Three-Dimensional (3D) Ordered Macroporous Bimetallic (Mn,Fe) Selenide/Carbon Composite with Heterojunction Interface for High-Performance Sodium Ion Batteries

Multitrack Boosted Hard Carbon Anodes: Innovative Paths and Advanced Performances in Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are emerging as a potential alternative to traditional lithium-ion batteries due to the abundant sodium resources. Carbon anodes, with their stable structure, wide availability, low cost, excellent conductivity, and tunable morphology and pore structure, exhibit outstanding performance in SIBs. This review summarizes the research progress of hard carbon anodes in SIBs, emphasizing the innovative paths and advanced performances achieved through multitrack optimization, including dimensional engineering, heteroatom doping, and microstructural tailoring. Each dimension of carbon material-0D, 1D, 2D, and 3D-offers unique advantages: 0D materials ensure uniform dispersion, 1D materials have short Na+ diffusion paths, 2D materials possess large specific surface areas, and 3D materials provide e-/Na+ conductive networks. Heteroatom doping with elements such as N, S, and P can tune electronic distribution, expand interlayer spacing of carbon, and induce Fermi level shifts, thereby enhancing sodium storage capability. In addition, defect engineering improves electrochemical performance by modifying graphitic crystal structure. Furthermore, suitable pore structure design, particularly closed pore structures, can increase capacity, minimizes side reactions, and suppress degradation. In future studies, optimizing morphology design, exploring heteroatom co-doping, and developing environmentally friendly, low-cost carbon anode methods will drive the application of high-performance and long cycle life SIBs.

High-entropy selenides derived from Prussian blue analogues as electrode materials for sodium-ion batteries

Transition metal selenides (TMS) have received much attention as anode materials for sodium-ion batteries (SIBs) because of their high theoretical capacity and excellent redox reversibility. However, their further development is constrained by the dissolution of transition metal ions and substantial volume changes experienced during cycling. Herein, the high-entropy Prussian blue analogues were selenized by the vapor infiltration method, resulting in the formation of a core-shell structured high-entropy selenides (HESe-6). The core-shell structure with voids and abundant selenium vacancies on the surface effectively mitigates bulk expansion and enhances electronic conductivity. Furthermore, the high-entropy property endows an ultra-stable crystal structure and inhibits the dissolution of metal ions. The ex-situ EIS and in-situ XRD results show that HESe-6 is able to be reversibly transformed into highly conductive ultrafine metal particles upon Na+ embedding, providing more Na+ reactive active sites. In addition, despite the incorporation of up to seven different elements, it exhibits minimal phase transitions during discharge/charge cycles, effectively mitigating stress accumulation. HESe-6 could retain an ultralong-term stability of 765.83 mAh g-1 after 1000 loops even at 1 A g-1. Furthermore, when coupled with the Na3V2(PO4)2O2F cathode, it maintains a satisfactory charge energy density of 303 Wh kg-1 after 300 cycles, which shows promising application prospect in the future.

Prussian Blue Analogue-Templated Nanocomposites for Alkali-Ion Batteries: Progress and Perspective

Lithium-ion batteries (LIBs) have dominated the portable electronic and electrochemical energy markets since their commercialisation, whose high cost and lithium scarcity have prompted the development of other alkali-ion batteries (AIBs) including sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). Owing to larger ion sizes of Na+ and K+ compared with Li+, nanocomposites with excellent crystallinity orientation and well-developed porosity show unprecedented potential for advanced lithium/sodium/potassium storage. With enticing open rigid framework structures, Prussian blue analogues (PBAs) remain promising self-sacrificial templates for the preparation of various nanocomposites, whose appeal originates from the well-retained porous structures and exceptional electrochemical activities after thermal decomposition. This review focuses on the recent progress of PBA-derived nanocomposites from their fabrication, lithium/sodium/potassium storage mechanism, and applications in AIBs (LIBs, SIBs, and PIBs). To distinguish various PBA derivatives, the working mechanism and applications of PBA-templated metal oxides, metal chalcogenides, metal phosphides, and other nanocomposites are systematically evaluated, facilitating the establishment of a structure-activity correlation for these materials. Based on the fruitful achievements of PBA-derived nanocomposites, perspectives for their future development are envisioned, aiming to narrow down the gap between laboratory study and industrial reality.

Architectural Decoration of Bioleached NiFeP Surfaces by Co3O4 Flowers for Efficient Electrocatalytic Hydrogen Generation

In the quest for sustainable hydrogen production via water electrolysis, the development of high-performance, noble-metal-free catalytic systems is highly desired. Herein, we proposed an innovative strategy for the development of an electrocatalyst by refining the surface characteristics of a NiFeP alloy through microbiological techniques and subsequent enrichment of active sites by tailoring 3D hierarchical flower-like structures with intact and interconnected two-dimensional (2D) Co3O4. The resultant 3D Co3O4@NiFeP-5/24h has a porous structure comprised of intercrossed nanoparticles covering the entirety of the catalytic surface. This design ensures comprehensive electrolyte ion penetration and facilitates the release of gas bubbles while reducing bubble adhesion rates. Remarkably, the Co3O4@NiFeP-5/24h electrode demonstrates superior hydrogen evolution (HER) performance in an alkaline medium, characterized by its high stability, low overpotential (106 mV at a current density of 10 mA cm-2), and reduced Tafel slope (98 mV dec-1). Besides, the minimized interfacial contact resistance among the phases of electrode and electrolyte emphasizes the high HER performance of the 3D Co3O4@NiFeP-5/24h electrode. The innovative design and fabrication strategy employed herein holds significant potential for advancing the field of water-splitting electrocatalysis, offering a promising path toward the rational design and development of noble-metal-free electrocatalysts.

Enhanced redox kinetics in hierarchical tubular FeSe2 by incorporating Se quantum dots towards high-performance sodium-ion batteries

Metal selenides have emerged as promising Na-storage anode materials owing to their substantial theoretical capacity and high cost-effectiveness. However, the application of metal selenides is hindered by inferior electronic conductivity, huge volume variation, and sluggish kinetics of ionic migration. In response to these challenges, herein, a hierarchical hollow tube consisting of FeSe2 nanosheets and Se quantum dots anchored within a carbon skeleton (HT-FeSe2/Se/C) is strategically engineered and synthesized. The most remarkable feature of HT-FeSe2/Se/C is the introduction of Se quantum dots, which could lead to high electron density near the Fermi level and significantly enhance the overall charge transfer capability of the electrode. Moreover, the distinctive hollow tubular structure enveloped by the carbon skeleton endows the HT-FeSe2/Se/C anode with robust structural stability and fast surface-controlled Na-storage kinetics. Consequently, the as-synthesized HT-FeSe2/Se/C demonstrates a reversible capacity of 253.5 mAh/g at a current density of 5 A/g and a high specific capacity of 343.9 mAh/g at 1 A/g after 100 cycles in sodium-ion batteries (SIBs). Furthermore, a full cell is assembled with HT-FeSe2/Se/C as the anode, and a vanadium-based cathode (Na3V2(PO4)2O2F), showcasing a high specific capacity of 118.1 mAh/g at 2 A/g. The excellent performance of HT-FeSe2/Se/C may hint at future material design strategies and advance the development and application of SIBs.

Towards metal selenides: a promising anode for sodium-ion batteries

Metal selenides have garnered significant attention as promising anode materials for sodium-ion batteries, thanks to their high theoretical capacity, excellent conductivity, and natural abundance. However, their potential is hampered by disappointing capacity retention and unsatisfactory lifespan, primarily attributed to volume expansion and unwanted structural collapse resulting from the insertion and extraction of relatively large Na+ ions during the charge and discharge processes. This feature article provides a brief overview of our endeavors to address the challenges associated with metal selenide-based anode materials, aiming to achieve high-performance electrode materials for sodium-ion batteries. Our strategy encompasses nanostructure design, materials composite engineering, heteroatoms doping, and topography and interface engineering. Additionally, future research directions are also outlined.

Transition Metal Selenide-Based Anodes for Advanced Sodium-Ion Batteries: Electronic Structure Manipulation and Heterojunction Construction Aspect

In recent years, sodium-ion batteries (SIBs) have gained a foothold in specific applications related to lithium-ion batteries, thanks to continuous breakthroughs and innovations in materials by researchers. Commercial graphite anodes suffer from small interlayer spacing (0.334 nm), limited specific capacity (200 mAh g-1), and low discharge voltage (<0.1 V), making them inefficient for high-performance operation in SIBs. Hence, the current research focus is on seeking negative electrode materials that are compatible with the operation of SIBs. Many studies have been reported on the modification of transition metal selenides as anodes in SIBs, mainly targeting the issue of poor cycling life attributed to the volume expansion of the material during sodium-ion extraction and insertion processes. However, the intrinsic electronic structure of transition metal selenides also influences electron transport and sodium-ion diffusion. Therefore, modulating their electronic structure can fundamentally improve the electron affinity of transition metal selenides, thereby enhancing their rate performance in SIBs. This work provides a comprehensive review of recent strategies focusing on the modulation of electronic structures and the construction of heterogeneous structures for transition metal selenides. These strategies effectively enhance their performance metrics as electrodes in SIBs, including fast charging, stability, and first-cycle coulombic efficiency, thereby facilitating the development of high-performance SIBs.

Prussian blue analogue-derived CoP nanocubes supported on MXene toward an efficient bifunctional electrode with enhanced overall water splitting

The exploration of bifunctional catalyst with economic, durable, and efficient performance plays a crucial role to boost both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in overall water splitting. Herein, we report a feasible strategy to design effective heterostructure between CoP and Ti3C2Tx MXene (denoted as CoP/Ti3C2Tx). This approach allows for the growth of CoP nanoparticles with uniform size of 5 nm on the Ti3C2Tx MXene, further enhancing the water electrolysis efficiency. The CoP/Ti3C2Tx bifunctional catalyst demonstrates an exceptional HER activity with a satisfactory overpotential of 103 mV at 10 mA cm-2, and also can drive 10 mA cm-2 for OER with the overpotential of 312 mV in 1.0 M KOH. Moreover, the CoP/Ti3C2Tx-based electrolyzer exhibits high electrochemical stability for 24 h with a low required voltage of 1.66 V at 10 mA cm-2. The density functional theory (DFT) calculations reveal that the introduction of Ti3C2Tx MXene significantly adjusts d-band center towards Fermi level and expand total density of states, resulting in great electrical conductivity, enhanced water adsorption, and activation. This study provides an available mode for effective design and construction of non-noble-metal-based dual-functional catalyst toward practical energy conversion.

Bidirectional enhancement of Li2S redox reaction by NiSe2/CoSe2-rGO heterostructured bi-functional catalysts

The high activity barriers of Li2S nucleation and deposition limit the redox reaction kinetics of lithium polysulfides (LiPSs), meanwhile, the significant shuttle effect of LiPSs hampers the advancement of Li-S batteries (LSBs). In this work, a NiSe2/CoSe2-rGO (NiSe2/CoSe2-G) sulfur host with bifunctional catalytic activity was prepared through a hard template method. Electrochemical experiment results confirm that the combination of NiSe2 and CoSe2 not only facilitates the bidirectional catalytic function during charge and discharge processes, but also increases the active sites toward LiPSs adsorption. Simultaneously, the highly conductive rGO network enhances the electronic conductivity of NiSe2/CoSe2-G/S and provides convenience for loading NiSe2/CoSe2 catalysts. Benefitting from the exceptional catalytic-adsorption capability of NiSe2/CoSe2 and the presence of rGO, the NiSe2/CoSe2-G/S electrode exhibits excellent electrochemical properties. At 1C, it demonstrates a low capacity attenuation of 0.087 % per cycle during 500 cycles. The electrode can maintain a discharge capacity of 927 mAh/g at a sulfur loading of 3.3 mg cm-2. The bidirectional catalytic activity of NiSe2/CoSe2-G offers a prospective approach to expedite the redox reactions of active S, meanwhile, this work also offers an ideal approach for designing efficient S hosts for LSBs.

Evoking C2+ production from electrochemical CO2 reduction by the steric confinement effect of ordered porous Cu2O

Selective conversion of carbon dioxide (CO2) to multi-carbon products (CO2-to-C2+) at high current densities is in essential demand for the practical application of the resultant valuable products, yet it remains challenging to conduct due to the lack of efficient electrocatalysts. Herein, three-dimensional ordered porous cuprous oxide cuboctahedra (3DOP Cu2O-CO) were designed and synthesized by a molecular fence-assisted hard templating approach. Capitalizing on the merits of interconnected and uniformly distributed pore channels, 3DOP Cu2O-CO exhibited outstanding electrochemical CO2-to-C2+ conversion, achieving faradaic efficiency and partial current density for C2+ products of up to 81.7% and -0.89 A cm-2, respectively, with an optimal formation rate of 2.92 mmol h-1 cm-2 under an applied current density of -1.2 A cm-2. In situ spectroscopy and simulation results demonstrated that the ordered pores of 3DOP Cu2O-CO can effectively confine and accumulate sufficient *CO adsorption during electrochemical CO2 reduction, which facilitates efficient dimerization for the formation of C2+ products. Furthermore, the 3DOP structure induces a higher local pH value, which not only enhances the C-C coupling reaction, but also suppresses competing H2 evolution.