Electrodeposition of Self-Supported High-Entropy Spinel Oxides for Stable Oxygen Evolution.

Spinel oxides have attracted increasing interest due to their excellent activity in the oxygen evolution reaction (OER). However, despite the high intrinsic OER activity, their poor electrical conductivity and weak structural stability prevented their application for a long time. These shortcomings can be solved by effectively adjusting the electronic structures of spinel oxides through a high-entropy strategy. Herein, a rapid two-step method was developed to prepare self-supported high-entropy spinel-type oxides on a carbon cloth (CC) to yield (Fe0.2Co0.2Ni0.2Mn0.2Cr0.2)3O4@CC (abbreviated as FeCoNiMnCr@CC). The unique electronic structure and stable crystal configuration of the resulting FeCoNiMnCr@CC materials required only an overpotential of 287 mV for the OER at a current density of 10 mA cm-2 coupled with excellent cyclic stability. In summary, the proposed high-entropy strategy looks promising for improving the catalytic performance of spinel oxides.

Electron-ion conjugation sites co-constructed by defects and heteroatoms assisted carbon electrodes for high-performance aqueous energy storage.

Rapid preparation strategies of carbon-based materials with a high power density and energy density are crucial for the large-scale application of carbon materials in energy storage. However, achieving these goals quickly and efficiently remains challenging. Herein, the rapid redox reaction of concentrated H2SO4 and sucrose was employed as a means to destroy the perfect carbon lattice to form defects and insert large numbers of heteroatoms into the defects to rapidly form electron-ion conjugated sites of carbon materials at room temperature. Among prepared samples, CS-800-2 showed an excellent electrochemical performance (377.7 F g-1, 1 A g-1) and high energy density in 1 M H2SO4 electrolyte owing to its large specific surface area and a significant number of electron-ion conjugated sites. Additionally, CS-800-2 exhibited desirable energy storage performance in other aqueous electrolytes containing various metal ions. The theoretical calculation results revealed increased charge density near the carbon lattice defects, and the presence of heteroatoms effectively reduced the adsorption energy of carbon materials toward cations. Accordingly, the constructed "electron-ion" conjugated sites comprising defects and heteroatoms on the super-large surface of carbon-based materials accelerated the pseudo-capacitance reactions on the material surface, thereby greatly enhancing the energy density of carbon-based materials without sacrificing power density. In sum, a fresh theoretical perspective for constructing new carbon-based energy storage materials was provided, promising for future development of high-performance energy storage materials and devices.

Efficient fabrication of flower-like core-shell nanochip arrays of lanthanum manganate and nickel cobaltate for high-performance supercapacitors.

The low energy density issue raises serious concerns for the large-scale application of supercapacitors. However, the development and utilization of new electrode materials with a high specific capacity to improve the energy density of supercapacitors remain challenging. Herein, an LaMnO3@NiCo2O4/carbon cloth (LMO@NCO/CC) composed of a multilayer flower-like nanochip array is prepared for the first time using an efficient electrodeposition method. This novel structure exploits the high conductivity of LaMnO3/carbon cloth (LMO@CC) to provide an efficient electron transport path for the outer layer of the NiCo2O4/carbon cloth (NCO@CC) nanoarrays, broadening the potential window. Due to the unique nanostructure configuration and the strong synergistic effect of the developed LMO@NCO/CC, the prepared electrodes show excellent supercapacitor performance. At a current density of 1 A g-1, LMO@NCO/CC has a higher specific capacitance value of 942 F g-1. The application value is extended through the fabrication of asymmetric supercapacitors with a maximum energy density of 49 Wh kg-1 and excellent cycle stability (the initial capacitance value remains 106 % after 10,000 cycles of charging and discharging at a high current density of 10 A g-1). Our work paves the way for the development of next-generation electrode materials for high-performance supercapacitors.

Coaxial cable-like dual conductive channel strategy in polypyrrole coated perovskite lanthanum manganite for high-performance asymmetric supercapacitors.

Perovskite transition metal oxides are promising materials for supercapacitor electrodes due to their high theoretical capacities. However, these materials still suffer from poor conductivity, low specific capacitance, and moderate cycle stability, restraining their practical applications. In this study, LaMnO3@CC-PPy materials were prepared by two-step electrodeposition based on the inspiring design of coaxial cables. To this end, electrochemically active LaMnO3 was first grown on carbon cloth (CC) with good flexibility and conductivity and then followed by further coating with polypyrrole (PPy) layer. The best PPy load was identified by adjusting the deposition time. The resulting LaMnO3@CC-PPy electrodes showed excellent specific capacitance reaching 862F g-1 at 1 A g-1 with retention rate of 75% at high current density of 10 A g-1, indicative of excellent rate performance. The cycle stability of the electrodes also improved after 3000 cycles at 10 A g-1 with a retention rate reaching 66%. To assemble asymmetric supercapacitor (ASC) devices, NiCo2O4@CC cathodes were prepared by electrodeposition. Ultra-high energy density of about 73 Wh kg-1 and good cycle stability were recorded with the devices. The high performance of the as-obtained materials was attributed to the existence of internal and external double electric channels, as well as the abundant internal space. These features ensured good conductivity, rapid charge transfer, and fast ion diffusion, thereby significantly improving the overall material cycle stability. In sum, these findings look promising for future preparation of high-performance perovskite supercapacitors.