Nanostructure Transformation as a Signature of Oxygen Redox in Li-Rich 3d and 4d Cathodes.

Lithium-rich nickel manganese cobalt oxide (LRNMC) is being explored as an alternative to stoichiometric nickel manganese cobalt oxide (NMC) cathode materials due to its higher, initially accessible, energy-storage capacity. This higher capacity has been associated with reversible O oxidation; however, the mechanism through which the change in O chemistry is accommodated by the surrounding cathode structure remains incomplete, making it challenging to design strategies to mitigate poor electrode performance resulting from extended cycling. Focusing on LRNMC cathodes, we identify nanoscale domains of lower electron density within the cathode as a structural consequence of O oxidation using small-angle X-ray scattering (SAXS) and operando X-ray diffraction (XRD). A feature observed in the small angle scattering region suggests the formation of nanopores, which first appears during O oxidation, and is partially reversible. This feature is not present in traditional cathode materials, including stoichiometric NMC and lithium nickel cobalt aluminum oxide (NCA) but appears to be common to other Li-rich systems tested here, Li2RuO3 and Li1.3Nb0.3Mn0.4O2.

How Bulk Sensitive is Hard X-ray Photoelectron Spectroscopy: Accounting for the Cathode-Electrolyte Interface when Addressing Oxygen Redox.

Sensitivity to the "bulk" oxygen core orbital makes hard X-ray photoelectron spectroscopy (HAXPES) an appealing technique for studying oxygen redox candidates. Various studies have reported an additional O 1s peak (530-531 eV) at high voltages, which has been considered a direct signature of the bulk oxygen redox process. Here, we find the emergence of a 530.4 eV O 1s HAXPES peak for three model cathodes-Li2MnO3, Li-rich NMC, and NMC 442-that shows no clear link to oxygen redox. Instead, the 530.4 eV peak for these three systems is attributed to transition metal reduction and electrolyte decomposition in the near-surface region. Claims of oxygen redox relying on photoelectron spectroscopy must explicitly account for the surface sensitivity of this technique and the extent of the cathode degradation layer.

Optoelectronic response of hybrid PbS-QD/graphene photodetectors.

Lead sulfide quantum dots (QDs) have been widely used for various optoelectronic devices due to their high absorption coefficient and tunable bandgap. However, the low mobility of QD films results in poor charge collection and device performance. By combining QDs with graphene into hybrid graphene/QD photodetectors, photocarriers from QDs are transferred to graphene, improving charge collection and transport, drastically increasing the photoresponsivity. Herein, we carry a systematic analysis on how critical tuning parameters such as QD size and QD film thickness affect responsivity, spectral response, and time response. We report the absorption coefficient, refractive index (n, k), penetration depth, and energy bandgap of PbS QDs of different sizes. We study systematically how the photocurrent, photoresponsivity, time response, and power density dependence vary with QD size in hybrid Gr/QD. The bandgap of lead sulfide quantum dots was size-tuned between 0.86 and 1.39 eV. The time response shows that subsecond modulation can be achieved for different QD sizes with a responsivity up to 107 A/W at power densities of 10-5 mW/cm2. We also studied how the performance of the photodetectors is affected by the thickness, discussing the limitations on the thickness by the compromise between light absorption and charge collection. We describe how the optical response shifts toward the infrared as QD films get thicker. Time responses below 1 s are obtained for graphene/QD devices with thickness from 150 nm to 1 µm. This systematic study provides important guidelines to design hybrid graphene/QD photodetectors and tune their spectral response and performance.

Liquefied gas electrolytes for electrochemical energy storage devices.

Electrochemical capacitors and lithium-ion batteries have seen little change in their electrolyte chemistry since their commercialization, which has limited improvements in device performance. Combining superior physical and chemical properties and a high dielectric-fluidity factor, the use of electrolytes based on solvent systems that exclusively use components that are typically gaseous under standard conditions show a wide potential window of stability and excellent performance over an extended temperature range. Electrochemical capacitors using difluoromethane show outstanding performance from -78° to +65°C, with an increased operation voltage. The use of fluoromethane shows a high coulombic efficiency of ~97% for cycling lithium metal anodes, together with good cyclability of a 4-volt lithium cobalt oxide cathode and operation as low as -60°C, with excellent capacity retention.

Orexin administration to mice that underwent chronic stress produces bimodal effects on emotion-related behaviors.

Orexin plays diverse roles in regulating behaviors, such as sleep and wake, reward processing, arousal, and stress and anxiety. The orexin system may accomplish these multiple tasks through its complex innervations throughout the brain. The emerging evidence indicates a role of orexin in emotional behaviors; however, most of the previous studies have investigated the function of orexin in naïve animals. Here, we examined a functional role of orexin in mice that had been exposed to repeated stress. Chronic social defeat stress produced differential social interaction behaviors in mice (susceptible versus resilient) and these two groups of mice displayed different levels of prepro-orexin in the hypothalamus. Exogenously added orexin A to the brain induced an antidepressant-like effect in only the susceptible mice but not in the resilient mice. In contrast, orexin A and orexin B infused together produced an anxiogenic effect in only the resilient mice and not in the susceptible mice. Furthermore, we found that the antidepressant-like effect of orexin A is mediated by the bed nucleus of the stria terminalis (BNST) after exposure to chronic restraint stress. These findings reveal a bimodal effect of the orexin system in regulating emotional behavior that depends on stress susceptibility.

Novel co-matrix systems for the MALDI-MS analysis of polystyrene using a UV absorber and stabilizer.

Co-matrix systems composed of a UV absorber and a UV stabilizer applied to the analysis of polystyrene (PS) using a matrix-assisted laser desorption/ionization-mass spectrometer (MALDI-MS) equipped with a N(2) laser (337 nm) as the light source were investigated. Various UV absorbers such as Tinuvin 234, Tinuvin 326, Tinuvin 327, Tinuvin 328, Tinuvin 329, and Tinuvin 1577 and a UV stabilizer of Tinuvin 770 were used. Analytical results using the co-matrix systems were compared with those using anthracene-1,8,9-triol (DIT) as the most common matrix for PS analysis. The MALDI mass spectrum of PS obtained using single DIT showed higher ionization efficiency than that using a mixture of DIT and Tinuvin 770 as the matrix. In contrast to this, for the UV absorbers, the ionization efficiencies were notably enhanced by using the co-matrix systems of the UV absorber and Tinuvin 770. The analytical results were explained with the enhanced compatibility with PS by the formation of a complex between the UV absorber and Tinuvin 770 and with the capability of transferring silver cations. Prices of Tinuvin 770 and the UV absorbers are much cheaper than those of the common matrices. The co-matrix systems are recommendable for the MALDI-MS analysis of PS, especially the co-matrix system composed of Tinuvin 234 and Tinuvin 770.