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 singlestep 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 m 2 /g). The synergism in structural and chemical frameworks, along with openended 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.
Metal borides when subjected to dissolution and recrystallization exhibit a tendency to grow preferentially in lateral dimensions and form nanosheets. Such derived nanosheets exhibit unusual properties that can potentially be used in energy conversion and storage applications. Here we report boride-based nanosheets derived from titanium diboride through a scalable one-pot chemical approach as a sodium-ion battery anode material. The half-cell with TiB 2 -derived nanosheets (TiB 2 -NS) as anode delivers an initial discharge capacity of 252 mAh g À 1 at 0.1 A g À 1 , and appreciable cycling stability is achieved at 1 A g À 1 current density. Further, a sodium-ion full cell assembled with TiB 2 -NS as anode and sodium vanadium phosphate/carbon as cathode is demonstrated. The full cell delivers an energy density of 111 Wh kg À 1 at a power density of 500 W kg À 1 . Being the first report of its kind, our study exemplifies the rich potential that the TiB 2 -NS deliver as an anode material upon nanoscaling and substantiates the theoretical prediction on using transition metal boride-based anode material for sodium-ion battery.
The development of earth-abundant
and highly efficient electrocatalysts
for hydrogen evolution reaction (HER) in alkaline media is essential
for practical alkaline water electrolysis. The possibility of tuning
the electrocatalytic activity of alkaline HER electrocatalysts through
various approaches, such as interfacial engineering or doping, has
been recently explored. In this work, electrochemically exfoliated
Co(OH)2 and chemically derived 1T-MoS2 nanostructures
are electrostatically coupled to form a synergistic nanostructured
two-dimensional heterostructure, which is shown to remarkably improve
the HER activity in an alkaline medium. The Co(OH)2/1T-MoS2 heterostructure with an optimal 1:5 ratio (Co1Mo5) showed
a low overpotential of 151 mV at a current density of 10 mA cm–2 and a Tafel slope of 94 mV dec–1 in alkaline media. The shift in the overpotential achieved for the
heterostructure (>250 mV) compared to the individual MoS2 component is remarkably high, as per the earlier reports.
Hybrid ion capacitors (HICs) are emerging as promising energy-storage devices exhibiting the advantages of both batteries and supercapacitors. However, the difference in the electrodes' specific capacities and rate capabilities makes it extremely challenging to achieve optimum mass balancing for a full-cell HIC device. Here, we demonstrate a method to predict well-performing mass ratios of electrodes for a Na-HIC by analyzing the capacities of anodes and cathodes as a function of the actual current densities experienced by the individual electrodes. We employ a simple design tool, a "Ragone Plot Simulator", to predict specific energy and specific power on Ragone plots and study the performance trend of devices with varying electrode mass ratios. The validation of the proposed method is done based on the experimental data obtained from several hybrid ion capacitor devices reported in the literature, which closely matches with the simulated Ragone plots. Further, we exemplify the validity of our calculations by comparing the simulated Ragone plot with that of a Na-HIC fabricated using in-house-made carbon. This unique approach presents a simple, generalized, yet never reported, method, which could be employed as a design tool to guide the selection of optimized HIC devices for the intended applications.
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