super(-1) at 10.9 W h kg super(-1)). The ASCs demonstrate remarkable cycling stability (capacitance retention of 90.2-83.5% after 10 000 cycles), which is among the best reported for ASCs with both electrodes made of non-carbon electroactive materials. Also the ASCs are able to perfectly retain their electrochemical performance at different bending angles. These ASCs demonstrate great potential as power sources for flexible and lightweight electronic devices.
Sodium-ion batteries are a potentially low-cost and safe alternative to the prevailing lithium-ion battery technology. However, it is a great challenge to achieve fast charging and high power density ...for most sodium-ion electrodes because of the sluggish sodiation kinetics. Here we demonstrate a high-capacity and high-rate sodium-ion anode based on ultrathin layered tin(II) sulfide nanostructures, in which a maximized extrinsic pseudocapacitance contribution is identified and verified by kinetics analysis. The graphene foam supported tin(II) sulfide nanoarray anode delivers a high reversible capacity of ∼1,100 mAh g(-1) at 30 mA g(-1) and ∼420 mAh g(-1) at 30 A g(-1), which even outperforms its lithium-ion storage performance. The surface-dominated redox reaction rendered by our tailored ultrathin tin(II) sulfide nanostructures may also work in other layered materials for high-performance sodium-ion storage.
Studies have found that oxygen-rich-containing functional groups in carbon-based materials can be used as active sites for the storage performance of K
+
, but the basic storage mechanism is still ...unclear. Herein, we construct and optimize 3D honeycomb-like carbon grafted with plentiful COOH/C = O functional groups (OFGC) as anodes for potassium ion batteries. The OFGC electrode with steady structure and rich functional groups can effectively contribute to the capacity enhancement and the formation of stable solid electrolyte interphase (SEI) film, achieving a high reversible capacity of 230 mAh g
−1
at 3000 mA g
−1
after 10,000 cycles (almost no capacity decay) and an ultra-long cycle time over 18 months at 100 mA g
−1
. The study results revealed the reversible storage mechanism between K
+
and COOH/C = O functional groups by forming C-O-K compounds. Meanwhile, the in situ electrochemical impedance spectroscopy proved the highly reversible and rapid de/intercalation kinetics of K
+
in the OFGC electrode, and the growth process of SEI films. In particular, the full cells assembled by Prussian blue cathode exhibit a high energy density of 113 Wh kg
−1
after 800 cycles (calculated by the total mass of anode and cathode), and get the light-emitting diodes lamp and ear thermometer running.
While it has long been known that different types of support oxides have different capabilities to anchor metals and thus tailor the catalytic behavior, it is not always clear whether the support is ...a mere carrier of the active metal site, itself not participating directly in the reaction pathway. We report that catalytically similar single-atom-centric Pt sites are formed by binding to sodium ions through −O ligands, the ensemble being equally effective on supports as diverse as TiO2, L-zeolites, and mesoporous silica MCM-41. Loading of 0.5 wt % Pt on all of these supports preserves the Pt in atomic dispersion as Pt(II), and the Pt–O(OH) x – species catalyzes the water-gas shift reaction from ∼120 to 400 °C. Since the effect of the support is “indirect,” these findings pave the way for the use of a variety of earth-abundant supports as carriers of atomically dispersed platinum for applications in catalytic fuel-gas processing.
Abstract
Despite the maximized metal dispersion offered by single-atom catalysts, further improvement of intrinsic activity can be hindered by the lack of neighboring metal atoms in these systems. ...Here we report the use of isolated Pt
1
atoms on ceria as “seeds” to develop a Pt-O-Pt ensemble, which is well-represented by a Pt
8
O
14
model cluster that retains 100% metal dispersion. The Pt atom in the ensemble is 100–1000 times more active than their single-atom Pt
1
/CeO
2
parent in catalyzing the low-temperature CO oxidation under oxygen-rich conditions. Rather than the Pt-O-Ce interfacial catalysis, the stable catalytic unit is the Pt-O-Pt site itself without participation of oxygen from the 10–30 nm-size ceria support. Similar Pt-O-Pt sites can be built on various ceria and even alumina, distinguishable by facile activation of oxygen through the paired Pt-O-Pt atoms. Extending this design to other reaction systems is a likely outcome of the findings reported here.
The nitrogenous nucleophile electrooxidation reaction (NOR) plays a vital role in the degradation and transformation of available nitrogen. Focusing on the NOR mediated by the β‐Ni(OH)2 electrode, we ...decipher the transformation mechanism of the nitrogenous nucleophile. For the two‐step NOR, proton‐coupled electron transfer (PCET) is the bridge between electrocatalytic dehydrogenation from β‐Ni(OH)2 to β‐Ni(OH)O, and the spontaneous nucleophile dehydrogenative oxidation reaction. This theory can give a good explanation for hydrazine and primary amine oxidation reactions, but is insufficient for the urea oxidation reaction (UOR). Through operando tracing of bond rupture and formation processes during the UOR, as well as theoretical calculations, we propose a possible UOR mechanism whereby intramolecular coupling of the N−N bond, accompanied by PCET, hydration and rearrangement processes, results in high performance and ca. 100 % N2 selectivity. These discoveries clarify the evolution of nitrogenous molecules during the NOR, and they elucidate fundamental aspects of electrocatalysis involving nitrogen‐containing species.
During urea electrooxidation over a Ni(OH)2 electrode the dehydrogenation reaction from β‐Ni(OH)2 to β‐Ni(OH)O can lead to spontaneous urea dehydrogenation. Spontaneous intramolecular coupling of the N−N bond and hydration of urea dehydrogenation intermediates play important roles in the oxidation path from urea to N2 and CO2.
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