Designing a New Class of Mechanophoric Polymer Based on Epoxy-Functionalized Rhodamine Derivative.

Mechanophoric polymers are an interesting class of smart polymers which contains a special force-sensitive molecular motif that can lead to a chemical change within the polymer network in response to mechanical force. This investigation reports the design of a mechanophoric polymer based on epoxy-functionalized rhodamine via a monomeric approach. In this case, rhodamine (Rh) is modified with glycidyl methacrylate (GMA) through an epoxy-amine reaction to design a vinyl-functionalized multi-armed macromonomer (Rh-GMA), which is reacted with butyl acrylate (BA) to prepare the crosslinked polymeric film. The crosslinked polymeric film demonstrates mechanophoric properties under UV and stretching conditions.

Hybrid Organosulfur Network/MWCNT Composite Cathodes for Li-S Batteries.

Lithium-sulfur (Li-S) batteries hold a promising position as candidates for next-generation high-energy storage systems. Here, we combine inverse vulcanization of sulfur with multiwalled carbon nanotubes (MWCNTs) to increase the conductivity of cathode materials for Li-S batteries. The mixing process of inversely vulcanized sulfur copolymer networks with MWCNTs is aided by shear in a two-roll mill to take advantage of the soft nature of the copolymer. The high-throughput mixing method demands a source of conductive carbon that can be intimately mixed with the S copolymer, rendering MWCNTs an excellent choice for this purpose. The resulting sulfur copolymer network-MWCNTs composites were thoroughly characterized in terms of structure, chemical composition, thermal, and electronic transport properties, and finally evaluated by electrochemical benchmarking. These promising hybrids yielded electrodes with high sulfur content and demonstrate stable electrochemical performance exhibiting a specific capacity of ca. 550 mAh·gsulfur-1 (380 mAh·gelectrode-1) even after 500 charge-discharge cycles at specific current of 167 mA·g-1 (corresponds to 0.1C discharge rate), and thus are superior to melt-infiltrated reference samples.

Multiple Carbon Morphologies Derived from Polyion Complex-Based Double Hydrophilic Block Copolymers as Templates and Phenol as a Carbon Precursor.

This study demonstrates the multiple carbon morphology forming abilities of two dissimilar polyion complex (PIC)-based double hydrophilic block copolymers (DHBC) along with three different phenol concentrations when subjecting the blend in aqueous media via a hydrothermal-assisted carbonization strategy. The morphological transition from worm-like to spherical along with granular is found for the blend of oppositely charged poly(ethylene glycol) (PEG)-conjugated poly(amino acid) block copolymers, PEG-poly(l-lysine) (PEG-PLys) and PEG-poly(glutamic acid) (PEG-PGlu), along with three different concentrations of phenol. In contrast, after mixing the combination of PEG-PLys and PEG-poly(aspartic acid) (PEG-PAsp) separately with three different phenol contents, elliptical to irregular to spherical structural transition occurred. Fourier transform infrared and circular dichroism spectroscopic studies indicated that the formation of worm-like hybrid micellar structures is attributed to the presence of the ß-sheet structure, whereas spherical-shaped hybrid micellar structures are formed due to the existence of α-helix and random coil structures. We discuss the mechanism for the secondary structure-induced morphology formation based on the theory related to the packing parameter, which is commonly used for analyzing the shape of the micellar structures. Secondary structures of the PIC-based DHBC system are responsible for forming multiple carbon morphologies, whereas these structures are absent in the case of the amphiphilic block copolymer (ABC) system. Furthermore, ABC-based template methods require organic solvent, ultrasonication, and a prolonged solvent evaporation process to obtain multiple carbon morphologies. Scanning electron microscopy observations suggested there is no significant morphological change even after subjecting the hybrid micelles to carbonization at elevated temperatures. Raman scattering studies revealed that the degree of graphitization and the graphitic crystallite domain size of the carbonized sample depend on the phenol content. Carbon materials exhibited the highest specific surface area of 579 m2 g-1 along with a pore volume of 0.398 cc g-1, and this observation suggests that the prepared carbons are porous. Our findings illustrate the facile and effective strategy to fabricate the multiple carbon morphologies that can be used as potential candidates for energy storage applications.

All-Carbon Monolithic Composites from Carbon Foam and Hierarchical Porous Carbon for Energy Storage.

We designed high-volumetric-energy-density supercapacitors from monolithic composites composed of self-standing carbon foam (CF) as the conducting matrix and embedded hierarchically organized porous carbon (PICK) as the active material. Using multiprobe scanning tunneling microscopy at selected areas, we were able to disentangle morphology-dependent contributions of the heterogeneous composite to the overall conductivity. Adding PICK is found to enhance the conductivity of the monoliths by providing additional links for the CF network, enabling high and stable performance. The resulting all-carbon CF-PICK composites were used as self-standing electrodes for symmetric supercapacitors without the need for a binder, additional conducting additive, metals as a current collector, or casting/drying steps. Supercapacitors achieved a capacitance of 181 F g-1 based on the entire mass of the monolithic electrode as well as an outstanding rate capability. Our symmetrical supercapacitors also delivered a record volumetric energy density of 19.4 mW h cm-3 when using aqueous electrolytes. Excellent cycling stability with almost quantitative retention of capacitance was found after 10,000 cycles in 6.0 M KOH as the electrolyte. Furthermore, charge-discharge testing at different currents demonstrated the fast charge-discharge capability of this material system that meets the requirements for practical applications.

High Mass Loading Asymmetric Micro-supercapacitors with Ultrahigh Areal Energy and Power Density.

High mass loading asymmetric micro-supercapacitors (MSCs) are key components for the development of high-performance energy and power supply systems. Here, a concept for achieving high mass loading electrodes is presented and applied to high mass loading micro-supercapacitors with ultrahigh areal energy and power density. The positive electrode is made from porous carbon with birnessite coverage and multiwalled carbon nanotubes (CNTs) as conducting additives (PIC-CNTs-MnO2). The negative electrode is prepared from hierarchically porous active carbon mixed with CNTs (PICK-CNTs). Both positive and negative electrode materials are tailored to ensure a high content of macro- and mesopores. MSCs with an optimized mass loading of 13.9 mg·cm-2 (maximum: 23.6 mg·cm-2) provide an ultrahigh areal capacitance of 1.13 F·cm-2 (volumetric capacitance: 22.6 F·cm-3), an outstanding energy of 627.8 µWh·cm-2, and a maximum power density of 64 mW·cm-2. About 85% of the initial capacitance remained after 5000 cycles. Moreover, shunt and tandem device testing confirmed a high uniformity of these MSCs, meeting the requirements of adjustable output currents and voltages in microchips.

Pseudocapacitive Desalination of Brackish Water and Seawater with Vanadium-Pentoxide-Decorated Multiwalled Carbon Nanotubes.

A hybrid membrane pseudocapacitive deionization (MPDI) system consisting of a hydrated vanadium pentoxide (hV2 O5 )-decorated multi-walled carbon nanotube (MWCNT) electrode and one activated carbon electrode enables sodium ions to be removed by pseudocapacitive intercalation with the MWCNT-hV2 O5 electrode and chloride ion to be removed by non-faradaic electrosorption of the porous carbon electrode. The MWCNT-hV2 O5 electrode was synthesized by electrochemical deposition of hydrated vanadium pentoxide on the MWCNT paper. The stable electrochemical operating window for the MWCNT-hV2 O5 electrode was between -0.5 V and +0.4 V versus Ag/AgCl, which provided a specific capacity of 44 mAh g-1 (corresponding with 244 F g-1 ) in aqueous 1 m NaCl. The desalination performance of the MPDI system was investigated in aqueous 200 mm NaCl (brackish water) and 600 mm NaCl (seawater) solutions. With the aid of an anion and a cation exchange membrane, the MPDI hybrid cell was operated from -0.4 to +0.8 V cell voltage without crossing the reduction and oxidation potential limit of both electrodes. For the 600 mm NaCl solution, the NaCl salt adsorption capacity of the cell was 23.6±2.2 mg g-1 , which is equivalent to 35.7±3.3 mg g-1 normalized to the mass of the MWCNT-hV2 O5 electrode. Additionally, we propose a normalization method for the electrode material with faradaic reactions based on sodium uptake capacities.

High Performance Hybrid Energy Storage with Potassium Ferricyanide Redox Electrolyte.

We demonstrate stable hybrid electrochemical energy storage performance of a redox-active electrolyte, namely potassium ferricyanide in aqueous media in a supercapacitor-like setup. Challenging issues associated with such a system are a large leakage current and high self-discharge, both stemming from ion redox shuttling through the separator. The latter is effectively eliminated when using an ion exchange membrane instead of a porous separator. Other critical factors toward the optimization of a redox-active electrolyte system, especially electrolyte concentration and volume of electrolyte, have been studied by electrochemical methods. Finally, excellent long-term stability is demonstrated up to 10 000 charge/discharge cycles at 1.2 and 1.8 V, with a broad maximum stability window of up to 1.8 V cell voltage as determined via cyclic voltammetry. An energy capacity of 28.3 Wh/kg or 11.4 Wh/L has been obtained from such cells, taking the nonlinearity of the charge-discharge profile into account. The power performance of our cell has been determined to be 7.1 kW/kg (ca. 2.9 kW/L or 1.2 kW/m(2)). These ratings are higher compared to the same cell operated in aqueous sodium sulfate. This hybrid electrochemical energy storage system is believed to find a strong foothold in future advanced energy storage applications.

Nanoporous Cathodes for High-Energy Li-S Batteries from Gyroid Block Copolymer Templates.

This study reports on a facile approach to the fabrication of nanoporous carbon cathodes for lithium sulfur batteries using gyroid carbon replicas based on use of polystyrene-poly-4-vinylpyridine (PS-P4VP) block copolymers as sacrificial templates. The free-standing gyroid carbon network with a highly ordered and interconnected porous structure has been fabricated by impregnating the carbon precursor solution into the gyroid block copolymer nanotemplates and subsequently carbonizing them. A wide range of analytical tools have been employed to characterize fabricated porous carbon material. Prepared nanostructures are envisioned to have a great potential in myriad areas such as energy storage/conversion devices owing to their fascinating morphology exhibiting high surface area and uniform porosity with interconnected three-dimensional networks. The resulting carbon nanoporous structures infused with elemental sulfur have been found to work as a promising electrode for lithium sulfur batteries demonstrating a high cycling stability over more than 200 cycles.