Capacitive-Controlled Prussian White with a Nickel Iron Hexacyanoferrate Composite Cathode for Rapid Sodium Diffusion

Prussian blue analogues receive tremendous attention owing to their spacious three-dimensional skeleton, high theoretical specific capacity, facile synthesis procedure, and high cost-effectiveness as among the most promising candidates for cathode materials in sodium-ion batteries (SIBs). Nonetheless, the practical specific capacity, especially under high current, is particularly frail due to the sluggish ion diffusion. In this study, the strategy of Ni substitution and formation of water-coordinated Fe is applied to lower the crystal field energy and elevate the active low-spin (LS) Fe content, which leads to a capacitive sodium storage mechanism, resulting in a substantial specific capacity under high current density. The delivered specific capacity of PW-325@2NiFe-55 is 95 mAh g–1 at 50 C, which is 72.5% capacity retention of the one at 0.5 C. Also, it maintains 80.2% of its initial specific capacity after 500 cycles at 5 C. Furthermore, a hypothesis of a joint diffusion-controlled and capacitive mechanism for high-spin (HS) Fe and a mere capacitive mechanism for LS Fe is put forward and verified through potentiastatic tests, operando 57Fe Mössbauer spectroscopy, and ex situ XRD, which provides a new horizon to enhance the electrochemical performance for SIBs

Towards mid-infrared computational temporal ghost imaging

Ghost imaging in the time domain opens new possibilities to reconstruct an unknown temporal object by correlating the multiple probing temporal intensity patterns with the integrated signal measured after transmission through the temporal object. By using the pre-programmed temporal patterns as the probe, computational temporal ghost imaging (TGI) can reconstruct the fast temporal object with only one slow photodetector and significantly reduce the number of measurement realizations. However, direct implementation of computational TGI requires the use of suitable instrumentation such as, e.g., ultrafast modulators to pre-program temporal patterns at the source wavelength, which are not necessarily available in all wavelength regions, such as mid-infrared region. Here, we experimentally demonstrated MIR computational TGI for the first time, to the best of our knowledge, based on the frequency down-conversion scheme. Instead of directly pre-programming temporal patterns at MIR light, in the frequency down-conversion temporal ghost imaging, the pre-programmed temporal patterns are modulated at 1.5 um light and then the pre-programmed 1.5 um light is interacted with another 1 um continuous-wave light to realize difference-frequency generation (DFG) process in periodically poled lithium niobate crystal. In this way, the pre-programmed temporal patterns can be transferred from 1.5 um light to the generated DFG light source at 3.4 um, and computational TGI could be performed to image a fast temporal object in MIR with a MIR slow detector. With the use of near-infrared optical modulator and wavelength-versatile near-infrared fiber lasers, the concept of frequency down-conversion based ghost imaging unlocks new possibilities to realized computational imaging in the spectral region where preprogrammed modulation is difficult to applied, such as the mid-infrared and THz regions

Characterization and regulation of statistical properties in Er-doped random fiber laser

Er-doped random fiber laser (ERFL) is a complex physical system, and understanding its intrinsic physical mechanisms is crucial for promoting applications. In this paper, we experimentally investigate the time-domain statistical properties of ERFL under full-bandwidth condition for the first time. We also analyze the effects of the transmission process and amplification process on the output characteristics of ERFL, on the basis of which we realize its regulation. This study guides RFL systems requiring transmission and amplification, offering fresh insights for regulating the time-domain stability