Pseudocapacitive Electrode Research Articles

In Situ-Grown Heterostructured Co3S4/CNTs/C Nanocomposites with a Bridged Structure for High-Performance Supercapacitors.

As one of the most competitive candidates for energy storage devices, supercapacitors have attracted extensive research interest due to their incomparable power density and ultralong cycling stability. However, the large surface area required for charge storage is an irreconcilable contradiction with the requirement of energy density. Therefore, a high energy density is a major challenge for supercapacitors. To solve the contradiction, Co3S4/CNTs/C with a bridged structure is designed, where CNTs generated in situ serve as a bridge to connect a porous carbon matrix and a Co3S4 nanoparticle, and Co3S4 nanoparticles are anchored on the topmost of CNTs. The porous carbon and Co3S4 are used for electrochemical double-layer capacitors and pseudocapacitors, respectively. This bridged structure can efficiently utilize the surface of Co3S4 nanoparticles to increase the overall energy storage capacity and provide more electrochemically active sites for charge storage and delivery. The materials show an energy density of 41.3 Wh kg–1 at 691.9 W kg–1 power density and a retaining energy density of 33.1 Wh kg–1 at a high power density of 3199.9 W kg–1 in an asymmetrical supercapacitor. The synthetic technique provides a simple method to obtain heterostructured nanocomposites with a high energy density by maximizing the effect of pseudocapacitor electrode active materials.

Sol-gel synthesized nickel oxide nanostructures on nickel foam and nickel mesh for a targeted energy storage application

The nickel-based oxides are treated as favourable pseudocapacitive electrode materials for energy storage application owing to their inexpensive nature, well-defined redox activity, as well as liberty in tuning the microstructures by changing the synthesis process optimizing its vital parameters. However, a real challenge for fabricating nickel-based materials is to sustain the uniform morphology onto a conductive substrates like FTO, ITO, stainless steel, nickel foam, nickel mesh, and copper foam etc. Herein, nickel oxide (NiO) nanostructures (NSs) with high pseudocapacitive performance have been prepared via the sol-gel technique for energy storage application. The structural identity of NiO-NSs is documented by X-ray diffraction, which confirmed the monoclinic crystal structure of the synthesized NSs. The X-ray photoelectron spectroscopy confirmed the valence state of the nickel as ‘+2′ and oxygen as ‘-2′. The field-emission scanning electron microscopy of NiO-NSs revealed non-uniform large spherical clusters agglomerated onto the surface. The NiO-NSs manifested the mesoporous channels and exhibit a surface area of 31.4 m2g-1, which is evaluated through Brunauer-Emmett-Teller analysis. The fabricated NiO-nickel foam (NF) electrode exhibit a high specific capacitance of 871 Fg−1 at a scan rate of 5 mVs−1 in 4 M KOH solution. Moreover, the NiO−NF electrode displayed the cyclic retention of 86.5 % after 10,000 cycles. The mesoporous channels of the electrode material afford plentiful, accessible, active sites to the effective charge transportation of electrolyte charges over the electrolyte-electrode interface and boost the electrochemical performance of NiONF −electrodes. Moreover, an asymmetric supercapacitor device constructed with NiO−NF as the anode and AC−NF as the cathode delivers high specific energy and specific power (24 Whkg−1 at 2.9 kWkg−1), and good cycling stability (retention of 89.7 % over 5 000 cycles)

Electrochemical Performance of Delafossite, AgFeO2: A Pseudo-Capacitive Electrode in Neutral Aqueous Na2SO4 Electrolyte

Layered delafossite AgFeO2 with open channel structure is envisaged as a pseudo capacitor electrode using Fe2+/Fe3+ redox couple. A simple co-precipitation method was employed for the phase formation of delafossite AgFeO2 resulting in a mixture of 2H and 3R-phase. Phase tuning of 2H phase was done by controlling the calcination conditions and characterizing by powder XRD, FT-IR, and Raman methods. 2H AgFeO2 was used to synthesize as a majority phase because it have the larger inter layer spacing than 3R phase shown. HRTEM study confirms the formation 2H phase in majority. All of the synthesized samples exhibit predominantly faradic battery-type redox behavior along with surface charge storage. Flower like microarchitectures of AgFeO2 show outstanding electrochemical performance with high specific capacity of 110.4 F g−1 at 1 A g−1 current density, that retained up to 89% after 2000th times charge/discharge in 1 M Na2SO4 electrolyte. In an asymmetric device mode, AFO-400//AC full cell exhibits superior electrochemical performance by delivering high energy density (33.5 Wh kg−1) and high power density (454.3 W kg−1) with excellent cycling stability (86% retention after 2000th cycles). The results clearly demonstrate that the synthesized delafossite AgFeO2 containing mixture of 2H and 3R-phases have remarkable potential to be used as a negative electrode material for supercapacitor and other energy storage technologies.

Methods—On the Reliability of the Electrochemical Data Recorded on Nickel Foam in Alkaline Solution: The Illusive Surface Oxide Layer

The extensive application of nickel foam (Ni foam) as current collector in supercapacitors has raised caveats on the contribution of the redox-active Ni foam to the measured capacities. However, due to the overlooked qualitative features (i.e., shapes) of the cyclic voltammograms (CVs), the redox reaction of the Ni foam oxide layer (NiFOL) has been frequently confused with the true electrochemical signature of the coated materials in alkaline solution. Herein, experimental CVs, scanning electron microscopy images, and estimations reveal that due to the high porosity of the Ni foam and its surface reactivity in alkaline solution (1–6 M KOH), the redox peak couple of the NiFOL can potentially be confused with or lead to misinterpretation of the true electrochemical features of the coatings. A classification of previous papers on a group of metal oxides investigated as battery-type or pseudocapacitive electrodes in the positive potential window is also presented to reveal the confusion between NiFOL and the coating when operated in alkaline solution.

Highly ordered nanoscale phosphomolybdate-grafted polyaniline/metal hybrid layered structures prepared via secondary sputtering phenomenon as high-performance pseudocapacitor electrodes

The development of energy storage electrode materials is important for enhancing the electrochemical performance of supercapacitors. Despite extensive research on improving electrochemical performance with polymer-based materials, electrode materials with micro/nanostructures are needed for fast and efficient ion and electron transfer. In this work, highly ordered phosphomolybdate (PMoO)-grafted polyaniline (PMoO-PAI) deposited onto Au hole-cylinder nanopillar arrays is developed for high-performance pseudocapacitors. The three-dimensional nanostructured arrays are easily fabricated by secondary sputtering lithography, which has recently gained attention and features a high resolution of 10 nm, a high aspect ratio greater than 20, excellent uniformity/accuracy/precision, and compatibility with large area substrates. These 10 nm scale Au nanostructures with a high aspect ratio of ∼30 on Au substrates facilitate efficient ion and electron transfer. The resultant PMoO-PAI electrode exhibits outstanding electrochemical performance, including a high specific capacitance of 114 mF cm−2, a high-rate capability of 88%, and excellent long-term stability.

Improved volumetric pseudocapacitance electrode obtained by solvothermal treatment of diethanolamine and different auxiliary solvents with MXene

Flexible supercapacitors (SCs) can usually be used as potential candidates for small flexible electronic devices, due to their good flexibility, rapid charge-discharge ability, and long-term cycling stability. Here, a facile solvothermal approach has been developed to prepare flexible and high-performance nitrogen-doped Ti3C2 MXene film electrodes for symmetric SCs. The effects of different solvents on the atomic structure, surface microstructure, and charge storage mechanism of N-doped Ti3C2 films were studied to explore the defect engineering of MXene for the enhancement of capacitive performance. Because of the comprehensive effects of the mixed solvents (diethanolamine (DEA) and isopropyl alcohol (IPA)) and the large inner pressure under the ex situ solvothermal process, the as-prepared N-doped Ti3C2 film fabricated from DEA and IPA with a volume ratio of 1:1 (IPAD-Ti3C2) shows a superhigh capacitance of 2846.5 F cm−3 at 5 mV s−1 and excellent stability. In addition, the IPAD-Ti3C2 film-assembled symmetric SC delivers a relatively large volumetric energy density of 64.0 Wh L−1 and a superhigh volumetric power density of 118,033.3 W L−1 at 1000 mV s−1. This work provides a feasible solution to improve the application potential of MXenes and, more broadly, binary metal carbides by ex situ nitrogen doping with mixed solvents.

La1-x K x FeO3-δ: An Anion Intercalative Pseudocapacitive Electrode for Supercapacitor Application.

The green energy alternative to a fossil fuel-based economy can be provided only by coupling renewable energy solution solutions such as solar or wind energy plants with large-scale electrochemical energy storage devices. Enabling high-energy storage coupled with high-power delivery can be envisaged though high-capacitive pseudocapacitor electrodes. A pseudocapacitor electrode with multiple oxidation state accessibility can enable more than 1e– charge/transfer per molecule to facilitate superior energy storage. K-doped LaFeO3 (La1–xKxFeO3−δ) is presented here as an electrode having a high pseudocapacitance storage, equivalent to 1.32e– charge/transfer per molecule, resulting in a capacity equivalent of 662 F/g at 1 mV/s scan rate by introduction of a layered potential over the Fe-ion octahedral to utilize higher redox state energies (Fe4+→ Fe2+). La/K ordering in orthorhombic perovskite (La1–xKxFeO3−δ) made the Fe4+ oxidation state accessible, and a systematic shift in the redox energies of Fe4+/3+ and Fe3+/2+ redox couples was observed with K+ ion doping in the A site of the LaFeO3 perovskite, which resulted in a high faradic contribution to the capacitance, coupled with anionic intercalation of H2O/OH– in the host perovskite lattice. The surface capacitive and diffusion control contributions for capacitance are about 42 and 58%, respectively, at −0.6 V, with a scan rate of 1 mV/s. A high gravimetric capacitance, equivalent to 619, 347, 188, 121, and 65 F/g, respectively, at 1, 2, 3, 5, and 10 A/g constant current, was observed for the La0.5K0.5FeO3−δ electrode. Up to 88.9% capacitive retention and 97% Coulombic efficacy were obtained for continuous 5000 cycles of charge/discharge for the La0.5K0.5FeO3−δ electrode. The gravimetric capacitance values of ASCs (activated carbon//La0.5K0.5FeO3−δ) are 348, 290, 228, and 147 F/g at current densities of 1, 2, 3, and 5 A/g, respectively. A maximum specific power of ∼3594 W/kg was obtained when the specific energy reached ∼117 Wh/kg at 5 A/g of current density.

3D printable ink for double-electrical-layer-enhanced electrode of microsupercapaitors

The key of the development of interdigital microsupercapacitors (MSCs) is to increase their areal energy density. 3D printing technology can build the pseudocapacitive electrodes companying with increasing the load capacity of pseudocapacitive materials in electrodes, resulting in the great increase of the areal energy density of MSCs. However, its major challenge is to design high electrical conductive pseudocapacitive materials and the related 3D printable inks. Here, a double-electrical-layer-enhanced structure of pseudocapacitive materials for electrodes is designed and its 3D printable ink is proposed and prepared in a simple method. The ink is used directly to 3D print the MSCs electrodes with double-electrical-layer-enhanced structure of pseudocapacitive materials simultaneously. The structure enhanced electrical conductivity of pseudocapacitive electrodes and their high load capacity boom the electrochemical performance of MSCs, especially the areal energy density. The method developed here is a good reference for research communities in this field. • A double-electrical-layer-enhanced structure of electrode material is designed. • A 3D printable ink is proposed to print the design-structured electrode. • The designed structure of electrode enhances its electrical conductivity. • The electrode has good charge storage due to its structure and high load capacity.

Unraveling the Role of Water on the Electrochromic and Electrochemical Properties of Nickel Oxide Electrodes in Electrochromic Pseudocapacitors

Although nickel oxide (NiO) is currently the most promising for industrialization as a counter electrode, it has proven challenging to achieve long-term-stable electrochromic devices. One of the crucial components is the mechanism of action of water on the active interface of the NiO counter electrode in the Li+-based electrolyte, which gives a basis of determinants for improving long-term cycling stability in devices. Herein, we investigate the role of water on the electrochemical and electrochromic properties of nickel oxide (NiO) electrodes. The finding of improved pseudocapacitive characteristics and reaction kinetics of NiO electrodes after introducing H2O into the Li+-based electrolyte can be originated from the increase of the number of ions and reduction of the electrolyte resistance and the interfacial charge-transfer resistance. On the one hand, the mechanisms for improved electrochemical and electrochromic properties such as a high coloration efficiency of 157.58 cm2 C−1 under the potential window of ±1.4 V, an excellent rate capability and a superior long-term cycling stability of over 10,000 cycles in the ESCs based on WO3 and NiO electrodes are elaborated. On the other hand, electrical water splitting can give rises to a degradation of optically cyclic stability of the NiO-based ESCs under the potential of > +1.23 V. These results provide a significant contribution to the reversibility and stability of the active interfaces for high performance electrochromic devices.

Pseudocapacitive and battery-type organic polymer electrodes for a 1.9 V hybrid supercapacitor with a record concentration of ammonium acetate

Aqueous all-organic battery-supercapacitor hybrid (BSH) devices are emerging as promising alternative energy storage systems to conventional metal-ion batteries/supercapacitors in terms of their easy processability, high tunability, cost-effectiveness, and recyclability. In this study, we demonstrate an all-organic BSH device using a record concentration of ammonium acetate (30 m NH4Ac) as a cheap and green electrolyte. This novel water-in-salt system possesses an electrochemical stability window up to 2.1 V. In addition, organic polymers comprising of perylenetetracarboxy diimide core and the mixed aromatic amine groups are employed as negative and positive electrodes, respectively. The polymers show low water solubility, good crystallinity, and nano-morphology, which make them decent candidates for the all-organic aqueous BSH device. More importantly, electrochemical kinetic analysis of polymer electrodes reveals that the negative and positive electrodes display pseudocapacitive and battery-type behaviors, respectively. For the first time, an all-organic BSH device with 30 m NH4Ac is fabricated, which delivers a specific capacity of 42 mA h g−1 at 200 mA g−1 and capacity retention of ca. 63% after 5000 cycles. It further shows the maximum energy density of 16.5 Wh kg−1 and power density of 719 Wh kg−1, depicting great potential in energy storage applications.

Fabrication of various metal hexacyanoferrates@CNF through acid-regulation for high-performance supercapacitor with superior stability

Prussian blue analogs, as a pseudo-capacitor electrode materials hold great potential due to their unique framework structure, excellent electrochemical activity and high specific capacity. Herein, a versatile method for the growth of series of metal hexacyanoferrates (MHCF) on carbon nanofiber with high conductivity and flexibility was proposed. By controlling the releasing rate of metal ions through acid modulation of solution, the series of MHCF nanocubes were successfully embedded on the carbon nanofibers with super stability. Different MHCF presented various loading density. Among the MHCFs, nickel hexacyanoferrate (NiHCF) is the most easily formed with high density and uniform distribution. The obtained self-supporting NiHCF@CNF, as a representative electrode, exhibited high specific capacitance (507 F g−1, 1 A g−1) and remarkable rate performance (67% retention at 10 A g−1). Moreover, the NiHCF@CNF-based hybrid supercapacitor cell delivered a high energy density of 60 Wh kg−1 at the power density of 810 W kg−1. Meanwhile, the capacitor showed extremely high stability due to tight anchoring of NiHCF on CNFs. This work provides a simple and versatile method to produce self-supporting MHCF@CNF composites for constructing high performance supercapacitor.

In Situ Growth of Ni–Zn–Fe Layered Double Hydroxide on Graphene Aerogel: An Advanced Two‐in‐One Material for Both the Anode and Cathode of Supercapacitors

The push toward high‐performance supercapacitors calls for the development of efficient pseudocapacitive negative electrode materials that can better match the high capacitance of the typical positive electrodes. Herein, a facile and one‐pot hydrothermal approach for the in situ growth of the nickel–zinc–iron layered double hydroxide (LDH) onto the graphene aerogel (GA) substrate is introduced. Proper selection of the metal precursors with prominent pseudocapacitive behavior over a wide potential range coupled with the excellent double‐layer capacitive and charge transport properties of the GA network results in an LDH–GA nanocomposite that displays outstanding supercapacitive performances as both negative (387 F g−1, 101 mA h g−1, at 1.0 A g−1) and positive (1235 F g−1, 103 mA h g−1) electrodes. An aqueous LDH–GA//LDH–GA device with a wide voltage window (1.55 V) that demonstrates a significantly enhanced specific capacitance (304 F g−1 at 1.0 A g−1), outstanding specific energy (95 W h kg−1), appreciable specific power (81 kW kg−1), along with 88% retention of the initial capacitance after 10 000 cycles, is also fabricated. The superior supercapacitive performance of the Ni–Zn–Fe LDH–GA nanocomposite over both negative and positive voltage ranges opens a promising pathway toward manufacturing high‐energy supercapacitors for state‐of‐the‐art applications.

MOF derived hierarchical carbon-enhanced MCo2S4 for high-performance hybrid supercapacitors

Ternary transition metal sulfides have attracted great research attention as effective pseudocapacitive electrode materials for high-performance supercapacitors. Herein, hierarchical carbon structure is derived from 2D zeolitic imidazolate framework to enhance overall electrochemical performances of MCo2S4 (M = Fe, Ni) nanospheres. Due to a positive synergistic effect induced by carbon substrate with excellent conductivity and the MCo2S4 with high electrochemical activity, the composite (C@MCo2S4) exhibits a specific capacity of 342.5 mAh g−1 at a current density of 1 A g−1 and a capacity retention of 69% at 10 A g−1. In addition, a hybrid supercapacitor with C@MCo2S4 and soybean derived porous carbon as the positive and negative electrodes delivers a high energy density of 45.9 Wh kg−1 at a power density of 775 W kg−1.

Lignin-based carbon nanofibe rs: Morphologies, properties, and features as substrates for pseudocapacitor electrodes

In this work, lignin-based carbon nanofibers (LCNFs) were for the first time served as substrate for in-situ electrodeposition of polyaniline (PANI) and tested as pseudocapacitor. Two LCNFs with different lignin ratios were designed to distinguish their morphology and structural properties. Next, PANI deposition mechanisms on both LCNFs were investigated and the electrochemical performance of the resulting LCNF/PANIs were evaluated. It was found although LCNF2 was composed of less uniform nanofibers due to more presence of lignin in precursor dope, it had higher tensile strength/modulus than LCNF1 (strength: 34.3MPa to 24.2 MPa; Modulus: 2.40 GPa to 1.45GPa) and was more cost-effective. Particularly, the beaded fibers on LCNF2 contributes to the deposition of PANI with higher specific mass capacitance (612.8 F g−1 to 547.0 F g−1). Upon assembling into solid-state supercapacitors, the Cm of LCNF2/PANI device was determined to be 229 F g−1 and the maximum energy density was 11.13Wh kg−1 at a power density of 0.08 kW kg−1. This work showed LCNF produced from renewable and low-cost lignin could be directly used as substrate for PANI deposition. Moreover, the composition in spinning dope played an important role in determining the performances of resulting pseudocapacitors.

Fast and stable potentiometric Na+ ion response of Na0.44MnO2 nanorod-based pseudocapacitive electrode via a short time activation

In this paper, Na0.44MnO2 nanorods were prepared by a hydrothermal reaction and used as sensing materials of Na+ ion selective electrode (ISE). After 30 min activation, the ISE showed rapid (about 2 s), steady and linear Nernstian-like responds (52.4 mV/dec) to Na+ concentrations ranging from 1 mol/L to 2.9 × 10−4 mol/L. The short time activation of Na0.44MnO2 nanorod electrode may be attributed for its pure Na0.44MnO2 phase (97.91%). The fast and stable potentiometric Na+ ion response of ISE resulted from the pseudocapacitive Na+ ion storage mechanism, because iso-oriented nanorod can short the diffusion path of Na+ ions and accommodate the stress from deinsert reaction of Na+ ions. The ISE can be used to monitoring NaCl concentration of petrochemical wastewater.

Enhancing Li-Ion Affinity of Molybdenum Dioxide/Carbon Fabric to Achieve High Pseudocapacitance.

High-energy electrodes at high mass loadings (usually >8.0mgcm-2 ) are desired for aqueous pseudocapacitors. Yet, how to overcome the thickness-dependent resistance increase of ion/electron transport in pseudocapacitive materials is still challenging. Herein, a high-performance electrode (denoted as AMC) adapted to high mass loading is achieved by promoting the Li-ion affinity of 3D MoO2 /carbon fabric. The experimental results and corresponding computational results reveal that the oxygen-activated surface of AMC, combined with the wettability and conductivity superiority of 3D graphite network, significantly facilitates the Li-ion adsorption and diffusion at the electrode/electrolyte interface, even at large thicknesses. Consequently, even at a high mass loading up to 8.1mg cm-2 , the AMC electrode also displays an impressive specific capacity (567.5 C g-1 at 2.5 A g-1 ), substantially superior to most advanced pseudocapacitive electrodes. The strategy of boosting energy characteristic by enhancing the affinity of charge carriers is applicable to other pseudocapacitive electrodes.

Simple, green organic acid-based hydrometallurgy for waste-to-energy storage devices: Recovery of NiMnCoC2O4 as an electrode material for pseudocapacitor from spent LiNiMnCoO2 batteries

A simple, green approach to recover NiMnCoC2O4 as an electrode material for high-performance pseudocapacitors from spent LiNiMnCoO2 (NMC) batteries is proposed. Four strategic metals (Li, Ni, Co, and Mn) were leached from spent NMC batteries using several organic acids as model green leachants. Among the various candidates of green leaching agents, 2 M citric acid and 5 wt% glucose were selected as the leachant and reductant, respectively. Microwave irradiation was conducted during the leaching step to maximize the performance of the leaching rate and efficiency. The leaching efficiencies within 0.5 h for Ni(II), Li(I), Mn(II), and Co(II) were 90.7 ± 1.6%, 98.3 ± 2.4%, 94.9 ± 4.3%, and 95.6 ± 1.4%, respectively, and were thus as efficient as using aqua regia leaching. After the leaching process, divalent metal ions, that is, Ni(II), Co(II), and Mn(II), were immediately separated at room temperature using oxalic acid. The recovered samples were not further treated and used directly for energy storage applications. The recovered NiMnCoC2O4⋅nH2O has been demonstrated as a promising electrode for pseudocapacitors, providing a specific capacitance of 1641 F/g, good rate-retention capability (80% of low-current capacitance), and good cycle stability over 4000 charge–discharge cycles.

Tween modified CuFe2O4 nanoparticles with enhanced supercapacitor performance

Binary metal oxides CuFe2O4 can be a low-cost and high-performance pseudo-capacitive electrode material. However, their large size distributions and low dispersion caused by agglomeration can not exert their potential capacity. Hence, we used tween to modify CuFe2O4 (CuFe2O4-T) nanoparticles via a facile hydrothermal method. The composite nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-Vis reflectance spectroscopy, and Fourier transform infrared spectroscopy. After modification, CuFe2O4-T showed high purity, greatly reduced particle size with the diameter about 10–20 nm, and decreased bandgap energy. When serving as supercapacitor electrodes, their electrochemical behaviors were examined by cyclic voltammetry, galvanostatic charge-discharge study, and electrochemical impedance spectroscopy. CuFe2O4-T exhibited improved supercapacitor behavior, with a specific capacitance of 437.3 F g−1 at the scan rate of 0.004 Vs−1 in 0.5 M H2SO4 electrolyte, 88.6% capacitance stability retention over 2000 cycles. An asymmetric supercapacitor device was assembled by using CuFe2O4-T as a positive electrode, which showed good capacitive behavior and cyclic stability. This work indicates that tween can effectively improve the performance of CuFe2O4 nanoparticles, and CuFe2O4-T will have great promise for wide electrochemical application.

Ultrafine Mn3O4 nanowires synthesized by colloidal method as electrode materials for supercapacitors with a wide voltage range

Manganese oxide is considered an ideal pseudo-capacitive electrode material for supercapacitors due to its low cost, environmental friendliness and large theoretical capacity. However, it is difficult to obtain manganese electrodes with a high specific capacitance and a large voltage range. In this study, ultrafine Mn3O4 nanowires with an average diameter of 4.0 nm were synthesized using a colloidal method. They have a large specific surface area of 175.1 m2 g−1, and can provide numerous active sites to enhance their specific capacitances. They also show a large pore volume of 0.7960 cm3 g−1, which can provide essential channels for ion transport during charging and discharging processes. The supercapacitor electrode made of these ultrafine Mn3O4 nanowires exhibits a predominant surface capacitive behavior during charge/discharge processes, and achieves a large specific capacitance of 433.1 F g−1 at a current density of 0.5 A g−1 with a very wide voltage range from -0.5 to 1.1 V in 1 M Na2SO4 electrolyte. An asymmetric supercapacitor (ASC) was assembled using a cathode electrode made of these ultrafine Mn3O4 nanowires and an active carbon (AC) anode electrode, and a high energy density of 26.68 Wh kg−1 at a power density of 442 W kg−1 was achieved. The ASC showed a good cycling stability, and its capacitance value was still maintained at 75.8% after 64,000 charge/discharge cycles.

MnOx-Electrodeposited Fabric-Based Stretchable Supercapacitors with Intrinsic Strain Sensing.

The increasing number of devices needed by wearable systems to bring radical advances in healthcare, robotics, and human-machine interfaces is a threat to their growth if the integration and energy-related challenges are not managed. A natural solution is to reduce the number of devices while retaining the functionality or simply using multifunctional devices, as demonstrated here through a stretchable supercapacitor (SSC) with intrinsic strain sensing. The presented SSC was obtained by electrodeposition of nanoflower MnOx on fabric (as a pseudocapacitive electrode) and three-dimensional conductive wrapping of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) to boost the performance. Among fabricated devices, the stretchable PEDOT:PSS/MnOx/PEDOT:PSS supercapacitor (SPMP-SC) showed the best performance (specific capacitance of 580 mF·cm-2 (108.1 F·g-1); energy density of 51.4 μWh·cm-2 at 0.5 mA). The stretchability (0-100%; 1000 cycles) analysis of SPMP-SC with Ecoflex encapsulation showed high capacitance retention (>90% for 40% stretch). The intrinsic strain sensing of the SSC was confirmed by the linear variation of capacitance (sensitivity -0.4%) during stretching. Finally, as a proof-of-concept, the application of SSC with intrinsic sensing was demonstrated for health monitoring through volumetric expansion of a manikin during ventilator operation and in robotics and by measuring the joint angle of a robotic hand.