Similar Specific Capacitance Research Articles

Coupling Metal Oxides and Dendritic Gold Current Collectors for High-Performance Hybrid Supercapacitors on Silicon Wafer

Hybrid supercapacitors have gained significant attention in recent years due to their potential to combine the advantages of both batteries and capacitors. In this study, we investigate the use of metal oxides materials in a hybrid supercapacitor using a dendritic gold current collector, the device was implanted on a silicon wafer. Metal oxide materials, such as iron Oxide (Fe2O3) and manganese oxide (Mn2O3), are known for their high pseudo-capacitance and excellent electrochemical performance in water based electrolyte.By integrating dendritic gold current collectors with these materials, we aim to enhance its energy storage capacity and cycling stability. The silicon substrate provides mechanical support and pave the way for on-chip application, while the dendritic gold current collector offers a high surface area for efficient ion adsorption and desorption along the electrode-electrolyte interface. The metal oxide is coated onto the porous gold electrode using a simple and low cost-effective method, the electroplating, by mean of a solution based on FeSO4. The performance of the hybrid supercapacitor is evaluated through various electrochemical tests, including cyclic voltammetry, galvanostatic charge-discharge cycling, and electrochemical impedance spectroscopy, adopting neutral water based electrolyte. The results show that the enhanced hybrid supercapacitor with metal oxide materials exhibits significantly improved electrochemical performance compared to the device with a flat metal oxide electrode. The Fe-coated dendritic electrode exhibits a high specific capacitance over 20 mF cm-2, while the MnO2-coated flat electrode demonstrates similar specific capacitance over 25 mF cm-2. Additionally, the hybrid supercapacitor shows excellent cycling stability with negligible capacitance loss after 1000 cycles.In conclusion,the results suggest that mixing micro-structured current collectors with metal oxides can lead to simplified area's balancing technique for planar electrochemical cells, destinated to the development of on-chip devices with large operating voltage window, high energy storage capability and efficiency. Figure 1

Investigation on the pseudocapacitive charge storage mechanism of MnO2 in various electrolytes by electrochemical quartz crystal microbalance (EQCM)

A manganese dioxide (MnO2) film is electrodeposited onto a gold-coated quartz crystal electrode by a galvanostatic method. The scanning electron microscopy (SEM) image shows that the electrodeposited MnO2 film consists of nanorods with diameters of 15–20 nm. The cyclic voltammetric (CV) and electrochemical quartz crystal microbalance (EQCM) results demonstrate that the MnO2 electrodes exhibit similar specific capacitance (SC) and mass-to-charge ratios (MCR) in those electrolytes that contain the same cation but different anions. However, the SC and MCR are different in those electrolytes that contain the same anion but different cations. The SC of MnO2 electrodes increases with a decrease of the cationic radius and an increase of the cationic charge. The smaller the cationic radius, the smaller the deviation of the MCR from the equivalent weight (EW) of the cation. The results illustrate that the pseudocapacitive charge storage mechanism of MnO2 involves the cation in the electrolyte and its intercalation/deintercalation, which are affected by the charge number and the cationic radius. This work offers a theoretical basis for selecting suitable electrolytes to couple MnO2-based electrodes in supercapacitors.

Nucleation and Growth of Porous MnO₂ Coatings Prepared on Nickel Foam and Evaluation of Their Electrochemical Performance.

Porous MnO2 was uniformly electrodeposited on nickel foam in MnSO4 solution, which was applied as the electrode of supercapacitors. The nucleation/growth mechanisms of porous MnO2 were investigated firstly. Then two kinds of electrochemical measuring technologies, corresponding to the cycle voltammetry (CV) and galvanostatic charge-discharge, were adopted to assess the electrochemical performance of MnO2 electrodes. The results demonstrated that the deposition of MnO2 on nickel foam included four stages. Prior to the deposition, an extremely short incubation period of about 2 s was observed (the first stage). Then the exposed nickel foam was instantly covered by a large number of MnO2 crystal nuclei and crystal nuclei connected with each other in a very short time of about 3 s (the second stage). Nucleation predominated in the second stage. The sharply rise of current was caused by the increase in substrate surface area which due to nucleation of MnO2. Grain boundaries grew preferentially due to their high energy, accompanied with a honeycomb-like structure with the higher surface area was formed. However, accompanied with the electrochemical reactions gradually diffusion-controlled, the current presented the decline trend with increasing the time (the third stage). When the electrochemical reactions were completely diffusion-controlled, the porous MnO2 coating with an approximately constant surface area was formed (the fourth stage). MnO2 coatings deposited for different time (30, 60, 120, 300 s) exhibited a similar specific capacitance (CV: about 224 F/g; galvanostatic charge-discharge: about 264 F/g). Comparatively speaking, the value of MnO2 deposited for 600 s was highest (CV: 270 F/g; galvanostatic charge-discharge: 400 F/g).

Predominance of two dimensional (2D) Mn2O3 nanowalls thin film for high performance electrochemical supercapacitors

Well-defined, organized and highly dense Mn2O3 nanowalls are synthesized on nickel (Ni) foam by a facile hydrothermal route and utilize as efficient electro-active electrode for the electrochemical supercapacitors. The crystal structure and quality studies by X-rays diffraction (XRD) and Raman spectroscopy describe the formation of orthorhombic Mn2O3 phases. Uniform and well-organized nanowalls like morphology are grown on the Ni foam in the high aspect ratios with the average wall thickness of 20–30nm. The highly dense network of Mn2O3 nanowalls in electrochemical system could favor the better electrolyte penetration and supply the ion buffer reservoir to assure the constant supply of electrolyte. From cyclicvoltammetry analysis, the fabricated supercapacitor with Mn2O3 nanowalls electrode accomplishes the excellent capacitance of 480Fg−1 at 10mVs−1 in 6M KOH electrolyte. Interestingly, similar specific capacitance of 461Fg−1 at 0.5Ag−1 has obtained from the galvanostat charge-discharge measurements of fabricated supercapacitor with Mn2O3 nanowalls electrode. The grown Mn2O3 nanowalls electrode show the fantabulous cycling stability by maintaining the retention ratio 82% after 5000 cycles. This work paves a new and effective way for the direct preparation of nanowalls-like Mn2O3 thin film to achieve high performance electrochemical supercapacitors.

Electrochemical accessibility of porous submicron MnO2 spheres as active electrode materials for electrochemical capacitors

The electrochemical utilization of various submicron amorphous manganese dioxide spheres (SMnO2) with highly controlled shape and size was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. MnO2 spheres were synthesized by reaction between KMnO4 and 1–butanol in aqueous butyric acid solution at room temperature. Particle size was tuned by adjusting the concentration of KMnO4. The materials were characterized by X-ray diffraction, scanning electron microscopy, dynamic light scattering and nitrogen gas adsorption measurements. SEM results reveal that spheres with average diameter of 451±9, 218±12 and 195±85nm were produced by using a 20, 8 and 2mM of KMnO4 solution, respectively. DLS measurements showed similar mean particle diameter with a relatively high polydispersity-index that indicates the presence of larger agglomerated particles. The BET surface area of the three SMnO2 is ranging between 216 and 259m2g−1. Since very similar specific capacitance values of about 200Fg−1 (per active material mass) at 2mVs−1 were found for all three samples, MnO2 electrochemical utilization is more related to the pore size distribution rather than the particle size.

A melt route for the synthesis of activated carbon derived from carton box for high performance symmetric supercapacitor applications

Activated carbon materials have been playing a significant role in addressing the challenges posed with the ever-increasing demand for alternative clean and sustainable energy technologies. In the present study, a facile strategy is proposed for generating porosity in porous carbons by using carton box as the precursor and eutectic NaOH–KOH melt as the activating agent. The prepared carbon materials have a very high specific surface area up to 2731 m2 g−1 with large pore volume of 1.68 cm3 g−1, which is greater than that of only KOH was used at the same mass ratio. Electrochemical studies based on symmetric supercapacitor devices demonstrating that the NaOH–KOH melt activated porous carbon exhibits significantly improved rate capability in the range of 0.5–75 A g−1 despite of the similar specific capacitance with respect to KOH activated carbon at a low current density of 0.5 A g−1. The remarkable deviations in capacitive behavior at high current density for the NaOH–KOH melt activated porous carbon and KOH activated samples highlighting the specific surface area is not the only parameter that determines the capacitive performance especially at high charge–discharge rate.

Three-dimensional α-Fe2O3/carbon nanotube sponges as flexible supercapacitor electrodes

The porous, flexible and compressible CNT@Fe2O3 sponges show high specific capacitance (>300 F g−1).

Effect of the Components of the Electrode on the Morphological and Electrochemical Performance of Manganese Dioxide-Based Electrode for Application in Hybrid Electrochemical Capacitor 1

There are two classes of electrochemical capacitors categorized by their energy storage mechanism: electrical double layer capacitors (EDLCs) exclusively made with high specific surface area carbon-based materials and pseudocapacitors including generally conducting polymers or transition-metal oxides. In transition metal oxide-based electrodes such as manganese oxide, the reversible redox processes occurring at or near the surface of the electrode material leads to higher charge storage properties than carbon-based electrode EDLCs.2 However, due to the low potential stability window of MnO2-based electrode of about 1V, a hybrid electrochemical capacitor using electrodes with different potential range has been proposed.3 Such hybrid electrochemical capacitor can consist of a carbon negative electrode, a manganese dioxide-based positive electrode and a mild neutral electrolyte.4 Manganese dioxide is characterized by a theoretical specific capacitance of about 1233 F/g, which is far from being experimentally attainable.5 For example, in the case of thicker composite electrode and higher loading of MnO2 the electrochemically addressable material is commonly in the 10 to 20 % range. 6, 7 To maximize the utilization of MnO2, more fundamentals studies are needed to understand the role of all components of a composite electrode.Composite electrode based on manganese dioxide, a binder (poly(tetrafluoroethylene, PTFE) and a carbon additive (Acetylene black or high surface area Black Pearls 2000) were characterized by scanning electron microscopy and nitrogen gas adsorption. The electrochemical performances of the MnO2-Carbon-PTFE composite electrodes materials are evaluated by cyclic voltammetry. Brunauer–Emmett–Teller (BET) surface area measurements indicate that the addition of the PTFE binder does not block access to the porous network of MnO2 and the two carbon powders. Only acetylene black appears to slightly adversely affect the mesoporous surface, presumably because of its larger particle size compared to Black Pearls 2000. The electrochemical utilization of MnO2 is similar whether acetylene black or Black Pearls 2000 is used as carbon additive. This suggests that the porosity of Black Pearls, which could perhaps act as a reservoir of ionic species, does not appear to play a significant role as demonstrated by similar specific capacitance at slow scan rate. On the other hand, the effect of additional conductive agent such as acetylene black induces a slight increase of the specific capacitance at high scan rate. Finally, a plot of Coulombic efficiency as a function of the upper positive potential limit showed that using a high surface carbon support with MnO2 can cancel the effect of the larger potential window of electroactivity of MnO2because of its smaller electrochemical potential stability range.

Effect of the Components of the Electrode on the Pore Texture and Electrochemical Performance of Manganese Dioxide-Based Electrode for Application in Hybrid Electrochemical Capacitor 1

In the 1970s, Conway and others observed that the reversible redox processes occurring at or near the surface of an appropriate electrode material led to electrical double layer capacitor (EDLC)-like electrochemical properties and also a higher charge storage.2 Later, Lee and Goodenough were the first to report the pseudocapacitive behavior of manganese dioxide.3 Since that, it has been widely studied as active electrode material for application in aqueous electrochemical capacitors. Due to the low potential stability window of MnO2-based electrode of about 1V, a hybrid electrochemical capacitor using electrodes with different potential range has been proposed.4 Such hybrid electrochemical capacitor can consist of a carbon negative electrode, a manganese dioxide-based positive electrode and a mild neutral electrolyte.5 Manganese dioxide is characterized by a theoretical specific capacitance of about 1233 F/g, which is far from being experimentally attainable.6 Even for very thin film (< 100 nm) and very low mass (< 100 µg) loading, of MnO2, the specific capacitance rarely exceeds 1000 F/g.7-9 On the other hand, in the case of thicker composite electrode and higher loading of MnO2 the electrochemically addressable material is commonly in the 10 to 20 % range. 10, 11 To meet the requirements mentioned above, more fundamentals studies are needed to understand the role of all components of a composite electrode.Composite electrode based on manganese dioxide, a binder (poly(tetrafluoroethylene, PTFE) and a carbon additive (Acetylene black or high surface area Black Pearls 2000) were characterized by scanning electron microscopy and nitrogen gas adsorption. The electrochemical performances of the MnO2-Carbon-PTFE composite electrodes materials are evaluated by cyclic voltammetry. Brunauer–Emmett–Teller (BET) surface area measurements indicate that the addition of the PTFE binder does not block access to the porous network of MnO2 and the two carbon powders. Only acetylene black appears to slightly adversely affect the mesoporous surface, presumably because of its larger particle size compared to Black Pearls 2000. The electrochemical utilization of MnO2 is similar whether acetylene black or Black Pearls 2000 is used as carbon additive. This suggests that the porosity of Black Pearls, which could perhaps act as a reservoir of ionic species, does not appear to play a significant role as demonstrated by similar specific capacitance at slow scan rate. On the other hand, the effect of additional conductive agent such as acetylene black induces a slight increase of the specific capacitance at high scan rate. Finally, a plot of Coulombic efficiency as a function of the upper positive potential limit showed that using a high surface carbon support with MnO2 can cancel the effect of the larger potential window of electroactivity of MnO2 because of its smaller electrochemical potential stability range.

Effect of the formulation of the electrode on the pore texture and electrochemical performance of the manganese dioxide-based electrode for application in a hybrid electrochemical capacitor

A composite electrode based on manganese dioxide, a binder (poly(tetrafluoroethylene), PTFE) and a carbon additive were characterized by scanning electron microscopy, nitrogen gas adsorption and electrochemistry. Two different carbon additive materials were investigated: acetylene black and a high surface area carbon black (Black Pearls 2000). It was found that the addition of the PTFE binder does not block access to the porous network of MnO2 and the two carbon powders. Unlike Black Pearls that affect the pore texture, acetylene black appears to slightly adversely affect the mesoporous surface, presumably because of its larger particle size. The electrochemical utilization of MnO2 is similar whether acetylene black or Black Pearls 2000 is used as a carbon additive. This suggests that the porosity of the latter, which could provide a pool of ionic species, does not appear to play a significant role as demonstrated by similar specific capacitance at a slow scan rate. On the other hand, the highest conductivity of acetylene black leads to slightly higher specific capacitance at higher scan rate. Finally, it is shown that using a high surface carbon support with MnO2 can cancel the effect of the larger potential window of electroactivity of MnO2 because of its smaller electrochemical potential stability range.

Highly deformation-tolerant carbon nanotube sponges as supercapacitor electrodes

Developing flexible and deformable supercapacitor electrodes based on porous materials is of high interest in energy related fields. Here, we show that carbon nanotube sponges, consisting of highly porous conductive networks, can serve as compressible and deformation-tolerant supercapacitor electrodes in aqueous or organic electrolytes. In aqueous electrolytes, the sponges maintain a similar specific capacitance (>90% of the original value) under a predefined compressive strain of 50% (corresponding to a volume reduction of 50%), and retain more than 70% of the original capacitance under 80% strain while the volume normalized capacitance increases by 3-fold. The sponge electrode maintains a stable performance after 1000 large strain compression cycles. A coin-shaped cell assembled with these sponges shows excellent stability over 15,000 charging cycles with negligible degradation after 500 cycles. Our results indicate that carbon nanotube sponges have the potential to fabricate deformable supercapacitor electrodes with stable performance.

Capacitive properties of RuO 2 and Ru–Co mixed oxide deposited on single-walled carbon nanotubes for high-performance supercapacitors

Composite electrodes for use in redox supercapacitors were prepared by electrochemical deposition of RuO 2 or the co-deposition of Ru–Co mixed oxides on the surface of single-walled carbon nanotubes. Electrodes coated with the Ru–Co mixed oxide [Ru (13.13 wt%) and Co (2.89 wt%)] or RuO 2, exhibited a similar specific capacitance (∼620 F g −1) at low potential scan rates (10 mV s −1). However, at higher scan rates (500 mV s −1) the mixed metal oxide electrode showed superior performance (570 F g −1) when compared to the RuO 2 electrode (475 F g −1). This increase in capacitance at high scan rates is attributed to the role of the Co in providing enhanced electronic conduction.

Co-deposition of conducting polymers in a room temperature ionic liquid

This work focuses on the co-deposition of two different conducting polymers in a room temperature ionic liquid. The combination of poly(pyrrole) (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) is investigated in 1-butyl-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (C4mpyr TFSI). In the past, the deposition of the homopolymers from ionic liquids has proven difficult with the resultant layers exhibiting poor kinetics of both the charge and discharge reactions. Combining the two polymers as one layer, using a mixed monomer solution in an ionic liquid as the deposition media, creates a superior polymer layer. Desirable properties of the poly(pyrrole) are high specific capacitance and good mechanical properties while the desirable properties of the poly(thiophene) derivative are high electrical conductivity, good mechanical properties and high porosity. Characterisation of the co-deposited polymer layers is carried out using cyclic voltammetry, capacitance measurements, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) imaging. The co-deposited film is found to exhibit an improved morphology and higher ionic transport, while maintaining a similar specific capacitance to the homo-polymer PPy.