The development of high-energy and high-power density supercapacitors (SCs) is critical for enabling next-generation energy storage applications. Nanocarbons are excellent SC electrode materials due to their economic viability, high-surface area, and high stability.Although nanocarbons have high theoretical surface area and hence high double layer capacitance, the net amount of energy stored in nanocarbon-SCs is much below theoretical limits due to two inherent bottlenecks: i) their low quantum capacitance and ii) limited ionaccessible surface area. Here, we demonstrate that defects in graphene could be effectively used to mitigate these bottlenecks by drastically increasing the quantum capacitance and opening new channels to facilitate ion diffusion in otherwise closed interlayer spaces. Our results support the emergence of a new energy paradigm in SCs with 250% enhancement in double layer capacitance beyond the theoretical limit.Furthermore, we demonstrate prototype defect engineered bulk SC devices with energy densities 500% higher than state-of-the-art commercial SCs without compromising the power density. IntroductionSupercapacitors (SCs) are novel electrochemical devices that store energy through reversible adsorption of ionic species from an electrolyte on highly porous electrode surfaces. SCs are highly durable (lifetime >10,000 cycles) with power densities (10 kW/kg) that are an order of magnitude larger than batteries. But the low energy density (10 Wh/kg) of SCs 1 relative to batteries precludes their use in practical applications despite their ability to withstand >10,000 cycles. Graphene-based nanocarbons are ideal electrode materials for SCs due to their low cost, high stability, and high specific surface area. Indeed, an outstanding characteristic of single-layer graphene is its high specific surface area ~2675 m 2 /g, which sets an upper limit for electrical double layer capacitance (C dl ) ~21 µF/cm 2 (~550 F/g). 1-4 Notwithstanding this theoretical limit, there are two intrinsic bottlenecks that are impeding the emergence of high energy density SC devices:i) typically only 50-70% of the theoretical surface area is accessible to ionic species from the electrolyte, which limits the overall capacitance (10-15 µF/cm 2 ) and leads to low energy density, and ii) although the total energy that can be harnessed from a SC device depends predominantly on ion-accessible surface area, it is not the only factor. The presence of the so-called small quantum capacitance (C Q ) in series for nanocarbon electrodes, arising from their low electronic density of states at the Fermi level (DOS(E F )), overwhelms the high C dl further reducing the already limited capacitance and low energy density. 5-7While the efforts to increase energy density have been focused either on increasing the active surface area or the addition of pseudo-capacitance through redox active materials, there is a clear lack of methodologies to simultaneously address the inherent challenges described above. Here, we experimentally show that eng...

Over the past two decades several nano-structuring methods have helped improve the figure of merit (ZT) in the state-of-the art bulk thermoelectric materials. While these methods could enhance the thermoelectric performance of p-type Bi2Te3, it was frustrating to researchers that they proved ineffective for n-type Bi2Te3 due to the inevitable deterioration of its thermoelectric properties in the basal plane. Here, we describe a novel chemical-exfoliation spark-plasma-sintering (CE-SPS) nano-structuring process, which transforms the microstructure of n-type Bi2Te3 in an extraordinary manner without compromising its basal plane properties. The CE-SPS processing leads to preferential scattering of electrons at charged grain boundaries, and thereby increases the electrical conductivity despite the presence of numerous grain boundaries, and mitigates the bipolar effect via band occupancy optimization leading to an upshift (by ~ 100 K) and stabilization of the ZT peak over a broad temperature range of ~ 150 K.

It is shown that charged defect generation, through argon ion-based plasma processing, in few layer graphene, could substantially enhance the electrical capacitance for electrochemical energy storage. Detailed consideration of the constituent space charge and quantum capacitances were used to delineate a new length scale, correlated to electrically active defects contributing to the capacitance, and was found to be smaller than a structural correlation length determined through Raman spectroscopy. The study offers insights into an industrially viable method (i.e., plasma processing) for modifying and enhancing the energy density of graphene-based electrochemical capacitors.

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Although carbon nanomaterials are being increasingly used in energy storage, there has been a lack of inexpensive, continuous, and scalable synthesis methods. Here, we present a scalable roll-to-roll (R2R) spray coating process for synthesizing randomly oriented multi-walled carbon nanotubes electrodes on Al foils. The coin and jellyroll type supercapacitors comprised such electrodes yield high power densities (∼700 mW/cm3) and energy densities (1 mW h/cm3) on par with Li-ion thin film batteries. These devices exhibit excellent cycle stability with no loss in performance over more than a thousand cycles. Our cost analysis shows that the R2R spray coating process can produce supercapacitors with 10 times the energy density of conventional activated carbon devices at ∼17% lower cost.

In any physiological media, carbon nanomaterials (CNM) strongly interact with biomolecules leading to the formation of biocorona, which subsequently dictate the physiological response and the fate of CNMs. Defects in CNMs play an important role not only in material properties but also in the determination of how materials interact at the nano-bio interface. In this article, we probed the influence of defect-induced hydrophilicity on the biocorona formation using micro-Raman, photoluminescence, infrared spectroscopy, electrochemistry, and molecular dynamics simulations. Our results show that the interaction of proteins (albumin and fibrinogen) with CNMs is strongly influenced by charge-transfer between them, inducing protein unfolding which enhances conformational entropy and higher protein adsorption.

Our detailed Raman, non-linear optical, and photoemission spectroscopic studies evince that the N-dopant configuration in graphene (blue-pyridinic, orange-graphitic, and red-pyrrolic) can be effectively tuned to mitigate electron-defect scattering.

The promise of multiwalled carbon nanotubes (MWNTs) for supercapacitor electrodes remains unfulfilled due to their poor energy density, which is limited by their redox inactivity. Here, we show a simple, alternative path to achieve Faradaic charge storage by harnessing intrinsic heterogeneity (e.g., Fe catalyst) of as-synthesized MWNTs, obviating the challenges of combining disparate materials in hybrid composite electrodes. In acidic solutions, MWNTs are ruptured by voltammetric cycling beyond the electrolysis limit, thereby exposing residual catalyst nanoparticles. The addition of Faradaic charge storage associated with the Fe2+/Fe3+ transition, results in a 4-fold increase in peak capacitance of MWNT electrodes (290 F/g) compared to purified MWNT electrodes (70 F/g), along with a 60% increase in charge capacity.