Electric Double Layer Capacitance Research Articles

Carbon Nanotube-Based Printed All-Organic Microelectrode Arrays for Neural Stimulation and Recording

In this paper, we report a low-cost printing process of carbon nanotube (CNT)-based, all-organic microelectrode arrays (MEAs) suitable for in vitro neural stimulation and recording. Conventional MEAs have been mainly composed of expensive metals and manufactured through high-cost and complex lithographic processes, which have limited their accessibility for neuroscience experiments and their application in various studies. Here, we demonstrate a printing-based fabrication method for microelectrodes using organic CNT/paraffin ink, coupled with the deposition of an insulating layer featuring single-cell-sized sensing apertures. The simple microfabrication processes utilizing the economic and readily available ink offer potential for cost reduction and improved accessibility of MEAs. Biocompatibility of the fabricated microelectrode was suggested through a live/dead assay of cultured neural cells, and its large electric double layer capacitance was revealed by cyclic voltammetry that was crucial for preventing cytotoxic electrolysis during electric neural stimulation. Furthermore, the electrode exhibited sufficiently low electric impedance of 2.49 Ω·cm2 for high signal-to-noise ratio neural recording, and successfully captured model electric waves in physiological saline solution. These results suggest the easily producible and low-cost printed all-organic microelectrodes are available for neural stimulation and recording, and we believe that they can expand the application of MEA in various neuroscience research.

Microwave irradiation-induced yield enhancement of coconut shell biomass-derived graphene-like material

This paper reports a new strategy (rapid and selective microwave irradiation) to achieve an improved yield of graphene-like material derived from coconut shell biomass. The influence of various microwave irradiation (MWI) powers (80, 240, and 400 W) treatment on the crystalline structures, morphology, and electrochemical performance of the produced samples was determined and compared with the virgin-untreated specimen. The obtained samples were analyzed using varied analytical techniques. The FESEM images of the irradiated samples revealed the existence of graphene-like morphologies accompanied by some thin and transparent sheets. The sample at 80 W displayed the best quality with the highest yield, improving the carbon content, reducing the oxygen functional groups, and increasing the BET-specific surface area by as much as 1238.48 m2/g. The electrochemical properties of the sample treated at 80 W (optimum MWI power treatment) exhibited rectangular curves against scanning speeds, indicating an ideal capacitive behaviour called electric double-layer capacitance (EDLC). It is asserted that the proposed systematic and eco-friendly approach in obtaining the high-performance graphene-like material at low cost may open up sundry opportunities for practical applications, leading towards sustainable development.

High-efficient water splitting over an in-situ growth novel electrocatalyst of metal-organic framework-based nanostructures

Metal-organic frameworks (MOFs) as emerging material have drawn much attention to apply to the field of water splitting. In this paper, layered NiFe-MIL-53 and nanoflower-like CoFe-MOF-74 were sequentially grown on nickel foam through two-step in-situ growth to construct a MOF-74/MIL-53 heterojunction. On this basis, we used the localized surface plasmon resonance (LSPR) effect of gold nanoparticles (Au NPs) to significantly improve the oxygen evolution reaction performance of MOF-74/MIL-53 heterojunction. Under illumation, the obtained Au-MOF-74/MIL-53 exhibits a lower overpotential of 218 mV, which is far superior to commercial catalyst. The reaction kinetics are significantly enhanced due to the lower charge transfer resistance and the higher electric double layer capacitance. We confirmed the existence of charge transfer between Au NPs and MOFs, and at the same time, the deposition of Au NPs significantly reduced the charge transfer resistance of MOF-74/MIL-53. On the basis of our work, we provide a novel MOF-based electrocatalytic nanocomposite structure for efficient water splitting.

Electro-assisted sorption behavior and mechanism of low-concentration rare earth elements on carbon based materials

With increasing demands for rare earth elements (REEs) in high-tech and futuristic applications, developing efficient methods for recovering low-concentration REEs is necessary. Here, electro-assisted sorption of low-concentration REEs, La(III), Gd(III) and Y(III) (as symbol of light, medium, and heavy REEs) on carbon-based materials, activated carbon (AC), graphene, and graphite by a facile method was reported. Recovery of La(III), Gd(III) and Y(III) could reach ∼100 % under low-concentration condition where the maximum adsorption capacity was up to 342.38 mg/(g·dm2). Variants including applied voltage, electrodes-distance, pH, impurities, and concentration were considered to study the effects on REEs recovery. Interestingly, adsorption capacity and recovery under low voltage were respectively almost 20 and 14 folds than that without voltage, because voltage promoted REEs transfer and strengthened electrostatic interaction between electrodes and REEs. The mechanism for enhancing REEs recovery on carbon-based electrodes was resulted from high electric double layer (EDL) capacitance and low charge transfer resistance. Total desorption of REEs from electrodes could be quickly realized using NH4Cl or HCl solution. Overall, the study gave a new insight of low-concentration REEs recovery using carbon-based materials, and provided an efficient route using electric method with porous materials for REEs recovery.

Ion‐Impregnated Intermediate Layer for Enhancing Triboelectric Nanogenerator Performance

AbstractThe triboelectric nanogenerator (TENG) is gaining recognition as a highly promising, eco‐friendly self‐powered device for the growth of the Internet of Things (IoT). To improve the performance of TENGs, diverse materials are employed as interlayers. However, challenges related to cost and stability persist. Herein, a strategy that incorporates ion‐containing electrolyte polymers as interlayers is presented. This approach effectively mitigates charge decay and maximizes TENG efficiency by leveraging the high charge capacitance of the ionic electric double layer (iEDL). The incorporation of iEDL into TENG results in an approximate tenfold increase in current density (10–92 mA m−2) and a 13‐fold increase in power density (2–26 W m−2). The robust energy generation capabilities of iEDL‐TENG enable the operation of 100 LED lights and the charging of a 470 µF capacitor. Furthermore, the demonstrated device exhibits significant stability across 10,000 operational cycles and effectively maintains its performance when subjected to external physical forces such as blade‐induced cuts, penetrating wounds, and severe crumpling.

High Capacitance Based on Vacancy Defective Porous Carbon in Ionic Liquid

AbstractPorous carbons have been extensively studied in electrochemical capacitors (ECs). However, low capacitance remains a limitation due to the electrical double layer (EDL) storage mechanism when porous carbons are used in ionic liquids (ILs) based ECs. Herein, the nitrogen‐derived vacancy defects in porous carbon nanospheres are found which can boost capacitive charge storage and present reversible high capacitance of 427 F g−1 in pure IL electrolyte, equal to a normalized area capacitance (CA) of 16 µF cm−2, surpassing the theoretical EDL CA (≈11 µF cm−2). When used as capacitive cathode, the assembled Lithium hybrid capacitor express high energy density of 635 Wh kg−1 based on active material under much high‐power density of 14.5 kW kg−1. A combination of control experiments and density functional theory investigation indicate that the EC's performance improvement mostly stems from strong interactions at vacancy defects, triggering extraordinary faradaic capacitance. The results shed light on defect engineering for realizing extra faradaic capacitance of carbon materials, and open up new opportunities for improving EC's energy density.

Electrochemical Investigation of Lithium Perchlorate-Doped Polypyrrole Growing on Titanium Substrate

Lithium perchlorate-doped polypyrrole growing on titanium substrate (LiClO4-PPy/Ti) has been fabricated to act as electroactive electrode material for feasible electrochemical energy storage. A theoretical and experimental investigation is adopted to disclose the conductivity, electroactivity properties and interfacial interaction-dependent capacitance of LiClO4-PPy/Ti electrode. The experimental measurement results disclose that LiClO4-PPy/Ti reveals lower ohmic resistance (0.2226 Ω cm−2) and charge transfer resistance (2116 Ω cm−2) to exhibit higher electrochemical conductivity, a more reactive surface, and feasible ion diffusion to present higher double-layer capacitance (0.1930 mF cm−2) rather than LiClO4/Ti (0.3660 Ω cm−2, 65,250 Ω cm−2, 0.0334 mF cm−2). LiClO4-PPy/Ti reveals higher Faradaic capacitance caused by the reversible doping and dedoping process of perchlorate ion on PPy than the electrical double-layer capacitance of LiClO4/Ti caused by the reversible adsorption and desorption process of the LiClO4 electrolyte on Ti. Theoretical simulation calculation results prove that a more intensive electrostatic interaction of pyrrole N···Ti (2.450 Å) in LiClO4-PPy/Ti rather than perchlorate O···Ti (3.537 Å) in LiClO4/Ti. LiClO4-PPy/Ti exhibits higher density of states (57.321 electrons/eV) at Fermi energy and lower HOMO-LUMO molecule orbital energy gap (0.032 eV) than LiClO4/Ti (9.652 electrons/eV, 0.340 eV) to present the enhanced electronic conductivity. LiClO4-PPy/Ti also exhibits a more declined interface energy (−1.461 × 104) than LiClO4/Ti (−5.202 × 103 eV) to present the intensified interfacial interaction. LiClO4-PPy/Ti accordingly exhibits much higher specific capacitances of 0.123~0.0122 mF cm−2 at current densities of 0.01~0.10 mA cm−2 rather than LiClO4/Ti (0.010~0.0095 mF cm−2, presenting superior electroactivity and electrochemical capacitance properties. LiClO4-PPy/Ti could well act as the electroactive supercapacitor electrode for feasible energy storage.

Effect of endogenous chloride ion on the corrosion behavior of reinforcement embedded in sea-sand UHPC matrix in different immersion environments

Ultra-high performance concrete (UHPC) is an innovative cement-based composite material characterized by extremely high durability and mechanical properties, which provides a potential possibility of using non-desalted sea-sand as aggregate. However, the long-term steel corrosion behavior in UHPC prepared by simulated sea-sand under different immersion environments remains unclear, which is of great significance for the application of sea-sand UHPC in practical engineering. In this study, the pore structure of sea-sand UHPC matrix was measured using nitrogen adsorption/desorption method. The corrosion behavior of rebar in sea-sand UHPC with different endogenous chloride ion contents soaking in pure water and NaCl solution was characterized by linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and cyclic polarization (CP). The experimental results show that the initial UHPC pore structure is refined by incorporation of sea-sand, and is similar to that of ordinary UHPC at the later hydration. Regardless of the endogenous chloride ion content and immersion environment, the corrosion rate evaluated by corrosion current density (icorr) and polarization resistance (Rp) of reinforcement in UHPC is extremely low. The measurement of EIS shows that UHPC group has higher matrix resistance (Rc) and charge transfer resistance (Rct), while lower electric double layer capacitance (CPEdl) of reinforcement, which indicates that the steel in UHPC made of sea-sand is still in a state of passivation. However, the steel bar in comparison specimen OPC soaking in NaCl solution is in the corrosion stage. Furthermore, sea-sand UHPC possesses of excellent ability of anti-pitting corrosion of reinforcement after 180 days of immersion in NaCl solution.

Redox transformation of bismuth active units encapsulated on carbon nanorods for efficient fluoride Electrosorption: Synergistic roles of Faradaic effect and EDL capacitance

Remediation of fluoride in groundwater through electrosorption to cope with its high charge density and the smallest anion radius remains a promising strategy. Composite carbon materials obtained by calcining metal–organic frameworks contribute to the performance of conventional fluoride electrosorption systems. This study provides a redox-active electrode (MBiC@tE) that incorporates the Faradaic ion trapping effect for fluoride removal. Under potential control, MBiC@tE reversibly traps/releases fluoride anions from the aqueous solution through the combined roles of Faradaic pseudocapacitance and electrical double layer capacitance, with an electrosorption capacity of approximately 37.9 mgF- gelectrode-1. The target contaminant anions are directly involved in the Faradaic reaction on the bismuth sites, with the formation of Bi-F bond excited by an electric field, thus resulting in the removal of fluoride as a consequence of the generation of insoluble substance (BiF3). Furthermore, as expected (Bi0 + 3F- ⇌ BiF3 + 3e-), the working electrode exhibits good reversibility and maintains a high fluoride removal capacity even after multiple cycles. This study presents a comprehensive elucidation on the synergistic roles of Faradaic effect and electrical double layer capacitance induced by the electric field, and offers profound insights into the phase transition of bismuth and its affinity for fluoride during the electrosorption.

Near‐Infrared Active Tri‐nanohybrid for Enhanced Energy Harvesting

AbstractEfficient energy harvesting through full solar spectrum utilization has been considered a promising solution to world energy and environmental issues. In this direction, lead sulphide (PbS) quantum dot (QD) based hybrid materials find greater application due to their near‐infrared (NIR) active photo response. Slower charge injection and inefficient charge separation limit photoactive response of such NIR active low band gap semiconductor like PbS QDs. Moreover, constructing dual charge transfer pathways in a PbS QDs based nanocomposite through the formation of hybrids with suitable materials can be advantageous in suppressing the charge recombination. In this work, we have synthesized a nanocomposite after decorating the PbS‐QDs with semiconducting TiO2 nanoparticles modified with multiwall carbon nanotubes (MWCNT) and thus forming the tri‐hybrid (PbS‐TiO2‐MWCNT) nanocomposites. The enhanced photo‐activities of the tri‐hybrid, as compared to di‐hybrids like PbS‐TiO2, PbS‐MWCNT were confirmed by the steady state, time‐resolved photoluminescence (TRPL) measurements and reactive oxygen species (ROS) generation measurements. Higher ROS generation in the tri‐hybrid has been correlated with a faster interfacial electron transfer due to the dual charge injection pathway of PbS QD to TiO2 and MWCNT. The enhanced activity of the trio‐hybrid has also been analyzed from the first principal calculations in light of an efficient interfacial electron transfer as a result of the dual charge injection pathway. The photoelectrochemical water‐spilling response of the photoanodes in terms of photocurrent density, electrochemical impedance, and Mott–Schottky measurements on PbS‐TiO2 and PbS‐TiO2‐MWCNT photoanodes reveal that a combination of MWCNT and TiO2 exhibits an increase in electrical double layer capacitance, decrease in series resistance and enhancement of carrier density with NIR illumination at the heterojunction. Overall, all the dynamical studies at the interface of the trihybrid‐based photoanodes demonstrate its potential of utilization as a futuristic NIR‐ active photoelectrochemical water‐splitting material.

Effect of fluoride (CoF2) based electrode material for high energy and power density asymmetric flexible supercapacitors

Herein, an asymmetric supercapacitor (ASC) device was assembled by employing the pristine CoF2 as active positive electrode material and activated carbon (AC) as negative electrode material. The CoF2 electrode exhibited an outstanding electrochemical behavior with enhanced specific capacitance (Cs) of 872 F/g at 1 A/g current density in three electrode configurations. The reversible Faradaic redox reactions in CoF2 instigate the formation of cobalt-oxyfluorides and generating the mixed valence state of Co (Co2+ and Co3+) which improves its electrical conductivity and electrochemical behaviors. Furthermore, the room temperature paramagnetic nature of CoF2 increases the gradient force of ions which could possibly increase the redox reactions at the electrolyte/electrode interface. The constructed asymmetric device structure of CoF2//AC revealed a quasi-rectangular shaped cyclic voltametric curve and symmetrical semi-triangular shaped galvanostatic charge-discharge profiles, respectively, which affirms the combined electric double layer capacitance and pseudocapacitive nature by its hybrid assembly. Hence, the constructed CoF2//AC ASC demonstrated a remarkable specific capacitance of 141 F/g, energy density of 44.06 Wh.Kg−1, and power density of 422.97 W.Kg−1 at 1 A/g with the high cell voltage of 1.5 V. The CoF2//AC ASC device retained c.a. 92 % of its initial capacitance and attained over 96 % of Coulombic efficiency after 2000 cycles of charge-discharge profiles at 1 A/g, which suggests the high electrochemical stability. This admirable electrochemical performance and the origin towards the magneto-capacitance of CoF2 could pave a new way to explore next generation high-performance supercapacitors.

Synergistic contribution of activated carbon and PEDOT:PSS in hybrid electrodes for high-performance planar micro-supercapacitors

The high-performance miniaturized micro-supercapacitors exhibit great potential due to their inherent properties of high-power density, fast charge–discharge rates, long cycle life, and wide working temperature range. However, there is a need to further enhance the energy density of micro-supercapacitors. In this study, we investigate a hybrid electrode material combination comprising activated carbon (AC) and polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) to fabricate symmetric micro-supercapacitors (SMSCs) and employ the advanced Microplotter technique for the effective loading of active materials onto microelectrodes. The combination of AC and PEDOT:PSS is fine-tuned to attain optimal charge storage. This involves leveraging the synergistic impact of electrical double-layer capacitance from AC and pseudocapacitance from PEDOT:PSS, resulting in enhanced charge storage performance. Additionally, PEDOT:PSS acts as a mixed ion–electron conducting adhesive, effectively binding AC particles together and facilitating the rapid transport of both ions and electrons. As a result, the AC-PEDOT:PSS SMSCs demonstrate an impressive charge storage performance compared to AC SMSCs. At 1 mA/cm2, the measured areal capacitance (device areal capacitances) is 29.5 mF/cm2 (11.8 mF/cm2) for AC-PEDOT:PSS and 15.7 mF/cm2 (6.3 mF/cm2) for AC SMSCs. Furthermore, the areal energies and powers, considering active materials, are found to be 2.79 µWh/cm2 at 0.8 mW/cm2, and considering the device area of the SMSC, they are 1.12 µWh/cm2 at 0.32 mW/cm2. Notably, the AC-PEDOT:PSS SMSCs exhibit a stable long-term capacitance with 85% capacitance retention even after 5000 cycles. This work highlights the significant potential of hybrid materials in improving energy storage performance and showcases the innovative application of the Microplotter technique.

Droplet-Based Direct-Current Electricity Generation Induced by Dynamic Electric Double Layers.

Harvesting energy from water droplets has received tremendous attention due to the pursuit of sustainable and green energy resources. The droplet-based electricity generator (DEG) provides an admirable strategy to harvest energy from droplets into electricity. However, most of the DEGs merely generate electricity of alternating current (AC) output rather than direct current (DC) without the utilization of rectifiers, impeding its practical applications in energy storage and power supply. Here, a direct current droplet-based electricity generator (DC-DEG) is developed by the simple configuration of the electrodes. The DC output originates from the dynamical electric double layer (EDL) formed at two electrodes and droplet interfaces where the charging/discharging process of EDL capacitance occurs. Several experiments are exhibited to demonstrate the rationality of the proposed principle. The influence of some factors on the output is investigated for further insight into the DC-DEG device. This work provides a novel strategy to harvest energy from water droplets directly into DC electricity and may expand the application of DEGs in powering electronic devices without the help of rectifiers.

Characteristics of low-pressure-plasma-processed NiRu-MOFs/nickel foam for Hydrogen evolution reaction

NiRu bimetallic metal–organic frameworks (NiRu-MOFs) are grown by a simple hydrothermal method on nickel foam (NF) as an the electrocatalyst for the hydrogen evolution reaction. Low-pressure plasmas of pure Ar, 95%Ar + 5%H2, and 95% Ar + 5%O2 are used for the post-treatment of the NiRu-MOFs. NiRu-MOFs-AO with post-plasma treatment with 95%Ar + 5%O2 show the lowest overpotential of 123.3 mV at a current density of 10 mA cm−2 and a Tafel slope of 72.0 mV dec−1 in 1 M KOH electrolyte. Electrochemical impedance spectroscopy results indicate that post-plasma treatment can further reduce the charge transfer resistance. Moreover, the electric double-layer capacitance (Cdl) is calculated based on the cyclic voltammetry results, and the electrocatalyst subjected to 95%Ar + 5%O2 post-plasma treatment shows a 2Cdl value of 3.69 mF/cm2, suggesting a larger electrochemically active surface area after oxygen-containing-plasma treatment.

A Cross-linked n-Type Conjugated Polymer with Polar Side Chains Enables Ultrafast Pseudocapacitive Energy Storage.

Pseudocapacitors bridge the performance gap between batteries and electric double-layer capacitors by storing energy via a combination of fast surface/near-surface Faradaic redox processes and electrical double-layer capacitance. Organic semiconductors are an emerging class of pseudocapacitive materials that benefit from facile synthetic tunability and mixed ionic-electronic conduction. Reported examples are mostly limited to p-type (electron-donating) conjugated polymers, while n-type (electron-accepting) examples remain comparatively underexplored. This work introduces a new cross-linked n-type conjugated polymer, spiro-NDI-N, strategically designed with polar tertiary amine side chains. This molecular design aims to synergistically increase the electroactive surface area and boost ion transport for efficient ionic-electronic coupling. Spiro-NDI-N demonstrates excellent pseudocapacitive energy storage performance in pH-neutral aqueous electrolytes, with specific capacitance values of up to 532 F g-1 at 5 A g-1 and stable cycling over 5000 cycles. Moreover, it maintains a rate capability of 307 F g-1 at 350 A g-1 . The superior pseudocapacitive performance of spiro-NDI-N, compared to strategically designed structural analogues lacking either the cross-linked backbone or polar side chains, validates the essential role of its molecular design elements. More broadly, the design and performance of spiro-NDI-N provide a novel strategy for developing high-performance organic pseudocapacitors.

Exploring optical and electrochemical studies on thulium selenite (TmSeO3)

Abstract Thulium selenite (TmSeO3) has been synthesized by precipitation method. It shows interesting smooth surface with nearly non-symmetric texture similar to water droplets spreading on hydrophobic surface. TmSeO3 is found to be monoclinic structure with lattice parameters a = 5.919±0.01 Å, b = 12.422±0.01 Å, c = 8.717±0.01 Å, α = γ = 90°, β = 106.01° and V = 616.1 Å3. Fourier transform infrared spectroscopy confirms the presence of Tm–Se bonding. X-ray photo emission spectrum confirmed the presence of thulium, selenium and oxygen in the samples in oxide form. Magnetic study between 300 and 20 K, shows decrease of magnetic moment with temperature, then reaches saturation and aligns all thulium spins. This results cooperative interaction of thulium spins. M–H curve at 300 K confirms the paramagnetic nature of sample. Cyclic voltammogram of three electrode system, manifests electric double layer capacitance with a potential window of 0.55 V. Specific capacitance is 102 F/g. Chronopotentiometry analysis shows 75 F/g specific capacitance, 11 Wh kg−1 energy density, and 275 W kg−1 power density. Impedance analysis confirms electric double layer capacitor behavior. Hence, TmSeO3 electrode based symmetric supercapacitor device was successfully fabricated and tested by two electrode configuration in aqueous electrolyte of KOH. A specific capacitance of 64.60 F/g at 1 A/g within a potential window of 1.85 V was achieved. Impedance analysis also confirms electric double layer capacitor nature with low series resistance of 0.2596 Ω and charge transfer resistance of 1.6352 Ω. The improved cycling performance after 4000 cycles is 51.5 % specific capacitance retention. Thus, symmetric supercapacitor electrodes based TmSeO3 materials are expected to have good electrochemical properties and good stability for energy storage and conversion applications. Furthur, optical parameters 5.28 eV energy gap, 0.4924 eV Urbach energy value and 1.959 refractive index are determined.

Vanadate-based Fe-MOFs as promising negative electrode for hybrid supercapacitor device

In the supercapacitor field, negative electrodes are mainly concentrated in carbon-based materials, such as activated carbon, carbon nanotubes, graphene, and so forth. However, materials based on metal–organic frameworks (MOFs) as negative active components are relatively rare. Herein, a series of composite materials based on graphene oxide (GO) and vanadate-based Fe-organic frameworks have been prepared by hydrothermal method namely GO/Fe-VO4-BIPY. The deposition amount of polyoxometalate-based metal–organic frameworks (POMOFs) on the surface of graphene is adjusted by changing the content of POMOFs. Through the deposition, it can effectively reduce the accumulation between graphene, and increase the dispersion of POMOFs. As a result, the charge storage performance of the as-obtained materials is greatly improved. Among these materials, GO/Fe-VO4-BIPY-1 has the most prominent performance, with a specific capacitance of 190 F g−1 at 0.5 A g−1, which is attributed to the excellent synergistic effect between the Faraday chemical reaction and electric double-layer capacitance. In comparison with pristine Fe-VO4-BIPY, GO/Fe-VO4-BIPY-1 delivers more excellent surface area and therefore exhibits abundant redox reaction sites, achieving better electrochemical performance the best. After assembly with the positive Ni(OH)2 electrode, the maximum energy density of 46.84 W h kg−1 at a power density of 850 W kg−1 is achieved.

Janus molybdenum di-chalcogenides based van der Waals bilayers for supercapacitor electrode design- effects of interlayer stacking orientations on quantum capacitance

In this work, for the first time, the quantum capacitance of an artificial two-dimensional (2D) material system based on van der Waals (vdW) bilayer heterostructures of Janus Molybdenum Di-chalcogenides, MoXY (X≠Y, X/YS, Se, Te) have been extensively investigated for electrode design of electrical double-layer (EDL) supercapacitor. The effects of different interlayer stacking orientations on local charge distribution, interlayer charge transfer, energy band structure, and density of states (DOS) have been comprehensively analyzed and correlated with the excess charge density and quantum capacitance variation with local electrode potential. Furthermore, the total capacitance reduction with respect to EDL capacitance has been analyzed over a wide range of EDL capacitance, and the performance of vdW Janus bilayers has been systematically benchmarked against the natural monolayers/bilayers and Janus monolayers of Molybdenum Di-chalcogenides. The results demonstrate that the large interlayer charge transfer induced built-in interlayer electric field significantly reduces the energy band gap of vdW Janus bilayers for S–Te and Se–Te interlayer stacking, thus leading to a significantly superior quantum capacitance. Finally, the favorable valley-dependent effective mass and band-degeneracy in MoSTe/MoSeTe have greatly enhanced quantum capacitance in S–Te and Se–Te stacking, rendering these bilayers a highly attractive candidate for supercapacitor electrode design.

Highly conductive, conformable ionic laser-induced graphene electrodes for flexible iontronic devices

Iontronic devices, recognized for user-friendly soft electronics, establish an electrical double layer (EDL) at the interface between ion gels and electrodes, significantly influencing device performance. Despite extensive research on ion gels and diverse electrode materials, achieving a stable interfacial formation remains a persistent challenge. In this work, we report a solution to address this challenge by employing CO2 irradiation as a bottom-up methodology to directly fabricate highly conductive, conformable laser-induced graphene (LIG) electrodes on a polyimide (PI)-based ion gel. The PI ion gel exhibits exceptional EDL formation at the electrode interface, primarily attributable to efficient ion migration. Particularly, ionic laser-induced graphene (i-LIG) electrodes, derived from the PI ion gel as a precursor, yield high-quality graphene with enhanced crystallinity and an expanded porous structure in the upward direction. This outcome is achieved through a pronounced thermal transfer effect and intercalation phenomenon between graphene layers, facilitated by the presence of ionic liquids (ILs) within the PI ion gel. Ultimately, in comparison to alternative soft electrode-based vertical capacitors, the utilization of i-LIGs and PI ion gels in the vertical capacitor demonstrates reduced interfacial resistance and increased EDL capacitance, emphasizing the extensive potential of iontronic devices. These results not only highlight these features but also introduce a new perspective for advancing next-generation iontronic devices.

Redox-Active Phenanthrenequinone Molecules and Nitrogen-Doped Reduced Graphene Oxide as Active Material Composites for Supercapacitor Applications.

Carbon-based supercapacitor electrodes are generally restricted in energy density, as they rely exclusively on electric double-layer capacitance (EDLC). The introduction of redox-active organic molecules to obtain pseudocapacitance is a promising route to develop electrode materials with improved energy densities. In this work, we develop a porous nitrogen-doped reduced graphene oxide and 9,10-phenanthrenequinone composite (N-HtrGO/PQ) via a facile one-step physical adsorption method. The electrochemical evaluation of N-HtrGO/PQ using cyclic voltammetry showed a high capacitance of 605 F g-1 in 1 M H2SO4 when the composite consisted of 30% 9,10-phenanthrenequinone and 70% N-HtrGO. The measured capacitance significantly exceeded pure N-HtrGO without the addition of redox-active molecules (257 F g-1). In addition to promising capacitance, the N-HtrGO/30PQ composite showed a capacitance retention of 94.9% following 20,000 charge/discharge cycles. Based on Fourier transform infrared spectroscopy, we postulate that the strong π-π interaction between PQ molecules and the N-HtrGO substrate enhances the specific capacitance of the composite by shortening pathways for electron transfer while improving structural stability.