Pseudocapacitive Electrode Research Articles

Pulsed-waveform electrocatalytic detoxification of hexavalent chromium promoted by pseudocapacitive effects

We report a pulsed-voltage method using a pseudocapacitive electrode to improve the efficiency of the electrochemical reaction for aqueous Cr(vi) detoxification.

Sputtered titanium nitride films as pseudocapacitive electrode for on chip micro-supercapacitors

Sputtered titanium nitride films as pseudocapacitive electrode for on chip micro-supercapacitors

A geopolymer membrane for application in a structural mechanics and energy storage difunctional supercapacitor.

A structural mechanics and energy storage difunctional supercapacitor based on a geopolymer membrane injected with a 0.5 M Na2SO4 electrolyte and a pseudocapacitive electrode Mn7O13 is designed and assembled. The geopolymer membrane is prepared as a structural electrolyte with metakaolin and alkaline activator solution. The wide channels in the geopolymer matrix provide paths for ion movement. The Mn7O13 electrode is prepared by different hydrothermal treatments at different temperatures and times, and assembled with activated carbon and a geopolymer with different moduli to form a difunctional supercapacitor. The results show that the electrode sample annealed at 300 °C for 45 min after hydrothermal treatment at 160 °C for 24 h exhibits the best comprehensive performance. The specific capacitance of the electrode is 175.5 F g-1 (2392.6 F m-2) at 1 A g-1, and the specific capacitance of the difunctional structure supercapacitor assembled with a geopolymer with a modulus of 1.2 and cured for 28 days is 144.12 F g-1 (1960.0F m-2) at 1 A g-1 under 15 MPa.

Framework structured Ce2(C2O4)3·10H2O as a pseudocapacitive electrode of a hybrid (asymmetric) supercapacitor (HSC) for large scale energy storage applications.

The electrochemical kinetics of the electrode material plays a crucial role in the development of various energy storage devices such as batteries, supercapacitors, and hybrid supercapacitors. Battery-type hybrid supercapacitors are envisaged as excellent candidates to bridge the performance gap between supercapacitors and batteries. Due to its open pore framework structure and more structural stability, porous cerium oxalate decahydrate (Ce2(C2O4)3·10H2O) is found here to be a potential energy storage material partly because of the presence of planer oxalate anions (C2O42-). Superior specific capacitance equivalent to 78 mA h g-1 (capacitance: 401 F g-1) at 1 A g-1 in the potential window of -0.3 to 0.5 V was observed in an aqueous 2 M KOH electrolyte. The predominant pseudocapacitance mechanism seems to operate because of the high charge storage capacity of the electrode as intercalative (diffusion control) and surface control charges stored by the porous anhydrous Ce2(C2O4)3·10H2O, which were close to 48% and 52%, respectively, at a 10 mV s-1 scan rate. Further, in the full cell asymmetric supercapacitor (ASC) mode in which porous Ce2(C2O4)3·10H2O is the positive electrode and activated carbon (AC) is the negative electrode, at the operating potential window of 1.5 V, the highest specific energy of 96.5 W h kg-1 and a specific power of ∼750 W kg-1 at 1 A g-1 current rate and a high power density of 1453 W kg-1, the hybrid supercapacitor still attains an energy density of 10.58 W h kg-1 at a 10 A g-1 current rate, which was obtained with a high cyclic stability. The detailed electrochemical studies confirm a high cyclic stability and a superior electrochemical charge storage property of porous Ce2(C2O4)3·10H2O making it a potential pseudocapacitive electrode for use in large energy storage applications.

Tailoring the phase composition of carbon-coated nickel sulfides to achieve a high specific capacitance.

As significant transition metal sulfides, nickel sulfides integrated with carbon were successfully synthesized in the presence of polyethylenimine and glutaraldehyde with a solvothermal route at 180 °C followed by carbonization. Glutaraldehyde prevented complete sulfur loss and allowed the formation of a mixed phase of nickel sulfide. The electrochemical performances of pure NiS2, NiS@C0, NiS2/NiS@C1, and NiS2/NiS@C2 electrodes were tested by a series of measurements. The specific capacitances obtained from GCD analysis were 698, 1160, 1484, and 908 F g-1 at 1 A g-1 for NiS2, NiS@C0, NiS2/NiS@C1, and NiS2/NiS@C2 electrodes, respectively. The results implied that the NiS2/NiS@C1 electrode possessed the highest specific capacitances and this study can be a good reference for the preparation of other hybrid metal sulfides as pseudocapacitive electrode materials.

Hierarchical design of NiCo-LDH NFs@Co(OH)2 nanosheets supercapacitor electrode material with boosted electrochemical performance

Layered double hydroxides (LDHs) have been considered as excellent pseudocapacitive electrode materials for supercapacitors because of their controllable layered structures and high theoretical specific capacitances. However, poor conductivity and shortage of effective active sites hinder their applications. Herein, in order to boost the capacitance performance, an electrode material composed of NiCo-LDH nanofibers with cobalt hydroxide (Co(OH)2) nanosheets firmly anchored to or uniformly immobilized onto NiCo-LDH nanofibers surface is constructed. The material architecture takes advantage of superior capacitive activity from Co(OH)2 with good electronic conductivity and dispersibility over the surface of NiCo-LDH nanofibers. The merits based on the elegant synergy between NiCo-LDH nanofibers and Co(OH)2 nanosheets induce an outstanding specific capacitance of 858.9 F/g at a current density of 0.5 A/g. With the current density increasing from 0.5 to 10 A/g, the specific capacitance retention is 67.3%, indicating a good rate capability. Furthermore, the electrode material exhibits a capacitance retention of 83.7% after 2000 cycles at 10 A/g. These excellent electrochemical properties are due to the hierarchically designed structure and the cooperative contributions of NiCo-LDH nanofibers and Co(OH)2 nanosheets, which shows great potential for energy storage applications.

Bricks of Co, Ni doped Fe3O4 as high performing pseudocapacitor electrode

Iron oxide has been a widely used electrode material for energy storage devices. It has also been recently utilized in magnetic supercapacitors. To improve its performance, a strategy of co-doping with cobalt and nickel is proposed. This leads to nearly 85 % improvement in the performance, which can be further tuned by varying the concentrations of cobalt and nickel. Performance of Ni1-xCoxFe2O4 (x = 0, 0.3, 0.5, 0.7 and 1.0) is discussed in the paper. Owing to the varying order of electrolyte ions in different materials, the specific capacitance value also changes. This is established using a theoretical model. Performance of an asymmetric device, fabricated using optimized composition i.e. Ni0.5Co0.5Fe2O4 as positive and graphene oxide (GO) as the negative electrode is also presented. The asymmetric Ni0.5Co0.5Fe2O4//GO device is able to deliver high energy density i.e. 21.5 Wh kg−1 and excellent cyclic stability (~92 % after 5000 cycles).

High energy density supercapattery empowered by efficient binder-free three-dimensional carbon coated NiCo2O4/Ni battery and Fe3S4@NiCo pseudocapacitive electrodes

Through the progress of science and technology, the findings of supercharged electrodes are provoked to design the electrode material. Herein, a novel electrode made up of binary metallic oxide surrounded by a carbon matrix is designed as the positive electrode material that is substantially more active and efficient than the most reported electrode materials. The as-synthesized 3D-C-NiCo2O4 electrode revealed a specific capacity of 558.3C g−1 at 1 A g−1. Likewise, the 3D-Fe3S4@NiCo/SS electrode is effectively synthesized via the vapour phase growth method that worked as a negative pseudocapacitive material. It provides a gravimetric capacitance of 808.05 F g−1 at 1 A g−1. Moreover, the assembled 3D-C-NiCo2O4//3D-Fe3S4@NiCo/SS reveals a higher gravimetric capacitance of 150 F g−1 at 1 A g−1 with 70 % stability over 10,000 cycles. It offers a maximum energy and power density of 49.8 Wh kg−1 and 8100 W kg−1, respectively. These exceptional outcomes highlight that the as-fabricated 3D-C-NiCo2O4//3D-Fe3S4@NiCo/SS device can be an ultimatum source for high-performance energy findings. The present result demonstrates the combined approach of prepared electrodes, merits of battery type 3D-C-NiCo2O4 electrode, and the faradaic capacitance of 3D-Fe3S4@NiCo electrode.

Redox-active ligand-mediated assembly for high-performance transition metal oxide nanoparticle-based pseudocapacitors

The important issues in preparing transition metal oxide nanoparticle (TMO NP)-based energy storage electrodes, such as pseudocapacitor electrodes, are to effectively minimize the amount of electrochemically inactive organics (i.e., polymeric binders and ligands stabilizing NPs) and simultaneously increase the amount of high-energy TMO NPs within a limited electrode area/volume without a significant loss in charge transfer kinetics. Herein, we introduce a redox-active ligand-mediated layer-by-layer (LbL) assembly as a novel approach for significantly enhancing the energy storage performance of TMO NP-based pseudocapacitor electrodes. In this study, high-energy TMO NPs and conductive NPs are periodically LbL-assembled using redox-active porphyrin ligands instead of polymeric binders. During LbL deposition, the insulating native ligands on the NP surface are successfully exchanged with carboxylic acid-functionalized porphyrin ligands, forming a densely NP-packed structure that can minimize the mass and volume of electrochemically inactive components. Based on this redox-active ligand-mediated LbL approach, the resultant pseudocapacitor electrodes exhibit much higher energy capacities (areal, volumetric, and specific capacities) and superior rate capability than insulating polymeric ligand-mediated electrodes as well as previously reported electrodes. Our approach can provide a fundamental basis for fully exploiting the energy efficiency of components and further designing a variety of high-performance electrochemical electrodes.

Facile synthesis of CoCo2O4/rGO spinel nanoarray as a robust electrode for energy storage devices

• Graphene based CoCo 2 O 4 nanostructure array was developed through hydrothermal route. • The electrochemical activity of CoCo 2 O 4 /rGO was performed for supercapacitor application. • The fabricated electrode CoCo 2 O 4 /rGO exhibited the specific capacitance of 1352.2 F g -1 with high energy density (E d ) of 75.96 Wh Kg -1 at low current density of 2 A g -1 . • The enhanced CoCo 2 O 4 /rGO was ascribed to the synergistic effect, diverse morphology and larger surface area. Pseudocapacitor electrodes made of spinel oxide nanomaterial is considered as a better solution to overcome the current energy crisis. In this work, CoCo 2 O 4 is fabricated and then combined with reduced graphene oxide (rGO) through clean hydrothermal method. The microscopic and spectroscopic tools were employed to examine the properties of the fabricated electrode material. The electrochemical activity of the material was determined by using polarization curves (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge methods (GCD) and chronoamperometry (CA). The electrochemical results revealed that the addition of rGO into CoCo 2 O 4 electrode, increases the discharge duration, improves its specific capacitance, and its extensive stability. The electrochemical results of CoCo 2 O 4 /rGO display the specific capacitance (Csp) of 1352.2 Fg -1 , energy density (E d ) of 75.96 Wh Kg -1 and power density (P d ) of 636 W Kg -1 at low current density of 2 Ag -1 . The nanocomposite exhibited the capacitance retaining of 98.22% over 2000 cycles and stable for 40 h. Though, the capacitive activity of fabricated electrode was further improved with change in electronic and structural arrangement, alteration in the morphology, or incorporation of other metal or non-metals.

Core-shell structured hierarchical Ni nanowires and NiS/Co3S4 microflowers arrays as a high-performance supercapacitor electrode

To develop new positive electrode materials with high electrochemical performance for practical applications in energy storage, the design of new complex morphologies with a core-shell structure based on MS sulfide materials with M = Ni, Co, Fe or Mn and nanomaterials metallic is a very essential technique. In this study, an asymmetric supercapacitor (ASC) with high energy density was fabricated by combining a NiS/Co3S4@h-Ni NWs battery-like electrode with α-MnO2 as a pseudo-capacitive electrode. Firstly, hierarchical Nickel Nanowires, h-Ni NWs, were prepared by the reduction of Ni2+ ions by hydrazine, and then the h-Ni NWs are coated with NiS/Co3S4 by the hydrothermal method to form a core-shell structure with good electrical conductivity. The electrochemical performance of the NiS/Co3S4@h-Ni NWs electrode was evaluated in the 4 M LiOH electrolyte. The results showed that the NiS/Co3S4@h-Ni NWs electrode had a specific capacity of 1893 C/g at a current density of 1 A/g and an excellent retention of 98.63 % of its initial specific capacity after 10,000 charge-discharge cycles at 20 A/g due to the synergistic interaction between the nickel nanowires and (Ni/Co) sulfides in the developed core-shell structure. Furthermore, the fabricated ASC device provided a high energy density of 101.05 Wh/kg at a power density of 850 W/kg. At a maximum power density of 17 kW/kg, the device provided an energy density of 57.13 Wh/kg along with excellent capacity retention (83.56 %) after 10,000 charge-discharge cycles at 20 A/g.

Transparent, photosensitive and highly efficient pseudocapacitive binder-free Mo-modified NiO thin film electrode for bifunctional optoelectronic and energy storage applications

We report a novel highly sensitive and pseudocapacitive transparent nickel oxide (NiO) thin film based electrode material fabricated on a conductive glass substrate using a facile binderless electrodeposition process. Effect of the incorporation of Mo-dopant ion on some surface structural and electrochemical properties of the electrode was examined for high performance optoelectronic and charge storage potentials. The material showed some uniqueness in some microstructural features and enhanced degree of crystallinity, suitable for charge extraction and transport with Mo doping. The deposited NiO film demonstrated red shift in band structure by exhibiting optical band gap narrowing from 3.88 to 3.61 eV with increasing Mo content. The degree of disorder as revealed from Urbach response of NiO film was found varying with Mo-content. The material also exhibited enhanced Ni2+ electronic transition states with increasing Mo content which quenched at a critical dopant concentration of 2.4 %. The fabricated NiO thin film electrode showed increased supercapacitive specific capacitance and areal capacity up to a peak value of 1412 Fg−1 and 101 mAh m−2 for 3 % Mo dopant content at 5 mVs−1 scan rate and 0.5 mA cm−2, respectively, but returned diminished at higher dopant content. Excellent cycling stability at ∼ 85 % after 5000 cycles, was also exhibited. Impedance spectroscopic features of Mo-doped NiO electrode indicated fast electrolytic ion transfer response with high rate charge storage capability. The study presents successful fabrication of Mo-modified NiO nanostructured electrode film and demonstrated the influence of Mo impurity on tailoring the properties of NiO host film as suitable electrode in high performance photocatalytic and supercapacitor devices.

High mass loading MnO2/graphite felt electrode with marked stability over a wide potential window of 1.9 V for supercapacitor application

Herein, a facile method is employed to prepare a high mass loading (3.7 mg cm−2) MnO2/graphite felt (GF) to serve as a pseudocapacitive electrode type with a marked extended potential window of 1.9 V. MnO2 is electrochemically deposited on 3-D porous GF substrate via optimizing the bath concentration and deposition potential window. GF is in-situ modified concurrently with the electrodeposition of MnO2. Starting from a high positive potential, GF is modified via functionalization and making defects in its fibers. Moving toward lower potential, the amount of electrodeposited MnO2 is increased. Extending the potential window via moving toward more negative values, the loading amount of MnO2 is increased. Also, increasing the permanganate ions concentration, the degree of GF modification, and the loaded amount of MnO2 active material are increased. In-situ modification of GF is examined by SEM, EDX, XPS, Raman, and contact angle measurements. Interestingly, MnO2 forms a strong adhere uniform coat on the surface of the in situ modified GF resulting in high specific capacitance and extraordinary stability. Surprisingly, MnO2/GF displays a high specific capacitance of 832 mF cm−2 (226 F g−1) at a low current density of 1.4 mA cm−2 over a large potential window. Even though MnO2/GF operates in a large potential window, the specific capacitance was retained at 118 % at a current density of 14 mA cm−2 for 9000 cycles with excellent efficiency up to 98%. The excellent capacitive performance of MnO2/GF is attributed to the 3-D porous structure of GF with enhanced hydrophilicity, electronic conductivity, and strong adhering of MnO2 together with enhanced electrolyte accessibility to the underneath layers of MnO2 during cycling of the electrode over 9000 cycles.

Influence of the Molar Ratio of Co and V in Bimetallic Oxides on Their Pseudocapacitive Properties.

Bimetallic oxides have significant attraction as supercapacitor electrode materials due to their highly reversible redox processes, which are commonly associated with their surface chemistry and morphological features. Here, we report the synthesis, characterization, and electrochemical evaluation of bimetallic oxides with different molar compositions of Co and V (Co0.6V0.4, Co0.64V0.36, Co0.68V0.32, and Co0.7V0.3 denoted as S1, S2, S3, and S4 samples, respectively). The materials were synthesized by a modified solvothermal method using glycerol as a stabilizing agent, characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy-energy-dispersive X-ray spectroscopy, X-ray fluorescence spectroscopy, N2 adsorption isotherms, cyclic voltammetry, and galvanostatic charged/discharged in a three-electrode cell. The role of the CoV oxide compositions on the pseudocapacitive properties was studied through the analysis of the energy storage mechanism following the power law and Dunn's methodology to obtain the b values. An important finding of this work is that CoV oxides exhibited electrochemical characteristics of a pseudocapacitive electrode material even though the charge storage occurs in bulk. This behavior is consistent with the pseudocapacitance generated by redox processes, showing b values of 0.67, 0.53, 0.75, and 0.84, with a capacitive current contribution of 74, 74, 63, and 70% analyzed at a scan rate of 1 mV s-1, for S4, S3, S2, and S1 samples, respectively. Co0.7V0.3 (S4) oxide presented the highest specific capacitance of 299 F g-1 at 0.5 A g-1 with a Coulombic efficiency of 93% tested at 4 A g-1. The better electrochemical performance of this sample was attributed to the synergistic effect of the Co and V atoms since a minimum amount of V in the structure may distort the crystal lattice and improve the electrolyte diffusion, in addition to the formation of several oxidation states due to reduction of V5+, including V3+ and V4+ as well as to the formation of the metastable V4O9.

HKUST-1/LaNiO3 hybrid composite as superior material for symmetrical pseudocapacitors

Perovskite phase metal oxides are extensively explored due to their structural and compositional flexibility and excellent electrocatalytic activity. Its composite with the porous and conductive materials has potential application for the energy storage devices due to its additional conductive pathways for enhancing the charge kinetics. In the present work synthesis of highly porous Cu-MOF(HKUST-1)/LaNiO3 heterostructure composite is explored as pseudocapacitive electrode in three electrode system using KOH as well as LiOH electrolytes. The prepared HKUST-1/LaNiO3 composite electrode has shown a high specific capacitance of 424.30 F/g, 786.0 F/g in LiOH and KOH electrolytes respectively at 1 A/g current density. The obtained value is significantly better than the pristine LaNiO3 perovskite electrode (170 F/g and 273 F/g in LiOH and KOH respectively). The symmetrical supercapacitor using HKUST-1/LaNiO3 electrodes have displayed the energy densities of 28.24 Wh/kg and 28.15 Wh/kg and power densities of 775 W/kg, 836 W/kg in KOH and LiOH electrolytes respectively.

Coupling W18 O49 /Ti3 C2 Tx MXene Pseudocapacitive Electrodes with Redox Electrolytes to Construct High-Performance Asymmetric Supercapacitors.

A pseudocapacitive electrode with a large surface area is critical for the construction of a high-performance supercapacitor. A 3D and interconnected network composed of W18 O49 nanoflowers and Ti3 C2 Tx MXene nanosheets is thus synthesized using an electrostatic attraction strategy. This composite effectively prevents the restacking of Ti3 C2 Tx MXene nanosheets and meanwhile sufficiently exposes electrochemically active sites of W18 O49 nanoflowers. Namely, this self-assembled composite owns abundant oxygen vacancies from W18 O49 nanoflowers and enough active sites from Ti3 C2 Tx MXene nanosheets. As a pseudocapacitive electrode, it shows a big specific capacitance, superior rate capability and good cycle stability. A quasi-solid-state asymmetric supercapacitor (ASC) is then fabricated using this pseudocapacitive anode and the cathode of activated carbon coupled with a redox electrolyte of FeBr3 . This ASC displays a cell voltage of 1.8V, a capacitance of 101 F g-1 at a current density of 1 A g-1 , a maximum energy density of 45.4Wh kg-1 at a power density of 900W kg-1 , and a maximum power density of 18000W kg-1 at an energy density of 10.8Wh kg-1 . The proposed strategies are promising to synthesize different pseudocapacitive electrodes as well as to fabricate high-performance supercapacitor devices.

Effect of Protonation Doping of Polyaniline Electrodes using Hydrochloric Acid on Its Pseudocapacitor Capacitance

Pseudocapacitor is a supercapacitor that can store charge faradically through a reversible redox reaction. Polyaniline (PANi) is one of the promising active materials for pseudocapacitor electrodes since it can produce theoretical specific capacitance up to 750 F/g. We prepared leucomeraldine base polyaniline (LB-PANi) electrodes by deposition of dissolved LB-PANi powder in N,N-Dimethylformamide (DMF) using spraycoating technique. The LB-PANi electrodes was then doped with 1 M HCl through protonation process to obtain emeraldine salt polyaniline (ES-PANi) electrodes. We used both electrode materials and 1 M KCl to prepare a symmetrical sandwich supercapacitor model of <LB-PANi|KCl|LB-PANi> and <ES-PANi|KCl|ES-PANi>, as well as measured their performance. The results show a significant increase of the specific capacitance of PANi supercapacitor from 15.02 F/kg to 1876.87 F/kg when the electrodes of the LB-PANi were changed with the ES-PANi electrodes.

Mn3P2O8/TiN on Titanium Substrate for Superapacitor Electrode with Long Cycle Stability in KOH and Na2SO4 Aqueous Eletrolytes

The limitation of low-cost and high-safety aqueous manganese-based materials for electrochemical energy storage is largely hampered by their poor cyclic stability, which is usually caused by the manganese dissolution and interfacial kinetics. Here we synthesize a composite electrode which possesses unique structural properties for aqueous supercapacitor application and exhibits higher area specific capacitance. The remarkable long cycle stability of Mn3P2O8/TiN on titanium (Mn3P2O8/TiN@Ti) outperforms that most manganese-based pseudocapacitive electrode materials. The designed unique structure is attractive for quick charge migration, which confirms that the appropriate anodizing of substrate, electrodeposition of active substances and their in situ loading, is an efficient strategy to improve kinetics for high power density pseudocapacitive supercapacitor energy storage application.

Mixed-valence iron phosphate: Superhydrophilic multi-plated microflakes towards symmetric supercapacitor

Mixed valance state iron phosphate microflakes have been successfully grown by using binder-free, simple, and low-cost chemical bath deposition (CBD) method. Interestingly, grown microflakes embedded with layered flakes platelets are responsible for capillary action to exhibit a superhydrophilic nature. Iron phosphate includes two-oxidation (Fe+2 and Fe+3) states of cation and unique surface architecture that will play important role in the charge storage by providing more redox-active centres which motivated us to employ as liquid configured supercapacitive electrode. To get insight, structural, valence state, surface morphological, and wettability investigations have been performed through XRD, XPS, SEM, HR-TEM, and contact angle measurements. Multilayer hierarchical iron phosphate pseudocapacitive electrode exhibited specific capacitance of 927 F/g and specific capacity of 668 C/g at a 3 mV/s scan rate through cyclic voltammetry and excellent coulombic efficiency through galvanostatic charge-discharge with 96.7% stability at 4000 cycles in KOH electrolyte. First-ever fabricated liquid configured symmetric supercapacitor device based on iron phosphate electrode yield capacitance of 80 F/g and specific capacity of 104 C/g at the scan rate of 10 mV/s with cycling stability of 80% after 2500 cycles forming basis for future practical applications.

Efficient Recovery Annealing of the Pseudocapacitive Electrode with a High Loading of Cobalt Oxide Nanoparticles for Hybrid Supercapacitor Applications.

Electrochemical pseudocapacitors, along with batteries, are the essential components of today’s highly efficient energy storage systems. Cobalt oxide is widely developing for hybrid supercapacitor pseudocapacitance electrode applications due to its wide range of redox reactions, high theoretical capacitance, low cost, and presence of electrical conductivity. In this work, a recovery annealing approach is proposed to modify the electrochemical properties of Co3O4 pseudocapacitive electrodes. Cyclic voltammetry measurements indicate a predominance of surface-controlled redox reactions as a result of recovery annealing. X-ray diffraction, Raman spectra, and XPES results showed that due to the small size of cobalt oxide particles, low-temperature recovery causes the transformation of the Co3O4 nanocrystalline phase into the CoO phase. For the same reason, a rapid reverse transformation of CoO into Co3O4 occurs during in situ oxidation. This recrystallization enhances the electrochemical activity of the surface of nanoparticles, where a high concentration of oxygen vacancies is observed in the resulting Co3O4 phase. Thus, a simple method of modifying nanocrystalline Co3O4 electrodes provides much-improved pseudocapacitance characteristics.