Protic Electrolyte Research Articles

Longevous Protic Hybrid Supercapacitors Using Bimetallic Prussian Blue Analogue/rGO-Based Nanocomposite Against MXene Anode.

MXenes exhibit a unique combination of properties-2D structure, high conductivity, exceptional capacity, and chemical resistance-making them promising candidates for hybrid supercapacitors (HSCs). However, the development of MXene-based HSCs is often hindered by the limited availability of cathode materials that deliver comparable electrochemical performance, especially in protic electrolytes. In this study, this challenge is addressed by introducing a durable protic HSC utilizing a bimetallic Prussian Blue Analogue (PBA) decorated on reduced graphene oxide (rGO) as a nanocomposite cathode paired with a single-layered Ti3C2Tx MXene (SL-MXene) anode. The bimetallic PBA, specifically nickel hexacyanocobaltate (NiHCC), is utilized by virtue of its open and stable structure that facilitates efficient charge storage, leading to enhanced stability and energy storage capabilities. The resulting NiHCC/rGO//SL-MXene cell demonstrates impressive performance, achieving a maximum specific energy of 38.03Wh kg-1 and a power density of 20666.67W kg-1. Remarkably, the NiHCC/rGO//SL-MXene HSC cell also exhibits excellent cycling stability without any loss even after 15000 cycles while retaining ≈100% coulombic efficiency. This work underscores the potential of bimetallic PBA materials with conductive rGO backbone for overcoming the limitations of current MXene-based protic HSCs, highlighting the significance of this work.

Suppressing proton-induced HER and cathode fading by an aprotic hybrid electrolyte for long-cycle stability of aqueous Na||Zn hybrid batteries

Aqueous zinc metal batteries with unique advantages of intrinsic safety and low cost are considered as one of the most promising next-generation energy-storage technologies. However, their lifespan is significantly constrained by the electrolyte, specifically due to limitations caused by proton-induced HER and dendritic growth at the anode side and dissolution phenomena at the cathode. Unlike most studies on the protic electrolyte systems, herein, a new aprotic hybrid electrolyte of Na/Zn tetrafluoroborate-trimethyl phosphate with ultralow proton activity tuned by reconstruction of hydrogen bonding network and ultrahigh interfacial stability endowed by simultaneous formation of SEI and CEI were designed for the first time. Attributed to the synergistic effect of proton activity attenuation and ZnF2-Zn3(PO4)2 SEI formation, HER-trigged corrosion current was decreased by 96.52%, which leads to an exceptionally high coulombic efficiency up to 99.63%, and operational lifespan exceeding 2000 hours at 1 mA cm−2/ 1 mAh cm−2 for Zn||Cu asymmetric cell and Zn||Zn symmetric cell, respectively. Furthermore, the suppression of excess hydrated proton co-insertion reaction and construction of inorganic-organic CEI enabled the PBAs||Zn full cell a prolonged cycling life of 6000 cycles with an ultralow decay rate of 0.004% per cycle. The special electrolyte utilizing cheap tetrafluoroborate salts in conjunction with cost-effective PBA cathode and Zn anode provides a new choice for low-cost, high-safety, non-toxic batteries for practical applications.

Nanoscale Investigations of the Electric Double Layer in Protic Ionic Liquids

A hydrogen-based energy storage system will be the backbone of a future energy grid using renewable energies. Polymer electrolyte membrane fuel cells (PEMFCs) are a key element in this energy system as they convert chemical energy stored as hydrogen into electrical energy on demand. PEMFC systems, especially for automotive application, could be significantly improved by increasing the operation temperature above 100 °C. Protic ionic liquids are promising candidates as non-aqueous protic electrolytes for next-generation high-temperature polymer electrolyte membrane fuel cells. These fuel cells have a target operation temperature of 160 °C and allowing for a more efficient water and heat management compared to conventional Nafion®-based PEMFCs, which operate at temperatures below 80 °C [1].In order to ensure a reliable and efficient operation an electrolyte with a high electrochemical performance and stability has to be selected. For this purpose, protic ionic liquids have been proposed and first fuel cell tests have shown promising results [2]. Hence, we aim on understanding the properties of this class of novel electrolytes on an atomistic level, which would allow designing suitable material combinations and predicting their properties for an efficient fuel cell operation. As ionic liquids are molten salts, which are liquid below 100 °C, their electrochemical properties differ significantly from those of aqueous solutions. Instead of a classical electric double layer, which can be described by the models provided by Helmholtz, Gouy-Chapman and Stern, the interface structure formed between the electrolyte and a charged electrode is governed by the interplay between coulomb interaction and steric effects between the (large) molecular ions [3]. In order to understand the formation of this double layer on a metallic electrode, we employ atomic force microscopy and infrared spectroscopy in combination with molecular dynamics simulations. Our results show that in the interface region between the prototype protic ionic liquid diethylmethylammonium triflate ([Dema][TfO]) and a Pt electrode, a dense layered structure consisting of alternating anion and cation layers is present, that extends several nanometres into the bulk of the electrolyte [4]. The composition and structure changes with applied potential due to a preferential attraction of anions or cations depending on the electrode charge. When water is added to the ionic liquid, the layered structure becomes distorted and water molecules appear near the electrode. Since the presence of water will also influence the relevant electrochemical processes such as the oxygen reduction reaction (ORR), the analysis of the double layer structure on an atomistic scale is necessary in order to understand the subtle interactions between the molecules in the electrolyte and to propose design routes for novel more efficient ionic liquid-based electrolytes. Wippermann, K.; Suo, Y.; Korte, C. Oxygen Reduction Reaction Kinetics on Pt in Mixtures of Proton-Conducting Ionic Liquids and Water: The Influence of Cation Acidity. J. Phys. Chem. C 2021, 125, 4423–4435, doi:10.1021/acs.jpcc.0c11374.Skorikova, G.; Rauber, D.; Aili, D.; Martin, S.; Li, Q.; Henkensmeier, D.; Hempelmann, R. Protic Ionic Liquids Immobilized in Phosphoric Acid-Doped Polybenzimidazole Matrix Enable Polymer Electrolyte Fuel Cell Operation at 200 °C. Journal of Membrane Science 2020, 608, 118188, doi:10.1016/j.memsci.2020.118188.Rodenbücher, C.; Wippermann, K.; Korte, C. Atomic Force Spectroscopy on Ionic Liquids. Applied Sciences 2019, 9, 2207, doi:10.3390/app9112207.Rodenbücher, C.; Chen, Y.; Wippermann, K.; Kowalski, P.M.; Giesen, M.; Mayer, D.; Hausen, F.; Korte, C. The Structure of the Electric Double Layer of the Protic Ionic Liquid [Dema][TfO] Analyzed by Atomic Force Spectroscopy. International Journal of Molecular Sciences 2021, 22, 12653, doi:10.3390/ijms222312653. Figure 1

Influence of Acidity, Water and Temperature on the Double Layer Properties of Protic Ionic Liquids for Future Fuel Cell Applications

Polymer electrolyte membrane fuel cells (PEMFC) are a viable alternative to combustion engines and rechargeable batteries for automotive applications. However, the operating temperature of PEMFCs using sulfonated fluoropolymers, e.g. NAFION®, is limited below 80 °C (ambient pressure), because the proton conduction relies on the presence of water. A PEMFC operating above 100 °C would allow a much more simplified system setup for water and heat management. This requires novel non-aqueous protic electrolytes. Proton conducting ionic liquids (PIL) are promising candidates. [1,2]. However, the fuel cell relevant electrode reactions—oxygen reduction and hydrogen oxidation reaction (ORR/HOR)—are not as well understood as in aqueous electrolytes.In this study, we employed electrochemical impedance spectroscopy (EIS), cyclovoltammetry (CV), chronoamperomery (CA) and steady state current measurements to elucidate the double layer properties of the platinum electrode/PIL interface, the kinetics and possible mechanism of the ORR. Three PILs with different cation acidities with an Brønsted-acidic cation [HA+][X−] are compared, [Dema][TfO], [1-EIm][TfO] and [2-Sema][TfO].Comparing the PILs with different cation acidity strongly suggest that the first reduction step including the proton transfer to the (catalytic) active sites on the electrode is mainly determining the ORR rate. The presence of residual water, unavoidable also at fuel cell operation >100 °C, is another important parameter. H2O modifies the ordered structure of the electrochemical double layer. Its protolysis equilibrium with an acidic PIL cation results in the formation of H3O+ that serves as a proton donor in the rate determining step and thus influences the ORR kinetics. Highly acidic PIL cations serve as a proton donor as well, particularly at low H2O concentrations, whereas the role of H3O+ as proton donor in the ORR becomes more prominent at higher water concentrations [3]. In low acidic PILs, H3O+ is the predominant proton donor and the ORR rate is significantly smaller resulting in considerably higher overpotentials. Thus, the onset potential of the ORR in a PIL based fuel cell will depend on both the concentration of residual water and the PIL cation acidity.Plots of the potential-dependent data from EIS measurements in the complex capacitance plane (CCP) show that at least two differential double layer capacitances are present, depending on the cell potential U (vs. RHE), water concentration c(H2O) and temperature T. The double layer properties of the highly acidic [2-Sema][TfO] are significantly different compared to the less acidic PILs [1-EIm][TfO] and [Dema][TfO]. The potential dependent capacitance curves were discussed by taking a mean field model, the presence of water and short range correlations of ions into account. [4, 5] The combined electrochemical kinetics and double layer measurements provide a deeper insight into the double layer structure at the Pt electrode/PIL interface to reveal the rate limiting parameters of the ORR and its mechanism.[1] K. Wippermann, J. Giffin, S. Kuhri, W. Lehnert and C. Korte, Phys. Chem. Chem. Phys. 19, 24706 (2017)[2] K. Wippermann, Y. Suo and C. Korte, J. Phys. Chem. C 125(8), 8 (2021)[3] H. Hou, H. M. Schütz, J. Giffin, K. Wippermann, X. Gao, A. Mariani, S. Passerini and C. Korte, ACS Appl. Mater. Interfaces 13, 8370 (2021)[4] Z. A. H. Goodwin, G. Feng and A. A. Kornyshev, Electrochim. Acta 225, 190 (2017)[5] J. Friedl, I. I. E. Markovits, M. Herpich, G. Feng, A. A. Kornyshev and U. Stimming, ChemElectroChem 4, 216 (2017)Figure: ORR rate constant of PILs [HA+][X−] with different cation acidity vs. content of residual water (50 mol% H2O corresponds to 5–6 wt% H2O) Figure 1

Stable p-Type Molybdenum and Copper Ion-Containing Coordination Polymer Photocathode in Protic Electrolytes

Photoelectro-redox catalysts for multiproton-coupled electron transfer are vital for photo-assisted electrochemical energy conversion and electrosynthetic processes. Herein, we describe a facile method for the preparation of the molybdenum and copper ion-containing coordination polymer using a bridging functional triazine ligand. X-ray photoelectron spectroscopy (XPS) analysis reveals the presence of mixed-valent molybdenum and copper ions in the coordination polymer. In contrast to the p-type copper oxide photocathode, this photocathode material displays excellent photoelectrochemical stability in strong protic electrolytes. High photocurrent responses were observed for the molybdenum and copper ions-incorporated metallopolymers and nearly 20 times higher acidic pH than in a neutral electrolyte. The constant-potential photocurrent measurements in protic electrolytes for a longer duration display a stable p-type response of nearly 50–60 μA cm–2. The photoelectrocatalyst exhibits an improved electrochemical oxygen reduction and carbon dioxide reduction.

Hydrogen Production and Utilization in a Membrane Reactor.

Industrial hydrogenation consumes ~11 Mt of fossil-derived H2 gas yearly. Our group invented a membrane reactor to bypass the need to use H2 gas for hydrogenation chemistry. The membrane reactor sources hydrogen from water and drives reactions using renewable electricity. In this reactor, a thin piece of Pd separates an electrochemical hydrogen production compartment from a chemical hydrogenation compartment. The Pd in the membrane reactor acts as (i) a hydrogen-selective membrane, (ii) a cathode, and (iii) a catalyst for hydrogenation. Herein, we report the use of atmospheric mass spectrometry (atm-MS) and gas chromatography mass spectrometry (GC-MS) to demonstrate that an applied electrochemical bias across a Pd membrane enables efficient hydrogenation without direct H2 input in a membrane reactor. With atm-MS, we measured a hydrogen permeation of 73%, which enabled the hydrogenation of propiophenone to propylbenzene with 100% selectivity, as measured by GC-MS. In contrast to conventional electrochemical hydrogenation, which is limited to low concentrations of starting material dissolved in a protic electrolyte, the physical separation of hydrogen production from utilization in the membrane reactor enables hydrogenation in any solvent or at any concentration. The use of high concentrations and a wide range of solvents is particularly important for reactor scalability and future commercialization.

Vibrational signature of hydrated protons confined in MXene interlayers

The hydration structure of protons has been studied for decades in bulk water and protonated clusters due to its importance but has remained elusive in planar confined environments. Two-dimensional (2D) transition metal carbides known as MXenes show extreme capacitance in protic electrolytes, which has attracted attention in the energy storage field. We report here that discrete vibrational modes related to protons intercalated in the 2D slits between Ti3C2Tx MXene layers can be detected using operando infrared spectroscopy. The origin of these modes, not observed for protons in bulk water, is attributed to protons with reduced coordination number in confinement based on Density Functional Theory calculations. This study therefore demonstrates a useful tool for the characterization of chemical species under 2D confinement.

Visible light-active binary metal ion containing functional triazine metallopolymers as a stable p-type photo-electrocatalyst in protic electrolytes

Triazine-based visible light-active metal–organic coordination system for improved photoelectrochemical activity in protic electrolytes.

Pseudocapacitance of Vanadium Carbide MXenes in Basic and Acidic Aqueous Electrolytes

Pseudocapacitive charge storage with Ti3C2Tx in protic electrolytes has received significant attention. However, other MXene compositions have received less attention so far. Additionally, pseudocapacitance of MXenes has only been reported in acidic electrolytes. Herein, we report on the pseudocapacitance of two vanadium carbide MXenes (V2CTx and V4C3Tx) in various basic electrolytes and sulfuric acid, showing distinct redox couples in their cyclic voltammograms. Freestanding V2CTx film electrodes could deliver gravimetric capacitances above 250 F g–1 in different basic electrolytes with the highest capacitance of 386 F g–1 in 1 M LiOH at 2 mV s–1. Moreover, the cycle life performance showed an increasing capacitance over thousands of cycles (121% of initial capacitance after 60,000 cycles at 10 A g–1 in 6 M KOH). Both materials also exhibit higher capacitances than Ti3C2Tx in 3 M sulfuric acid, with 475 and 284 F g–1 for V2CTx and V4C3Tx, respectively.

All Redox‐Active 2D MXene and 0D Phosphomolybdic Acid Nanoclusters‐Anchored Polypyrrole Nanotubes for High‐Performance Aqueous Hybrid Supercapacitors

AbstractThe construction of a hybrid supercapacitor (HSC) with 2D Ti3C2Tx MXene anode is restricted by the scarcity of promising cathode materials that can demonstrate the superior electrochemical features in protic electrolytes. To circumvent this issue, we demonstrate an innovative high‐performance HSC cell in a protic electrolyte by combining a redox‐active 0D phosphomolybdic acid (PMo12) nanoclusters‐anchored polypyrrole nanotubes (PMo12/PPyNT) cathode against the pseudocapacitive Ti3C2Tx MXene anode. Decorating PMo12, a Keggin‐type polyoxometalates material known for their high redox activities on polypyrrole nanotubes (PPyNT) resulting in a nanocomposite that matches the electrochemical performance of MXene in a protic electrolyte so that a high‐performance HSC cell can be acquired. The gathered PMo12/PPyNT//MXene HSC cell delivers the specific energy (36.1 Wh/kg) and specific power (6.66 kW/kg) superior to the state‐of‐the‐art MXene‐based supercapacitor (SC) cells. The cell also exhibits impressive coulombic efficiencies over various current densities and adequate stability over 5000 charge‐discharge cycles. These results show that combining polyoxomolybdate‐based cathode materials against the MXene anode can overcome the boundaries associated with the existing HSC cells.

Adjustable electrochemical properties of solid-solution MXenes

MXenes are promising pseudocapacitive materials with ultrahigh specific capacitance. Currently, more than 30 stoichiometric MXene compositions and about 20 solid solutions have been experimentally synthesized. However, most studies focus on Ti 3 C 2 T x or a few other single-M MXenes, and little is known about the electrochemical properties of solid-solution MXenes. Herein, two sets of niobium-based solid-solution MXenes (Ti 2−y Nb y T x and V 2−y Nb y T x ; 0 ≤ y ≤ 2) were synthesized and the dependence of their electrochemical properties on the ratio of M elements in the structure was investigated. Relationships between the chemistry and charge storage ability, including capacitive properties and cycling stability in aqueous protic electrolyte, were determined. There is an inverse relationship between the prominence of the redox peaks and cycling stability; the latter increases with the niobium content. For instance, the capacitance retention after 20,000 cycles is less than 1% for Ti 2 CT x , but 78% for Ti 0.4 Nb 1.6 CT x . This study shows that electrochemical properties of MXenes can be controlled by tuning the ratio of transition metals in the MXene structure. • Double-metal solid-solution MXenes (Ti 2−y Nb y T x and V 2−y Nb y T x ; 0 < y < 2) were synthesized and investigated. • The capacitive properties and cycling stability of solid-solution MXenes directly depend on their composition. • The redox peak intensity decreases while the cycling stability increases with the Nb content. • This study provides a guide for adjusting the electrochemical properties of MXenes by tuning the M-site chemistry.

An aqueous high-performance hybrid supercapacitor with MXene and polyoxometalates electrodes

Two-dimensional (2D) titanium carbide (Ti3C2Tx), MXene, is an attractive pseudocapacitive electrode material that exhibits its highest capacitance at a negative potential in an aqueous protic (H2SO4) electrolyte. Developing hybrid supercapacitors (HSCs) using diverse cathode materials is the best way to identify a material with high energy density in aqueous electrolytes. However, it is difficult to find redox-active positive cathode materials that are suitable for use with MXene in an H2SO4 electrolyte. Here, 2D nanocomposite of reduced graphene oxide (rGO) decorated with phosphomolybdic acid (PMo12) polyoxometalates (POMs) are reported as promising cathode materials suitable for use against an MXene anode. The complementary potential window of MXene and rGO-POMs along with the redox activity and 2D nanostructured features of these materials can significantly enhance the electrochemical properties of HSC cell. An all-redox active HSC cell with rGO-POM cathode and MXene anode can deliver a maximum specific energy and power of 50.46 Wh/kg and 7000 W/kg, respectively, with capacitance retention of 87.12 % over 10,000 cycles and superb energy and coulombic efficiency over all applied current densities. These results suggest that the rGO-POMs cathode can be potentially coupled with an MXene anode in a protic electrolyte to enhance the electrochemical parameters of the HSC cells.

Regulating Oxygen Substituents with Optimized Redox Activity in Chemically Reduced Graphene Oxide for Aqueous Zn‐Ion Hybrid Capacitor

AbstractFunctionalizing carbon cathode surfaces with oxygen functional groups is an effective way to simultaneously tailor the fundamental properties and customize the electrochemical properties of aqueous Zn‐ion hybrid capacitors. In this work, the oxygen functional groups of chemically reduced graphene oxide (rGO) are systematically regulated via a series of reductants and varied experimental conductions. Carboxyl and carbonyl have been proven to significantly enhance the aqueous electrolyte wettability, Zn‐ion chemical adsorption, and pseudocapacitive redox activity by experimental study and computational analysis. The rGO cathode produced through hydrogen peroxide assisted hydrothermal reduction exhibits a specific capacitance of 277 F g−1 in 1 m ZnSO4 after optimization of surface oxygen functional groups. In addition, a quasi‐solid‐state flexible Zn‐ion hybrid capacitor (ZHC) with a polyacrylamide gel electrolyte and a high loading mass of 5.1 mg cm−2 are assembled. The as‐prepared quasi‐solid state ZHC can offer a superior areal capacitance of 1257 mF cm−2 and distinguished areal energy density of 342 µW h cm−2. The significant enhancement of redox activity and Zn‐ion storage capability by regulating the oxygen functional groups can shed light on the promotion of electrochemical charge storage properties even beyond protic electrolyte systems.

Stability Investigations of Platinum Electrodes in Nonaqueous Systems

Fundamental understanding of electrode dissolution processes in nonaqueous media is crucial for applications like nonaqueous battery systems, sensors, capacitors but also organic electrochemistry and is inextricably related to economic considerations. The reasons for electrode degradation are among others anodic dissolution, cathodic dissolution or cathodic corrosion. Enhanced knowledge of dissolution mechanisms and factors like composition or structure of electrodes, electrolyte and temperature are important to optimize the operation conditions, limit electrode degradation and increase the lifetime of devices.The development of the scanning flow cell (SFC) combined with an Inductively Coupled Mass Spectrometer (ICP-MS), allowing online stability studies, has given valuable insights into degradation mechanisms of different electrodes and catalyst materials in aqueous media which are relevant for applications like fuel cells and electrolyzers. We have developed an electrochemical flow cell (EFC) coupled to the ICP-MS which is suitable for the use in aggressive nonaqueous electrolytes. The flow cell is operated in an argon filled glovebox which allows us to conduct electrochemical experiments in completely inert atmosphere under the exclusion of oxygen and water.Platinum is one of the most extensively studied electrode materials due to its excellent electrocatalytic activity and inertness in various applications. Our novel method allows new insights into the complex behavior of platinum in nonaqueous electrolytes, among others in its dissolution. New aspects regarding the stability of platinum in different nonaqueous electrolytes are unveiled depending on the chemical properties of the solvent and the conducting salt. While the dissolution behavior of completely water free protic electrolytes like methanol and aprotic electrolytes like acetonitrile is very similar, the dissolution behavior changes completely in presence of trace amounts of water. Furthermore, different cations and anions in the electrolyte effect the anodic dissolution and cathodic corrosion, respectively.The controlled addition of water to nonaqueous electrolytes is an important tool to study the behavior of the formation and dissolution of the platinum oxide passivation layer and is not only relevant for nonaqueous electrocatalysis but also gives new insights into the dissolution mechanisms in aqueous electrolytes.The details of the method and different platinum dissolution profiles in several nonaqueous electrolytes will be discussed. Additionally, dissolution mechanisms will be proposed based on studies with changing water content.

Hierarchically 3D Porous Ag Nanostructures Derived from Silver Benzenethiolate Nanoboxes: Enabling CO2 Reduction with a Near-Unity Selectivity and Mass-Specific Current Density over 500 A/g.

Silver nanostructures with hierarchical porosities of multiple length scales have been synthesized through electrochemical reduction of silver benzenethiolate nanoboxes. The porous Ag nanostructures exhibit superior catalytic performance toward electrochemical reduction of CO2. The Faradaic efficiency of reducing CO2 to CO can be close to 100% at high cathodic potentials, benefiting from the readsorbed benzenethiolate ions on the Ag surface that can suppress the hydrogen evolution reaction (HER). Density functional theory calculations using the SCAN functional reveal that the disfavored H binding on the benzenethiolate-modified Ag surface is responsible for inhibiting the HER. The mass-specific activity of CO2 reduction can be over 500 A/g because the multiple-scale porosities maximize the diffusion of reactive species to and away from the Ag surface. The unique multiscale porosities and surface modification of the as-synthesized Ag nanostructures make them a class of promising catalysts for electrochemical reduction of CO2 in protic electrolytes to achieve maximum activity and selectivity.

High-Efficiency Conversion of CO2 to Oxalate in Water Is Possible Using a Cr-Ga Oxide Electrocatalyst

Electrochemical transformation of CO2 into commodity chemicals such as oxalate is a strategy for profitably remediating high atmospheric CO2 levels. Electrocatalysts for oxalate generation, however, have required prohibitively large applied potentials, forcing the use of nonaqueous electrolytes. Here, a thin film comprised of alloyed Cr and Ga oxides on glassy carbon is shown to electrocatalytically generate oxalate from aqueous CO2 with high Faradaic efficiencies at 690 mV overpotential. Oxalate is produced at a surface anion site via a CO-dependent pathway; the process is highly sensitive to the hydrogen-bonding environment and avoids the commonly invoked CO2•– intermediate. Ultimately, this catalytic system accomplishes efficient CO2 to oxalate conversion in protic electrolyte.

Anion amphiprotic ionic liquids as protic electrolyte matrices allowing sodium metal plating.

The sodium-ion battery (SIB) is proposed as a complementary technology to today's commercially dominant lithium-ion battery (LIB). While much know-how can be transferred from LIBs to SIBs, adjustments are still necessary, not the least for the electrolytes employed. Here the use of anion amphiprotic ionic liquid (AAIL) based electrolytes is proposed for SIB application. Two different AAILs, based on organic trifluoromethylsulfonylamide (TFSAm) and inorganic HSO4- anions, respectively, doped with NaTFSI salt have been studied, focusing on electrochemical stability and transport properties, complemented by studies of the ion-ion interactions, and final sodium-ion battery performance via stripping/plating vs. sodium metal electrodes.

MXene—Conducting Polymer Asymmetric Pseudocapacitors

AbstractConducting polymers (CPs) are attractive pseudocapacitive materials which show the highest capacitance under positive potentials in aqueous protic electrolytes. One way to expand their voltage window (thus energy density) in aqueous electrolytes is to manufacture asymmetric supercapacitors using distinctly different anodes. However, CPs lack matching pseudocapacitive anode materials that can perform well in protic electrolytes (e.g., sulfuric acid). 2D titanium carbide (Ti3C2Tx), MXene, as a universal pseudocapacitive anode material for a range of CPs, such as polyaniline, polypyrrole, and poly(3,4‐ethylenedioxythiophene) deposited on reduced graphene oxide (rGO) sheets, is reported here. All‐pseudocapacitive organic–inorganic asymmetric devices with MXene cathodes and rGO–polymer anodes can operate in voltage windows up to 1.45 V in 3 m H2SO4. Most importantly, these devices show outstanding cycling performance, outperforming many reported asymmetric pseudocapacitors.

Bipolar carbide-carbon high voltage aqueous lithium-ion capacitors

MXenes - two-dimensional (2D) transition metal carbides and nitrides - are an emerging class of high rate pseudocapacitive materials due to their combination of fast surface redox reactions with metallic conductivity. The ability of MXenes to spontaneously intercalate aqueous cations, broadens the scope for developing metal-ion capacitors beyond the protic electrolytes. In this study, 2D titanium carbide (MXene) free-standing films are employed to evaluate the dependence of electrochemical performance in aqueous Li and Na-ion electrolytes. By contrast, high surface area porous nanoscale carbide derived carbon (nano-CDC) is employed as a surface electrosorbing electrode at anodic potentials. Both, 2D MXene and zero-dimensional (0D) nano-CDC, with contrasting charge storage mechanisms and complementary potential windows of operation, enable the construction of an aqueous Li-ion capacitor with a 2 V voltage window of operation. This asymmetric device shows high rate capability (71% retention from 10 to 1000 mV s−1) and good cycling stability with 99.3% retention after 10,000 cycles. Furthermore, we demonstrate here the design of flexible bipolar carbide-carbon devices.

Synthesis and Properties of La0.95Sr0.05ScO3–δ Protic Electrolyte Films on Porous Cathode Material

Fundamental aspects of the phase formation and morphology of films of the proton-conducting solid electrolyte La0.95Sr0.05ScO3–δ, produced by wet deposition from inorganic salts on a porous cathode substrate La0.6Sr0.4MnO3–δ. The conditions in which gas-tight films are deposited onto substrates with porosity of up to 25% were determined. The electrical conductivity of La0.95Sr0.05ScO3–δ films was examined in relation to temperature and gas-phase composition (рН2О, рО2). The effect of the architecture of the electrolyte membrane on its transport properties was analyzed. The results of the study are of fundamental importance for development of proton-ceramic fuel cells with a supporting electrode.