Na3V2(PO4)2O2F (NVPOF) has received considerable interest as a promising cathode material for sodium-ion batteries because of its high working voltage and good structural/thermal stability. However, the sluggish electrode reaction resulting from its low intrinsic electronic conductivity significantly restricts its electrochemical performance and thus its practical application. Herein, Nb-doped Na3V2−xNbx(PO4)2O2F/graphene (rGO) composites (x = 0, 0.05, 0.1) were prepared using a solvothermal method followed by calcination. Compared to the un-doped NVPOF/rGO, doping V-site with high-valence Nb element (Nb5+) (Na3V1.95Nb0.05(PO4)2O2F/rGO (NVN05POF/rGO)) can result in the generated V4+/V3+ mixed-valence, ensuring the lower bandgap and thus the increased intrinsic electronic conductivity. Besides, the expanded lattice space favors the Na+ migration. With the structure feature where NVN05POF particles are attached to the rGO sheets, the electrode reaction kinetics is further accelerated owing to the well-constructed electron conductive network. As a consequence, the as-prepared NVN05POF/rGO sample exhibits a high specific capacity of ~72 mAh·g−1 at 10C (capacity retention of 65.2% (vs. 0.5C)) and excellent long-term cycling stability with the capacity fading rate of ~0.099% per cycle in 500 cycles at 5C.
To meet the low-cost concept advocated by the sodium metal anode, this paper reports the use of a pulsed electrodeposition technology with ionic liquids as electrolytes to achieve uniform nanoplating of metallic magnesium films at around 20 nm on spaced titanium dioxide (TiO2) nanotubes (STNA-Mg). First, the sodiophilic magnesium metal coating can effectively reduce the nucleation overpotential of sodium metal. Moreover, three-dimensional STNA can limit the volume expansion during sodium metal plating and stripping to achieve the ultrastable deposition and stripping of sodium metals with a high Coulombic efficiency of up to 99.5% and a small voltage polarization of 5 mV in symmetric Na||Na batteries. In addition, the comparative study of sodium metal deposition behavior of STNA-Mg and STNA-Cu prepared by the same route further confirmed the advantage of magnesium metal to guide sodium metal growth. Finally, the prepared STNA-Mg–Na metal anode and commercial sodium vanadium phosphate cathode were assembled into a full cell, delivering a discharge capacity of 110.2 mAh·g−1 with a retention rate of 95.6% after 110 cycles at 1C rate.
The separator is a key component of sodium-ion battery, which greatly affects the electrochemical performances and safety characteristics of the battery. Conventional glass fiber separator cannot meet the requirements of large-scale application because of high cost and poor mechanical properties. Herein, the novel composite separators are prepared by a simple slurry sieving process using glass fiber separator scraps and ordinary qualitative filter paper as raw materials. As the composite mass ratio is 1:1, the composite separator has excellent comprehensive properties, including tensile strength of 15.8 MPa, porosity of 74.3%, ionic conductivity of 1.57 × 10−3 S·cm−1 and thermal stability at 210°C. The assembled sodium-ion battery shows superior cycling performance (capacity retention of 94.1% after 500 cycles at 1C) and rate capacity (retention rate of 87.3% at 10C), and it maintains fine interface stability. The above results provide some new ideas for the separator design of high-performance and low-cost sodium-ion batteries.
The effect of Na-excess content in the precursor on the structural and electrochemical performances of sodium nickel manganese oxide (NNMO) prepared by sol–gel and electrospinning methods is investigated in this paper. X-ray diffraction results of the prepared NNMO without adding Na-excess content indicate sodium loss, while the mixed phase of P2/O′3-type layered NNMO presented after adding Na-excess content. Compared with the sol–gel method, the secondary phase of NiO is more suppressed by using the electrospinning method, which is further confirmed by field emission scanning electron microscope images. N2 adsorption–desorption isotherms show no remarkably difference in specific surface areas between different preparation methods and Na-excess contents. The analysis of X-ray absorption near edge structure indicates that the oxidation states of Ni and Mn are +2 and +4, respectively. For the electrochemical properties, superior electrochemical performance is observed in the NNMO electrode with a low Na-excess content of 5wt%. The highest specific capacitance is 36.07 F·g−1 at 0.1 A·g−1 in the NNMO electrode prepared by using the sol–gel method. By contrast, the NNMO electrode prepared using the electrospinning method with decreased Na-excess content shows excellent cycling stability of 100% after charge–discharge measurements for 300 cycles. Therefore, controlling the Na excess in the precursor together with the preparation method is important for improving the electrochemical performance of Na-based electrode materials in supercapacitors.
All solid-state electrolytes have the advantages of good mechanical and thermal properties for safer energy storage, but their energy density has been limited by low ionic conductivity and large interfacial resistance caused by the poor Li+ transport kinetics due to the solid–solid contacts between the electrodes and the solid-state electrolytes. Herein, a novel gel polymer electrolyte (UPP-5) composed of ionic liquid incorporated metal-organic frameworks nanoparticles (IL@MOFs) is designed, it exhibits satisfying electrochemical performances, consisting of an excellent electrochemical stability window (5.5 V) and an improved Li+ transference number of 0.52. Moreover, the Li/UPP-5/LiFePO4 full cells present an ultra-stable cycling performance at 0.2C for over 100 cycles almost without any decay in capacities. This study might provide new insight to create an effective Li+ conductive network for the development of all-solid-state lithium-ion batteries.
Commercial hydrogen production involves the development of efficient hydrogen evolution reaction catalysts. Herein, we adopted a friction stir processing (FSP) technique to mix immiscible metals homogenously and obtain a self-supporting copper–silver (CuAg) catalyst. The gust of Ag atoms with larger atomic sizes caused a tensile strain in the Cu matrix. Meanwhile, the chemical-potential difference induced electron transfer from Cu to Ag, and the two factors jointly led to the upshift of Cu d-band and improved the catalytic activity. Consequently, the CuAg electrode exhibited a high turnover frequency (12 times that of pure Cu), a low overpotential at high current density (superior to platinum foil), and high durability (1.57% decay over 180 h). Our work demonstrates that FSP is a powerful method for preparing self-supporting catalysts of immiscible alloys with high catalytic performance.
Reducing the cost and improving the electrocatalytic activity are the key to developing high efficiency electrocatalysts for oxygen evolution reaction (OER). Here, bimetallic NiFe-based metal-organic framework (MOF) was prepared by solvothermal method, and then used as precursor to prepare NiFe-based MOF-derived materials by pyrolysis. The effects of different metal ratios and pyrolysis temperatures on the sample structure and OER electrocatalytic performance were investigated and compared. The experimental results showed that when the metal molar ratio was Fe : Ni = 1:5 and the pyrolysis temperature was 450°C, the sample (FeNi5-MOF-450) exhibits a composite structure of NiFe2O4/FeNi3/C and owns the superior electrocatalytic activity in OER. When the current density is 100 mA·cm−2, the overpotential of the sample was 377 mV with Tafel slope of 56.2 mV·dec−1, which indicates that FeNi5-MOF-450 exhibits superior electrocatalytic performance than the commercial RuO2. Moreover, the long-term stability of FeNi5-MOF-450 further promotes its development in OER. This work demonstrated that the regulatory methods such as component optimization can effectively improve the OER catalytic performance of NiFe-based MOF-derived materials.
Seawater splitting is a prospective approach to yield renewable and sustainable hydrogen energy. Complex preparation processes and poor repeatability are currently considered to be an insuperable impediment to the promotion of the large-scale production and application of electrocatalysts. Avoiding the use of intricate instruments, corrosion engineering is an intriguing strategy to reduce the cost and presents considerable potential for electrodes with catalytic performance. An anode comprising quinary AlCoCrFeNi layered double hydroxides uniformly decorated on an AlCoCrFeNi high-entropy alloy is proposed in this paper via a one-step corrosion engineering method, which directly serves as a remarkably active catalyst for boosting the oxygen evolution reaction (OER) in alkaline seawater. Notably, the best-performing catalyst exhibited oxygen evolution reaction activity with overpotential values of 272.3 and 332 mV to achieve the current densities of 10 and 100 mA·cm−2, respectively. The failure mechanism of the obtained catalyst was identified for advancing the development of multicomponent catalysts.
This article delivers a robust overview of potential electrode materials for use in symmetrical solid oxide fuel cells (S-SOFCs), a relatively new SOFC technology. To this end, this article provides a comprehensive review of recent advances and progress in electrode materials for S-SOFC, discussing both the selection of materials and the challenges that come with making that choice. This article discussed the relevant factors involved in developing electrodes with nano/microstructure. Nanocomposites, e.g., non-cobalt and lithiated materials, are only a few of the electrode types now being researched. Furthermore, the phase structure and microstructure of the produced materials are heavily influenced by the synthesis procedure. Insights into the possibilities and difficulties of the material are discussed. To achieve the desired microstructural features, this article focuses on a synthesis technique that is either the most recent or a better iteration of an existing process. The portion of this analysis that addresses the risks associated with manufacturing and the challenges posed by materials when fabricating S-SOFCs is the most critical. This article also provides important and useful recommendations for the strategic design of electrode materials researchers.
Metal corrosion causes billions of dollars of economic losses yearly. As a smart and new energy-harvesting device, triboelectric nanogenerators (TENGs) can convert almost all mechanical energy into electricity, which leads to great prospects in metal corrosion prevention and cathodic protection. In this work, ﬂexible TENGs were designed to use the energy harvested by flexible polydimethylsiloxane (PDMS) films with ZrB2 nanoparticles and effectively improve the dielectric constant by incorporating ZrB2. The open-circuit voltage and short-circuit current were 264 V and 22.9 µA, respectively, and the power density of the TENGs reached 6 W·m−2. Furthermore, a self-powered anti-corrosion system was designed by the rectifier circuit integrated with TENGs, and the open-circuit potential (OCP) and Tafel curves showed that the system had an excellent anti-corrosion effect on carbon steel. Thus, the system has broad application prospects in fields such as metal cultural relics, ocean engineering, and industry.
The development of tin-based devices with low toxicity is critical for the commercial viability of perovskite solar cells. However, because tin halide is a stronger Lewis acid, its crystallization rate is extremely fast, resulting in the formation of numerous defects that affect the device performance of tin-based perovskite solar cells. Herein, propylamine hydrobromide (PABr) was added to the perovskite precursor solution as an additive to passivate defects and fabricate more uniform and dense perovskite films. Because propylamine cations are too large to enter the perovskite lattices, they only exist at the grain boundary to passivate surface defects and promote crystal growth in a preferred orientation. The PABr additive raises the average short-circuit current density from 19.45 to 25.47 mA·cm−2 by reducing carrier recombination induced by defects. Furthermore, the device’s long-term illumination stability is improved after optimization, and the hysteresis effect is negligible. The addition of PABr results in a power conversion efficiency of 9.35%.
Lattice structures have drawn much attention in engineering applications due to their lightweight and multi-functional properties. In this work, a mathematical design approach for functionally graded (FG) and helicoidal lattice structures with triply periodic minimal surfaces is proposed. Four types of lattice structures including uniform, helicoidal, FG, and combined FG and helicoidal are fabricated by the additive manufacturing technology. The deformation behaviors, mechanical properties, energy absorption, and acoustic properties of lattice samples are thoroughly investigated. The load-bearing capability of helicoidal lattice samples is gradually improved in the plateau stage, leading to the plateau stress and total energy absorption improved by over 26.9% and 21.2% compared to the uniform sample, respectively. This phenomenon was attributed to the helicoidal design reduces the gap in unit cells and enhances fracture resistance. For acoustic properties, the design of helicoidal reduces the resonance frequency and improves the peak of absorption coefficient, while the FG design mainly influences the peak of absorption coefficient. Across broad range of frequency from 1000 to 6300 Hz, the maximum value of absorption coefficient is improved by 18.6%–30%, and the number of points higher than 0.6 increased by 55.2%–61.7% by combining the FG and helicoidal designs. This study provides a novel strategy to simultaneously improve energy absorption and sound absorption properties by controlling the internal architecture of lattice structures.
The integration of organic and inorganic materials has been widely used in various applications to generate novel functional nanomaterials characterized by unique properties. Functional crystalline framework nanosheets and their synergistic effects have been studied recently for possessing the advantages of functional species as well as crystalline framework nanosheets. Hence, we have focused on the preparation methods and applications of functional crystalline framework nanosheets in this review. We introduced crystalline framework nanosheets and discussed the importance of integrating functional species with nanosheets to form functional crystalline framework nanosheets. Then, two aspects of the preparation methods of functional crystalline framework nanosheets were reviewed: in situ synthesis and post-synthesis modification. Subsequently, we discussed the properties of the crystalline framework nanosheets combined with various functional species and summarized their applications in catalysis, sensing, separation, and energy storage. Finally, we have shared our insights on the challenges of functional crystalline framework nanosheets, hoping to contribute to the knowledge base for optimizing the preparation methods, expanding categories, improving stability, and exploring potential applications.
Cobalt nanoparticles (NPs) catalysts are extensively used in heterogeneous catalytic reactions, and the addition of alkali metal promoters is a common method to modulate the catalytic performance because the catalyst’s surface structures and morphologies are sensitive to the addition of promoters. However, the underlying modulation trend remains unclear. Herein, the adsorption of alkali metal promoters (Na and K) on the surfaces of face-centered-cubic (FCC) and hexagonal-closest packed (HCP) polymorphous cobalt was systematically investigated using density functional theory. Furthermore, the effect of alkali promoters on surface energies and nanoparticle morphologies was revealed on the basis of Wulff theory. For FCC-Co, the exposed area of the (111) facet in the nanoparticle increases with the adsorption coverage of alkali metal oxide. Meanwhile, the (311), (110), and (100) facets would disappear under the higher adsorption coverage of alkali metals. For HCP-Co, the Wulff morphology is dominated by the (0001) and (
The activation of CO on iron-based materials is a key elementary reaction for many chemical processes. We investigate CO adsorption and dissociation on a series of Fe, Fe3C, Fe5C2, and Fe2C catalysts through density functional theory calculations. We detect dramatically different performances for CO adsorption and activation on diverse surfaces and sites. The activation of CO is dependent on the local coordination of the molecule to the surface and on the bulk phase of the underlying catalyst. The bulk properties and the different local bonding environments lead to varying interactions between the adsorbed CO and the surface and thus yielding different activation levels of the C–O bond. We also examine the prediction of CO adsorption on different types of Fe-based catalysts by machine learning through linear regression models. We combine the features originating from surfaces and bulk phases to enhance the prediction of the activation energies and perform eight different linear regressions utilizing the feature engineering of polynomial representations. Among them, a ridge linear regression model with 2nd-degree polynomial feature generation predicted the best CO activation energy with a mean absolute error of 0.269 eV.
The synthesis of oxygen vacancies (OVs)-modified TiO2 under mild conditions is attractive. In this work, OVs were easily introduced in TiO2 lattice during the hydrothermal doping process of trivalent iron ions. Theoretical calculations based on a novel charge-compensation structure model were employed with experimental methods to reveal the intrinsic photocatalytic mechanism of Fe-doped TiO2 (Fe–TiO2). The OVs formation energy in Fe–TiO2 (1.12 eV) was only 23.6% of that in TiO2 (4.74 eV), explaining why Fe3+ doping could introduce OVs in the TiO2 lattice. The calculation results also indicated that impurity states introduced by Fe3+ and OVs enhanced the light absorption activity of TiO2. Additionally, charge carrier transport was investigated through the carrier lifetime and relative mass. The carrier lifetime of Fe–TiO2 (4.00, 4.10, and 3.34 ns for 1at%, 2at%, and 3at% doping contents, respectively) was longer than that of undoped TiO2 (3.22 ns), indicating that Fe3+ and OVs could promote charge carrier separation, which can be attributed to the larger relative effective mass of electrons and holes. Herein, Fe–TiO2 has higher photocatalytic indoor NO removal activity compared with other photocatalysts because it has strong light absorption activity and high carrier separation efficiency.
B and N mixed anions co-doped titania with various crystal phases such as anatase, brookite, and rutile were successfully synthesized by a hydrothermal synthesis followed by heat treatment in an ammonia gas atmosphere at 550–650°C (denoted as BN-Ana_x, BN-Bro_x, and BN-Rut_x, x is the treatment temperature). The colors of as-prepared BN-Ana, BN-Bro, and BN-Rut are red, yellow-green, and cyan-green, respectively. The color changing mechanism of titania was related to their various band gap structure and the existence of B–N bonding. The nitridation temperature exhibits effective color changing compared to that of nitridation time. The different phases of the mixed anion co-doped titania possess different photocatalytic deNOx activity. The BN-Ana and BN-Rut show poor photocatalytic deNOx activity, while the BN-Bro shows excellent photocatalytic deNOx activity, better than that of standard titania photocatalyst Degussa P25. The colorful titania with low-photocatalytic activity is heavy metal elements free, indicating their possible applications as nontoxic color pigments or novel cosmetic raw materials.
Piezocatalysis has attracted unprecedented research interest as a newly emerging catalysis technology. However, the inherent insulating property of ferroelectric materials ultimately leads to the poor vibration–electricity conversion ability. Herein, this work reports the (K0.52Na0.48)NbO3 ferroelectric ceramics (KNNFCx), for which the FeCo modification strategy is proposed. The substitution of the moderate amount of FeCo (x = 0.015) at Nb site not only optimizes ferroelectricity but also produces beneficial defects, notably increasing Rhodamine B water purification efficiency to 95%. The pinning effect of monovalent oxygen vacancies on ferroelectric domains is responsible for the excellent ferroelectric polarization of KNNFC0.015 through the generation of an internal field to promote charge carriers separation and reduce nonradiative recombination. Importantly, the accompanying electron carriers can easily move to the material surface and participate in redox reactions because they have low activation energy. Therefore, ferroelectric polarization and defects play synergetic roles in enhancing piezocatalytic performance.