Long-term cycling behavior of asymmetric activated carbon/MnO2 aqueous electrochemical supercapacitor

Activated carbon–MnO2 hybrid electrochemical supercapacitor cells have been assembled and characterized in K2SO4 aqueous media. A laboratory cell achieved 195,000 cycles with stable performance. The maximal cell voltage was 2V associated with 21±2Fg−1 of total composite electrode materials (including activated carbon andMnO2, binder and conductive additive) and an equivalent serie resistance (ESR) below1.3cm2. Long-life cycling was achieved by removing dissolved oxygen from the electrolyte, which limits the corrosion of current collectors. Scaling up has been realized by assembling several electrodes in parallel to build a prismatic cell. A stable capacity of 380 F and a cell voltage of 2V were maintained over 600 cycles. These encouraging results show the interest of developing such devices, including non-toxic and safer components as compared to the current organic-based devices

Ion Sieving Effects in Chemically Tuned Pillared Graphene Materials for Electrochemical Capacitors

Supercapacitors offer high power densities but require further improvements in energy densities for widespread commercial applications. In addition to the conventional strategy of using large surface area materials to enhance energy storage, recently, matching electrolyte ion sizes to material pore sizes has been shown to be particularly effective. However, synthesis and characterization of materials with precise pore sizes remain challenging. Herein, we propose to evaluate the layered structures in graphene derivatives as being analogous to pores and study the possibility of ion sieving. A class of pillared graphene based materials with suitable interlayer separation were synthesized, readily characterized by X-ray diffraction, and tested in various electrolytes. Electrochemical results show that the interlayer galleries could indeed sieve electrolyte ions based on size constrictions: ions with naked sizes that are smaller than the interlayer separation access the galleries, whereas the larger ions are restricted. These first observations of ion sieving in pillared graphene-based materials enable efficient charge storage through optimization of the d-spacing/ion size couple

Investigation of ion transport in chemically tuned pillared graphene materials through electrochemical impedance analysis

Chemically tuned pillared graphene structures show ability to limit restacking of graphene sheets for electrochemical energy storage in SCs. A comprehensive electrochemical characterization using various ion sizes allowed identification of ion-sieving in the cross-linked galleries of reduced pillared graphene materials (RPs). The access to the cross-linked galleries, which provide additional ion sorption sites, offered slightly increased capacitances in RPs compared to completely restacked sheets in reduced graphene oxide (RGO). We performed electrochemical impedance analyses on RPs and RGO to understand the ion transport inside the cross-linked graphene galleries. RGO adsorbs ions in the inter-particle micro/meso pores and the ion access to such sites from the bulk electrolyte occurs with relative ease. RPs sieve ions into their inter-layer gallery pores based on effective ion sizes and the ion transport process is resistive compared to RGO. A control study using 3D pillared graphene hydrogel with improved macro porosity assigns this resistive behavior and the moderate capacitances to limited ion access to the active sites due to excess number of pillars. The obtained results on the ion transport dynamics between graphene layers provide perspectives towards further optimization of these graphene materials for SCs

Sparsely Pillared Graphene Materials for High-Performance Supercapacitors: Improving Ion Transport and Storage Capacity

Graphene-based materials are extensively studied as promising candidates for supercapacitors (SCs) owing to the high surface area, electrical conductivity, and mechanical flexibility of graphene. Reduced graphene oxide (RGO), a close graphene-like material studied for SCs, offers limited specific capacitances (100 F·g–1) as the reduced graphene sheets partially restack through π–π interactions. This paper presents pillared graphene materials designed to minimize such graphitic restacking by cross-linking the graphene sheets with a bifunctional pillar molecule. Solid-state NMR, X-ray diffraction, and electrochemical analyses reveal that the synthesized materials possess covalently cross-linked graphene galleries that offer additional sites for ion sorption in SCs. Indeed, high specific capacitances in SCs are observed for the graphene materials synthesized with an optimized number of pillars. Specifically, the straightforward synthesis of a graphene hydrogel containing pillared structures and an interconnected porous network delivered a material with gravimetric capacitances two times greater than that of RGO (200 F·g–1vs 107 F·g–1) and volumetric capacitances that are nearly four times larger (210 F·cm–3vs 54 F·cm–3). Additionally, despite the presence of pillars inside the graphene galleries, the optimized materials show efficient ion transport characteristics. This work therefore brings perspectives for the next generation of high-performance SCs

Macrophage-derived Wnt opposes Notch signaling to specify hepatic progenitor cell fate in chronic liver disease

During chronic injury a population of bipotent hepatic progenitor cells (HPCs) become activated to regenerate both cholangiocytes and hepatocytes. Here we show in human diseased liver and mouse models of the ductular reaction that Notch and Wnt signaling direct specification of HPCs via their interactions with activated myofibroblasts or macrophages. In particular, we found that during biliary regeneration, expression of Jagged 1 (a Notch ligand) by myofibroblasts promoted Notch signaling in HPCs and thus their biliary specification to cholangiocytes. Alternatively, during hepatocyte regeneration, macrophage engulfment of hepatocyte debris induced Wnt3a expression. This resulted in canonical Wnt signaling in nearby HPCs, thus maintaining expression of Numb (a cell fate determinant) within these cells and the promotion of their specification to hepatocytes. By these two pathways adult parenchymal regeneration during chronic liver injury is promoted

Enhanced Electrochemical capacitors (CAP 2017): Foreword

International audienc

Enhanced electrochemical capacitors (CAP 2019): Foreword

International audienc

Sodium borohydride (NaBH 4 ) as a high-capacity material for next-generation sodium-ion capacitors

International audienceEnergy storage is an integral part of the modern world. One of the newest and most interesting concepts is the internal hybridization achieved in metal-ion capacitors. In this study, for the first time we used sodium borohydride (NaBH 4 ) as a sacrificial material for the preparation of next-generation sodium-ion capacitors (NICs). NaBH 4 is a material with large irreversible capacity of ca. 700 mA h g −1 at very low extraction potential close to 2.4 vs Na + /Na 0 . An assembled NIC cell with the composite-positive electrode (activated carbon/NaBH 4 ) and hard carbon as the negative one operates in the voltage range from 2.2 to 3.8 V for 5,000 cycles and retains 92% of its initial capacitance. The presented NIC has good efficiency >98% and energy density of ca. 18 W h kg −1 at power 2 kW kg −1 which is more than the energy (7 W h kg −1 at 2 kW kg −1 ) of an electrical double-layer capacitor (EDLC) operating at voltage 2.7 V with the equivalent components as in NIC. Tin phosphide (Sn 4 P 3 ) as a negative electrode allowed the reaching of higher values of the specific energy density 33 W h kg −1 (ca. four times higher than EDLC) at the power density of 2 kW kg −1 , with only 1% of capacity loss upon 5,000 cycles and efficiency >99%

Ag2V4O11: from primary to secondary battery

Ag2V4O11 (silver vanadium oxide, SVO) is the positive electrode in primary lithium/SVO batteries that had known an extraordinary success as a power source in implantable cardiac defibrillators (ICD). However, its use in rechargeable batteries is questioned due to the need of the negative lithium metal electrode that acts as the lithium source and that cannot be safely recharged in standard liquid electrolytes. In this study, a proof of concept of rechargeable graphite/SVO battery is demonstrated. The introduction of 3,4-dihydroxybenzonitrile dilithium salt (Li2DHBN) as a sacrificial lithium source in the positive electrode allows in situ lithiation of the graphite electrode. The cell can further be cycled as a secondary battery. Different parameters have been investigated such as the particle size of Ag2V4O11 synthesized by solid state and hydrothermal processes, especially with regard to peak power delivery. In situ XRD was used to investigate the link between irreversible silver reduction, which allows high electronic conductivity, and amorphization of the SVO structure