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Natural salinity gradients are a promising source of so-called blue energy, a renewable energy source that utilizes the free energy of mixing for power generation. One promising blue energy technology that converts these salinity gradients directly into electricity is reverse electrodialysis (RED). Used at its full potential, it could provide a substantial portion of the worlds electricity consumption. Previous theoretical and experimental works have been done on optimizing RED devices, with the latter often focusing on precious and expensive metal electrodes. However, in order to rationally design and apply RED devices, we need to investigate all related transport phenomena─especially the fluidics of salinity gradient mixing and the redox electrolyte at various concentrations, which can have complex intertwined effects─in a fully functioning and scalable system. Here, guided by fundamental electrochemical and fluid dynamics theories, we work with an iron-based redox electrolyte with carbon electrodes in a RED device with tunable microfluidic environments and study the fundamental effects of electrolyte concentration and flow rate on the potential-driven redox activity and power output. We focus on optimizing the net power output, which is the difference between the gross power output generated by the RED device and the pumping power input, needed for salinity gradient mixing and redox electrolyte reactions. We find through this holistic approach that the electrolyte concentration in the electrode rinse solution is crucial for increasing the electrical current, while the pumping power input depends nonlinearly on the membrane separation distance. Finally, from this understanding, we designed a five cell-pair (CP) RED device that achieved a net power density of 224 mW m-2 CP-1, a 60% improvement compared to the nonoptimized case. This study highlights the importance of the electrode rinse solution fluidics and composition when rationally designing RED devices based on scalable carbon-based electrodes.

Due to the increasing global energy demand, there is an urgent need for more efficient energy storage systems. Redox-active electrolytes offer a promising, long-term solution for high-energy–density supercapacitors, as they enhance energy density and pseudo-capacitance through redox reactions. This study introduces a symmetric supercapacitor utilizing a dual-redox-active electrolyte, achieving the highest levels of pseudo-capacitance and energy density with a biomass-derived carbonaceous aerogel (BCA) electrode. The BCA electrode's unique flower-like cubic-sphere structure, partially graphitized edges, and high specific surface area of around 1299 m2g-1 enable efficient access for electrolyte ions, enhancing charge storage. The dual-redox electrolyte, comprising KBr and methyl viologen dichloride (MVCl2), enhances the performance of both electrodes through redox reactions, resulting in a maximum half-cell specific capacitance of about 887 Fg-1 at 1 Ag-1 current density. When incorporated into a supercapacitor device, this dual-redox-electrolyte system achieves a maximum specific capacitance of 560 Fg-1 and an energy density of approximately 77 WhKg-1 at the same 1 Ag-1 current density, with outstanding capacitance retention of approximately 93% over 10,000 charge–discharge cycles. Thus, the combination of KBr and MVCl2 in the KOH electrolyte, as demonstrated in this work, enhances redox behavior, leading to significantly more efficient energy storage solutions. [ABSTRACT FROM AUTHOR]

The present work focuses on the synthesis of hybrid La2CoCrO6/Co3O4/rGO composite via solvothermal technique for supercapacitor application. X-ray diffraction, field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller (BET), and Barrett-Joyner-Halenda analyses are employed to assess phase structure, morphology, chemical state, surface area, and porosity of synthesized materials, respectively. The formation of mesoporous spheres is confirmed through FESEM and BET analysis. The inclusion of redox additive KMnO4 in KOH electrolyte enhances the accessibility of electrochemical sites in the mesoporous spheres of the La2CoCrO6/Co3O4/rGO electrode, resulting in excellent charge storage. Electrochemical analysis of the La2CoCrO6/Co3O4 exhibits specific capacitance of 633.2 F/g at 2 A/g in a redox electrolyte (6 M KOH + 0.05 M KMnO4) with capacitive retention of approximately 81 % over 5000 cycles. Furthermore, the addition of rGO improves the overall performance of La2CoCrO6/Co3O4/rGO composite (763.9 F/g at 2 A/g with capacitive retention of approximately 86 %). The electrochemical analysis of hybrid La2CoCrO6/Co3O4/rGO composite showed improved performance, owing to the synergy of double perovskite (La2CoCrO6), cobalt oxide (Co3O4), and reduced graphene oxide (rGO). These findings suggest promising applications for the material in advanced energy storage devices.

Incorporation of redox nature at the electrode‐electrolyte interface is of the current research approach for enhancing the specific capacity as well the energy density of the carbon supercapacitor. In the present studies, symmetric carbon supercapacitor cells are fabricated by using gel polymer electrolytes (GPEs) with and without addition of redox‐additive (MB) and activated carbon (AC) extracted from natural bio‐waste honeycomb (HCAC). The redox‐additive polymeric electrolyte offers high room temperature ionic conductivity (σRT ~ 2.3 × 10−3 S cm−1) and electrochemical stability window of ~1.4 V on the addition of 0.1 g of MB. The HC‐based activated carbon (HCAC) offers high surface area ~ 586 m2 g−1 and dominant meso‐porosity. The performance optimization of the supercapacitor cells are examined by using cyclic voltammetry, charge‐discharge (CD) and electrochemical impedance spectroscopy (EIS) techniques. The supercapacitor with redox‐additive GPE shows the electric double layer features along with faradaic reaction at the electrode‐electrolyte interface, which offers high capacitance ~114 F g−1 and specific energy ~7.76 Wh kg−1 at a power density 0.49 kW kg−1, which is almost ~2.5 times higher than the supercapacitor cell without redox‐additive GPE. Furthermore, the supercapacitor cell with 0.1 g MB redox‐additive based electrolyte shows almost stable capacitance up to 10 000 CD cycles with ~36% initial fading. [ABSTRACT FROM AUTHOR]

This work investigates the electrochemical behavior of hybrid supercapacitors with carbon-based electrodes of different porosity using 5M NaNO3 + 0.5M KBr electrolyte to optimize energy storage processes. Three types of carbon materials were synthesized: activated carbon from rice husk (RH) with a specific surface area of ~2300 m2/g and pore size < 1 nm, and templated carbons from magnesium citrate (MP-8) and glucose with SiO2 as a template (G7), having surface areas of 1976 and 1320 m2/g and pore sizes of 3.4 and 7 nm, respectively. The microporous structure of activated carbon (AC) obtained from RH shows limitations in the diffusion of electrolyte ions, which affects the charge-discharge kinetics. In contrast, the larger mesoporous structures of templated carbons promoted better adsorption and ion transport, significantly affecting the dynamics of redox reactions. The RH/MP-8 hybrid capacitor, combining high surface area and large pore size, demonstrated a 54% increase in specific capacitance, 128% increase in specific energy and 51% increase in energy efficiency at high current densities of 5 A/g, comparing to the symmetric RH/RH hybrid capacitor. This study highlights the critical importance of the relationship between electrode pore structure and electrolyte composition for optimizing supercapacitor performance, which provides valuable information for the development of efficient energy storage technologies.

In the present study, an iodide/triiodide (I−/I3−) redox couple is used in hybrid electrochromic devices (ECDs), and the effects of the applied bias potential and bias time on device performance are studied. An applied bias potential of ~1 V is sufficient to achieve an initial contrast ratio of 8:1 in less than 5 min. Increasing both the bias potential and bias time results in an enhancement in loss reactions at the WO3/electrolyte interface, rather than improving optical performance. Moreover, long-term performance depends on the testing procedure (regularly cycling or after storage), while the formation of iodine (I2) decreases the initial transparency of the ECDs and affects their overall performance. However, its formation cannot be avoided, even without cycling the ECDs, and the restoration of the optical performance can take place only when the electrolyte is replaced with a fresh one. Finally, a new methodology is applied for calculating the loss current, and a suggestion is made to avoid a common mistake in calculating the coloration efficiency of these hybrid ECDs. [ABSTRACT FROM AUTHOR]

This work investigates the electrochemical behavior of hybrid supercapacitors with carbon-based electrodes of different porosity using 5M NaNO3 + 0.5M KBr electrolyte to optimize energy storage processes. Three types of carbon materials were synthesized: activated carbon from rice husk (RH) with a specific surface area of ~2300 m²/g and pore size < 1 nm, and templated carbons from magnesium citrate (MP-8) and glucose with SiO2 as a template (G7), having surface areas of 1976 and 1320 m²/g and pore sizes of 3.4 and 7 nm, respectively. The microporous structure of activated carbon (AC) obtained from RH shows limitations in the diffusion of electrolyte ions, which affects the charge-discharge kinetics. In contrast, the larger mesoporous structures of templated carbons promoted better adsorption and ion transport, significantly affecting the dynamics of redox reactions. The RH/MP-8 hybrid capacitor, combining high surface area and large pore size, demonstrated a 54% increase in specific capacitance, 128% increase in specific energy and 51% increase in energy efficiency at high current densities of 5 A/g, comparing to the symmetric RH/RH hybrid capacitor. This study highlights the critical importance of the relationship between electrode pore structure and electrolyte composition for optimizing supercapacitor performance, which provides valuable information for the development of efficient energy storage technologies. [ABSTRACT FROM AUTHOR]

In the present study, defective mesoporous carbon (DMC) was successfully synthesized via a facile hard templating route. Thanks to its interconnected porous framework with a high specific surface area of 1350 m2 g−1 was adapted as electrode material for supercapacitor application. In addition, the possibility of Reactive Red 198 as novel and efficient redox mediator was investigated using different techniques. The supercapacitor performance of DMC electrode was significantly enhanced through introducing of 5 mM Reactive red 198 into 1 M aqueous solution of H 2 SO 4. Analysis of scan rate by Trasatti method indicated that 86.5% of the overall capacitance was originated through the insertion of Reactive Red 198. The presented supercapacitor system exhibited a high specific capacitance of 282 F g−1, a good rate capability of 158 F g−1 at 10 A g−1 with 56% capacitance retention. Moreover, reasonable cycle durability with about 73% retention after a prolonged successive cycling process (2000 cycles) at current densities of 2 A g−1 was obtained. Finally, the specific energy of 9.8 W h kg−1 at specific power of 254 W kg −1 was achieved for symmetric device which shows 2.3 times increase in specific Energy over the DMC electrode with pure H 2 SO 4 electrolyte. • Defective mesoporous carbon (DMC) was synthesized. • Reactive Red 198 was applied as Redox additive electrolyte. • The specific capacity of 282 F g−1 was obtained. • Energy density of 9.8 W h kg−1 was delivered in redox-added electrolyte. [ABSTRACT FROM AUTHOR]

• Strong electron-withdrawing STFSI substitute functionalizes AQ with high stability. • AQSTFSI-K exhibits fast and highly reversible two-electron redox reactions in acetonitrile. • AQSTFSI-K shows 1.8 times specific capacitance of corresponding EDLCs. • The AQSTFSI-based ORECs display 3.2 V wide voltage, high energy density and excellent cycling stability. Organic redox electrolyte-enhanced electrochemical double layer capacitors (ORECs) are potentially better solution for combining both high power and energy density. The critical factor of ORECs is to develop high-performance organic redox electrolytes. Anthraquinone (AQ) derivatives are the promising organic redox electrolyte candidates because of their low redox potential and fast two-electron redox kinetics. Low solubility and poor longevity in aprotic solvents of charged AQ species are main issues for effective enhancement. Here we report two-electron redox ionic compounds by functionalizing AQ with a robustly electron-withdrawing sulfonyl(trifluoromethanesulfonyl)imide (AQSTFSI) anion and pairing counter monovalent cations for high-performance ORECs. The highly electron-conjugate substitute markedly stabilizes the radical and 2e−-charged forms of AQ by decentralizing the electron density of the C O heads, preventing the adverse reaction of electrophilic/nucleophilic attack, revealing by theoretical simulation. Also, the STFSI− substituent enables AQSTFSI-compounds significantly improved solubility, thermostability, and redox reversibility. Consequently, the AQSTFSI-K applied in OREC shows all-roundly superior performance containing 3.2 V cell voltage, specific energy of 58 Wh kg−1 with 1.8 times of corresponding electrochemical double layer capacitors (EDLCs), specific power over 8 kW kg−1, cycling stability over 12,000 cycles, low self-discharge, and wide working-temperature range. This molecular strategy grounded on electron density modulation of redox electrolyte structures provides valuable insights into the design for high-performance ORECs in practical applications. [ABSTRACT FROM AUTHOR]

With the continuous advancement in the dual-carbon strategy, the upswell in the demand for renewable energy sources has motivated extensive research on the development of novel energy storage technologies. As a new type of energy storage device, carbon-based redox-enhanced supercapacitors (RE-SCs) are designed by employing soluble redox electrolytes into the existing devices, exploiting the merits of the diffusion-controlled faradaic process of the redox electrolyte at the surface of carbon electrodes, thus leading to improved energy density without the cost of power density. During the past years, great progress has been made in the design of novel redox electrolytes and the configuration of new devices. However, the development of these systems is plagued by severe self-discharge. Herein, a comprehensive picture of the fundamentals, together with a discussion and outline of the challenges and future perspectives of RE-SCs, are provided. We highlight the impacts of redox electrolytes on capacitance, energy density, and power output. Notably, the self-discharge behavior owing to the introduction of redox electrolyte and its mechanism are also discussed, followed by a summary of the strategies from materials to system optimization. Furthermore, possible directions for future research are discussed.

In the present study, an iodide/triiodide (I−/I3−) redox couple is used in hybrid electrochromic devices (ECDs), and the effects of the applied bias potential and bias time on device performance are studied. An applied bias potential of ~1 V is sufficient to achieve an initial contrast ratio of 8:1 in less than 5 min. Increasing both the bias potential and bias time results in an enhancement in loss reactions at the WO3/electrolyte interface, rather than improving optical performance. Moreover, long-term performance depends on the testing procedure (regularly cycling or after storage), while the formation of iodine (I2) decreases the initial transparency of the ECDs and affects their overall performance. However, its formation cannot be avoided, even without cycling the ECDs, and the restoration of the optical performance can take place only when the electrolyte is replaced with a fresh one. Finally, a new methodology is applied for calculating the loss current, and a suggestion is made to avoid a common mistake in calculating the coloration efficiency of these hybrid ECDs.

Exploration of innovative strategies aiming to boost energy densities of supercapacitors without sacrificing the power density and long-term stability is of great importance. Herein, highly porous nitrogen-doped carbon spheres (NPCS) are decorated onto the graphite sheets (GSs) through a hydrothermal route, followed by a chemical activation. The capacitive performance of the NPCS is then enhanced by hydroquinone sulfonic acid (HSQA) incorporation in both cathodic electrolyte and electrode materials. Later, NPCS are decorated with polypyrrole (PPY), in which HSQA takes a versatile role as conjugated polymer dopant and cathodic redox additive. The capacitive performance of the negative electrodes is enhanced by incorporating of alizarin red S (ARS) as anodic redox additive. Finally, PPY(HQSA)@NPCS-GS//NPCS-GS asymmetric supercapacitor is assembled and tested in dual redox electrolyte system containing HQSA-cathodic and ARS-anodic electrolytes. This device delivers a remarkable energy density of 60.37 Wh kg -1 , which is close or even better than lead acid batteries. Thus, the present work provides a novel pathway to develop high energy supercapacitors using redox active electrolytes for next-generation energy storage applications., (© 2024 The Author(s). Small published by Wiley‐VCH GmbH.)

Developing efficient electrochemical capacitors relies heavily on the quality of electrode materials and electrolytes used. This report presents the successful solvothermal synthesis of three cobaltites, NiCo 2 O 4 , CuCo 2 O 4 , and ZnCo 2 O 4 , and their electrochemical performance in a 2 M KOH electrolyte. Among the three cobaltites, NiCo 2 O 4 showed the best electrochemical performance, delivering a specific capacity of 178 C/g when using FTO (fluorine-doped tin oxide) as the current collector. In addition, the performance of NiCo 2 O 4 was tested in different aqueous electrolytes, including KOH, NaOH, NaCl, and Na 2 SO 4 , and the specific capacity was found to vary in the order of 2 M KOH > 2 M NaOH > 2 M NaCl > 2 M Na 2 SO 4. The performance of NiCo 2 O 4 was also assessed in various concentrations of KOH electrolyte (2 M KOH, 3 M KOH, and 4 M KOH), and the best performance was observed in 3 M KOH with a specific capacity of 928.3 C/g with Ni foam as the current collector. Finally, using redox additive electrolytes, the electrochemical performance of NiCo 2 O 4 was evaluated in both 3-electrode and 2-electrode systems. No studies have been conducted on the electrochemical performance of NiCo 2 O 4 using KFCN redox additive in a 3 M KOH electrolyte. In the three-electrode system, NiCo 2 O 4 showed a high specific capacity of 1005.5 C/g at 1 A/g, with 167 % capacity retention after 1000 charge-discharge cycles at a high current density of 30 A/g. The NiCo 2 O 4 //Activated Carbon asymmetric hybrid supercapacitors(AHSC) exhibited a maximum specific capacity of 115.6 C/g and a specific energy density of 85 Wh/kg at current density of 1 A/g. The AHSC also showed a capacitive retention of 120 % after 5000 charge-discharge cycles. The maximum power density was 13225 W/kg at a current density of 5 A/g while maintaining an energy density of 22 Wh/kg. [ABSTRACT FROM AUTHOR]

CoS 2 nano-arrays were first prepared on conductive carrier carbon cloth (CC) by electrodeposition, oxidation and thermal vulcanization. CoS 2 /CC in the redox active electrolyte has higher specific capacitance (2325.5 mF cm−2) and better cycling stability (92.98% capacity retention after 5000 cycles). In-situ XPS reveals the charge storage mechanism of transition metal sulfide electrode materials. In addition, the self-discharge mechanism and influential factors of redox-active supercapacitors were investigated using open circuit potential tests and mathematical models. [Display omitted] • CoS 2 /CC solves the problem of agglomeration and poor stability of single component CoS 2. • Redox electrolyte enhanced supercapacitor based on CoS 2 /CC generates fast self-discharge. • Weak adsorption of redox active groups at the electrode leads to rapid self-discharge. Transition metal sulfides used as electrode materials are becoming increasingly attractive to researchers because of their excellent conductivity and capacitance in supercapacitors with alkaline electrolytes (KOH). However, the mechanism of self-discharge at an open circuit is still unclear. Herein, KOH electrolyte was replaced with redox electrolyte KOH + K 3 Fe(CN) 6 (PFC) to explore the self-discharge mechanism of nanosheet-like CoS 2 /CC. It was found that the CoS 2 /CC electrode in the redox electrolyte has high specific capacitance (2325.5 mF cm−2) at the current density of 1 mA cm−2. Afterwards, the self-discharge mechanism and influential factors of redox electrolyte enhanced supercapacitors were investigated using open circuit potential tests and mathematical models. It is worth noting that the device voltage assembled with CoS 2 /CC electrode decreased from 1.6 V to 0.8 V after the 2680 s in the redox electrolyte, which was faster than the self-discharge time (6435 s) in the KOH electrolyte. The main reason for the rapid self-discharge phenomenon is the limited surface area of the CoS 2 /CC electrode which has a weak adsorption capacity for redox active groups, allowing charged redox active substances to be transported freely in the electrolyte. At the same time, it objectively shows that the energy stored in the device is constantly dissipating. [ABSTRACT FROM AUTHOR]

Zinc-ion hybrid capacitors (ZIHCs) with high energy density is commercial need as energy storing devices, but facile preparation is still a challenge. Herein, we proposed a combined strategy for preparation of ZIHCs with high performance. For this purpose, a nanoemulsion assembly approach with Pluronic F127 as structure-directing agent, 1, 3, 5-trimethylbenzene as pore-expanding agent, polydopamine as carbon and nitrogen source, was used to synthesize hierarchically N-doped porous carbon spheres (N-HNCSs). The optimized sample of N-HNCS-1 exhibited uniform size of 150 nm, hierarchically porous structure, large surface area (705.46 m2 g−1), and N-doping amount of 6.51 %. These properties were beneficial for the transportation of the electrolyte ions resulted in that the N-HNCS-1 electrode displayed superior electrochemical performance with specific capacity of 142 mAh g−1. Furthermore, the Zn//ZnSO 4 + ZnI 2 //N-HNCS-1 ZIHCs achieves an exceptionally high energy density of 347.7 Wh kg−1, which is 3-fold higher than that of Zn//ZnSO 4 //N-HNCS-1 ZIHCs. To elucidate this outstanding performance, we investigate the mechanisms involved, including Zn2+ deposition/stripping, SO 4 2-/I- adsorption/desorption, Zn 4 SO 4 (OH) 6 ⋅0.5 H 2 O precipitation/dissolution, and redox reactions relating to iodine ions. The incorporation of ZnI 2 redox-electrolyte significantly enhanced the energy density by providing prominent pseudocapacitance via the faradaic reaction. Therefore, the high performance of Zn//ZnSO 4 + ZnI 2 //N-HNCS-1 ZIHCs is attributed to the introduction of nitrogen (N) species, advantageous 3D carbonaceous framework, and redox reactions triggered by adding zinc iodide (ZnI 2) into the aqueous zinc sulfate (ZnSO 4) electrolyte. This groundbreaking research opens up possibilities for the development of high-energy ZIHCs, and advancements in energy storage technology. [Display omitted] [ABSTRACT FROM AUTHOR]

Herein, we present pore architecture-tailorable porous carbons through a time-adjustable hydrothermal reaction and subsequent KOH chemical activation method. Accordingly, platanus spiky (Ps) fruits, taro (T) roots, and green bell peppers (Pp) biowaste substrates were utilized as sustainable precursors to construct novel hierarchical porous carbons (HPCs) with highly interconnected porous frameworks and smart micro/meso/macroporous architecture for supercapacitors. The heterogeneous feedstocks were pre-carbonized under hydrothermal conditions for different hold durations (12 h, 24 h, 36 h) at 200 °C. The optimized Ps-24h material exhibits a high capacitance of 371.6 F g−1 at 1 A g−1 in an aqueous Na 2 SO 4 electrolyte and an outstanding rate performance (94% capacitance retention after 10,000 charge-discharge cycles). Surprisingly, the specific gravimetric capacitance of HPCs can be significantly manipulated by establishing a high-performance redox electrolytic system. In particular, the tailored Ps-24h-based electrode delivers a superior capacitance of 843 F g−1 at 1 A g−1 with an exceptional rate capability (64.7% capacitance retention from 1 to 20 A g−1 in K 3 [Fe(CN) 6 ]/Na 2 SO 4 electrolyte). Consequently, the as-integrated Ps-24h//Ps-24h symmetric supercapacitor device with a working voltage of 1.8 V presents enhanced energy/power outcomes (63.8 W h kg−1/900.2 W kg−1) with remarkable long-term cyclic durability (90.4% capacitance retention after 15,000 cycles) in a redox electrolytic system. An eco-benign time-adjustable thermochemical strategy was adopted to form hydrochar-based HPCs from heterogeneous platanus spiky fruits, taro roots, and green bell pepper waste substrates. The effect of the hydrothermal reaction hold time on key characteristics was found to be of significant influence. The achievable Ps-24h material displays a high specific surface area (1801.74 m2 g−1), large total pore volume (⁓ 1.212 cm3 g−1), and prominent micro/meso/macropore structure. With these advantages, the optimized Ps-24h electrode realizes the combined EDLC-like behavior and Faradaic pseudocapacitance mechanism. The constructed Ps-24h//Ps-24h symmetric supercapacitor device reveals an outstanding charge storage performance, yielding a high specific energy density of 63.8 W h kg−1 at a specific power density of 900.2 W kg−1 and sustaining 90.4 % of its initial capacitance after 15,000 charge-discharge cycles. [Display omitted] • Time-adjustable hydrothermal approach to construct hydrochar-based HPCs. • The retention time affects the development of hierarchical porosities. • The achievable Ps-24h HPCs display prominent micro/meso/macroporous architecture. • The Ps-24h approaches combined EDLC-like behavior and Faradaic pseudocapacitance. • The Ps-24h//Ps-24h symmetric supercapacitor yields 63.8 W h kg−1 at 900.2 W kg−1. [ABSTRACT FROM AUTHOR]

A novel method of introducing a Limonene obtained from orange fruit skin (Lim) is successfully incorporated in Poly (ethylene oxide) (PEO) with KI and I2 redox couple and employed in a dye‐sensitized solar cell (DSSC). Scanning electron microscopy (SEM), X‐ ray diffraction (XRD) Ultra violet‐visible spectrum (UV‐Visible), Fourier transform infrared spectrum (FTIR), Thermo gravimetric analysis (TGA) and electrochemical impedance spectroscopy (EIS) studies described the influence of Lim on ionic conductivity and the photovoltaic properties of the PEO/KI/I2 system. The temperature‐dependent conduction mechanism of ionic motion and ionic interactions as a function of frequency has been studied. The dielectric behavior of the electrolyte samples were carried out over a wide frequency range (∼1 MHz to 20 Hz) at various temperatures. A DSSC system fabricated with the prepared PEO/KI/I2/Lim polymer electrolyte facilitating a fill factor of 0.52, a short‐circuit current density (Jsc) of 14.1 mAcm−2 and an open‐circuit voltage (Voc) of 795 mV yields the achieved solar to electrical energy conversion efficiency of 5.83 % under irradiation of 1 sun (100 mWcm−2). The compound Lim thus effectively enhanced the ionic conductivity of the composite polymer electrolyte and hence the photovoltaic performance of the fabricated DSSC. [ABSTRACT FROM AUTHOR]

Nanocomposites of PEDOT:PSS with V2O5 nanoparticles are synthesized by simple physical mixing of the two with different weight percentages of the latter and their performance as supercapacitor electrode materials is verified. Best performance is obtained for an optimum weight percent of 16.8% of V2O5. The specific capacitance and specific energy of the composite with 16.8% V2O5 increases by more than two fold, with increase in specific power, as compared to that of pristine PEDOT:PSS device. This is attributed to increase in conductivity brought about by the presence of V2O5 nanoparticles, easier transportation and intimate contact of electrolyte ions with the nanolayers of V2O5 due to the intercalation of PEDOT:PSS between the layers, and additional redox reactions due to various oxidation states of vanadium element, besides redox electrolyte effects. This is further confirmed by the reduced ESR of the composite device as compared to that of pristine PEDOT:PSS device. [ABSTRACT FROM AUTHOR]

We report a new electrochemical capacitor with an aqueous KI-KOH electrolyte that exhibits a higher specific energy and power than the state-of-the-art nonaqueous electrochemical capacitors. In addition to electrical double layer capacitance, redox reactions in this device contribute to charge storage at both positive and negative electrodes via a catholyte of IOx-/I- couple and a redox couple of H2O/Had, respectively. Here, we, for the first time, report utilizing IOx-/I- redox couple for the positive electrode, which pins the positive electrode potential to be 0.4-0.5 V vs Ag/AgCl. With the positive electrode potential pinned, we can polarize the cell to 1.6 V without breaking down the aqueous electrolyte so that the negative electrode potential could reach -1.1 V vs Ag/AgCl in the basic electrolyte, greatly enhancing energy storage. Both mass spectroscopy and Raman spectrometry confirm the formation of IO3- ions (+5) from I- (-1) after charging. Based on the total mass of electrodes and electrolyte in a practically relevant cell configuration, the device exhibits a maximum specific energy of 7.1 Wh/kg, operates between -20 and 50 °C, provides a maximum specific power of 6222 W/kg, and has a stable cycling life with 93% retention of the peak specific energy after 14,000 cycles.

Device level performance of aqueous halide supercapatteries fabricated with equal electrode mass of activated carbon or graphene nanoplatelets has been characterized. It was revealed that the surface oxygen groups in the graphitic structures of the nanoplatelets contributed toward a more enhanced charge storage capacity in bromide containing redox electrolytes. Moreover, the rate performance of the devices could be linked to the effect of the pore size of the carbons on the dynamics of the inactive alkali metal counterion of the redox halide salt. Additionally, the charge storage performance of aqueous halide supercapatteries with graphene nanoplatelets as the electrode material may be attributed to the combined effect of the porous structure on the dynamics of the non‐active cations and a possible interaction of the Br−/(Br2 + Br3−) redox triple with the surface oxygen groups within the graphitic layer of the nanoplatelets. Generally, it has been shown that the surface groups and microstructure of electrode materials must be critically correlated with the redox electrolytes in the ongoing efforts to commercialize these devices. [ABSTRACT FROM AUTHOR]

• The compatibility of different redox species with ZIF-67 electrodes was studied. • K₄[Fe(CN)₆], p-phenylenediamine (PPD), and KI were studied as active redox species. • The structure of ZIF-67 is decomposed at high potentials in an alkaline medium. • Ferrocyanides and halides promote large increases in capacitance but limit cycling. • PPD operates at low potential and promotes the greatest capacitance retention. The zeolitic imidazolate framework-67 (ZIF-67) is an attractive material as electrodes for energy storage applications due to its scalability, and high surface area. Although, its low electrical conductivity limits the specific capacitance and rate capabilities, properties which can be significantly increased when redox electrolytes are employed. Furthermore, the successful application of ZIF-67 electrodes depends on their cyclic stability. However, this material undergoes decomposition in alkaline electrolyte, which is the most commonly employed electrolyte in previously published studies, but this effect has not been taken into account. In this study the capacitance, efficiencies and stability of ZIF-67 electrodes was studied in conventional electrolyte (KOH) and with the addition of three different redox species: p -phenylenediamine (PPD), potassium hexacyanoferrate (II), and potassium iodide. Our results reveal that the addition of ferrocyanide and halides promote the greatest increases in capacitance, but their high oxidation potentials limit capacitance retention to 42% (10,000 cycles). With a lower formal potential, the use of PPD allows retentions of more than 80%. To the best of our knowledge, this is the first study that demonstrates the impact of formal potentials in the performance of ZIF-67 electrodes, highlighting the importance of a judicious selection of electrolytes to comprise this electrode. [Display omitted] [ABSTRACT FROM AUTHOR]

Carbon materials with hierarchical porous structures hold great potential for redox electrolyte-enhanced supercapacitors. However, restricted by the intrinsic inert and nonpolar characteristics of carbon, the energy barrier of anchoring redox electrolytes on the pore walls is relatively high. As such, the redox process at the interface less occurs, and the rate of mass transfer is impaired, further leading to a poor electrochemical performance. Here, a ferricyanide anion-philic interface made of in situ inserted boron species into carbon rings is constructed for enhanced charge storage in supercapacitors. Profiting from the unique component-driven effects, the polar anchoring sites on the pore wall can be built to grasp the charged redox ferricyanide anion from the bulk electrolyte and promote the redox process; the dynamics process is fastened correspondingly. Especially, the boron atoms in BC 2 O and BCO 2 units with higher positive natural bond orbital values in the carbon skeleton are pinpointed as intrinsic active sites to bind the negatively charged nitrogen atoms in the ferricyanide anion via electrostatic interaction, confirmed by density functional theoretical calculations. This will suppress the shuttle and diffusion effects of the ferricyanide anion from the surface of the electrode to the bulk electrolyte. Finally, the well-designed PC-3 with high content of BC 2 O and BCO 2 units can reach 1099 F g -1 at 2 mV s -1 , which is a more than 2-fold increase over boron-free units of carbon (428 F g -1 ). The work offers a novel version for designing high-performance carbon materials with unique yet reaction species-philic effects.

Electrical double-layer capacitors (EDLCs) using a biomass-derived activated carbon electrode with Na2SO4–NaI–KI as a redox additive electrolyte were investigated. Biomass-derived activated carbon materials from pomelo peels were prepared by chemical activation in potassium hydroxide followed by carbonization. The biomass-derived activated carbon has a high specific surface area of 1360 m2 g−1, which is suitable for electrode materials. Moreover, a stable couple inorganic redox additive electrolyte were studied by the addition of NaI and KI to Na2SO4 forming a redox additive electrolyte. The electrical double-layer based on activated carbon/Na2SO4–NaI–KI/activated carbon has an excellent specific capacitance (334.3 F g−1), which is 412% higher in comparison with that of activated carbon/Na2SO4/activated carbon (81.14 F g−1) at the same current density of 0.5 A g−1. The EDLC using Na2SO4–NaI–KI electrolyte has a high energy density of 22.75 W h kg−1, which is approximately four times higher than EDLCs based on Na2SO4 (5.52 W h kg−1). [ABSTRACT FROM AUTHOR]

Supercapacitors (SCs) have attracted widespread attention due to their short charging/discharging time, long cycle life, and good temperature characteristics. Electrolytes have been considered as a key factor affecting the performance of SCs. They largely determine the energy density based on their decomposition voltage and the power density from their ionic conductivity. In recent years, redox electrolytes obtained a growing interest due to an additional redox activity from electrolytes, which offers an increased charge storage capacity in SCs. This article summarizes the latest progress in the research of redox electrolytes, and focuses on their properties, mechanisms, and applications based on different solvent types available. It also proposes potential solutions for how to effectively increase the energy density of the SCs while maintaining their high power and long life.

The low energy density for conventional supercapacitors has limited their further application in a large scale. To enhance the energy density of supercapacitor, a novel redox Zn-ion supercapacitor is fabricated by using B, N codoped carbon nanosheets as cathode material and hydroquinone as redox electrolyte. The B, N co-doping is found to be beneficial for the enhanced electrochemical performance, and the introduced redox electrolyte has increased the capacitance of supercapacitor greatly. The B, N codoped carbon nanosheets shows a capacity of 168 mAhg−1 in the hydroquinone based redox electrolyte at 2 Ag−1, nearly 2 times as that (83 mAhg−1) in conventional Zn-ion electrolyte. Density functional calculation shows B, N- dual doping can increase the adsorption capability of carbon toward hydroquinone. This work shows that the combination of cathode material modification and redox electrolyte can enhance Zn-ion hybrid supercapacitor. [Display omitted] • B, N doped 3D carbon nanosheets were prepared via a facile method. • The prepared B, N-doped carbon nanosheets showed high capacitance in ZICs. • The carbon sheets provides 168 mAhg−1 in HQ modified electrolyte at 2 Ag−1. • DFT calculation discloses the B, N doping enhances the interaction of HQ and carbon. [ABSTRACT FROM AUTHOR]

Multiple oxidation-state metal oxide has presented a promising charge storage capability for aqueous supercapacitors (SCs); however, the ion insert/deinsert behavior in the bulk phase generally gives a sluggish reaction kinetic and considerable volume effect. Herein, iron oxide/poly(3,4-ethylenedioxythiophene) (Fe 2 O 3 /PEDOT) heterointerface was constructed and enabled boosted Faradaic pseudocapacitance by dual-ion-involved redox reactions in Na 2 SO 3 electrolytes. The Fe 2 O 3 /PEDOT interface served as a "bridge" to couple electrode and anion SO 3 2- and exhibited a strong force and stable bonding with SO 3 2- , thus providing an additional Faradaic charge storage contribution for SCs. Significantly, the PEDOT-capsulated Fe 2 O 3 nanorod array (Fe 2 O 3 @PEDOT) electrode presented a specific capacitance of 338 mF cm -2 at 1 mA cm -2 with 1 M Na 2 SO 3 electrolyte, which was twice that of the pristine Fe 2 O 3 nanorod electrode. The boosted interfaced Faradaic reaction of SO 3 2- partially hindered the intercalation of Na + in the Fe 2 O 3 bulk phase, efficiently favoring the electrochemical stability.

The one of the most important issues in constructing light-harvesting photovoltaic (PV) systems with a charge storage element is its reliable and uninterrupted use in highly variable and weather-dependent conditions in everyday applications. Herein, we report the construction and applicability evaluation of a ready-to-use portable solar charger comprising a silicon solar cell and an enhanced energy hybrid supercapacitor using activated carbon electrodes and iodide-based aqueous electrolyte to stabilise the PV power under fluctuating light conditions. The optimised electrode/electrolyte combination of a supercapacitor was used for the construction of a 60 F/3 V module by a proper adjustment of the series and parallel connections between the CR2032 coin cells. The final photo-rechargeable device was tested as a potential supporting system for pulse electronic applications under various laboratory conditions (temperature of 15 and 25 °C, solar irradiation of 600 and 1000 W m−2).

Due to their unique physical and chemical properties, nanostructured metal sulfide materials have shown excellent electrochemical performance. Among them, the natural semiconductor cobalt disulfide (CoS) is a promising electrode material for supercapacitors owing to its two-dimensional layered structure and fast carrier transmission. However, the curling of the CoS layers and the structural stability of CoS materials should be improved. In this context, we developed a facile solvothermal method to fabricate CoS-AC composite to solve the inherent defects of individual materials. The AC both increased the electrical conductivity of the electrode and supported the active species, thus improving the stability of the composite during the charge–discharge processes. Furthermore, the addition of K3Fe(CN)6 to the electrolyte to form a redox electrolyte largely enhanced the pseudocapacitance. The CoS-AC composite exhibited a high specific capacitance of 797.79 F g−1 at a high current density of 10 A g−1. The as-prepared CoS-AC//AC asymmetric supercapacitor device showed a superior cycling stability (77.53% maintained after 2000 cycles). The synergy between the electrode and the redox electrolyte was crucial for improving the supercapacitor performance. The CoS-AC composites were simply synthesized using solvothermal approach with enhanced electrochemical properties. [ABSTRACT FROM AUTHOR]

This paper describes a hybrid capacitor based on identical activated carbon (AC) electrodes and the 1-ethyl-3-methylimidazolium selenocyanate, [EMIm][SeCN], liquid salt as redox-active electrolyte. [EMIm][SeCN] is a fluorine-free ionic liquid (IL) which combines good charge and mass transport properties (σ = 25 mS cm−1 and η = 17 mPa s−1), as well as redox activity originating from the pseudohalide anion. Owing to the impact of the SeCN−/(SeCN) 2 redox couple, the AC/AC capacitor based on this electrolyte displays remarkable discharge (from 1.5 V) capacitance of 49 and 56 F g−1 (expressed per total active mass of electrodes) using aluminum and stainless steel (SSt) current collectors, respectively. Although higher capacitance values were displayed for the hybrid capacitor with SSt components, more advantageous E 0 localization for cell hybridization was observed when using Al current collectors. [ABSTRACT FROM AUTHOR]

• Introduction of novel back contact dye-sensitized solar cells. • Simple cost effective organic compounds. • Blended polymer electrolyte improves electrical conductivity. • Ti metal as back contact electrode based BC DSSC shows efficiency of 8.9%. A newly designed back contact dye-sensitized solar cells (BCDSSC) with back contact electrode (BCE) of Ti for electron collection, is placed on the side opposite to side of light irradiation on TiO 2 with synthesized organic compound doped poly (ethylene oxide)/poly (vinylidene fluoride)/potassium iodide/Iodine polymer electrolyte was introduced for the application of solar energy to electric energy conversion. The surface morphology of the polymer electrolyte study was carried out by SEM, XRD, DSC, DTA, TGA and it proves that the synthesized organic compounds enhances the amorphous nature of the polymer due to well coordinate with redox couple. The movement of I−/I 3 − characterized with UV–vis spectroscopy proves of organic compound with Iodine in the redox couple to decrease the sublimation of iodine. The conductivity of polymer/potassium iodide/iodine/organic compound shows high conductivity of 4.9 × 10−4 S cm−1 and it confirms that the importance of synthesized organic compounds in polymer electrolyte. The TiO 2 /Ti (BCE)/N3dye/PEO/PVdF/Potassium iodide/Iodine/PDSD/Pt compounds yielded an efficiency of 8.9% under illumination of 70 mW cm−2 at A.M. 1.5. [ABSTRACT FROM AUTHOR]

We report on a carbon/carbon hybrid electrochemical capacitor (hybrid EC) based on an aqueous redox-active electrolyte, which operates efficiently down to −40 °C. The electrolyte comprises choline iodide (ChI; 0.5 mol kg−1) as redox active component and choline nitrate (ChNO 3 ; 5 mol kg−1) as supporting salt which enables the liquid state to be extended down to −42 °C, as proved by differential scanning calorimetry. Interestingly, the hybrid EC displays a high discharge capacitance of 81 F g−1 (at 0.1 A g−1; per total mass of electrodes), which is twice higher than its symmetric counterpart utilizing only an aqueous solution of ChNO 3 (41 F g−1). The doubling of cell capacitance results from hybridization of the positive battery-type electrode (harnessing redox reactions of polyiodides trapped in carbon porosity) with the negative electrical double-layer (EDL) capacitive electrode. Even at −40 °C, the hybrid EC retains a high capacitance of 50 F g−1 and shows negligible ohmic drop. As its energy and power performance is in the same range as for EDL capacitors using tetraethylammonium tetrafluoroborate in acetonitrile, this new hybrid EC is a highly cost-effective and green alternative to these traditional systems. An eco-friendly and cost-effective carbon/carbon hybrid capacitor in redox aqueous electrolyte based on choline salts shows excellent performance at sub-ambient temperature. Image 1 • Hybrid electrochemical capacitor in aqueous medium operates efficiently down to −40 °C. • Electrolyte comprises redox active choline iodide and choline nitrate supporting salt. • The positive and negative carbon electrodes are of battery- and EDL-type, respectively. • Energy and power of the hybrid EC reach the values of ECs in organic electrolyte. [ABSTRACT FROM AUTHOR]

Abstract The energy density of the lithium-ion capacitors are restricted by the low charge-storage capability of the capacitive electrodes. Fast redox reactions from the redox-active aqueous electrolytes can effectively boost the charge storage of the capacitive electrodes without sacrificing the power performance, but are limited by the narrow electrochemical stability window. The "water-in-salt" electrolytes can enlarge the electrochemical stability window by effectively passivating the electrodes, but on the other hand remarkably elevate the cost, impair the ion conductivity and sacrifice the functionality of free water. Herein, we energize the unexpected role of free water in the "water-in-salt" electrolytes as the solvent of high-potential redox-active species, combining with the lithium insertion/de-insertion reaction at the battery-electrode to constitute a bi-redox system for effectively boosting the energy density. In addition, the unexpected opposite shift of the bi-redox potentials resulted from the decreases of the electrolyte concentration leads to an increased discharging voltage plateau to 2.2 V, helping further increase energy density and reduce costs. Graphical abstract Image 1 Highlights • The aqueous lithium-ion capacitor with a high voltage of 2.7 V is reported. • The free water in high-voltage electrolyte is energized by dissolving redox agent. • The specific energy of lithium-ion capacitor is enhanced by redox electrolyte. • The voltage plateau is raised to 2.2 V by regulating electrolyte ion activities. [ABSTRACT FROM AUTHOR]

Abstract Over recent decades, a new type of electric energy storage system has emerged with the principle that the electric charge can be stored not only at the interface between the electrode and the electrolyte but also in the bulk electrolyte by redox activities of the electrolyte itself. Those redox electrolytes are promising for non-flow hybrid energy storage systems, or redox electrolyte-aided hybrid energy storage (REHES) systems; particularly, when they are combined with highly porous carbon electrodes. In this review paper, critical design considerations for the REHES systems are discussed as well as the effective electrochemical characterization techniques. Appropriate evaluation of the electrochemical performance is discussed thoroughly, including advanced analytical techniques for the determination of the electrochemical stability of the redox electrolytes and self-discharge rate. Additionally, critical summary tables for the recent progress on REHES systems are provided. Furthermore, the unique synergistic combination of porous carbon materials and redox electrolytes is introduced in terms of the diffusion, adsorption, and electrochemical kinetics modulating energy storage in REHES systems. [ABSTRACT FROM AUTHOR]

[Display omitted] Indoor photovoltaics has received much interest lately due to its applications in the daily human life in the small scale device applications like Internet of things, human-interactive machines based actuators, wireless sensors to name a few. Nevertheless, these devices possess light weight, low cost, less power for charging and environmental friendliness leads appropriate devices for indoor light applications. Thus, recent enormous progress in indoor photovoltaics prompts us to highlight the applicability of all three generations of solar cells i.e., crystalline silicon, amorphous silicon and thin films, and organic/dye-sensitized/perovskites working under indoor conditions, challenges and market perspectives in this review. [ABSTRACT FROM AUTHOR]

Although supercapacitors benefit from both long-cycle durability and extraordinary power density, unmet energy demands still remain the key challenge on the path of their practical applications. Boosting energy densities without sacrificing the remarkable power densities and long cycle life is of special significance in developing high-performance energy storage systems. Herein, the synergy between reversible redox mediator addition and heteroatom-doping of carbon-based electrode active materials represents an enhanced electrochemical performance of the fabricated energy storage devices. Green carbon spheres (CSs) were synthesized through the eco-benign hydrothermal carbonization (HTC) approach. CSs were then chemically decorated by metal nanoparticles. A carbothermic reduction, in which metallic nano particles nanoparticles played a role as a sacrificial agent, was conducted to prepare highly porous CSs (PCSs). The carbothermic reduction process was followed by heteroatom doping of the PCSs. Nitrogen- and boron-doped PCSs were then utilized as positive and negative electrode active materials, respectively. A combination of potassium iodide (KI) and sodium anthraquinone-2-sulfonic acid (AQSA) was employed as dual-redox mediators to boost the electrochemical performance of the fabricated N-PCS//B-PCS ASC devices. The assembled ASCs coupled with AQSA/KI dual redox additives rendered not only remarkable energy density (86.3 W h kg−1) at a reasonable power density of 340 W kg−1 but also exhibited outstanding cyclic stability (only 22 % decay of initial capacitance observed after 5000 charge/discharge cycle). The encouraging features parallel to the remarkable capacitive performance of the fabricated ASCs make these supercapacitors immensely promising for practical applications. [Display omitted] • Highly porous carbon spheres (PCS) are synthesized through the chemical activation rout. • Different heteroatoms including nitrogen, phosphorus, boron and sulfur are uniformly incorporated into PCS structure. • Effect of heteroatom doping on the electrochemical performance of PCS are investigated in attendance of two redox additives. • Asymmetric supercapacitor (ASC) are assembled using nitrogen doped and boron doped PCS as positive and negative electrode, respectively. • A dual redox additive system based on KI and AQSA sodium salt are applied as electrolyte in ASC fabrication. [ABSTRACT FROM AUTHOR]

• Synthesized defective mesoporous carbon were explored as an efficient electrode in supercapacitor. • Pseudocapacitive behaviour is studied under redox additive electrolyte, Reactive Blue 15. • Specific capacitance of DMC reached 207 F/g when using a redox-additive electrolyte. Herein, the application of Reactive Blue 15 as novel and efficient redox additive for natural aqueous electrolyte was reported in where defective mesoporous carbon (DMC) with the interconnected porous network was applied as electrode material. Excellent electrochemical performance is achieved at 0.05 M of R. B. 15 in 1 M Na 2 SO 4 electrolyte. The obtained data from RAMAN, SEM, TEM, and Nitrogen adsorption/desorption confirmed the DMC structure. The supercapacitive performance of DMC and DMC electrodes with RB redox additive in 1 M Na 2 SO 4 as electrolyte was evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge (GCD) techniques. Compared to DMC, the DMC-RB/Na 2 SO 4 delivered the highest specific capacitance reaching to 207 F/g at the applied current density of 0.5 A/g. Moreover, the DMC-RB/Na 2 SO 4 exhibited long term cyclability, in where 76% of specific capacitance was retained after 3000 GCD measurement at the high current density of 1 A/g. Also, the specific energy of 18.45 Wh/kg was obtained for the symmetric device which shows nearly threefold increase over the DMC electrode with pure Na 2 SO 4 electrolyte. [ABSTRACT FROM AUTHOR]

We report a high energy density thermally chargeable supercapacitor (TCSC) based on the thermogalvanic effect, built by sandwiching a potassium ferrocyanide/ferricyanide gel electrolyte film between two high surface area carbon cloth electrodes. In addition to the characteristic Seebeck coefficient of −1.21 mV K −1 , the pseudocapacitive property of the ferrocyanide/ferricyanide redox couple endows the device with a high area-specific capacitance of 13 F cm −2 which finally leads to high thermally induced energy storage density. Furthermore, the all-solid-state and flexibility of the device allows it to accommodate different heat source shapes. Overall, the device offers a simple, scalable and cost-effective means to harvest energy from intermittent waste heat sources. Lastly, we propose an equivalent circuit model to elucidate the working mechanisms of energy conversion and storage applicable to thermally chargeable supercapacitor devices in general. A fitting analysis aids in the evaluation of model circuit parameters providing good agreement with experimental voltage and current measurements. [ABSTRACT FROM AUTHOR]

Nitrogen doped porous carbons (NCs) with high specific surface areas, moderate graphitization degree and high N contents were synthesized by pyrolysis of melamine sponge-polyaniline composite. The as-prepared NCs demonstrate considerable capacitive performances in acidic electrolyte. More importantly, the NCs demonstrated high catalytic activity for the redox reaction of iodides in acidic electrolyte, thus enabled prominent pseudocapacitance via the faradic reaction of redox electrolyte. Under the optimal concentration of KI in acidic electrolyte, the electrode specific capacitance achieved 616 F g −1 , which is 3 folds higher over that in solely acidic electrolyte. High cycling performance was also maintained for the avoidance of volumetric variation of electrode during charge–discharge cycles. The current work proposed a viable way to ameliorate the capacitive performance via the catalytic NCs electrode-redox iodide electrolyte system. [ABSTRACT FROM AUTHOR]

Redox chemistry is the cornerstone of various electrochemical energy conversion and storage systems, associated with ion diffusion process. To actualize both high energy and power density in energy storage devices, both multiple electron transfer reaction and fast ion diffusion occurred in one electrode material are prerequisite. The existence forms of redox ions can lead to different electrochemical thermodynamic and kinetic properties. Here, we introduce novel colloid system, which includes multiple varying ion forms, multi-interaction and abundant redox active sites. Unlike redox cations in solution and crystal materials, colloid system has specific reactivity-structure relationship. In the colloidal ionic electrode, the occurrence of multipleelectron redox reactions and fast ion diffusion leaded to ultrahigh specific capacitance and fast charge rate. The colloidal ionic supercapattery coupled with redox electrolyte provides a new potential technique for the comprehensive use of redox ions including cations and anions in electrode and electrolyte and a guiding design for the development of next-generation high performance energy storage devices. [ABSTRACT FROM AUTHOR]

Due to the special three-dimensional structures and excellent physicochemical properties, vertical graphene (VG) has been extensively investigated as potential material for supercapacitors. However, achieving VG-based supercapacitors with high-energy density and high-power density is a still tremendous challenge. Here we attempt to synthesize large-scale VG films on flexible substrates and design a novel battery-like supercapacitor (BSCs) with the VG on Ni foil (VG@Ni) as a binder-free electrode operating in the KOH electrolyte with the redox additives of K 3 Fe(CN) 6 and/or K 4 Fe(CN) 6. The VG@Ni electrodes demonstrate an ultrahigh areal capacitance of 1453 mF cm−2 at 5 mA cm−2 in 1 M KOH electrolyte with adding 0.07 M K 3 Fe(CN) 6 and 0.07 M K 4 Fe(CN) 6 , coulombic efficiency greater than 90%, and long-life cycling stability (capacitance retention is 99.3% after 20000 charge-discharge cycles). The BSCs, which are assembled with two identical VG@Ni electrodes, deliver the areal capacitance of 231 mF cm−2 with energy density of 32 μWh cm−2 and power density of 2498 μW cm−2 at 1 mA cm−2. These outstanding performances can be ascribed to the special feature and excellent properties of VG materials, high electronic conductivity of binder-free VG@Ni electrode, faradaic properties of redox electrolyte, and synergistic effects between the VG film and redox electrolyte. • Large-scale VG films are obtained on nickel and graphite foils by PECVD technique. • The VG films present excellent electrochemical performance in redox electrolyte. • The VG-based BSCs show high energy and power densities as well as long stability. [ABSTRACT FROM AUTHOR]

Activated carbon (AC) based conventional capacitive deionization has shown extraordinary promise for energy efficient water treatment, but its capacity and cycle stability are limited by the mechanism of electric double-layer and the oxidation of anode, respectively. Redox electrolytes are proposed as one of the most promising strategies to improve the charge storage capacitance. Here, functional anode enabled by Cu2+/Cu+ redox couple is constructed by adding 10 mM CuCl 2 into 100 mM NaCl supporting electrolyte. A membrane capacitive deionization (MCDI) cell with the functional anode and anion exchange membrane, employing a two channel structure is proposed to remove the anions (F−, Cl−) from wastewater. The reverse constant current discharge mode with 1.2 V/−1.2 V cut-off voltage can realize Cu2+/Cu+ redox reaction. The water production rate of the MCDI cell is above 50 % and the Cl− removal capacity is increased by 163 % due to the additional faradaic process. The cell capacity can be maintained above 83 % after 40 cycles. In particular, fast charge balance and redox couple reaction processes of this functional anode could significantly alleviate the oxidation of the anode AC electrode. This work provides new opportunities for developing cost-effective technologies to remove the anions from wastewater. [Display omitted] • Functional anode enabled by Cu2+/Cu+ redox couple was constructed. • MCDI cell with the functional anode and anion exchange membrane was proposed. • This MCDI cell could remove the anions (F−, Cl−) from wastewater. • This MCDI cell could significantly mitigate anodic AC oxidation. [ABSTRACT FROM AUTHOR]

The cooperative effects between the PANI (polyaniline)/nano-NiO (nano nickel oxide) composite electrode material and redox electrolytes (potassium iodide, KI) for supercapacitor applications was firstly discussed in this article, providing a novel method to prepare nano-NiO by using β-cyelodextrin (β-CD) as the template agent. The experimental results revealed that the composite electrode processed a high specific capacitance (2122.75 F.g-1 at 0.1 A.g-1 in 0.05 M KI electrolyte solution), superior energy density (64.05 Wh.kg-1 at 0.2 A.g-1 in the two-electrode system) and excellent cycle performance (86% capacitance retention after 1000 cycles at 1.5 A.g-1). All those ultra-high electrical performances owe to the KI active material in the electrolyte and the PANI coated nano-NiO structure. [ABSTRACT FROM AUTHOR]

This paper reports a detailed electrochemical investigation of a symmetric carbon-carbon electrochemical device with a potassium bromide (KBr) electrolyte. Below 1.6 V, KBr gives electrochemical double layer behavior. At higher voltages the Br − / Br 3 − redox reaction comes into effect and enhances the energy storage. The redox-enhanced device has a high energy density, excellent stability, as well as high coulombic and energy efficiencies even at 1.9 V. More importantly, the redox contribution can be “triggered” by pre-cycling at 1.9 V, and remains beneficial after switching to 1.6 V. The triggering operation leads to a 22% increase in stored energy with negligible sacrifice of power. The intriguing behavior is accompanied by a series of complex variations including the shifts of electrode potential limits and the shift of potential of zero voltage. The electro-oxidation of the positive electrode and kinetics of the Br − / Br 3 − electrode reactions are proposed to be the main causes for the triggering phenomenon. These findings provide means to improve the design and operation of devices that contain bromine, or other redox species with a comparably high electrode potential. [ABSTRACT FROM AUTHOR]

Highly flexible and conductive fabric (CF)-supported cauliflower-like nickel selenide nanostructures (Ni3Se2 NSs) are facilely synthesized by a single-step chronoamperometry voltage-assisted electrochemical deposition (ECD) method and used as a positive electrode in supercapacitors (SCs). The CF substrate composed of multi-layered metallic films on the surface of polyester fibers enables to provide high electrical conductivity as a working electrode in ECD process. Owing to good electrical conductivity, high porosity and intertwined fibrous framework of CF, cauliflower-like Ni3Se2 NSs are densely integrated onto the entire surface of CF (Ni3Se2 NSs@CF) substrate with reliable adhesion by applying a chronoamperometry voltage of −1.0 V for 240 s. The electrochemical performance of the synthesized cauliflower-like Ni3Se2 NSs@CF electrode exhibits a maximum specific capacity ( CSC) of 119.6 mA h g−1 at a discharge current density of 2 A g−1 in aqueous 1 m KOH electrolyte solution. Remarkably, the specific capacity of the same electrode is greatly enhanced by introducing a small quantity of redox-additive electrolyte into the aqueous KOH solution, indicating the CSC≈251.82 mA h g−1 at 2 A g−1 with good capacity retention. Furthermore, the assembled textile-based asymmetric SCs achieve remarkable electrochemical performance such as higher energy and power densities, which are able to light up different colored light-emitting diodes. [ABSTRACT FROM AUTHOR]

The application of a redox electrolyte in hybrid type electrochromic devices allows a high charge capacity, thereby a high optical contrast can be achieved. However, the current between the redox electrolyte and the electrochromic layer (tungsten oxide, WO 3 ) interface in equilibrium at colored state of device is critical for a window with large area. This loss current should be maintained below 10 μA/cm 2 to avoid an inhomogeneous coloration of a large window caused by an ohmic voltage drop in transparent conductive oxide (TCO). The power consumption of such a loss current can be neglected. In this regard, we have investigated silicon nitride (Si 3 N 4 ) and silicon oxide (SiO 2 ) films as an intermediate electronic barrier layer on the top of the WO 3 with thicknesses of 12, 35, 80 and 180 nm. These films were coated by direct current reactive magnetron sputtering technique. The electron barrier properties were studied for the iodide/triiodide ( I − / I 3 − ) and tetramethylthiourea/tetramethylformaminium disulfide dication (TMTU/TMFDS 2+ ) redox couples for application in electrochromic devices. For both redox couples, Si 3 N 4 showed an effective electronic barrier layer. The thickness of 80 nm of Si 3 N 4 reduced the loss current from 240 down to 20 μA/cm 2 for the I − / I 3 − redox electrolyte with the visual (solar) transmission from 45% (33%)down to 0.7% (0.5%)at 1 V.Similarly, the loss current was reduced from 70 down to 7 μA/cm 2 with the visual (solar) transmission from 71% (54.5%) down to 3% (2%) for TMTU/TMFDS 2+ redox electrolyte. However no significant reduction of loss circuit current was achieved with SiO 2 barrier layer for both redox couples. [ABSTRACT FROM AUTHOR]