Elzbieta. Frackowiak

• Poznań University of Technology

Molybdenum disulfide (MoS2)‐based electrode materials can exhibit a pseudocapacitive charge storage mechanism induced by nanosized dimension of the crystalline domains, which is why control over material structure via synthesis conditions is of significance. In this study, we investigate how the use of different sulfide precursors, specifically thi...

Aqueous electrolytes containing sulfuric acid and organic electrolytes made by dissolving quaternary ammonium salts in propylene carbonate have long been used as electrolytes in supercapacitors. In the organic electrolyte system, acetonitrile was later also used as a solvent. This paper will describe more recent electrolytes for supercapacitors, in...

Molybdenum disulfide (MoS2)-based electrode materials can exhibit a pseudocapacitive charge storage mechanism induced by nanosized dimension of the crystalline domains. This effect is achievable through hydrothermal synthesis of MoS2, which often yields different properties of the final material, thereby affecting its electrochemical lithium interc...

New strategy using buffer solutions and iodide as additive for improvement of EC performance.

Conventional catalysts based on noble metals (Pt, Ru) are often used for production of oxygen during water electrolysis in four-electron pathway as they can decrease gas evolution overpotential. Another possible valuable product from water oxidation is hydrogen peroxide obtained via two-electron process. Currently, transition metal oxides, are read...

The operating voltage of electrochemical capacitor (EC) in aqueous medium is considerably limited due to the theoretical stability of water (1.23V). Hence, the delivered energy density of such systems is restricted compared to that of batteries. A traditional approach to tackle this issue is to focus on improving the capacitance rather than the wor...

This study provides meaningful insight into the charge storage in Ti3C2Tx MXene (M‐transition metal, X‐carbon, T‐Cl, F, O) for electrochemical capacitor (EC) application. The experiments show that this 2D material is especially adapted for the hydrogen electrosorption under negative polarization. It is found that hydrogen bonding to the Ti3C2Tx sur...

Supercapacitors are fast-charging energy storage devices of great importance for developing robust and climate-friendly energy infrastructures for the future. Research in this field has seen rapid growth in recent years. Therefore, consistent reporting practices must be implemented to enable reliable comparison of device performance. Although sever...

In the electrochemical capacitors (ECs) operating with aqueous electrolytes, corrosion of the current collector is one of critical issues that affects the cycling life, efficiency, and capacitance of the devices. So far, there are no stable metal current collectors in the water-based electrolyte because of its corrosive nature, even if the pH is cl...

A comprehensive comparison of electrochemical capacitors (ECs) with various aqueous alkali metal sulfate solutions (Li2SO4, Na2SO4, Rb2SO4, and Cs2SO4) is reported. The EC with a less conductive 1 mol L-1 Li2SO4 solution demonstrates the best long-term performance (214 h floating test) compared to the EC with a highly conductive 1 mol L-1 Cs2SO4 so...

Technological advances in various fields are frequently hampered by the insufficient capacity of energy storage devices. Electrochemical capacitors (ECs) emerge as high-power effective energy storage devices with a short charge/discharge time, long-term cycle life, and wide temperature range. The electrolyte is an important component influencing EC...

The paper puts forward the concept of a double-redox electrochemical capacitor operating in an aqueous electrolyte. The redox activity of sulphur from insoluble Bi 2 S 3 nanocrystals embedded in the negative electrode material (up to 10 wt%) operating in 1 mol L −1 Li 2 SO 4 electrolyte is demonstrated. It is also shown that the performance is sign...

The research is focused on hybrid, bifunctional composite materials, in terms of their application to innovative lightning systems. The main target was to obtain emissions in such materials for various colours other than red. In addition, the doping concentration was optimized and mechanical properties of the tested materials were improved. The mat...

The operando monitoring of pH during the charging and discharging of an electrochemical capacitor in an aqueous neutral salt solution is presented. Proper knowledge of transient and limiting pH values allows for a better understanding of the phenomena that take place during capacitor operation. It also enables the proper assignment of the reaction...

Electrochemistry is strongly related to redox reactions. Charge transfer processes are used for the current generation in all electrochemical cells. Nowadays, redox reactions are still of evitable importance for energy storage/conversion technology. For instance, the charge and discharge of batteries exploit redox reactions. Moreover, these process...

In electrochemical capacitors, also known as supercapacitors (SC), electrolytes and electrodes are the most important constituents and control the main characteristics of the device. The high energy density of a SC can be obtained by designing functional electrode materials along with appropriate electrolytes. Redox activity represents a groundbrea...

Electrochemical capacitors are attractive power sources, especially when they are able to operate at high frequency (high current regime). In order to meet this requirement their constituents should be made of high conductivity materials with a suitable porosity. In this study, enhanced power and simultaneously high capacitance (120 F g⁻¹ at 1 Hz o...

Reline Deep Eutectic Solvent (DES) is widely recognized as a novel and green electrolyte for industrial applications due to its low cost and tolerance to moisture. It has received significant attention, however, its application in the energy storage system is still in infancy. Generally, aqueous-based electrochemical capacitors (ECs) present an ide...

The presented work has undertaken a rational design of composite electrodes based on three-dimensional graphene-like (3DG) and transition metal-dichalcogenide (TMD), i.e., VS2. The aim was to expand the working voltage of TMD-based electrochemical capacitor (EC) in an aqueous medium above the thermodynamic limits. It has been found that designing t...

Remarkable changes in the volume of activated carbon electrodes operating with aqueous electrolytes were measured with scanning electrochemical microscopy (SECM) and electrochemical dilatometry (ECD) techniques. It appears that the electrolyte volume absorbed by the carbon electrode strongly depends on the polarization direction and the electrode p...

Deep eutectic solvents (DES) are an environmentally benign promising emerging class of versatile solvent systems. This paper proposes, for the first time, a new approach to the DES application of the Choline chloride-Urea, called commonly Reline, and its aqueous mixtures as an eco-friendly, affordable and anticorrosive electrolyte for the carbon-ba...

This chapter is a comprehensive overview of the recent advances in electrochemical capacitor characterization. Various modes, including in-situ/operando and ex-situ/post-mortem techniques, are described and compared. All the advantages resulting from each approach are highlighted. Special attention is given to the current limits of different modes...

Transition Metal Dichalcogenides Transition metal dichalcogenides (sulfides) have a layered structure. ReS2 and FeS2 in the form of composites with carbon nanotubes and 3D graphene (3DG)-like material are used as electrochemical capacitor electrodes. Sulfates (Li, Na) serve as electrolytic medium. Catalytic effect of Re for hydrogen evolution react...

This paper reports the successful attempts of symmetric aqueous electrochemical capacitor (EC) lifespan extension. A novel exploitation procedure, i.e., alternate floating, is herein proposed. Since only the positive electrode ages remarkably in EC systems with LiNO3 as the electrolyte, it is demonstrated that alternate polarization allows the prop...

Transition metal dichalcogenides (TMDs) are emerging low‐dimensional materials with potential applications for electrochemical capacitors (EC). Here, physicochemical and electrochemical characterizations of carbon composites with two sulfides ReS2 and FeS2 are reported. To enhance conductivity, multiwalled carbon nanotubes (NTs) serve as a support...

This paper reports on the ion fluxes at the interfaces of various porous carbon electrodes/aqueous solutions of alkali metal cations (Na + , K + and Rb +) and iodide anions, monitored by an electrochemical quartz crystal microbalance (EQCM). Different electrode material compositions as well as various electrolyte concentrations have also been consi...

Various alkali metal (Li+, Na+, K+, Rb+, and Cs+) chlorides with Pluronic F127 were used as a soft-salt template for tuning the textural and structural properties of carbon. Highly conductive metal hydroxide solutions, where the cations are the same as those in the salt template, have been used as electrolytes. By increasing the size of the cation...

Electrochemical capacitors (ECs) are considered to be the very promising energy storage systems because they possess a high power density as well as a long life span. However, contrarily to the batteries, the energy density of ECs is rather moderate. It is very well known that the energy stored in ECs is mostly dependent on the specific surface are...

This paper reports on the electrochemical performance of activated carbon electrodes in aqueous solutions of bromide‐based species and discusses the results in the broader context of redox‐active electrolytes in electrochemical capacitor applications. Operando techniques such as Raman spectroscopy and electrochemical quartz crystal microbalance hav...

This paper addresses the challenges of explaining the behavior of porous carbons in cutting-edge applications related to energy storage, catalysis, photocatalysis, and advanced separation based on reactive adsorption. It is a summary of the outcomes of the extensive discussion which took place during the workshop “Beyond Adsorption-II: new perspect...

This paper reports on the electrochemical performance of symmetric carbon/carbon electrochemical capacitors operating in aqueous electrolyte (0.5 mol L⁻¹ K2SO4 solution) and modified with various amounts of agar (up to 5 wt%). It has been found that a change in electrolyte form (from liquid to gel-like) increases the hydrogen storage efficiency on...

Soft- and salt-templating methods have been combined to obtain highly microporous carbon materials with mesopores in the narrow pore size range. Phenolic resin was used as a carbon source, and rubidium and caesium chloride were used as salt-templates, giving a well-developed microporosity with a high specific surface area, whereas a sacrificial tri...

This paper reports on the “water-in-salt” electrolyte concept, applying CsF as an ionic compound in a symmetric electrochemical capacitor. CsF has been selected as a highly soluble inorganic salt that allows the amount of free water in the electrolyte to be significantly reduced. Several activated carbons with various microtextural parameters have...

The “dual-circuit redox flow battery” takes advantage of a conventional all-vanadium redox flow battery (VRFB) combined with a separated catalytic hydrogen evolution reactor. Depending on demand, the VRFB can be conventionally discharged or supply H2 by using the catalytic reactor. However, during hydrogen generation, protons are consumed and a sta...

This paper reports on the ageing mechanisms in symmetric, carbon/carbon electrochemical capacitors operating with a 1 mol⋅L⁻¹ LiNO3 aqueous electrolyte. The carbon electrodes were subjected to a constant polarization protocol (i.e., floating) at various voltages and were analysed post-mortem by N2 sorption at 77 K, Raman spectroscopy, Scanning Elec...

Ionic fluxes at carbon electrode/electrolyte interface have been already well described for organic medium. This description allowed for comprehensive understanding of the phenomena occuring during electrochemical capacitor operation. However, the processes on-going in aqueous electrolytes still need to be investigated, since several accompanying p...

This paper provides a comprehensive overview of the recent state of the art in research on a neutral, water-based electrolyte, i.e., 1 mol⋅L−1 Li2SO4 solution, for sustainable electrochemical capacitors. The fundamental physicochemical properties of aqueous electrolytic solutions (conductivity, viscosity, etc.) are discussed together with the elect...

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...

This paper reports on the long-term performance of electrochemical capacitor operating in 1 mol⋅L ⁻¹ KI solution subjected to two ageing protocols, i.e., galvanostatic cycling and potentiostatic floating. Ageing tests have been performed at similar voltage conditions (1.5 V), estimated from the coulombic and energetic efficiency as well as the self...

In this paper we report on the electrochemical performance of the symmetric carbon/carbon electrochemical capacitor with water-based electrolyte, operating at the temperatures down to −40 °C. The electrolyte solution consists of inorganic salt based on the NO3⁻ anion and Mg²⁺ as a divalent cation, dissolved in the mixture of water and organic solve...

Electrical double‐layer capacitors (EDLCs) are rechargeable energy storage devices with excellent power and energy delivery metrics intermediate to conventional capacitors and batteries. Aqueous electrolyte‐based EDLCs are particularly attractive due to their high‐power capability, facile production and environmental advantages. EDLCs should last f...

Development of electrochemical capacitors focuses today on the improvement of their energy density (or specific energy) and cyclability. The energy density might be improved by capacitance enhancement and operating voltage increase. To some extent, the relation between capacitance and voltage and their impact on the energy output reflects an interf...

Electrochemical capacitors (ECs) are high-power energy storage devices able to operate for thousands of cycles. Nevertheless, their calendar and cycle life is limited, especially when high voltage is applied. On the other hand, that parameter (voltage, U) significantly increases their energy values according to the equation E=0.5CU ² . Therefore, t...

Electrochemical capacitor (EC) parameters are affected by the amount of charge reversibly accumulated at electrode/electrolyte interface, electrode material, type of electrolyte and its electrochemical stability as well as cell construction. It has been proved that asymmetric configuration, i.e., various electrode materials for positive and negativ...

This paper introduces the method which allows determining the accurate electrode contributions during cyclic voltammetry (CV) scan of electrochemical capacitor. As a result of theoretical considerations, a calculation method which reveals voltammetry response of both electrodes during CV of two-electrode cell with reference is developed. The techni...

The application of redox-active electrolytes to realize carbon/carbon electrochemical capacitors has created a great opportunity to enhance the mediocre energy of these devices. Taking advantage of the faradic current from the redox transformation of electrolyte species, which generates a large capacity at one electrode, the resulting hybrid cells...

This paper presents a unique strategy aiming at extending the operational voltage range in supercapacitor working in the neutral aqueous electrolyte. In-depth analysis of the equilibria formed at the carbon/electrolyte interface gives the possibility to reach 1.8 V with excellent reversibility during cycling. To reach the goal, the donor - acceptor...

Highly tunable properties of materials used for the construction of electrochemical capacitors make them a perfect choice for a broad scope of applications with high power demand. The ability to design the system according to the expected power/energy profile allows them being considered as powerful alternatives to conventional capacitors and batte...

This chapter provides an overview of electrochemical capacitors (ECs) technology. General principles of ion adsorption and interfacial phenomena governing the energy storage in these devices are discussed. True capacitance metrics and appropriate measurement conditions are demonstrated and followed by a discussion of the electrode materials and ele...

Successful implementation of silicon nanostructures as suitable electrodes for microcapacitors performing at the low temperatures (until -40oC) has been realized. In order to avoid the freezing of the electrolyte solution, two ionic liquids with low freezing point have been synthesized and applied as the electrolyte. Silicon nanotrees selected as t...

The described research is focused on the hybrid, bi-functional composite materials dedicated to the electrochemical capacitor electrodes. The novel material exhibits both luminescent and capacitive properties. The fabrication process of semi-products and the final composite is described. The structure and homogeneity of luminophors are confirmed wi...

Performance parameters and relationships typically reported about the electrodes in an electrochemical capacitor generally do not allow active material value to be determined. This is primarily due to non-ideal dynamical behavior of these storage materials, which typically is a result of having high surface area. We show that electrochemical capaci...

This paper reports on the operando study of degradation mechanisms in carbon-based electrochemical capacitors with Li2SO4 and LiNO3 electrolytes. Several electrochemical techniques, coupled with mass and Raman spectrometry have been implemented to recognize and describe the processes occurring at the carbon electrode/aqueous electrolyte interface....

Carbon based supercapacitors operating in aqueous electrolytes at extended voltage > 1.23 V attract significant attention for next-generation high power, low cost and environmentally friendly energy storage applications. Cell ageing is however markedly pronounced at elevated voltages and results in accelerated overall performance fade and increased...

Redox-active electrolytes and additives offer a large selection of available species serving for supercapacitor energy enhancement. The first group refers to typical organic compounds like hydroquinone with isomeric forms. There are also several reports on methylene blue and indigo carmine compounds tested on multi-walled carbon nanotubes. Neverthe...

Dynamic development of supercapacitors technology especially in terms of electrode materials design requires a novel and more in-depth approach for their investigation. Apart from numerous materials synthesis and characterization methods proposed to date, there is a need for their investigation during device operation, in order to recognize the maj...

This paper reports on the performance of the supercapacitor operating in aqueous acetic acid salts. Lithium, sodium and magnesium acetate aqueous solutions at various concentrations have been selected as electrolytes. Maximum operational voltage and the overall capacitor performance have been determined by several electrochemical techniques. Floati...

Increasing operating voltage is a straightforward approach to increase the specific energy of aqueous electrolyte based electrical double-layer capacitors (EDLCs). A broader operating voltage window, however, comes at the expense of accelerated cell ageing processes. Two complementary _in situ_ gas analysis techniques, i.e., internal cell pressure...

This chapter presents an overview of carbon-based electrochemical capacitors (ECs). It specifically focuses on systems operating in aqueous electrolytes, where the most novel developments have appeared during the last years. Perturbation phenomena, such as positive electrode degradation (oxidation), electrolyte decomposition, and corrosion of stain...

A high energy hybrid AC/AC electrochemical capacitor has been realized in aqueous Li2SO4+KI electrolyte mixture. Owing to the redox processes associated with the 2I−/I2 system, the positive electrode operates in narrow potential range and displays high capacity. During prolonged potentiostatic floating at 1.6 V, the hybrid cell demonstrates remarka...

This paper presents supercapacitors utilizing new redox-active electrolytes with bromine species. Two sources of Br specimen were investigated, i.e. dibromodihydroxybenzene dissolved in KOH and potassium bromide dissolved in KOH with hydroxybenzene additive. KOH-activated carbon, exhibiting a well-developed porosity, was incorporated as an electrod...

This paper reports on a primary study of the capacitor system that can successfully overcome the main drawback of aqueous electrolytes, i.e. low max. voltage and then low energy density of the device. Our idea employs hybridization of electrolytes, i.e. use of two separated electrolytes with different pH values, each for one electrode. In such a wa...

This work reports on a high-voltage, hybrid capacitor involving two separate redox reactions. Aqueous solutions of Mg(NO3)2 and KI have been used for negative and positive electrode, respectively. Adjusting pH=2 for electrode (+) with KI solution and modifying Mg(NO3)2 solution to pH=9 for negative side play a crucial role for a stable long-term op...

High-voltage aqueous electrolyte based supercapacitors (U > 1.23 V) attract significant attention for next-generation high power, low cost and environmentally friendly energy storage applications. Cell ageing is however markedly pronounced at elevated voltages and results in accelerated overall performance fade and increased safety concerns. Online...

In this study, continuous fast Fourier transform admittance voltammetry (CFFTAV) was used to study and characterize the surface morphology of polyaniline (PANI) on glassy carbon (GC) electrodes. Four polymer films with various thicknesses (0.5 mm to 11 mm) were synthesized by an electrochemical method. A new modified square wave voltammetry (SWV) m...

This paper is reports on the effect of plasma treatment with various discharge regimes and plasma sources (Ar, O2 and CO2) on hydrogen capacity of carbon electrodes. Among various modifications of carbon materials being undertaken to increase hydrogen storage capacity, plasma treatment seems to be quite interesting one. Obtained results confirmed t...

The paper reports on electrochemical characterization of several supercapacitors operating in aqueous electrolytes and discusses a strategy for enhancing their performance. Various electrolytes such as alkaline (6 mol L-1 KOH), acidic (1 mol L-1 H2SO4) and neutral (1 mol L-1 KI and 1 mol L-1 Na2S2O3) were investigated in terms of electrochemical st...

Chitin-a naturally occurring biopolymer-was employed for the first time as a binder for carbon electrodes and studied in electrochemical capacitors. Chitin-bound electrodes have shown excellent performance in neutral aqueous electrolytes up to 5 A g-1 current load with a capacitance retention of ca. 80% of the initial value for mild regimes. This s...

No abstract is available for this publication which is a record of the questions, answers and discussions during the Faraday Discussion meeting at Sheffield in September 2014.

No abstract is available for this publication which is a record of the questions, answers and discussions during the Faraday Discussion meeting at Sheffield in September 2014.

Highly microporous carbons with narrow pore size distribution have been prepared by simultaneous carbonization and self-activation of tobacco wastes at temperatures ranging from 600 to 1000 °C. The efficiency of porosity development, without pores broadening, is attributed to well-distributed alkalis at the molecular level in the tobacco precursor....

The electrochemical performance of various carbon materials as supercapacitor electrodes with redox active electrolytes has been presented. In situ Raman investigation was carried out to show possible iodine species, polyiodides and carbon/iodine interactions during electrode polarization. Apart from the electrolyte also the kind of current collect...

It has been long time accepted that capacitors with ACTIVATED carbon (AC) electrodes in aqueous electrolytes do not deliver a high energy due to their low voltage, e.g., 0.7 – 0.8 V in KOH and H2SO4. Recently, we have demonstrated that the voltage window can be dramatically enhanced by using salt solutions with pH close to 7 [1,2]. In that case, th...

This paper reports the electrochemical behaviour of supercapacitor carbon electrodes operating in different aqueous solutions modified by various redox-active species (hydroxybenzenes, bromine derivatives and iodide). Three dihydroxybenzenes with varying stereochemistry, i.e., –OH substitution, have been considered as electrolyte additives (0.38 mo...

Lately we have demonstrated that huge pseudo-capacitive contributions can be originated from the electrolyte when using high surface area activated carbon electrodes, for example by using iodide based solutions in water [1]. Although the use of such concept allows very high capacitance values to be reached, the energy of the AC/AC capacitors based...

It has been long time accepted that capacitors with activated carbon (AC) electrodes in aqueous electrolytes do not deliver a high energy due to their low voltage, e.g., 0.7 – 0.8 V in KOH and H 2 SO 4 . Recently, we have demonstrated that the voltage window can be dramatically enhanced by using salt solutions with pH close to 7 [1,2]. In that case...

Organic and inorganic iodides dissolved in protic ionic liquid (PIL) were used as source of pseudocapacitance at the activated carbon (AC) electrode/electrolyte interface. The organic iodide solutions were 0.25 mol·L-1 triethylammonium (protic) or tetraethylammonium (aprotic) iodide in triethylammonium bis(trifluoromethane)sulfonimide (PIL) and the...

Presented paper describes and critically comments major recent strategies for improving electrochemical capacitor performance. Particularly, carbon based electrodes and aqueous electrolytes have been considered. A novel concept of redox active electrolytes as a source of pseudocapacitance effect as well as profits and cons of such system have been...

The performance of AC/AC (AC = activated carbon) symmetric capacitors based on two commonly used binders–poly(vinylidene difluoride) (PVDF) and poly(tetrafluoroethylene) (PTFE)–introduced in the electrodes at same amount (10 wt%) has been compared in 1 mol·L−1 NaNO3 aqueous electrolyte. For capacitors charged up to 1.6 V, the PTFE and PVDF-based ca...

Electrical energy storage (EES) is one of the most critical areas of technological research around the world. Storing and efficiently using electricity generated by intermittent sources and the transition of our transportation fleet to electric drive depend fundamentally on the development of EES systems with high energy and power densities. Superc...

Electrical-energy storage has become one of the most critical areas of technological research. Electrochemical capacitors, also known as supercapacitors or ultracapacitors, are devices for rapid and highly efficient energy storage via interfacial ion electrosorption and fast redox reactions. F. Béguin and co-workers summarize on page 2219 the state...

The effect of halide ion concentration on the capacitor performance was considered during this study. Iodide anion has been selected as the most profitable halide taking into account its electrochemical properties and environmental impact. Several concentrations of NaI were tested (from 0.25 to 5 mol L−1 aqueous solutions) using as electrodes two c...

Among various energy storage systems, great interest is focused on electrochemical capacitors (ECs) because of their high power and long cycle life. The most typical devices operate through the charge/discharge of the electrical double-layer at the electrode/electrolyte interface in aqueous or organic medium and as well as in ionic liquid. The capa...

Typical electrostatic attraction of ions is at the origin of capacitance, however, some faradaic reactions may occur at electrode/electrolyte interface called pseudocapacitive phenomena. Such effects can be initiated from electrode but also from solutions with electroactive species (iodides, bromides, vanadium compounds, di-hydroxybenzenes etc.). R...

The synthesis of lambda-manganese oxide (λ-MnO2) with a developed porosity and an ordered and interconnected pore structure used as supercapacitor electrode is reported for the first time in the present study. A spinel-type LiMn2O4 material was first prepared by hard-templating pathway using KIT-6 mesoporous silica as a template and metal nitrates...

Quinone/hydroquinone redox couple has been utilized as a source of additional capacitance in typical capacitive energy-storage materials. By generation of functional groups on the carbon electrode surface (grafting) directly from electrolyte there is a possibility to enhance the capacitance value significantly. Hydroxybenzene solutions with differe...