Fluffy-Like Cation-Exchanged Prussian Blue Analogues for Sodium-Ion Battery Cathodes

Sodium-Rich Prussian Blue Analogs Synthesized with Reducing Sodium Salt for Enhanced Rate and Cycling Stability Sodium-Ion Storage

Prussian blue analogs (PBAs) as cathode material for sodium-ion batteries have attracted widespread attention due to their affordability, simple synthesis, and high theoretical capacity. Nevertheless, the oxidation of Fe2+ and sodium loss lead to poor electrochemical properties which restrict the practical use of PBAs. Herein, a simple coprecipitation approach based on sodium salt-reduction-assisted synthesis was proposed to construct high-sodium PBAs. The sodium bisulfite (NaHSO3) not only effectively inhibits the oxidation of Fe2+ but also increases the mole ratio of Na+ in the resulting products. The optimized sample exhibits excellent specific capacity (131.1 mAh g-1 at 0.1C), high rate performance (103.9 mAh g-1 at 10C), and good cyclic performance (94.8% capacity retention after 200 cycles). Experimental results reveal that the sample synthesized with sodium bisulfite possesses improved sodium-ion diffusion kinetics and stable crystal structure. In this study, a scalable method is introduced for the synthesis of PBAs with excellent electrochemical properties and further applications.

In Situ Balanced Synthesis of High-Activity Low-Spin Iron Cathode Prussian Blue for Enhanced Sodium-Ion Storage

The growing market for sodium-ion batteries has stimulated interest in research on Prussian blue-type cathode materials. Iron hexacyanoferrate (FeHCF) is considered a desirable Prussian blue-type cathode, but the incomplete electrochemical property of its low-spin iron sites hinders its further practical application. In this paper, carboxymethyl cellulose is demonstrated to have an appropriate binding energy through DFT calculations, synthesize Prussian blue in situ, balance Fe3+ and water in FeHCF, and introduce FeIII vacancies to activate low-spin Fe sites. Thus, at a 1 C rate, it achieves an initial discharge capacity of 154.7 mAh g-1 with an energy density of 470.8 Wh kg-1. The capacity retention is 70.2% after 4000 cycles at a rate of 100 C. This work provides a simpler way to develop more cost-effective, faster, and more durable cathode materials for sodium-ion energy storage.

Optimizing photocatalytic hydrogen evolution performance by rationally constructing S-scheme heterojunction to modulate the D-band center

The research in the field of photocatalysis has progressed, with the development of heterojunctions being recognized as an effective method to improve carrier separation efficiency in light-induced processes. In this particular study, CuCo2S4 particles were attached to a new cubic CdS surface to create an S-scheme heterojunction, thus successfully addressing this issue. Specifically, owing to the higher conduction band and Fermi level of CuCo2S4 compared to CdS, they serve as the foundation and driving force for the formation of an S-scheme heterojunction. Through in-situ X-ray photoelectron spectroscopy and electron paramagnetic resonance analysis, the direction of charge transfer in the composite photocatalyst under light exposure was determined, confirming the charge transfer mechanism of the S-scheme heterojunction. By effectively constructing the S-scheme heterojunction, the d-band center of the composite photocatalyst was adjusted, reducing the energy needed for electron filling in the anti-bonding energy band, promoting the transfer of photogenerated carriers, and ultimately enhancing the photocatalytic hydrogen production. performance. After optimization, the hydrogen evolution activity of the composite photocatalyst CdS-C/CuCo2S4-3 reached 5818.9 μmol g-1h-1, which is 2.6 times higher than that of cubic CdS (2272.3 μmol g-1h-1) and 327.4 times higher than that of CuCo2S4 (17.8 μmol g-1h-1), showcasing exceptional photocatalytic activity. Electron paramagnetic resonance and in situ X-ray photoelectron spectroscopy have established a theoretical basis for designing and constructing S-scheme heterojunctions, offering a viable method for adjusting the D-band center to enhance the performance of photocatalytic hydrogen evolution.

Compositing pine pollen derived carbon matrix with Na4FeV(PO4)3 nanoparticle for cost-effective sodium-ion batteries cathode

Na super-ion conductor type material Na3V2(PO4)3 has been widely researched as the cathode of sodium-ion batteries (SIBs) in recent years, but the unsatisfying cost of Na3V2(PO4)3 impedes its wide application in SIBs. In this study, iron element is used to replace part of vanadium in Na3V2(PO4)3 to reduce its expense, and pine pollen is applied for the first time as a very effective carbon source to improve the performance of Na4FeV(PO4)3. The fabricated composite material achieves a capacity of 105 mA h g-1 under 0.2 C and fascinating cycling stability over 94 % under 2 C for 500 cycles and 98 % under 10 C for 1000 cycles. The excellent cycle performance is caused by the involvement of pine pollen that acts as a carbon matrix to enhance the electron conductivity and block the agglomeration of active material effectively, thus the well-dispersed nano sized Na4FeV(PO4)3 shortens the diffusion path of sodium ion and gains a remarkable rate capability. Moreover, the distinguished reversibility during the charge and discharge procedures is ascribed also to the robust structure of Na4FeV(PO4)3. This work provides an efficient route to realize the economic cathode material of SIBs with good performance.

Research Progress of Prussian Blue and Its Analogs as High-Performance Cathode Nanomaterials for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are investigated as promising alternatives to lithium-ion batteries (LIBs) on account of the economical abundance and reliable availability of sodium, as well as its analogous chemical properties compared to lithium. Nevertheless, the performance of SIBs is severely restricted by the availability of satisfactory cathode nanomaterials with stable frameworks to accommodate the transportation of large-sized Na+ ions. These challenges can be effectively resolved when exploiting Prussian blue (PB) and its analogs (PBAs) as SIB cathodes. This is mainly because PB and PBAs have 3D open frameworks with large interstitial space, which are more favorable for fast insertion/extraction of Na+ ions during the charging/discharging process, thus enabling the improvement of integrated performance in SIB systems. This overview offers a comprehensive summarization of recent advancements in the electrochemical performance of PB and PBAs when employing them as cathodes in SIBs. For better understanding, the fabrication strategy, structural characterization, and electrochemical performance exposition are systematically organized and explained according to tuning PB and metal-based PBAs. Additionally, the current trajectories and prospective future directions pertaining to the utilization of PB and PBA cathodes in the SIB system are thoroughly examined and deliberated upon.

Hollow Layered Iron-Based Prussian Blue Cathode with Reduced Defects for High-Performance Sodium-Ion Batteries

Fe-based Prussian blue (Fe-PB) analogues have emerged as promising cathode materials for sodium-ion batteries, owing to their cost-effectiveness, high theoretical capacity, and environmental friendliness. However, their practical application is hindered by [Fe(CN)6] defects, negatively impacting capacity and cycle stability. This work reports a hollow layered Fe-PB composite material using 1,3,5-benzenetricarboxylic acid (BTA) as a chelating and etching agent by the hydrothermal method. Compared to benzoic acid, our approach significantly reduces defects and enhances the yield of Fe-PB. Notably, the hollow layered structure shortens the diffusion path of sodium ions, enhances the activity of low-spin Fe in the Fe-PB lattice, and mitigates volume changes during Na-ion insertion/extraction into/from Fe-PB. As a sodium-ion battery cathode, this hollow layered Fe-PB exhibits an impressive initial capacity of 95.9 mAh g-1 at a high current density of 1 A g-1. Even after 500 cycles, it still maintains a considerable discharge capacity of 73.1 mAh g-1, showing a significantly lower capacity decay rate (0.048%) compared to the control sample (0.089%). Moreover, the full cell with BTA-PB-1.6 as the cathode and HC as the anode provides a considerable energy density of 312.2 Wh kg-1 at a power density of 291.0 W kg-1. This research not only enhances the Na storage performance of Fe-PB but also increases the yield of products obtained by hydrothermal methods, providing some technical reference for the production of PB materials using the low-yield hydrothermal method.