Direct Electrodeposition of Electrically Conducting Ni3(HITP)2 MOF Nanostructures for Micro-Supercapacitor Integration.

Micro-supercapacitors emerge as an important electrical energy storage technology expected to play a critical role in the large-scale deployment of autonomous microdevices for health, sensing, monitoring, and other IoT applications. Electrochemical double-layer capacitive storage requires a combination of high surface area and high electronic conductivity, with these being attained only in porous or nanostructured carbons, and recently found also in conducting metal-organic frameworks (MOFs). However, techniques for conformal deposition at micro- and nanoscale of these materials are complex, costly, and hard to upscale. Herein, the study reports direct, one step non-sacrificial anodic electrochemical deposition of Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 - Ni3(HITP)2, a porous and electrically conducting MOF. Employing this strategy enables the growth of Ni3(HITP)2 films on a variety of 2D substrates as well as on 3D nanostructured substrates to form Ni3(HITP)2 nanotubes and Pt@ Ni3(HITP)2 core-shell nanowires. Based on the optimal electrodeposition protocols, Ni3(HITP)2 films interdigitated micro-supercapacitors are fabricated and tested as a proof of concept.

New Diglyme-based Gel Polymer Electrolytes for Na-based Energy Storage Devices.

This work presents for the first time a new diglyme-based gel polymer (DOBn-GPE) suitable for Na-based energy storage devices. The DOBn-GPE, which contains a methacrylate-based polymer, exhibited an excellent high ionic conductivity (2.3 mS cm-1 at 20 °C), broad electrochemical stability (>5.0 V), and high mechanical stability. DOBn-GPE could be successfully used for the realization of Na-ion capacitors, sodium-metal batteries, and sodium-ion batteries, displaying performance comparable with those of systems containing liquid electrolytes at room temperature and at 60 °C. The results of these investigation indicated that the development of diglyme-based gel polymer electrolytes represents a promising strategy for the realization of advanced Na-based energy storage devices.

Hierarchically Engineered Nanocarbon Florets as Bifunctional Electrode Materials for Adsorptive and Intercalative Energy Storage.

Three-dimensional dendritic nanostructured carbon florets (NCFs) with tailored porosity are demonstrated as electrochemically versatile electrodes for both adsorptive and intercalative energy storage pathways. Achieved through a single-step template-driven approach, the NCFs exhibit turbostratic graphitic lamellae in a floral assembly leading to high specific surface area and multi-modal pore distribution (920 m2/g). The synergism in structural and chemical frameworks, along with open-ended morphology, enables bifunctionality of hard carbon NCFs as symmetric adsorptive electrodes for supercapacitors (SCs) and intercalation anodes for hybrid potassium-ion capacitors (KICs). Flexible, all-solid-state SCs through facile integration of NCF with the ionic-liquid-imbibed porous polymeric matrix achieve high-energy density (20 W h/kg) and power density (32.7 kW/kg) without compromising on mechanical flexibility and cyclability (94% after 20k cycles). Furthermore, NCF as an anode in a full-cell hybrid KIC (activated carbon as cathode) delivers excellent electrochemical performance with maximum energy and power densities of 57 W h/kg and 12.5 kW/kg, respectively, when cycled in a potential window of 1.0-4.0 V. The exceptional bifunctional performance of NCF highlights the possibility of utilizing such engineered nanocarbons for high-performance energy storage devices.

Lithium-Ion-Based Electrochemical Energy Storage in a Layered Vanadium Formate Coordination Polymer.

A vanadium formate (VF) coordination polymer and its composite with partially reduced graphene oxide (prGO), namely VF-prGO, can be applied as anode materials for Li-ion based electrochemical energy storage (EcES) systems in the potential range of 0-3 V (vs Li+ /Li). This study shows that a reversible capacity of 329 mAh g-1 at a current density of 50 mA g-1 after 50 cycles can be realized for VF along with a high rate capability. The composite exhibits even a higher capacity of 504 mAh g-1 at 50 mA g-1 . A good capacity retention is observed even after 140 cycles for both VF and the composite. An ex-situ X-ray photoelectron spectroscopy study indicates the involvement of V3+ /V4+ redox couple in the charge storage mechanism. A significant contribution of this reversible capacity is attributed to the pseudocapacitive behavior of the system.

Nanostructured Na2Ti9O19 for Hybrid Sodium-Ion Capacitors with Excellent Rate Capability.

Herein, we report a new Na-insertion electrode material, Na2Ti9O19, as a potential candidate for Na-ion hybrid capacitors. We study the structural properties of nanostructured Na2Ti9O19, synthesized by a hydrothermal technique, upon electrochemical cycling vs Na. Average and local structures of Na2Ti9O19 are elucidated from neutron Rietveld refinement and pair distribution function (PDF), respectively, to investigate the initial discharge and charge events. Rietveld refinement reveals electrochemical cycling of Na2Ti9O19 is driven by single-phase solid solution reaction during (de)sodiation without any major structural deterioration, keeping the average structure intact. Unit cell volume and lattice evolution on discharge process is inherently related to TiO6 distortion and Na ion perturbations, while the PDF reveals the deviation in the local structure after sodiation. Raman spectroscopy and X-ray photoelectron spectroscopy studies further corroborate the average and local structural behavior derived from neutron diffraction measurements. Also, Na2Ti9O19 shows excellent Na-ion kinetics with a capacitve nature of 86% at 1.0 mV s-1, indicating that the material is a good anode candidate for a sodium-ion hybrid capacitor. A full cell hybrid Na-ion capacitor is fabricated by using Na2Ti9O19 as anode and activated porous carbon as cathode, which exhibits excellent electrochemical properties, with a maximum energy density of 54 Wh kg-1 and a maximum power density of 5 kW kg-1. Both structural insights and electrochemical investigation suggest that Na2Ti9O19 is a promising negative electrode for sodium-ion batteries and hybrid capacitors.

Exfoliation of Reduced Graphene Oxide with Self-Assembled π-Gelators for Improved Electrochemical Performance.

Among several methodologies to improve the solution processing of graphene-based materials, noncovalent functionalization has been considered as the simplest and nondestructive method. Herein, we show that molecular self-assembly process can be used as a useful tool to exfoliate reduced graphene oxide (RGO), resulting in hybrid materials with improved physical properties. Upon interacting with a π-gelator, the dispersing ability of the RGO increased significantly in most of nonpolar and polar aprotic solvents when compared to the bare one. The amount of RGO dispersed was 1.7-1.8 mg mL-1 in solvents such as toluene, o-dichlorobenzene (ODCB) and tetrahydrofuran (THF). Morphological studies revealed that aggregation of π-gelator over RGO helps to exfoliate graphene layers to remain as individual sheets with higher surface area. Experimental studies revealed enhanced surface area (250 m2 g-1) and better conductivity (3.7 S m-1) of the hybrid materials with 30% of RGO content resulting in excellent electrochemical performance (specific capacitance of 181 F g-1) as electrodes for supercapacitors.