High-performance Pseudocapacitive Materials Research Articles

Pseudocapacitive effects of polyoxometalate implanted on graphene oxide matrix with polypyrrole for symmetric Supercapacitor applications

Modern technological requirements emphasize designing and manufacturing electrochemical energy storage devices with high energy and power densities and longer cycle life. Supercapacitors with hybrid electrode materials have gained considerable attention as one of these systems due to their potential usage in futuristic applications such as electric vehicles and smart electric grids, among others. In this work, we synthesize potassium 9-tungsto-2-molybdo-1-vanadosilicate K5[α-SiMo2VW9O40]⋅10H2O and graphene oxide (GO) complex treating the latter as the supporting matrix for the former. We prepare the SiMo2VW9-polypyrrole (PPy) complex and then combine that with the GO matrix. The resulting nanohybrids GO-SiMo2VW9 and GO-PPy/SiMo2VW9 are found to have enhanced electrochemical properties when used in symmetric cells. Combining GO and pseudocapacitive materials can augment SC performance owing to their excellent redox properties. GO-SiMo2VW9 and GO-PPy/SiMo2VW9 showed 55.8 % and 85.5 % capacitive behavior at a scan rate of 10 mV/s, suggesting their use as high-performance pseudocapacitive materials as hybrid electrodes. GO-PPy/SiMo2VW9 electrode material shows a specific capacitance of 351.6 F/g with energy and power densities of 48.83 Wh/kg and 999.93 W/kg, respectively, at 0.5 A/g current density. Both the electrode materials yield capacitance retention of 60 % (GO-SiMo2VW9) and 80 % (GO-PPy/SiMo2VW9) after 5000 cycles at an 8A/g current density with almost 100 % coulombic efficiency, implying the stability of the electrode material.

CoNiMn-Layered Double Hydroxide/Ti3C2Tx Nanosheet Composites for Enhanced Pseudocapacitive Performance

Layered double hydroxides (LDHs) are considered prospective pseudocapacitors materials owing to their large theoretical capacitance and excellent redox capability. However, the low electrical conductivity and severe aggregation still hinder their practical applications. Herein, we synthesize CoNiMn-LDH/Ti3C2Tx nanosheet composites, of which Ti3C2Tx nanosheets enhance the electrical conductivity and provide a large surface area for LDH anchoring. Using metal-organic frameworks (MOFs) as sacrificial templates, the CoNiMn-LDHs are synthesized on the surface of Ti3C2Tx nanosheets via ion exchange, and the original organometallic hollow frameworks of the MOFs can be well retained. The as-prepared CoNiMn-LDH/Ti3C2Tx nanosheet composite delivers the largest specific capacitance as high as 1035 F g−1 at 1 A g−1 and retains 73.6 % of the capacitance at 10 A g−1. Moreover, the material of the electrode exhibits superior capacitance retention of 95.6 % with 5,000 charging/discharging cycles. This study might provide useful guidance for designing and constructing high-performance pseudocapacitive materials.

Exploring the origin of pseudocapacitive energy storage differences for molybdenum nitride-based electrodes

Molybdenum nitride-based materials have been extensively investigated as pseudocapacitive materials due to their superior metallic conductivity and thermal stability. Nevertheless, few studies have focused on the origin of pseudocapacitance (Credox) differences for charged molybdenum nitride electrodes with different crystal structures. Herein, taking cubic Mo2N (NaCl-type), Mo3N2 (CsCl-type) and hexagonal MoN (AlB2-type) as the research targets, we have systematically investigated the differences in rate performance and capacitance of these three materials by experimental methods and density functional theory (DFT) calculations to obtain the origin of Credox differences among them. DFT calculations prove that the proportions of Credox are 86.45%, 85.32% and 84.57% for Mo2N, Mo3N2 and MoN and thus the Mo2N features the most obvious pseudocapacitive behavior. Furthermore, the rigid band approximation (RBA) method reveals that the differences of work function change (ΔWF) are the root cause of Credox differences for these three kinds of charged materials. The highest electrochemical capacitance retention, highest conductivity, and fastest K+ ion mobility indicate that the MoN possesses the best rate performance among these three materials. Additionally, the most intact nanowire morphology and smallest ΔWF of Mo2N enable it to possess the highest electrochemical capacitance and theoretical total capacitance (Ctotal). The above findings will shed light on examining capacitance in a charged environment while screening the next-generation high-performance pseudocapacitive materials under various crystal structures.

Seed polymerization and capacitive performances of polyaniline nanofibers

Polyaniline (PANI) nanofibers have great potential application as a lightweight and high-performance pseudocapacitive material for supercapacitors. In this work, aniline oligomers as the seeds are produced in weak acidic solution of phosphoric acid through dilution polymerization, then these seeds were used to promote the grow of PANI nanofibers in the condition of hydrochloric strong acidic by adding more aniline monomers again. The microstructure and capacitance performances of PANI nanofibers were investigated by SEM, FT-IR, XRD and electrochemical measurements. When the current density is 1 A g-1, the specific capacitance could be as high as 442.9 F g-1. This work provides a route for the simple and efficient preparation of electrode materials with excellent performance.

Defect-rich CeO2 in a hollow carbon matrix engineered from a microporous organic platform: a hydroxide-assisted high performance pseudocapacitive material.

A microporous organic polymer (MOP) was utilized for the engineering of nanoparticulate CeO2 in a hollow carbon matrix (H-C/CeO2). After CeO2 nanoparticles were incorporated into a hollow MOP platform (H-MOP) through the decomposition of cerium acetate, successive carbonization produced H-C/CeO2. The redox feature of defective CeO2 in a conductive carbon matrix induced promising pseudocapacitive behavior. In particular, the H-C/CeO2 showed excellent electrochemical performance in an alkaline electrolyte (KOH), due to the hydroxide ion-assisted redox behavior of defective CeO2. H-C/CeO2-3 with an optimized amount of CeO2 showed specific capacitances of up to 527 (@0.5 A g-1) and 493 F g-1 (@1 A g-1). Even at high current densities of 10 and 20 A g-1, the H-C/CeO2-3 maintained high capacitances of 458 and 440 F g-1, respectively. After 10 000 cycling tests, the H-C/CeO2-3 retained the 94-95% capacitance of the first cycle.

Laser Synthesis of MOF-Derived Ni@Carbon for High-Performance Pseudocapacitors.

Although nanosizing of multiphase pseudocapacitive nanomaterials could dramatically improve their electrochemical properties, a proper way to simultaneously control both the size and the phase of the pseudocapacitive materials is still elusive. Herein, we employed a commercial CO2 laser engraver to do the transformation of a metal-organic framework (MOF-74(Ni)) into size-controlled Ni nanoparticles (4-12 nm) in porous carbon. The produced Ni@carbon hybrid showed the best specific capacitance of 925 F/g with excellent cycling stability when the particle size is 5.5 nm. We found that the highly redox-active α-Ni(OH)2 is more predominantly formed than the less redox-active β-Ni(OH)2 as the particle size becomes smaller. Our results substantiate that various MOFs could be created into high-performance pseudocapacitive materials with the controlled size and phase. It is believed that the laser-based synthesis could also serve as a powerful tool for the discovery of new MOF-derived materials in the field of energy storage and catalysis.

Experimental and Theoretical Investigation of the Effect of Oxygen Vacancies on the Electronic Structure and Pseudocapacitance of MnO2.

Defect engineering is an effective way to modulate the intrinsic physicochemical properties of materials. In this work, δ-MnO2 with oxygen vacancies is fabricated by a simple oxidation or reduction process, and the relationship between the electronic structure and pseudocapacitance is systematically studied through experimental analysis and theoretical calculations. The peaks in the Raman spectra of the as-prepared samples are shifted compared with those of pure MnO2 and the Mn3+ /Mn4+ ratio and O species content also change after the introduction of oxygen vacancies. The optimized samples exhibit a better specific capacitance of 207 F g-1 after the oxidation process and 181.4 F g-1 after the reduction treatment compared with only 143.9 F g-1 for the pure MnO2 . The samples obtained through the oxidation or reduction process also retain 93.3 or 86.4 % of the initial capacity after 5000 cycles. The excellent properties are attributed to the enhanced conductivity and increased surface reactivity or electrochemically active sites. Theoretical calculations demonstrate that the presence of oxygen vacancies leads to an increase in the density of states, which improves the redox reaction of MnO2 . This study will provide a reference for exploring and designing highperformance pseudocapacitive materials.

Modulating the electronic structure and pseudocapacitance of δ-MnO2 through transitional metal M (M = Fe, Co and Ni) doping

The experimental capacitance of manganese oxide (MnO2) is ordinarily less than 100 F/g due to their poor electronic conductivity and low structural stability. Herein, we demonstrate the design and synthesis of doped δ-MnO2 with enhanced electronic conductivity by the introduction of transitional metal Fe, Co and Ni. Structural characterizations shown that the Raman spectra of doped MnO2 has obviously blue shifted, as well as the separation values of Mn 3s XPS spectra has expanded, which indicate the transitional metal doping successfully changes the crystal lattice of δ-MnO2. The I-V measurements confirm that the electronic conductivity of MnO2 is significantly improved after doping. As a result, the Fe doped δ-MnO2 with a 0.5% doping amount displays the highest specific capacitance of 157 F/g at 0.5 A/g, by increasing 50.4% of the specific capacity than non-doped MnO2. Simultaneously, the Co doped δ-MnO2 exhibits the superb cycling stability (almost no degradation). Furthermore, the assembled 0.5% FeMO//AC, 1% CoMO//AC and 1% NiMO//AC asymmetric supercapacitor provide a specific energy densities of 30.3, 25.2 and 23.6 Wh/kg at a power density of 1000 Wh/kg. The excellent properties of as-prepared MnO2 are due to the enhanced conductivity after doping, which can ascribed to the forming of intermediate bands, or changing the intensity of valence band/conduction band as demonstrated by spin-polarized density functional (DFT) calculations. Thus, the current work will provide a pathway for the development of high-performance pseudocapacitive materials, as well as for other energy storage systems.

A facile one-step hydrothermal approach for the synthesis of a CuMoO4/MoS2 composite as a high performance pseudocapacitive material for supercapacitor applications

CuMoO4/MoS2-nanoparticle forest-like structures exhibit a very good specific capacitance and cyclic stability compared to the CuMoO4 and MoS2 electrodes.

A Few Atoms Thick Nickel–Cobalt Oxides Mesoporous Nanosheets and Their Arrays on Ni Foam for Supercapacitors with Ultra-Long Cycling Lifespan

Abundant electroactive sites, good electrical conductivity and rich channels are essential for high-performance pseudocapacitive materials, but their realization at the same time is still a great challenge. In this study, we prepare a few atoms thick and mesoporous nickel–cobalt (Ni−Co) oxides nanosheets for supercapacitors. The Ni−Co oxides have been synthesized via combining hydrothermal method with subsequent annealing treatment, which is very robust for the Ni−Co oxides with tuneable compositions and structures. The ultrathin and mesoporous nanosheets give rise to ultrahigh atom ratio at surface for high electroactive sites and abundant channels. In addition, by controlling the Ni to Co ratio and further supported on Ni foam, the electrochemical activity can be further promoted. As a result, the Ni0.5Co0.5O shows much higher specific capacitance values of 761 and 1616 F g−1 at 1 A g−1 for powder sample and its arrays on foam, which are both gradually increasing with repeated cycling. When used to assemble asymmetric supercapacitor, the two-electrode system shows a high energy density of 34.6 Wh kg−1 at 750 W kg−1, attractive power performance of 22.5 kW kg−1 at 21.5 Wh kg−1 with ultralong cycling stability (87% of capacitance retention after 10000 cycles).

High-performance carbon-coated ZnMn2O4 nanocrystallite supercapacitors with tailored microstructures enabled by a novel solution combustion method

Although ZnMn2O4 is widely studied as Li-ion battery anodes, it remains a challenge to tailor suitable microstructures of the oxide for supercapacitor applications. Carbon-coated ZnMn2O4 (C@ZMO) nanocrystallites showing high-performance pseudocapacitor behaviours in neutral aqueous electrolyte are for the first time successfully synthesised via a novel solution combustion process using polyethylene glycol as a multifunctional microstructure-directing agent. Controlling the molecular weight and amount of the polymer in the combustion solution enables the formation of highly-crystalline C@ZMO having substantially higher, by more than 5 folds, specific surface areas with mesoporous structures and conformal carbon coating via the one-pot synthesis process. The resulting C@ZMO supercapacitor electrodes in Na2SO4(aq) electrolyte exhibit ideal capacitive behaviours with specific capacitances up to 150 F g−1 and cycle stability showing no capacitance fade after 10,000 cycles at 60% of full capacity and >99% Coulombic efficiency. This study not only illustrates a new powerful synthesis route capable of producing conductive mesoporous crystalline oxide-based nanomaterials for energy storage applications but also reveals a new class of high-performance pseudocapacitive materials for neutral aqueous electrolytes.

Highly stable 3D porous heterostructures with hierarchically-coordinated octahedral transition metals for enhanced performance supercapacitors

Designing and tailoring the assembly of complex ternary transition metal oxide (TTMO) structures are a key step in the pursuit of high performance pseudo-capacitive materials for the development of next-generation energy storage devices. Here, we present uniquely assembled 3D porous heterostructures with hierarchically-coordinated TTMOs, comprising the multiply interconnected primary nanoporous frameworks of ZnCo2O4/NiMoO4 core-shell structures and the secondary protruding structures of NiMoO4 layered nanosheets. By benefiting from the combination of hierarchically cooperative two TTMOs, the developed 3D ZnCo2O4/NiMoO4 heterostructures with their stable, porous, and conductive features exhibit robust pseudo-capacitive performance with high capacitances of 6.07Fcm–2 and 1480.48Fg–1 at 2mAcm–2 as well as an excellent cycling stability of 90.6% over 15,000 cycles. Moreover, an asymmetric supercapacitor device can deliver a high energy density of 48.6Whkg–1 and a power density of 2820Wkg–1. The superior pseudo-capacitive energy storage characteristics are strongly attributed to the interconnected 3D nanoporous network architectures of the TTMOs along with the secondary layered nanosheets that provide 1) the enlarged surface area with the high conductivity, 2) the facile and multi-access ion paths, and 3) the favorable structural stability. Combined, these results highlight the importance of novel nanostructure design in maximizing the pseudo-capacitive performance and provide a viable way to develop new electrode materials.

One-Step Synthesis of Single-Layer MnO2 Nanosheets with Multi-Role Sodium Dodecyl Sulfate for High-Performance Pseudocapacitors.

A template-free, one-step and one-phase synthesis of single-layer MnO2 nanosheets has been developed via a redox reaction between KMnO4 and sodium dodecyl sulfate (SDS). The successful formation of single-layer MnO2 nanosheets has been confirmed by the characteristic absorption around 374 nm and the typical thickness of ~0.95 nm. The slow redox reaction controlled by the gradual hydrolysis of SDS is found to be the key factor for the successful formation of single-layer nanosheets. SDS not only serves as the precursor of dodecanol to reduce KMnO4 , but also aids the formation of single-layer MnO2 nanosheets as a structure-inducing agent. The resultant single-layer MnO2 nanosheets possess superior specific capacitance, which can be attributed to the extended surface and high porosity of MnO2 nanosheets on the electrode. The MnO2 nanosheets also show excellent durability, retaining 91% of the starting capacitance after 10 000 charge/discharge cycles. Moreover, the symmetric pseudocapacitor based on the synthesized single-layer MnO2 nanosheets exhibits a high specific capacitance, indicating great potential for real energy storage. Therefore, it has been demonstrated for the first time that a single readily available reagent, SDS, can play multiple roles in reducing KMnO4 to conveniently yield single-layer MnO2 nanosheets as a high-performance pseudocapacitive material.

Alignment of polyaniline nanofibers on 3-D templates: “Hairy” hollow microspheres as high-performance pseudocapacitive materials

A facile method was developed for growing the alignment of polyaniline (PANI) nanofibers on three-dimensional (3-D) templates, via the chemical oxidative polymerization of aniline in dilute solution at 0–5°C in presence of sulfonated polystyrene (SPS) microspheres and hydrochloric acid as template and dopant, respectively. Then the “hairy” PANI hollow microspheres were obtained after etching the templates with toluene. It was found that the formation of the “hairy” PANI hollow microspheres could be well controlled by altering the template concentration, thus the possible formation mechanism was deduced. The unique “hairy” PANI hollow microspheres prepared with the template concentration of 2.0mgmL−1 possessed the specific capacitance of 298Fg−1 and the capacitance retention of 63.6% after 900 cycles.

Synthesis and characterization of M3V2O8 (M = Ni or Co) based nanostructures: a new family of high performance pseudocapacitive materials

Binary metal oxides have recently attracted extensive attention from researchers in the energy storage field due to their multiple oxidation states and high energy density. In the present work, Ni3V2O8, Co3V2O8, and the Ni3V2O8/Co3V2O8 nanocomposite are designed and synthesized as a new class of high performance electrode material for supercapacitors. Ni3V2O8 and Co3V2O8 show a structure comprising nanoflakes and nanoparticles, respectively. The Ni3V2O8/Co3V2O8 nanocomposite is prepared by growing Co3V2O8 nanoparticles on the surface of Ni3V2O8 nanoflakes. The composite inherits the structural characteristics and combines the pseudocapacitive benefits of both Ni3V2O8 and Co3V2O8, showing higher specific capacitance than Co3V2O8 and superior rate capability as well as better cycle stability to Ni3V2O8. The dependence of pseudocapacitive properties of the Ni3V2O8/Co3V2O8 nanocomposite on the Ni/Co mass ratio is also investigated, indicating that the high specific capacitance of the composite is contributed by Ni3V2O8, while its excellent rate capability and cycle stability can be attributed to the Co3V2O8 component.