Understanding the phase transition and Li-ion diffusion kinetics of Li-ion storage nanomaterials holds promising keys to further improve the cycle life and charge rate of the Li-ion battery. Traditional electrochemical studies were often based on a bulk electrode consisting of billions of electroactive nanoparticles, which washed out the intrinsic heterogeneity among individuals. Here, we employ optical microscopy, termed surface plasmon resonance microscopy (SPRM), to image electrochemical current of single LiCoO nanoparticles down to 50 fA during electrochemical cycling, from which the phase transition and Li-ion diffusion kinetics can be quantitatively resolved in a single nanoparticle, in operando and high throughput manner. SPRM maps the refractive index (RI) of single LiCoO nanoparticles, which significantly decreases with the gradual extraction of Li-ions, enabling the optical read-out of single nanoparticle electrochemistry. Further scanning electron microscopy characterization of the same batch of nanoparticles led to a bottom-up strategy for studying the structure-activity relationship. As RI is an intrinsic property of any material, the present approach is anticipated to be applicable for versatile kinds of anode and cathode materials, and to facilitate the rational design and optimization toward durable and fast-charging electrode materials.

Excitons in two-dimensional (2D) materials are tightly bound and exhibit rich physics. So far, the optical excitations in 2D semiconductors are dominated by Wannier-Mott excitons, but molecular systems can host Frenkel excitons (FE) with unique properties. Here, we report a strong optical response in a class of monolayer molecular J-aggregates. The exciton exhibits giant oscillator strength and absorption (over 30% for monolayer) at resonance, as well as photoluminescence quantum yield in the range of 60–100%. We observe evidence of superradiance (including increased oscillator strength, bathochromic shift, reduced linewidth and lifetime) at room-temperature and more progressively towards low temperature. These unique properties only exist in monolayer owing to the large unscreened dipole interactions and suppression of charge-transfer processes. Finally, we demonstrate light-emitting devices with the monolayer J-aggregate. The intrinsic device speed could be beyond 30 GHz, which is promising for next-generation ultrafast on-chip optical communications.

Urea electrolysis is ap rospective technology for simultaneous H 2 production and nitrogen suppression in the process of water being used for energy production. Its sustainability is currently founded on innocuous N 2 products; however,w ed iscovered that prevalent nickel-based catalysts could generally over-oxidizeu rea into NO 2 À products with % 80 %F aradaic efficiencies,p osing potential secondary hazards to the environment. Trace amounts of over-oxidized NO 3À and N 2 Owere also detected. Using 15 Nisotopes and urea analogues,w ed erived an itrogen-fate network involving aN O 2 À -formation pathwayv ia OH À -assisted C À Nc leavage and two N 2 -formation pathwaysv ia intra-and intermolecular coupling.D FT calculations confirmed that C À Nc leavage is energetically more favorable.I nspired by the mechanism, ap olyaniline-coating strategy was developed to locally enrich urea for increasing N 2 production by af actor of two.T hese findings provide complementary insights into the nitrogen fate in water-energy nexus systems.

2D transition metal dichalcogenide (TMD)-based phototransistors generally work under photoconductive, photovoltaic, or photogating mode, in which photocarriers are generated from band-to-band excitation. Nevertheless, due to the relatively large bandgap, most TMD phototransistors working under these modes are restricted in visible spectrum. Here, photodetection in 2D multilayer rhenium disulfide (ReS 2 ) transistor via bolometric mode, which relies on light heating induced conductance change instead of bandto-band photoexcitation is reported, making it possible for sub-bandgap photon detection. The bolometric effect induced photoresponse is first revealed by an anomalous sign switching of photocurrent from positive to negative while increasing gate voltage under visible light, which is further validated by the temperature dependent electrical transport measurements. The phototransistor exhibits remarkable photoresponse under infrared regime, beyond the optical bandgap absorption edge of the ReS 2 flake. Additionally, it demonstrates a low noise equivalent power, less than 5 × 10 −2 pW Hz −1/2 , which is very promising for ultra-weak light detection. Moreover, the response time is below 3 ms, nearly 3-4 orders of magnitude faster than previously reported ReS 2 photodetectors. The findings promise bolometric effect as an effective photodetection mode to extend the response spectrum of large bandgap TMDs for novel and high-performance broadband photodetectors.