Graphite as an anode for the potassium ion battery (PIBs) has the merits of lowc ost and potentially high energy density,w hile suffering from limited cycle time and inferior stability.H erein we,u sing ac oncentrated electrolyte,d emonstrate that formation of ar obust inorganic-richp assivation layer on the graphite anode could resolve these problems. Consequently,the PIBs with graphite anode could operate for over 2000 cycles (running time of over 17 months) with negligible capacity decay, and had ah igh area capacity over 7.36 mAh cm À2 with ah igh mass loading of 28.56 mg cm À2 . These unprecedented performances of graphite are comparable to that of traditional lithium-ion batteries,and may promote the rapidly development of high performance PIBs.

Potassium‐ion batteries (PIBs) have attracted considerable attention due to the low redox potential, low price, and abundance, in comparison to lithium and sodium. Herein, a novel potassium MoSe2/N‐C battery with a new electrolyte, 1 m potassium bis(fluoro‐slufonyl)imide in ethyl methyl carbonate, is reported. The MoSe2/N‐C composite, which consists of carbon‐coated MoSe2 nanosheets, is synthesized through solvothermal and annealing method. As an anode material for PIBs, it exhibits an outstanding rate performance and long cycling stability. Meanwhile, a reversible capacity of 258.02 mA h g−1 is achieved after 300 cycles at 100 mA g−1, obtaining a Coulombic efficiency close to 100%. Even at a high current density, it can maintain 218 and 197 mA h g−1 at 500 and 1000 mA g−1, respectively. The charge/discharge mechanism of MoSe2/N‐C as the anode material for PIBs is investigated. These results reveal that the insertion and the extraction of K+ will lead to a phase transition of MoSe2. During the charge process, a part of the MoSe2 will transform to Mo15Se19 and the major final discharge product is K5Se3.

Plasmon-coupled circular dichroism has emerged as a promising approach for ultrasensitive detection of biomolecular conformations through coupling between molecular chirality and surface plasmons. Chiral nanoparticle assemblies without chiral molecules present also have large optical activities. We apply single-particle circular differential scattering spectroscopy coupled with electron imaging and simulations to identify both structural chirality of plasmonic aggregates and plasmon-coupled circular dichroism induced by chiral proteins. We establish that both chiral aggregates and just a few proteins in interparticle gaps of achiral assemblies are responsible for the ensemble signal, but single nanoparticles do not contribute. We furthermore find that the protein plays two roles: It transfers chirality to both chiral and achiral plasmonic substrates, and it is also responsible for the chiral three-dimensional assembly of nanorods. Understanding these underlying factors paves the way toward sensing the chirality of single biomolecules.

Porous Au nanoparticles with fine-controlled overall particle sizes have been fabricated using a kinetically controlled seed-mediated growth method. In contrast to spherical Au nanoparticles with smooth surfaces, the porous Au nanoparticles exhibit far greater size-dependent plasmonic tunability and significantly intensified local electric field enhancements exploitable for single-particle plasmon-enhanced spectroscopies. The effects of the nanoscale porosity on the far- and near-field optical properties of the nanoparticles have been investigated both experimentally by optical extinction and single-nanoparticle Raman spectroscopic measurements and theoretically through finite-difference time-domain calculations.

Noble metal nanoparticles have been of tremendous interest due to their intriguing size- and shape-dependent plasmonic and catalytic properties. Combining tunable plasmon resonances with superior catalytic activities on the same metallic nanoparticle, however, has long been challenging because nanoplasmonics and nanocatalysis typically require nanoparticles in two drastically different size regimes. Here, we demonstrate that creation of high-index facets on subwavelength metallic nanoparticles provides a unique approach to the integration of desired plasmonic and catalytic properties on the same nanoparticle. Through site-selective surface etching of metallic nanocuboids whose surfaces are dominated by low-index facets, we have controllably fabricated nanorice and nanodumbbell particles, which exhibit drastically enhanced catalytic activities arising from the catalytically active high-index facets abundant on the particle surfaces. The nanorice and nanodumbbell particles also possess appealing tunable plasmonic properties that allow us to gain quantitative insights into nanoparticle-catalyzed reactions with unprecedented sensitivity and detail through time-resolved plasmon-enhanced spectroscopic measurements.

Germanium is considered as a promising anode material because of its comparable lithium and sodium storage capability, but it usually exhibits poor cycling stability due to the large volume variation during lithium or sodium uptake and release processes. In this paper, germanium@graphene nanofibers are first obtained through electrospinning followed by calcination. Then atomic layer deposition is used to fabricate germanium@graphene@TiO2 core–shell nanofibers (Ge@G@TiO2 NFs) as anode materials for lithium and sodium ion batteries (LIBs and SIBs). Graphene and TiO2 can double protect the germanium nanofibers in charge and discharge processes. The Ge@G@TiO2 NFs composite as an anode material is versatile and exhibits enhanced electrochemical performance for LIBs and SIBs. The capacity of the Ge@G@TiO2 NFs composite can be maintained at 1050 mA h g−1 (100th cycle) and 182 mA h g−1 (250th cycle) for LIBs and SIBs, respectively, at a current density of 100 mA g−1, showing high capacity and good cycling stability (much better than that of Ge nanofibers or Ge@G nanofibers).

We demonstrate that Au nanoparticles with tipped surface structures, such as concave nanocubes, nanotrisoctahedra, and nanostars, possess size-dependent tunable plasmon resonances and intense near-field enhancements exploitable for single-particle surface-enhanced Raman spectroscopy (spSERS) under near-infrared excitation. We report a robust seed-mediated growth method for the selective fabrication of Au concave nanocubes, nanotrisoctahedra, and nanostars with fine-controlled particle sizes and narrow size distributions. Through tight control over particle sizes, the plasmon resonances of the nanoparticles can be fine-tuned over a broad spectral range with respect to the excitation laser, allowing us to systematically quantify the SERS enhancements on individual nanoparticles as a function of particle size for each particle geometry. Understanding of the geometry-dependent plasmonic characteristics and SERS activities of the nanoparticles is further enhanced by finite-difference time-domain (FDTD) calculations. Our results clearly show that strong SERS enhancements can be obtained and further optimized on individual Au nanoparticles with nanoengineered "hot spots" on their tipped surfaces when the plasmon resonances of the nanoparticles are tuned to the optimal spectral regions with respect to the excitation laser wavelength. Using tunable plasmonic nanoparticles with tipped surface structures as substrates for spSERS represents a highly promising and feasible approach to the optimization of SERS-based sensing and imaging applications.

We have discovered that magnetic Fe3O4 nanoparticles exhibit an intrinsic catalytic activity toward the electrochemical reduction of small dye molecules. Metallic nanocages, which act as efficient signal amplifiers, can be attached to the surface of Fe3O4 beads to further enhance the catalytic electrochemical signals. The Fe3O4@nanocage core-satellite hybrid nanoparticles show significantly more robust electrocatalytic activities than the enzymatic peroxidase/H2O2 system. We have further demonstrated that these nonenzymatic nanoelectrocatalysts can be used as signal-amplifying nanoprobes for ultrasensitive electrochemical cytosensing.