[en] Electrochemical capacitors deliver high power and have long operational lives; yet, their energy densities are limited. Compared to carbon-based electrical double-layer capacitors, pseudocapacitors with an aqueous electrolyte are predicated to provide both high gravimetric and volumetric capacitance while being cost-effective and eco-friendly. However, their narrow operational potential windows limit the practical delivery of energy. In this study, we synthesized novel NbCxN1-x nanoparticles encapsulated in a uniform carbon layer. This pseudocapacitive material exhibits a high volumetric capacitance, a wide potential window stability (~345 F cm^–3, 2.1 V, in 1 M of Li₂SO₄), and a long cycling life (>10 000 cycles). Moreover, the symmetric cells (2.2 V, in 1 M of Li₂SO₄) exhibit high energy density as well as excellent cyclability and rate performances. These results offer new chances for the design of aqueous energy storage devices having a wide applied potential difference and excellent performance.

[en] Two gold nanorod-polyaniline (Au-PANI) composites with different contents of Au were prepared by two methods. An ex situ method, in the presence of preformed gold nanorods (AuNRs) and in situ one, when an AuNRs and PANI matrix is produced simultaneously, were used. Both methods were performed in immiscible water/toluene biphasic system as a simple interfacial polymerization process. Optical, structural and morphological characteristics of the formed nanocomposites were identified. It was found that AuNRs are embedded in the conducting emeraldine salt form of PANI. Nanocomposites containing 2.0 and 28.9 wt% of Au were subsequently systematically studied for borohydride oxidation reaction (BOR) for potential application in direct borohydride-peroxide fuel cell (DBPFC). Reaction parameters: number of electrons exchanged, order of reaction and activation energy, were evaluated. Both Au-PANI nanocomposites showed activity for BOR. A laboratory DBPFC was tested reaching specific peak power density of 184 Wg(-1) at 65 degrees C with Au-PANI 1 nanocomposite (containing only 2.0 wt% of Au) as anode.

[en] A combination of cell testing and electrochemical-thermal modeling is used to investigate extreme fast charging (XFC) performance for cells with a low loading of 1.5 mAk.cm(-2) and moderate loading of 2.5 mAk.cm(-2). Cells with a low loading of 1.5 mAk.cm(-2) withstand XFC performance remarkably well even up to 9C constant current (CC) charging with high charge capacity, high coulombic efficiency and very little apparent lithium plating. For a moderate loading of 2.5 mAk.cm(-2), the 6C CC charge capacity is poor with significant amounts of visually observed lithium plating. Simulated electrolyte transport properties are revealed to be insufficient and majorly set limitations for XFC performance in case of the moderate and the only simulated higher loadings (>2.5 mAk.cm(-2)). Charging at elevated temperature is shown to be an effective strategy for moderate loading cells enabling good 10-min charge capacity, high coulombic efficiency, and mitigating lithium plating. Lastly, an electrochemical model is used to investigate strategies for enabling 4-6C CC charging for cells incorporating loading beyond 3 mAk.cm(-2). As a result, the combination of an increased cell temperature, reduced electrode tortuosity, and enhanced ion-transport in the electrolyte are most likely required to facilitate XFC for state of the art and future high energy lithium-ion batteries. (C) 2020 Elsevier Ltd. All rights reserved.

[en] The electrochemical behavior of plutonium fluoride species was investigated in molten LiF-CaF₂ medium in the 1093-1153 K temperature range with PuF₄ additions. A preliminary thermodynamic study supposed a Pu(IV) carboreduction into Pu(III) and that Pu(III) reduction into metal proceeds in one step. Then, an electrochemical study was carried out on an inert electrode (tungsten) and confirmed the thermodynamic predictions: Pu(IV) is spontaneously reduced into Pu(III) in presence of carbon and Pu(III) is directly reduced into Pu(0): Pu(III) + 3e^- = Pu(0). Moreover, Pu(III) reduction mechanism is a diffusion controlled process. Diffusion coefficients were calculated at different temperatures and obey to an Arrhenius' type law with an activation energy of 63 ± 3 kJ mol^-1. The standard potential of Pu(III)/Pu(0) was determined at 1113 K and is found to be -4.61 V vs. F_2(gaz)/F^-. This value permitted to calculate activity coefficients for several molalities. (authors)

[en] Cycle aging of commercial 2.5 Ah 18650 cylindrical lithium-ion batteries with LiNi0.8Co0.1Mn0.1O2(NCM)/graphite chemistry is investigated at different charging rates. The cells charged at 1C-3C follow a similar aging path, and the degradation mechanisms under 2C and 3C charging are characterized by non-destructive electrochemical techniques and post-mortem analyses. Electrochemical impedance spectroscopy measurements indicate that the impedance rise of cells is primarily attributed to the increase of charge transfer resistance. Post mortem analyses reveal that the side reactions on NCM cathode are secondary particle cracking and transition metal dissolution, and anode degradation is caused by the growth of solid-electrolyte interface layer and the lithium plating. Voltage fitting analyses of 3C charging demonstrate that the main degradation mode is the insufficient active lithium that is available for intercalation/deintercalation in highly-lithiated anodes. Quantitative analyses of the individual electrodes based on differential voltage curves identify that loss of lithium inventory (LLI) contributes the dominant aging mode to full cell, followed by loss of active material of delithiated negative electrode (LAM_deNE) and LAM of lithiated negative electrode (LAM_liNE), while LAM of positive electrode (LAM_PE) exerts a minor effect. Accurate identification of the battery degradation mechanisms cycling under fast charging conditions helps to provide guidance for charging optimization.

[en] Highlights: : • A reasonable design strategy for hierarchical porous structures was developed. • A new design of 3D conductive carbonaceous network structure has been proposed. • Fe₃Se₄@NC@CNTs electrode exhibited excellent Na⁺ storage and HER performance. -- Abstract: : The hierarchical porous structure has been attracted increasing attention during the design of advanced electrode materials for energy storage and conversion fields. Herein, hierarchical N-doped carbon network wrapped Fe₃Se₄ nanoparticles (Fe₃Se₄ @NC@CNTs) has been successfully fabricated by a facile freeze-drying method followed by in situ selenization process. The macroporous with a diameter of about 200 nm uniformly distributed into the hierarchical carbon network, guaranteeing favorable electronic conductivity as well as structural stability. When utilized as anodes for sodium ion batteries, the Fe₃Se₄ @NC@CNTs exhibit a capacity of 440 mAh g⁻¹ after 100 cycles at 100 mA g⁻¹ (based on the total mass of the composite). Even cycling at 500 mA g⁻¹ for 1000 cycles, the electrode still remains 311 mAh g⁻¹. In addition, the Fe₃Se₄ @NC@CNTs also shows excellent hydrogen evolution reaction performance (an overpotential of 167 mV at 10 mA cm⁻² and a Tafel slope of 68 mV dec⁻¹). The superior electrochemical performance of the Fe₃Se₄ @NC@CNTs could be ascribed to the unique hierarchical network and uniform porous structure, which accommodates the volume changes of inner Fe₃Se₄, accelerates the ions/electrons transportation and facilitates electrolyte penetration. These results may give insights for the rational design of advanced electrode materials.

[en] Highlights: • High surface area nano-structured Nb₂O₅ created via a simple hydrothermal method. • Anisotropically crystalline Nb₂O₅ related to T-structure characterised electrochemically. • Anisotropically crystalline, T and H- Nb₂O₅ capable of cycling to rates of 100 C. • H-Nb₂O₅ presented as a high rate anode without the need for carbon integration. • All materials have high current stability tested at 20C over 200 cycles. -- Abstract: Orthorhombic niobium pentoxide (T-Nb₂O₅) is known to be an effective anode material for Li-ion batteries (LIBs) with very high rate capability, but the other Nb₂O₅ polymorphs and non-crystalline phases have lacked thorough exploration. A simple hydrothermal mechanism is used to produce an anisotropically crystalline ‘as-synthesised material’, which has not previously been characterised electrochemically. The as-synthesised material is heat-treated to produce T-Nb₂O₅ at 600°C and monoclinic (H-) Nb₂O₅ at 1000°C. We present electrochemical properties for all of these materials. Collectively we report rate sweeps and demonstrate high current stability (20 C-rate capability) and a long life span, up to 200 cycles. We propose the H-phase as a high rate anode when prepared via an anisotropically crystalline precursor, as it is able to demonstrate 60 % capacity retention after 200 cycles at a notably high current flux of 20 C. Such high rates results are rare for this material without integration with carbon materials. For the anisotropically crystalline Nb₂O₅ material, we achieve cycling rates up to 100 C with 80% capacity recovery upon current reduction, representing an important discovery in the development of very high rate anode materials.

[en] Highlights: : • Improvement the electrochemical properties and charge transfer of GO@CMC.MgO NHM. • Multi-function nanocomposites for photocatalytic anti-fouling and solar cell applications. • The photocatalytic process with organic compounds pollution has been detected. • The supercapacitor and energy application have been revealed. -- Abstract: : A novel nanohybrid material (NHM) of magnesium oxide nanoparticle (MgO NPs) and modified antifouling membrane surface of graphene oxide nanosheet (GO) and carboxymethylcellulose (CMC) has been created via precipitation and ultrasonication methods, then characterized via various techniques for a novel antifouling membrane for water treatment, and supercapacitor applications for energy applications. The electrochemical properties of nanohybrid material (NHM) have been synthesized successfully by the cyclic voltammetry technique for detecting charge transfer, supercapacitor, and energy storage. Also, the optical properties of NHM antifouling nanomembrane have been detected by zeta potential and UV-spectroscopy apparatus for the following the generation of electrons, charge transfer, and formation of the reactive oxygen species (ROS) for oxidation of the organic materials pollutants for water treatment. The electron transfer of GO@CMC.MgO has been revealed via the photocatalytic process for the degradation of organic and inorganic pollutions. The supercapacitor and energy applications have been detected via the measurements of electrochemical impedance spectroscopy (EIS) by Nyquist plots, the following results have been obtained: A good electron transfer has been detected with GO@CMC.MgO NHM. The photocatalytic process with organic compounds pollution has been detected. The supercapacitor and energy application have been revealed.The Results demonstrated that the fabricated NHM is promising electrode material for supercapacitor applications, energy storage and water treatment.

[en] Stability is an essential metric of electrocatalysts, but the reported experimental results are often flawed, indicated by the highly inconsistent stability data of the reference catalysts seen in the literature. In this work, focusing on the Pt/C reference catalyst toward the oxygen reduction reaction, we attempted to clarify its genuine stability under the most used accelerated stress test conditions and understand the reasons for the flawed results. Efforts have been made to design an electrochemical cell and an extended test protocol to control all possible experimental factors that could influence the test results. We found that simple experimental errors such as incomplete catalyst activation and accumulated electrolyte impurities could significantly affect the stability test results. Under strictly controlled conditions, a reliable stability benchmark of Pt/C catalyst toward the oxygen reduction reaction has been established. The proposed experimental procedure could serve as a general reference for determining the stability of electrocatalysts for different electrochemical systems.

[en] Microbial fuel cell (MFC) is a potential technology for bioelectricity generation from waste. Unfortunately, it is still a challenge for practical application due to the low power density. Immense efforts have been extended to boost the design of bioanode, mainly including the improvement on bacterial adhesion and extracellular electron transfer (EET) between bacteria and anode. Herein, electrospun porous α-Fe₂O₃ nanofibers integrated with carbon nanotubes (CNTs) are developed for MFC. Benefiting from the good electricity, ultrahigh porosity and three-dimensional interpenetrated network of fabricated CNTs/α-Fe₂O₃, the decorated anode is capable of enriching active bacteria and promoting effective EET rate. Consequently, the MFC based on CNTs/α-Fe₂O₃ nanofibers as anode achieves the eminent power density of 1959 mW/m² and high COD removal efficiency of 85.04%, superior to that of α-Fe₂O₃ anode (940 mW/m²; 81.66%) and bulk carbon cloth anode (432 mW/m²; 65.83%). More importantly, the CNTs/α-Fe₂O₃ modified anode is favorable for electrogenic active bacteria attachment, thus improving the bioelectricity performance. The consequence suggests that this strategy can offer a potential application in power production and pollutant removal.