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...

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We report on a novel graphene/P(VDF-TrFE) heterostructure based highly sensitive, flexible, and biocompatible pressure/strain sensor developed through a facile and low-cost fabrication technique. The high piezoelectric coefficient of P(VDF-TrFE) coupled with outstanding electrical properties of graphene makes the sensor device highly sensitive, with an average sensitivity of 0.76 kPa −1 , a gauge factor of 445, and signal-to-noise ratio of 60.8 dB in the range of pressure up to 45 mmHg. A model was proposed to explain the sensor operation, based on carrier density and mobility changes induced by the piezoelectric charge generated in response to strain, which was supported by Hall measurements and Raman spectroscopy. Potential applications in wearable sensing for human activity monitoring were also demonstrated.

Composite nanoclusters with chemical, magnetic, and biofunctionality offer broad opportunities for targeted cellular imaging. A key challenge is to load a high degree of targeting, imaging, and therapeutic functionality onto stable metal-oxide nanoparticles. Here we report a route for producing magnetic nanoclusters (MNCs) with alkyne surface functionality that can be utilized as multimodal imaging probes. We form MNCs composed of magnetic Fe(3)O(4) nanoparticles and poly(acrylic acid-co-propargyl acrylate) by the co-precipitation of iron salts in the presence of copolymer stabilizers. The MNCs were surface-modified with near-infrared (NIR) emitting fluorophore used in photodynamic therapy, an azide-modified indocyanine green. The fluorophores engaged and complexed with bovine serum albumin, forming an extended coverage of serum proteins on the MNCs. These proteins isolated indocyanine green fluorophores from the aqueous environment and induced an effective "turn-on" of NIR emission.

Extending lithium–sulfur battery (LSB) electrode architecture into three dimensions (3D) has been proposed for more than a decade. A 3D lightweight and porous current collector that is capable of holding high amounts of sulfur (S) without any significant decrease in performance has been elusive. Although many material solutions (such as sulfurized polyacrylonitrile or SPAN) have been identified for alleviating polysulfide formation and the so-called shuttle effect, their incorporation into 3D current collectors with high capacity at the electrode level has not yet been realized. Here, we show that graphene foams (GFs) are ideally suited as 3D lightweight current collectors for LSBs and outperform the conventional carbon-coated Al (Al/C) foils at the electrode level. Specifically, we demonstrate that the open framework of GFs facilitates high mass loading of SPAN without any deterioration in capacity at the active material level even at high S loading. At the electrode level, GF-SPAN cathodes exhibited capacities of ∼200 mAh gelectrode –1 at 0.1C even with low S loadings (∼1.1 mg cm–2), which is at least 3 times higher than conventional Al/C electrodes. More importantly, we fabricated cells with a high mass loading of 26.5 mg cm–2 S by stacking multiple GFs to achieve an areal capacity as high as ∼20 mAh cm–2 (at a current density of 3.0 mA cm–2 up to 50 cycles), which is at least 3 times higher than LSB areal capacity (6 mAh cm–2) needed to displace LIBs.

Transport property variation in O2 plasma treated graphene and related enhancement in NH3 sensing.

Conductivity, carrier concentration and carrier mobility in graphene were investigated as a function of time in response to ionized donor and acceptor adsorbates. While a reduction in conductivity and hole density in graphene was observed upon exposure to a weak electron donor NH3, the carrier mobility was found to increase monotonically. The opposite behavior is observed upon exposure to NO2, which is expected based on its typical electron withdrawing property. Upon exposure to C9H22N2, a strong donor, it resulted in the transformation of graphene from p-type to n-type, although the inverse variation of carrier concentration and mobility was still observed. The variational trends remained unaltered even after intentional introduction of defects in graphene through exposure to oxygen plasma. The responses to C9H22N2, NH3 and NO2 exposures underline a strong influence by ionized surface adsorbates, that we explained via a simple model considering charged impurity scattering of carriers in graphene.