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The optimal performance of organic electrodes for aqueous batteries requires their full compatibility with selected electrolyte solutions. Electrode materials having 1-3-dimensional structures of variable rigidity possess a confined space in their structure filled with water and electrolyte solutions. Depending on the rigidity and confined space geometry, insertion and extraction of ions into electrode structures are often coupled with incorporation/withdrawal of water molecules. Aside from the scientific interest in understanding the charging mechanism of such systems, co-insertion of solvent molecules affects strongly the charge storage capability of the electrodes for energy storage devices. We present herein in situ electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) investigations of polyaniline (PANI) electrodes operating in various aqueous Na

The need for improved batteries and supercapacitors, which are not based on lithium compounds, promotes significant research efforts to find suitable alternative systems based on various mono and multivalent cations capable of delivering high energy and power density with good long-term stability. The progress in aqueous Zn-ion batteries and supercapacitors obtained over the past years lead to the development of new structures and compounds that enable revisable hosting of Zn-ions while keeping good structural integrity. Yet, as aqueous electrolytes involve also the generation and co-insertion of protons it is necessary to carefully define what is the charge storage mechanism in these Zn insertion compounds. In this work, the use of Ti3C2Tx as an anode for the Zn-ion system was evaluated for the first time in different ZnCl2 concentrations. Remarkable changes in the charge storage mechanism and the performance of the Ti3C2Tx electrodes were observed by moving from dilute Zn electrolytes (1 M) to higher concentrations. The high acidity of the concentrated ZnCl2 solutions results in an additional charge storage mechanism that arises from redox interactions between the MXene and the released protons and hence enhanced capacity values (60 mAh/g with good rate capability and capacity retention of 89.4% after 9000 cycles). In-situ EQCM-D measurements were employed to shed light on the charge storage mechanism of the Ti3C2Tx and the exact identity of the charge carrier inserted into the electrodes. The demonstrated EQCM-D based analysis provides precise quantification of the Zn-ion to proton ratio in the examined system and can be further applied for other aqueous Zn-ion electrodes and multivalent systems as well.

The newly emerging demand for ‘beyond-lithium’ electrochemical energy storage systems necessitates the development of alternative options in providing sustainable cost-effective storage capabilities. In pursuit of discovering such a solution, the intercalation of bisulfate anions into graphite in 17 ​M ​H2SO4 solutions has been revaluated. Although the insertion process of bisulfate into graphite was extensively studied many years ago, only poor electrochemical performance has been demonstrated. In this work, we discovered the superior performance of the graphite bisulfate system, associated with the electrodes’ fabrication method which presents a high energy density of more than 80 ​mW ​h/g and a surprising rate capability (75 ​mW ​h/g was obtained at 15 ​C) alongside impressive long-term stability of more than 1500 cycles with only 5% capacity fading. Potentiostatic intermittent titration technique followed by slow-scan-rate cyclic voltammetry (SSCV) was used to shed light on the bisulfate intercalation process. Combining the bisulfate intercalation into the graphite with a highly reversible proton insertion process into Ti3C2 MXene in such a concentrated acidic environment allows the development of a dual-ion device composed of graphite positive electrode (cathode) and MXene negative electrode (anode). This asymmetric system shows a high energy density of 35 ​mW ​h/g, good cyclability and an extended potential window of 1.5 ​V, demonstrating new opportunities for further developments of intercalation electrodes for large energy storage.

The emerging interest in aqueous rechargeable batteries has led to significant progress in the development of next-generation electrolytes and electrode materials enabling reversible and stable insertion of various multivalent ions into the electrode's bulk. Yet, despite its abundance, high salt solubility, and small ionic radius, the use of manganese ions for energy storage purposes has not received sufficient attention. Herein, we present the use of Mo6S8 (Chevrel phase) as an anode for Mn2+ insertion. By careful optimization of the electrolyte solution, high-capacity values exceeding 90 mAh/g and long-term stability (more than 1500 cycles) have been obtained. Based on in situ XRD analysis, the charging mechanism and the associated structural changes occurring during Mn2+ insertion have been carefully studied. Finally, we demonstrate for the first time a rocking chair aqueous Mn-ion battery comprising a Chevrel anode and NiHCF cathode., ACS Energy Letters, 7 (12), ISSN:2380-8195

Despite the continuous progress in the research and development of Ti3C2Tx (MXene) electrodes for high-power batteries and supercapacitor applications, the role of the anions in the electrochemical energy storage and their ability to intercalate between the MXene sheets upon application of positive voltage have not been clarified. A decade after the discovery of MXenes, the information about the possibility of anion insertion into the restacked MXene electrode is still being questioned. Since the positive potential stability range in diluted aqueous electrolytes is severely limited by anodic oxidation of the Ti, the possibility of anion insertion was evaluated in concentrated aqueous electrolyte solutions and aprotic electrolytes as well. To address this issue, we have conducted in situ gravimetric electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) measurements in highly concentrated LiCl and LiBr electrolytes, which enable a significant extension of the operation range of the MXene electrodes toward positive potentials. Also, halogens are among the smallest anions and should be easier to intercalate between MXene layers, in comparison to multiatomic anions. On the basis of mass change variations in the positive voltage range and complementary density functional theory calculations, it was demonstrated that insertion of anionic species into MXene, within the range of potentials of interest for capacitive energy storage, is not likely to occur. This can be explained by the strong negative charge on Ti3C2Tx sheets terminated by functional groups.

The need for low-cost, high-safety batteries for large-scale energy storage applications has sparked a surge in research of rechargeable aqueous batteries. While most research efforts are focused on the development of electrolyte formulations and electrode materials, it appears that the current collector impact on the battery performance is frequently overlooked. Even though the current collector is traditionally thought of as an inactive battery component, it is included in the battery energy density calculations, making its activation desirable. Furthermore, poor current collector selection can cause irreversible side reactions, resulting in rapid cell efficiency decay. Herein we propose a new approach to design current collectors that makes use of anodized Ti. The redox-active anodized Ti significantly improves the overall anode capacity and provides effective inhibition of hydrogen formation on the electrified interface. The use of TiO2 particles on an anodized Ti current collector in an aqueous electrolyte solution resulted in capacity of 130 mAh g−1 and exceptional capacity retention of 99% after 1000 cycles. Although the concept of active current collectors needs to be refined before it can be implemented in commercial cells, our findings indicate that this approach could be useful for improving overall cell performance without requiring significant changes to its configuration.

While many studies have been devoted to the development of new active materials for Na-ion aqueous batteries, much less attention has been given to the binders and other passive components, which largely determine the battery performance. This study demonstrates a beneficial use of MXene as a highly efficient binder for Na-ion anodes operating in aqueous electrolyte solutions. The high conductivity of 2D titanium carbide (Ti3C2Tx; T = terminal groups, mostly –OH, 0

A series of non-precious metal complexes, composed of five first-row transition-metal complexes with β-pyrrole-brominated 5,10,15-tris(pentafluorophenyl)corroles [M(tpfcBr8), M=Mn, Fe, Co, Ni, and Cu], was investigated as catalysts for oxygen reduction in an alkaline solution (0.1 m KOH). The corroles were adsorbed on a high surface area carbon powder (BP2000) prior to electrochemical measurements to create a unique composite material. The comparison between the different metal complexes revealed a high oxygen reduction reaction (ORR) catalytic performance in the case of the Fe- and Co-corroles. These complexes reduce oxygen at very low overpotentials (with E1/2=0.79 V and 0.77 V vs. RHE, respectively), which is better than other well-defined molecular catalysts and comparable to that of Pt on carbon (XC-72). The mechanism by which the most active complexes catalyze the ORR in alkaline solutions was also studied, disclosing that the dominant reaction path is a four-electron reduction of molecular oxygen to hydroxide.

In this work, new catalyst for the direct electro-oxidation of dimethyl ether (DME) was synthesized and studied using an array of techniques. One of the most prominent catalysts for this reaction, platinum copper alloy (PtCu), was synthesized in an easy and low cost approach. Structural characterizations such as X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM) and elemental analysis revealed that the synthesized PtCu nanoparticles (3 nm on average), formed homogeneous NanoChains without aggregation of metallic platinum or copper. The catalyst's activity towards electro-oxidation of DME was tested using cyclic - voltammetry (CV) and in membrane-electrode assembly (MEA) in a full cell. The catalyst performance was found to be promising. Direct DME fuel cell (DDMEFC) studied in this work has relatively high energy density, of 13.5 mW cm-1 and thus shows great potential as fuel for low power fuel cells. The electrocatalysis of the DME oxidation reaction (DOR) was compared between synthesized PtCu and commercial PtRu/C and exhibited almost double the performance with the newly synthesized catalyst.