Matching CP@NCOH/NF Cathode and GH/FNP/NF Anode for High-Performance Asymmetric Supercapacitor

Gas-Phase-Induced Engineering for Fabrication of 3D Hierarchical Porous Nickel and Its Application toward High-Performance Supercapacitors

Commercial nickel foam (NF), which is composed of numerous interconnected ligaments and hundred-micron pores, is widely acknowledged as a current collector/electrode material for catalysis, sensing, and energy storage applications. However, the commonly used NF often does not work satisfactorily due to its smooth surface and hollow structure of the ligaments. Herein, a gas-phase-induced engineering, two-step gaseous oxidation-reduction (GOR) is presented to directly transform the thin-walled hollow ligament of NF into a three-dimensional (3D) nanoporous prism structure, resulting in the fabrication of a unique hierarchical porous nickel foam (HPNF). This 3D nanoporous architecture is achieved by utilizing the spontaneous reconstruction of nickel atoms during volume expansion and contraction in the GOR process. The process avoids the involution of acid-base corrosion and sacrificial components, which are facile, environmentally friendly, and suitable for large-scale fabrication. Furthermore, MnO2 is electrochemically deposited on the HPNF to form a supercapacitor electrode (HPNF/MnO2). Because of the fully open structure for ion transport, superhydrophilic properties, and the increased contact area between MnO2 and the current collector, the HPNF/MnO2 electrode exhibits a high specific capacitance of 997.5 F g-1 at 3 A g-1 and remarkable cycling stability with 99.6% capacitance retention after 20000 cycles in 0.1 M Na2SO4 electrolyte, outperforming most MnO2-based supercapacitor electrodes.

Construction of CoNi2S4/Co9S8@Co4S3 nanocubes derived from Ni-Co prussian blue analogues@cobalt carbonate hydroxide core-shell heterostructure for asymmetric supercapacitor

Construction of Prussian blue analogues (PBAs) with heterostructure is beneficial to preparing PBAs derivatives with superior electrochemical performance. In this work, the core-shell nanostructured nanocubes composed of nickel hexacyanocobalt PBA (NiCo-PBA)@cobalt carbonate hydroxide (CCH) are synthesized through an in-situ epitaxial growth strategy, and the formation mechanisms of coating are carefully validated and specifically discussed. Then, the precursors are successfully transformed into hierarchical CoNi2S4/Co9S8@Co4S3 via the gas-phase vulcanization method. Benefiting from the intriguing heterostructure and multicomponent sulfides, the CoNi2S4/Co9S8@Co4S3-80 electrode exhibits a high specific capacity of 799 ± 16C/g (specific capacitance of 1595 ± 31F/g) at 1 A/g, ultra-high capacity retention of 80 % at a high current density of 20 A/g. The assembled asymmetric supercapacitor (ASC) device delivers a high energy density of 43.3 Wh kg-1 at a power density of 899 W kg-1 and exhibits superior cycling stability with the capacity retention of 88 % after 5,000 cycles. Subsequently, the fabricated all-solid-state ASC device shows an excellent energy density of 36.4 Wh kg-1 with a power density of 824 W kg-1. This work proposing rational design of combining multicomponent sulfides and core-shell heterostructure based on PBA nanocubes opens up a novel route for developing asymmetric supercapacitor electrode materials with superior performance.

Rational Design of High-Performance Electrodes Based on Ferric Oxide Nanosheets Deposited on Reduced Graphene Oxide for Advanced Hybrid Supercapacitors

The core strategy for constructing ultra-high-performance hybrid supercapacitors is the design of reasonable and effective electrode materials. Herein, a facile solvothermal-calcination strategy is developed to deposit the phosphate-functionalized Fe2O3 (P-Fe2O3) nanosheets on the reduced graphene oxide (rGO) framework. Benefiting from the superior conductivity of rGO and the high conductivity and fast charge storage dynamics of phosphate ions, the synthesized P-Fe2O3/rGO anode exhibits remarkable electrochemical performance with a high capacitance of 586.6 F g-1 at 1 A g-1 and only 4.0% capacitance loss within 10 000 cycles. In addition, the FeMoO4/Fe2O3/rGO nanosheets are fabricated by utilizing Fe2O3/rGO as the precursor. The introduction of molybdates successfully constructs open ion channels between rGO layers and provides abundant active sites, enabling the excellent electrochemical features of FeMoO4/Fe2O3/rGO cathode with a splendid capacity of 475.4 C g-1 at 1 A g-1. By matching P-Fe2O3/rGO with FeMoO4/Fe2O3/rGO, the constructed hybrid supercapacitor presents an admirable energy density of 82.0 Wh kg-1 and an extremely long working life of 95.0% after 20 000 cycles. Furthermore, the continuous operation of the red light-emitting diode for up to 30 min demonstrates the excellent energy storage properties of FeMoO4/Fe2O3/rGO//P-Fe2O3/rGO, which provides multiple possibilities for the follow-up energy storage applications of the iron-based composites.

High-performance aqueous rechargeable NiCo//Zn battery with molybdate anion intercalated CoNi-LDH@CP bilayered cathode

Seeking cathode materials with high areal capacity and excellent cycling tolerance is a key step to develop aqueous rechargeable zinc-based alkaline batteries with high energy density, power density and excellent stability. Here, the bilayered cathode composite (MCN-LDH@CP) of molybdate intercalated cobalt-nickel layered hydroxide nanosheets (MCN-LDH) grown on cobalt phosphate octahydrate microsheet (CP) was prepared by a two-step hydrothermal process. Molybdate intercalation significantly reduces the thickness of cobalt-nickel layered hydroxide, greatly increases its specific surface area, regulates its pore distribution, increases the crystal plane spacing, promotes the diffusion rate of hydroxide in it, and increases its specific capacity. Meanwhile, the bilayered MCN-LDH@CP electrode significantly improved the areal energy density (2.89 mWh/cm2) and peak power density (111.22 mW/cm2) and cycle stability (97.8 % after 7000 cycles) of the CoNi//Zn battery. The excellent stability is mainly due to the fact that the MCN-LDH overlay inhibits the loss of P element of CP and improves the structural stability of the sample. The quasi-solid-state MCN-LDH@CP//Zn battery can still charge a mobile phone even when hammered and pierced, showing excellent safety and reliability. This work opens a new avenue to develop CoNi//Zn batteries with high energy density, power density and excellent tolerance.

Construction of Binder-Free, Self-Supported, Hetero-Core-Shell Honeycomb Structured CuCo2 O4 @Ni0.5 Co0.5 (OH)2 with Abundant Mesopores and High Conductivity for High-Performance Energy Storage

Clever and rational design of structural hierarchy, along with precise component adjustment, holds profound significance for the construction of high-performance supercapacitor electrode materials. In this study, a binder-free self-supported CCO@N0.5 C0.5 OH/NF cathode material is constructed with hierarchical hetero-core-shell honeycomb nanostructure by first growing CuCo2 O4 (CCO) nanopin arrays uniformly on highly conductive nickel foam (NF) substrate, and then anchoring Ni0.5 Co0.5 (OH)2 (N0.5 C0.5 OH) bimetallic hydroxide nanosheet arrays on the CCO nanopin arrays by adjusting the molar ratio of Ni(OH)2 and Co(OH)2 . The constructed CCO@N0.5 C0.5 OH/NF electrode material showcases a wealth of multivalent metal ions and mesopores, along with good electrical conductivity, excellent electrochemical reaction rates, and robust long-term performance (capacitance retention rate of 87.2%). The CCO@N0.5 C0.5 OH/NF electrode, benefiting from the hierarchical structure of the material and the exceptional synergy between multiple components, demonstrates an excellent specific capacitance (2553.6 F g-1 at 1 A g-1 ). Furthermore, the assembled asymmetric CCO@N0.5 C0.5 OH/NF//AC/NF supercapacitor demonstrates a high energy density (70.1 Wh kg-1 at 850 W kg-1 ), and maintains robust capacitance cycling stability performance (83.7%) after undergoing 10 000 successive charges and discharges. It is noteworthy that the assembled supercapacitor exhibits an operating voltage (1.7 V) that is well above the theoretical value (1.5 V).

In-situ electrodeposited Co0.85Se@Ni3S2 heterojunction with enhanced performance for supercapacitors

Rational design of porous heterostructured electrode materials for high-performance supercapacitors remains a big challenge. Herein, we report the in situ synthesis of Co0.85Se@Ni3S2 hybrid nanosheet arrays supported on carbon cloth (CC) substrate though an efficient two-step electrodeposition method. Compared with pure Co0.85Se and Ni3S2, the well-defined Co0.85Se@Ni3S2 heterojunction possesses enriched active sites, improved electrical conductivity, and reduced ion diffusion resistance. Benefiting from its hierarchically porous nanostructure and the synergistic effect of Co0.85Se and Ni3S2, the as-synthesized Co0.85Se@Ni3S2 electrode delivers a gravimetric capacitance (Cg)/volumetric capacitance (Cv) of 1644.1F g-1/3161.7F cm-3 at 1 A g-1, outstanding rate capability of 60.7% capacitance retention at 20 A g-1, as well as good cycling performance of 87.8% capacitance retention after 5000 cycles. Additionally, a hybrid supercapacitor (HSC) device presents a maximum energy density (E) of 65.7 Wh kg-1 at 696.2 W kg-1 with 93.3% cyclic durability after 15,000 cycles. Thus, this work proposes a simple and effective strategy to fabricate porous heterojunctions as high-performance electrode materials for energy storage devices.

Electrode Materials, Structural Design, and Storage Mechanisms in Hybrid Supercapacitors

Currently, energy storage systems are of great importance in daily life due to our dependence on portable electronic devices and hybrid electric vehicles. Among these energy storage systems, hybrid supercapacitor devices, constructed from a battery-type positive electrode and a capacitor-type negative electrode, have attracted widespread interest due to their potential applications. In general, they have a high energy density, a long cycling life, high safety, and environmental friendliness. This review first addresses the recent developments in state-of-the-art electrode materials, the structural design of electrodes, and the optimization of electrode performance. Then we summarize the possible classification of hybrid supercapacitor devices, and their potential applications. Finally, the fundamental theoretical aspects, charge-storage mechanism, and future developing trends are discussed. This review is intended to provide future research directions for the next generation of high-performance energy storage devices.