Despite the continuous progress in the research and development of Ti 3 C 2 T x (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 Ti 3 C 2 T x sheets terminated by functional groups.
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.
Among the examined organic electrodes for aqueous mono and multivalent ions batteries, polyimide is considered a promising candidate because of its high capacity and good cyclability in different electrolyte solutions. While most of the studies so far were focused on the energetic performance of polyimide anodes, much less is known about their charge storage mechanism and particularly how such electrodes are affected by the solvation properties of the inserted cations. Using in situ EQCM-D, a direct assessment of the cationic fluxes and their hydration shells inserted/extracted to/from PI electrodes upon potential application was performed for a large variety of mono and multivalent cations. Our observations demonstrated a pronounced withdrawal of water molecules from the polymeric electrodes during insertion of chaotropic cations and significantly less water withdrawal upon insertion of kosmotropic cations. These findings are well correlated with the capacity and the rate capability of the polyimide electrodes in the examined systems and shed light on their charge storage mechanism.
A new platinum-copper alloy electrocatalyst for the direct electro-oxidation of dimethyl ether (DME) has been synthesized in an easy and low-cost approach and studied by using an array of techniques, including X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and elemental analysis. Structural characterization 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 and was found to be promising. The direct DME fuel cell (DDMEFC) studied in this work has relatively high energy density, of 13.5 mW cm and thus shows great potential as fuel for low power fuel cells. The newly synthesized PtCu catalyst exhibited almost double the performance of commercial PtRu in electrocatalytic DME oxidation.
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