Asymmetric supercapacitors by integrating high content Na+/K+-inserted MnO2 nanosheets and layered Ti3C2Tx paper

High-Performance Battery-Type Supercapacitors Based on Self-Oriented Growth of Nanorods/Nanospheres Composite Assembled on Self-Standing Conductive GO/CNF Frameworks

MnOx-based materials have limited capacity and poor conductivity over various voltages, hampering their potential for energy storage applications. This work proposes a novel approach to address these challenges. A self-oriented multiple-electronic structure of a 1D-MnO2-nanorod/2D-Mn2O3-nanosphere composite was assembled on 2D-graphene oxide nanosheet/1D-carbon nanofiber (GO/CNF) hybrids. Aided by K+ ions, the MnO2 nanorods were partially converted to Mn2O3 nanospheres, while the GO nanosheets were combined with CNF through hydrogen bonds resulting in a unique double binary 1D-2D mixed morphology of MnO2/Mn2O3-GO/CNF hybrid, having a novel mechanism of multiple Mn ion redox reactions facilitated by the interconnected 3D network. The morphology of the MnO2 nanorods was controlled by regulating the potassium ion content through a rinsing strategy. Interestingly, pure MnO2 nanorods undergo air-annealing to form a mixture of nanorods and nanospheres (MnO2/Mn2O3) with a distinct morphology indicating pseudocapacitive surface redox reactions involving Mn2+, Mn3+, and Mn4+. In the presence of the GO/CNF framework, the charge storage properties of the MnO2/Mn2O3-GO/CNF composite electrode show dominant battery-type behavior because of the unique mesoporous structure with a crumpled morphology that provides relatively large voids and cavities with smaller diffusion paths to facilitate the accumulation/intercalation of charges at the inner electroactive sites for the diffusion-controlled process. The corresponding specific capacity of 800 C g-1 or 222.2 mAh g-1 at 1 A g-1 and remarkable cycling stability (95%) over 5000 cycles at 3 A g-1 were considerably higher than those of the reported electrodes of similar materials. Moreover, a hybrid supercapacitor device is assembled using MnO2/Mn2O3-GO/CNF as the positive electrode and activated carbon as the negative electrode, which exhibits a superior maximum energy density (∼25 Wh kg-1) and maximum power density (∼4.0 kW kg-1). Therefore, the as-synthesized composite highlights the development of highly active low-cost materials for next-generation energy storage applications.

Sodium Pre-Intercalation-Based Na3-δ-MnO2@CC for High-Performance Aqueous Asymmetric Supercapacitor: Joint Experimental and DFT Study

Electrochemical energy storage devices are ubiquitous for personal electronics, electric vehicles, smart grids, and future clean energy demand. SCs are EES devices with excellent power density and superior cycling ability. Herein, we focused on the fabrication and DFT calculations of Na₃-δ-MnO₂ nanocomposite, which has layered MnO₂ redox-active sites, supported on carbon cloth. MnO₂ has two-dimensional diffusion channels and is not labile to structural changes during intercalation; therefore, it is considered the best substrate for intercalation. Cation pre-intercalation has proven to be an effective way of increasing inter-layered spacing, optimizing the crystal structure, and improving the relevant electrochemical behavior of asymmetric aqueous supercapacitors. We successfully established Na⁺ pre-intercalated δ-MnO₂ nanosheets on carbon cloth via one-pot hydrothermal synthesis. As a cathode, our prepared material exhibited an extended potential window of 0-1.4 V with a remarkable specific capacitance of 546 F g^-1(300 F g^-1 at 50 A g^-1). Moreover, when this cathode was accompanied by an N-AC anode in an asymmetric aqueous supercapacitor, it illustrated exceptional performance (64 Wh kg^-1 at a power density of 1225 W kg^-1) and incomparable potential window of 2.4 V and 83% capacitance retention over 10,000 cycles with a great Columbic efficiency.

Effect of Hydrothermal Method Temperature on the Spherical Flowerlike Nanostructures NiCo(OH)4-NiO

NiCo(OH)4-NiO composite electrode materials were prepared using hydrothermal deposition and electrophoretic deposition. NiCo(OH)4 is spherical and flowerlike, composed of nanosheets, and NiO is deposited on the surface of NiCo(OH)4 in the form of nanorods. NiCo(OH)4 has a large specific surface area and can provide more active sites. Synergistic action with NiO deposits on the surface can provide a higher specific capacitance. In order to study the influence of hydrothermal reaction temperature on the properties of NiCo(OH)4, the prepared materials of NiCo(OH)4-NiO, the hydrothermal reaction temperatures of 70 °C, 90 °C, 100 °C, and 110 °C were used for comparison. The results showed that the NiCo(OH)4-NiO-90 specific capacitance of the prepared electrode material at its maximum when the hydrothermal reaction temperature is 90 °C. The specific capacitance of the NiCo(OH)4-NiO-90 reaches 2129 F g−1 at the current density of 1 A g−1 and remains 84% after 1000 charge–discharge cycles.

Freestanding trimetallic Fe-Co-Ni phosphide nanosheet arrays as an advanced electrode for high-performance asymmetric supercapacitors

Transition metal phosphides hold great promise for high performance battery-type electrode materials due to their superb electrical conductivity and high theoretical capacity. Unfortunately, the electrochemical properties of single metal or bimetallic phosphides are unsatisfactory owing to their low energy density and poor cyclic stability, and one feasible approach is to introduce heteroatoms to form trimetallic phosphides. Here, novel Fe-Co-Ni-P nanosheet arrays are in situ synthesized on a flexible carbon cloth substrate via an electrodeposition method followed by a phosphorization treatment. Due to the presence of abundant redox active sites, large specific surface area with mesoporous channels, desirable electrical conductivity, modified electronic structure, and synergistic effect of Fe, Co, and Ni ions, the as-prepared Fe-Co-Ni-P electrode displays significantly enhanced electrochemical performance when compared to bimetallic phosphides Fe-Co-P and Fe-Ni-P. Remarkably, the Fe-Co-Ni-P electrode exhibits a large specific capacity of 593.0 C g^-1 at 1 A g^-1, exceptional rate performance (80.3% capacity retention at 20 A g^-1), and good cycling stability (84.2% capacity retention after 5000cycles). Besides, an asymmetric supercapacitor device with Fe-Co-Ni-P electrode as a positive electrode and a hierarchical porous carbon as a negative electrode shows a high energy density of 57.1 Wh kg^-1 at a power density of 768.5 W kg^-1 as well as excellent cyclability with 88.4% of initial capacity after 10,000cycles. This work manifests that the construction of trimetallic phosphides is an effective strategy to solve the shortcomings of single or bimetallic phosphides for high-performance supercapacitors.

Core-shell Ni1.5Sn@Ni(OH)2 nanoflowers as battery-type supercapacitor electrodes with high rate and capacitance

Poor conductivity and aggregation of two-dimensional Ni(OH)₂ nanosheets hinder their extensive applications in supercapacitors. In the current study, a core-shell nanoflower composite is successfully synthesized using a high conductivity Ni_1.5Sn alloy and Ni(OH)₂ nanosheets via a facile two-step hydrothermal reaction. The alloy material enhances the conductivity of the sample and promotes electron transport for Ni(OH)₂. The as-prepared core-shell structure effectively restrains the clustering of nanosheets and improves the specific surface area of active materials. The optimized NS@NL-3 displays an outstanding specific capacitance (1002.2C g^-1 at 1 A g^-1) and satisfactory capacitance retention rate (80.63% at 20 A g^-1) by adjusting the coating amount of Ni(OH)₂ nanosheets, which is significantly higher compared with the performance of pure Ni(OH)₂ (609.6C g^-1 at 1 A g^-1 and 55.64% at 20 A g^-1). The all-solid-state hybrid supercapacitor (HSC) is fabricated with activated carbon (AC) as the negative electrode and NS@NL-3 as the positive electrode, which shows a high energy density of 57.4 Wh kg^-1 at 803.6 W kg^-1 as well as a superior cycling stability (88.45 % after 10,000 cycles). Experiment shows that 42 LEDs are effortlessly lit by two series-wound solid-state HSC devices, which indicates its high potential for practical applications.

Doping regulates pyro-photo-electric catalysis to achieve efficient water splitting in Ba1−xSrxTiO3 through solar energy and thermal resources

The effect of Sr2+ doping concentration in Ba1−xSrxTiO3 photoelectrodes on pyro-photo-electric catalysis was discussed. The main reason for the performance improvement is that doping broadens the response range of the semiconductor to visible light.

Hierarchical porous CeO2 micro rice-supported Ni foam binder-free electrode and its enhanced pseudocapacitor performance by a redox additive electrolyte

A hierarchical porous CeO₂ micro rice/NF binder free electrode was fabricated via a facile hydrothermal method and the electrochemical performances were enhanced by the addition of 0.2 M K₄[Fe(CN)₆] redox additive in a 3 M KOH electrolyte.

Facile Synthesis of Lacunary Keggin-Type Phosphotungstates-Decorated g-C3N4 Nanosheets for Enhancing Photocatalytic H2 Generation

In this work, the lacunary Keggin-type phosphotungstates of [PW9O34]9- (PW9) clusters were loaded onto the g-C3N4 nanosheets (NSs) to synthesize the phosphotungstate clusters-decorated 2D heterojunction photocatalysts by using the electrostatic-force driven self-assembly process. The surface charge polarity of g-C3N4 NSs was changed from a negative to a positive charge through the acidizing treatment. The positively-charged g-C3N4 NSs allowed the negatively-charged PW9 clusters to be adsorbed and deposited onto the g-C3N4 NSs, forming the PW9/g-C3N4 heterojunction NSs. The as-synthesized samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and UV-VIS absorption spectra, respectively. The photocatalytic activity tests indicated that, upon simulated sunlight irradiation, the photocatalytic H2-generation rate of PW9/g-C3N4 heterojunction NSs (~23.8 μmol h-1) was ~3.3 times higher than that of the pure g-C3N4 NSs (~7.3 μmol h-1). The enhanced photocatalytic activity of PW9 cluster-decorated g-C3N4 NSs could be attributed to the enhanced separation process of the photoinduced charge-carriers, due to the Z-scheme-mediate charge transfer behavior across their hetero-interface.

Development of vertically aligned trimetallic Mg-Ni-Co oxide grass-like nanostructure for high-performance energy storage applications

Direct growth of nanostructured trimetallic oxide on substrate is considered as one of the promising electrode fabrication for high-performance hybrid supercapacitors. Herein, binder-free one-dimensional grass-like nanostructure was constructed on nickel foam by using electrodeposition approach. The admirable enhancement in rate capability was observed by the substitution of Mg and Ni in cobalt oxide crystallite. The prepared nickel cobalt oxide (NCO) and cobalt oxide (CO) electrode exhibited a rate capability of 57% and 58% (2 to 10 A g^-1) respectively. Interestingly, the rate capability was increased to 87% by the substitution of Mg and Ni simultaneously. The novel vertically aligned trimetallic Mg-Ni-Co oxide (MNCO) grass-like nanostructure electrode exhibited a high specific capacity of 846 C g^-1 at 2 A g^-1_, retained 97.3% specific capacity and showed an outstanding coulombic efficiency of 99% after 10,000 charge-discharge cycles. Moreover, we assembled hybrid supercapacitor (HSC) device for practical applications by using MNCO and activated carbon (AC) as the positive and negative electrode materials, respectively. HSC device exhibited a high specific capacity of 144 C g^-1 at 0.5 A g^-1. The high energy density of 31.5 Wh kg^-1 and the power density of 7.99 kW kg^-1 were achieved. All these interesting and attractive results demonstrate the significance of the vertically aligned electrode material towards practical applications.