Ti3C2Tx MXene-embedded MnO2-based hydrophilic electrospun carbon nanofibers as a freestanding electrode for supercapacitors

Herein, MnO2 nanoflowers are electrodeposited on a self-supported and electroconductive electrode in which 2D Ti3C2Tx nanosheets are encased in carbon nanofibers (MnO2@Ti3C2Tx/CNFs). This improves the conductivity and hydrophilicity of the MnO2 composite electrode. The asymmetric supercapacitor shows a high energy density of 46.4 W h kg-1 and a power density of 4 kW kg-1.

In situ exfoliation and modification of graphite foil in supercapacitor devices: a facile strategy to fabricate high-performance supercapacitors

Graphite foils (GFs) are emerging as a new class of electrodes in supercapacitors (SCs) based on their light weight, and high electrical conductivity, although the surface area remains low. A novel method of, in situ electrochemical exfoliation and modification of GF in the assembled SCs, showed high energy density and power density of the SC devices.

Simple fabrication for high performance supercapacitors.

Metal Organic Framework Derived MnO2-Carbon Nanotubes for Efficient Oxygen Reduction Reaction and Arsenic Removal from Contaminated Water

Even though manganese oxides are attractive materials for batteries, super-capacitors and electro-catalysts for oxygen reduction reactions, in most practical applications MnO₂ needs to be hybridized with conductive carbon nano-structures to overcome its inherent poor electrical conductivity. In this manuscript we report microwave-assisted synthesis of MnO₂ embedded carbon nanotubes (MnO₂@CNT) from Mn-H₃BTC (benzene-1,3,5-carboxylic acid) metal organic frameworks (MOF) precursors. Using graphene oxide as microwave susceptible surface, MnO₂ nano-particles embedded in three dimensional reduced graphene oxide (rGO) -CNT frameworks (MnO₂@CNT-rGO) were synthesized which when applied as electro-catalysts in oxygen reduction reaction (ORR) demonstrated comparable half-wave potential to commercial Pt/C, better stability, and excellent immunity to methanol crossover effect in alkaline media. When carbon fiber (CF) was used as substrate, three-dimensional MnO₂@CNT-CF were obtained whose utility as effective adsorbents for arsenic removal from contaminated waters is demonstrated.

Effects of electrode thickness and crystal water on pseudocapacitive performance of layered birnessite MnO2

Manganese dioxide (MnO₂) nanomaterials with two-dimensional (2D) layered birnessite structures are promising pseudocapacitive electrode materials. However, the effects of structural factors on their electrochemical performance is not fully understood. We synthesize alkali-free crystal water containing 2D layered birnessite MnO₂ electrodes with controllable mass loading from 0.1 to 19.3 mg cm^-2 to investigate the effects of electrode thickness and crystal water functions on crystal structure and pseudocapacitive behavior, to promote its industrialization. We find that the crystal water enlarges the interlayer space of birnessite MnO₂ with electrolyte ions transported much more easily, resulting in higher specific capacitance of 702 F g^-1 (70.2 mF cm^-2) and excellent cycling stability of 20 000 charge-discharge cycles even at a mass loading of up to 10.8 mg cm^-2. Such gains in specific capacitance are weakened significantly with raised mass loading. Thus, compared to a carbon cloth substrate, a carbon nanotube film with enhanced electron space transport capability presents better performance, indicating an effective strategy for higher mass loading cases. The present work sheds light on an efficient method for achieving high capacitance and mass loading together, for practical applications.

Polyelectrolyte Composite Membranes Containing Electrospun Ion-Exchange Nanofibers: Effect of Nanofiber Surface Charges on Ionic Transport

Poly(vinyl alcohol) (PVA)-based ion-exchange nanofibers (IEX-NFs) and their composite polyelectrolyte membranes were prepared and characterized. The PVA-based NFs are well dispersed and form a three-dimensional network structure in the polymer matrix, Nafion. All of the prepared membranes show a similar ion-exchange capacity of ∼1.0 mmol g^-1. The ionic conductivities through the PVA- b-PSS-NF/Nafion composite membranes are superior to that of the Nafion membranes, but the conductivity through the PVA-NF/Nafion composite membrane is half that of the Nafion membrane. Our electrokinetic measurements clearly indicate that a high density of ion-exchange groups on the NF surface results in a continuous ionic transport path in the polymer matrix. In addition, the mechanical strength of all of the NF-composite membranes is improved compared with that of the membranes without NF.