Afriyanti Sumboja

Facile Coating of Manganese Oxide on Tin Oxide Nanowires with High-Performance Capacitive Behavior

In this paper, a very simple solution-based method is employed to coat amorphous MnO2 onto crystalline SnO2 nanowires grown on stainless steel substrate, which utilizes the better electronic conductivity of SnO2 nanowires as the supporting backbone to deposit MnO2 for supercapacitor electrodes. Cyclic voltammetry (CV) and galvanostatic charge/discharge methods have been carried out to study the capacitive properties of the SnO2/MnO2 composites. A specific capacitance (based on MnO2) as high as 637 F g(-1) is obtained at a scan rate of 2 mV s(-1) (800 F g(-1) at a current density of 1 A g(-1)) in 1 M Na2SO4 aqueous solution. The energy density and power density measured at 50 A g(-1) are 35.4 W h kg(-1) and 25 kW kg(-1), respectively, demonstrating the good rate capability. In addition, the SnO2/MnO2 composite electrode shows excellent long-term cyclic stability (less than 1.2% decrease of the specific capacitance is observed after 2000 CV cycles). The temperature-dependent capacitive behavior is also discussed. Such high-performance capacitive behavior indicates that the SnO2/MnO2 composite is a very promising electrode material for fabricating supercapacitors.

Large Areal Mass, Flexible and Free-Standing Reduced Graphene Oxide/Manganese Dioxide Paper for Asymmetric Supercapacitor Device

Well-separated RGO sheets decorated with MnO2 nanoparticles facilitate easy access of the electrolyte ions to the high surface area of the paper electrode, enabling the fabrication of a thicker electrode with heavier areal mass and higher areal capacitance (up to 897 mF cm(-2) ). The electrochemical performance of the bent asymmetric device with a total active mass of 15 mg remains similar to the one in the flat configuration, demonstrating good mechanical robustness of the device.

Enhancing electrochemical reaction sites in nickel-cobalt layered double hydroxides on zinc tin oxide nanowires: a hybrid material for an asymmetric supercapacitor device.

Conducting nanowires are of particular interest in energy-related research on devices such as supercapacitors, batteries, water splitting electrodes and solar cells. Their direct electrode/current collector contact and highly conductive 1D structure enable conducting nanowires to provide ultrafast charge transportation. In this paper, we report the facile synthesis of nickel cobalt layered double hydroxides (LDHs) on conducting Zn(2)SnO(4) (ZTO) and the application of this material to a supercapacitor. This study also presents the first report of an enhancement of the active faradic reaction sites (electroactive sites) resulting from the heterostructure. This novel material demonstrates outstanding electrochemical performance with a high specific capacitance of 1805 F g(-1) at 0.5 A g(-1), and an excellent rate performance of 1275 F g(-1) can be achieved at 100 A g(-1). Furthermore, an asymmetric supercapacitor was successfully fabricated using active carbon as a negative electrode. This asymmetric device exhibits a high energy density of 23.7 W h kg(-1) at a power density of 284.2 W kg(-1). Meanwhile, a high power density of 5817.2 W kg(-1) can be achieved at an energy density of 9.7 W h kg(-1). More importantly, this device exhibits long-term cycling stability, with 92.7% capacity retention after 5000 cycles.

V2O5 Loaded on SnO2 Nanowires for High‐Rate Li Ion Batteries

The growing demand for high-power applications such as electric vehicles, hybrid electric vehicles, and other power-supply devices has triggered signifi cant research efforts on high-energy and power-density energy-storage devices. [ 1–5 ] Among the energystorage devices, electrochemical supercapacitors can deliver high power, but they suffer from low energy density. [ 5 ] Lithium batteries (LiBs) with their high energy density have attracted considerable attention. [ 6–9 ] However, for use as a versatile power source, it is still a challenge to achieve a high-power density compared with supercapacitors. [ 2–4 , 6 ]

Significant electrochemical stability of manganese dioxide/polyaniline coaxial nanowires by self-terminated double surfactant polymerization for pseudocapacitor electrode

Manganese dioxide/polyaniline coaxial nanowire networks are prepared by using double surfactant approach. This approach improves the interaction between the two active materials which has been confirmed by FTIR and XPS measurements, and yields a controllable uniform thin coating of polyaniline on the well-dispersed manganese dioxide nanowires. This hybrid heteronanostructure enhances the conductivity and capacitive performance of the supercapacitor electrode. The electrochemical test delivers specific capacitance as high as 498 and 873 F g−1 at 2 and 0.25 A g−1, respectively. Good cycling stability of up to 5000 cycles (5% capacitive degradation) outperforms other currently available redox nanocomposite electrodes. This result shows that the interaction among the active materials and improved nanostructure design are the two important factors to boost up the electrochemical performance of the hybrid nanomaterials. This work illustrates a promising platform that can be adopted for a myriad of metal oxide-conducting polymer nanocomposites while reaping the benefit as low cost electrode material for supercapacitor application.

Hollow Co3O4 Nanosphere Embedded in Carbon Arrays for Stable and Flexible Solid‐State Zinc–Air Batteries

Highly active and durable air cathodes to catalyze both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are urgently required for rechargeable metal-air batteries. In this work, an efficient bifunctional oxygen catalyst comprising hollow Co3 O4 nanospheres embedded in nitrogen-doped carbon nanowall arrays on flexible carbon cloth (NC-Co3 O4 /CC) is reported. The hierarchical structure is facilely derived from a metal-organic framework precursor. A carbon onion coating constrains the Kirkendall effect to promote the conversion of the Co nanoparticles into irregular hollow oxide nanospheres with a fine scale nanograin structure, which enables promising catalytic properties toward both OER and ORR. The integrated NC-Co3 O4 /CC can be used as an additive-free air cathode for flexible all-solid-state zinc-air batteries, which present high open circuit potential (1.44 V), high capacity (387.2 mAh g-1 , based on the total mass of Zn and catalysts), excellent cycling stability and mechanical flexibility, significantly outperforming Pt- and Ir-based zinc-air batteries.

Insights on the Fundamental Capacitive Behavior: A Case Study of MnO2

In this work, an insightful study on the fundamental capacitive behavior of MnO2 based electrodes is carried out using MnO2 hierarchical spheres (MHSs) and MnO2 nanoneedles (MNs) as examples. An overall understanding of the relationship between the capacitive performance and the electrode configuration as well as the morphology of active material, loading density, porosity of electrode, and electrolyte concentration is investigated comprehensively. Our analyses show that MnO2 with thin structure is of advantage to increase the utility of active material and to deliver higher specific capacitance, as the faradic reaction happens at/near the surface. Creation of an efficient path for the transport of electrons and ions is crucial to achieve high rate capabilities. Cycling stability could be improved by suppressing the side reaction. It is also important to shed light on the charge contribution from a graphite paper (GP) substrate since it may cause a misinterpretation of the capacitive behavior. This study provides a comprehensive understanding on the fundamental capacitive behavior of MnO2 based electrodes and gives useful clues for designing high performance supercapacitors.

Rational design of a high performance all solid state flexible micro-supercapacitor on paper

Micro-supercapacitors have attracted considerable attention due to their feasibility as power supplies for future integration into autonomous and portable devices. However, the conventional lab-on-chip fabrication method requires multiple patterning and metallization procedures, while the rigid substrate restricts versatility in applications such as flexible and wearable electronics. Here, we report the low cost, facile and scalable fabrication process of an all solid state flexible micro-supercapacitor on commercially available photo paper for the first time. Three dimensional interconnected coral-like polyaniline–manganese oxide composite material is electrochemically deposited on the interdigital finger electrodes. Electrochemical measurements reveal that the high aspect ratio finger electrode pattern and small gap interdigital finger electrode design is crucial to ensure superior performance. The optimized device shows an ultra high areal energy density of 6.3 μW h cm−2 at a power density of 35 μW cm−2 (94.73 mF cm−2 at 0.1 mA cm−2), while it maintains 4.8 μW h cm−2 at a power density of 3500 μW cm−2 (71.43 mF cm−2 at 10.0 mA cm−2). Meanwhile, it also has good flexibility. Such a flexible micro-supercapacitor is promising for future applications in lightweight, wearable or foldable electronics.

Progress in development of flexible metal–air batteries

Flexible electronics has gained great interest in emerging wearable or rolling-up gadgets, such as foldable displays, electronic papers, and other personal multimedia devices. Subsequently, there is a need to develop energy storage devices that are pliable, inexpensive, and lightweight. Metal–air batteries have been identified as one of alternative energy storages for cost effective and high energy density applications. They offer cheaper production cost and higher energy density than most of the currently available battery technologies. Thus, they are promising candidates for flexible energy storage devices. Flexible metal–air batteries have to maintain their performances during various mechanical deformations. To date, efforts have been focused on fabricating flexible components for metal–air batteries. This review presents a brief introduction to the field, followed by progress on development of flexible electrolytes, electrodes, and prototype devices. Challenges and outlook towards the practical use o...

One-Step Facile Synthesis of Cobalt Phosphides for Hydrogen Evolution Reaction Catalysts in Acidic and Alkaline Medium

Catalysts for hydrogen evolution reaction are in demand to realize the efficient conversion of hydrogen via water electrolysis. In this work, cobalt phosphides were prepared using a one-step, scalable, and direct gas-solid phosphidation of commercially available cobalt salts. It was found that the effectiveness of the phosphidation reaction was closely related to the state of cobalt precursors at the reaction temperature. For instance, a high yield of cobalt phosphides obtained from the phosphidation of cobalt(II) acetate was related to the good stability of cobalt salt at the phosphidation temperature. On the other hand, easily oxidizable salts (e.g., cobalt(II) acetylacetonate) tended to produce a low amount of cobalt phosphides and a large content of metallic cobalt. The as-synthesized cobalt phosphides were in nanostructures with large catalytic surface areas. The catalyst prepared from phosphidation of cobalt(II) acetate exhibited an improved catalytic activity as compared to its counterpart derived from phosphidation of cobalt(II) acetylacetonate, showing an overpotential of 160 and 175 mV in acidic and alkaline electrolytes, respectively. Both catalysts also displayed an enhanced long-term stability, especially in the alkaline electrolyte. This study illustrates the direct phosphidation behavior of cobalt salts, which serve as a good vantage point in realizing the large-scale synthesis of transition-metal phosphides for high-performance electrocatalysts.