Construction of MXene/Bi2WO6 Schottky Junction for Highly Efficient Piezocatalytic Hydrogen Evolution and Unraveling Mechanism.

For the first time, a series of MXene (Ti3C2Tx)/Bi2WO6 Schottky junction piezocatalysts were constructed, and the piezocatalytic hydrogen evolution activity was explored. Optimal Ti3C2Tx/Bi2WO6 exhibits the highest piezocatalytic hydrogen evolution rate of 764.4 µmol g-1 h-1, which is nearly 8 times higher than that of pure Ti3C2Tx and twice as high as that of Bi2WO6. This value also surpasses that of most recently reported typical piezocatalysts. Moreover, related experimental results and density functional theory calculations reveal that Ti3C2Tx/Bi2WO6 can provide unique channels for efficient electron transfer, enhance piezoelectric properties, optimize the adsorption Gibbs free energy of water, reduce activation energy for hydrogen atoms, endow robust separation capacity of charge carrier, and restrict the electron-hole recombination rate, thus significantly promoting the efficiency of hydrogen evolution reaction. Ultimately, we have unraveled an innovative piezocatalytic mechanism. This work broadens the scope of MXene materials in a sustainable energy piezocatalysis application.

Soluble starch-derived porous carbon microspheres with interconnected and hierarchical structure by a low dosage KOH activation for ultrahigh rate supercapacitors.

The developed porous structure and high density are essential to enhance the bulk performance of carbon-based supercapacitors. Nevertheless, it remains a significant challenge to optimize the balance between the porous structure and the density of carbon materials to realize superior gravimetric and areal electrochemical performance. The soluble starch-derived interconnected hierarchical porous carbon microspheres were prepared through a simple hydrothermal treatment succeeded by chemical activation with a low dosage of KOH. Due to the formation of interconnected spherical morphology, hierarchical porous structure, reasonable mesopore volume (0.33 cm3 g-1) and specific surface area (1162 m2 g-1), the prepared carbon microsphere has an ultrahigh capacitance of 394 F g-1 @ 1 A g-1 and a high capacitance retention of 62.7 % @ 80 A g-1. The assembled two-electrode device displays good cycle stability after 20,000 cycles and an ultra-high energy density of 11.6 Wh kg-1 @ 250 W kg-1. Moreover, the sample still exhibits a specific capacitance of 165 F g-1 @ 1 A g-1 at a high mass loading of 10 mg cm-2, resulting in a high areal capacitance of 1.65 F cm-2. The strategy proposed in this study, via a low-dose KOH activation process, provides the way for the synthesis of high-performance porous carbon materials.

Fabrication of Zn-Air Battery with High Output Capacity Under Ultra-Large Current.

Zn-air battery (ZAB) is advocated as a more viable option in the new-energy technology. However, the limited-output capacity at a high current density impedes the driving range in power batteries substantially. Here, a novel heterojunction-based graphdiyne (GDY) and Ag29Cu7 alloy quantum dots (Ag29Cu7 QDs/GDY) for constructing a high-performance aqueous ZAB are fabricated. The as-fabricated ZAB achieves discharge at up to 100 mA cm-2 (the highest value ever reported) along with a remarkable output specific capacity of 786.2 mAh g-1 Zn, which is mainly benefitted from the binary-synergistic effect toward a stable triple-phase interface for air electrode induced by the Ag29Cu7 QDs and GDY in harsh base, together with the decreasing reaction energy barrier and polarization. The results outperform the superior reports discharging at low current and will bring breakthrough progress toward the practical applications of ZAB on large power supply facilities.

Boosting Zinc Storage Performance of Li3 VO4 Cathode Material for Aqueous Zinc Ion Batteries via Carbon-Incorporation: A Study Combining Theory and Experiment.

In the search for sustainable cathode materials for aqueous zinc ion batteries (AZIBs), vanadium (V)-based materials have garnered interest, primarily due to their abundance and multiple oxidation states. Among the contenders, Li3 VO4 (LiVO) stands out for its affordability, high specific capacity, and elevated ionic conductivity. However, its limited electrical conductivity results in significant resistance polarization, limiting its rate capability, especially under high currents. Through density functional theory (DFT) calculations, this study evaluates the electrochemical implications of carbon (C) incorporation within the LiVO matrix. The findings indicate that C integration significantly ameliorates the conductivity of LiVO. Moreover, C serves as a barrier, mitigating direct interactions between Zn2+ and LiVO, which in turn expedites Zn2+ diffusion. When considering various C materials for this role, glucose is emerged as the optimal candidate. The LiVO/C-glucose composite (LiVO/C-G) is observed to undergo dual phase transitions during charge-discharge cycles, resulting in an amorphous vanadium-oxygen (VO) derivative, paving the way for subsequent electrochemical reactions. Collectively, the insights pave a promising avenue for refining AZIB cathode design and performance.

Gas Phase-Heat Absorption-Condensate Phase Stepwise Flame Retardant Strategy to Prepare Coal Tar Pitch-Based Porous Carbon for Supercapacitor.

Porous carbon is widely used in energy storage-conversion systems, and the question of how to explore an efficient strategy for preparation is very significant. Herein, the flame retardant capability of (NH4 )2 SO4 /Mg(OH)2 that contains gas phase-heat absorption-condensate phase components is assisted to carbonize coal tar pitch in air and obtain the porous carbon. The mechanism of stepwise inflaming retarding is systematically investigated. In the carbonization process in a muffle furnace, (NH4 )2 SO4 decomposes releasing gases at below 400 °C to act as the role of gas phase flame retardant. Mg(OH)2 starts to decompose at ≥ 400 °C, and it has the effect of heat absorption and condensed phase flame retardation (MgSO4 and MgO). What's more, the flame retardant also serves as an N, S source and template. The obtained porous carbon possesses an ultrahigh carbon yield of 56.9 wt.%, hierarchical pore structure, and multi-heteroatoms doping. It can still reach up to 244.7 F g-1 even loaded 20 mg of active material. In addition, the (NH4 )2 SO4 /agar gel electrolyte is synthesized, and the fabricated flexible ammonium ion capacitor exhibits a superior energy density of 40.8 Wh kg-1 . This work uncovers a new way to construct porous carbon, which is expected to synthesize more carbon materials using other carbon sources.

Insights into the SiO2 Stress Effect on the Electrochemical Performance of Si anode.

Silicon (Si) is regarded as the most potential anode material for next-generation lithium-ion batteries (LIBs). However, huge volume expansion hinders its commercial application. Here, a yolk-shell structural nitrogen-doped carbon coated Si@SiO2 is prepared by SiO2 template and HF etching method. The as-prepared composite exhibits superior cycling stability with a high reversible capacity of 577 mA h g-1 at 1 A g-1 after 1000 cycles. The stress effect of SiO2 on stabilizing the electrochemical performance of Si anode is systematically investigated for the first time. In situ thickness measurement reveals that the volume expansion thickness of Si@SiO2 upon charge-discharge is obviously smaller than Si, demonstrating the electrode expansion can be effectively inhibited to improve the cyclability. The density functional theory (DFT) calculation further demonstrates the moderate young's modulus and enhanced hardness after SiO2 coating contribute significantly to the mechanical reinforcement of overall Si@SiO2@void@NC composite. Various post-cycling electrode analyses also address the positive effects of inner stress from the Si core on effectively relieving the damage to electrode structure, facilitating the formation of a more stable inorganic-rich solid electrolyte interphase (SEI) layer. This study provides new insights for mechanical stability and excellent electrochemical performance of Si-based anode materials.

Cottonseed meal derived porous carbon prepared via the protease pretreatment and reduced activator dosage carbonization for supercapacitor.

The high catalytic activity and specificity of enzymes can be used to pretreat biomass. Herein, the resourceful, reproducible, cheap, and crude protein-rich cottonseed meal (CM) is selected as a precursor and the protease in the K2CO3-KHCO3 buffer solution is used as the enzyme degradation substance to pretreat CM. The crude protein content is significantly reduced by the protease degradation, and, meanwhile, it results in a looser and porous structure of CM. What is more, it significantly reduces the amount of activator. In the subsequent carbonization process, the K2CO3-KHCO3 in the buffer solution is also used as an activating agent (the mass ratio of CM to activator is 2:1), and after carbonization, the O, S, and N doped porous carbon is obtained. The optimized PCM-800-4 exhibits high heteroatom contents and a hierarchical porous structure. The specific capacitance of the prepared porous carbon reaches up to 233 F g-1 in 6M KOH even when 10 mg of active material is loaded. In addition, a K2CO3-KHCO3/EG based gel electrolyte is prepared and the fabricated flexible capacitor exhibits an energy density of 15.6 Wh kg-1 and a wide temperature range (-25 to 100 °C). This study presents a simple enzymatic degradation and reduced activator dosage strategy to prepare a cottonseed meal derived carbon material and looks forward to preparing porous carbon using other biomass.

Br-Doped BiOCl Nanosheet Exposed (001) Facet: Surface Oxygen Vacancy and Directed Electron Flow Boosting the Photocatalytic Performance.

The defective BiOCl nanosheet exposed (001) facet with favorable photocatalytic performance was designed. The surface microstructure analysis and theoretical calculation certified the dominant exposed (001) facet and rich surface oxygen defects of Br--doped BiOCl (B-6) nanosheets. The energy level structure analysis indicates that the band gap can be narrowed and the light absorption range can be widened by introducing Br- to BiOCl, and the presence of defective energy levels increases the photogenerated carrier transfer efficiency. Moreover, the doping of Br- in BiOCl promotes the directional flow of electrons to the surface of B-6, which improves the photocatalytic performance of the sample. Thus, the Br--doped BiOCl can degrade 96.5% RhB within 6 min under visible-light irradiation with high apparent reaction rate constants of 0.51 min-1, exhibiting the strongest photocatalytic degradation performance. This work provides guidance for the preparation of Bi-based photocatalysts with excellent performance.

Polypyrrole-Doped NH4 V3 O8 with Oxygen Vacancies as High-Performance Cathode Material for Aqueous Zinc-Ion Batteries.

The inherent slow diffusion dynamics of aqueous zinc-ion batteries (AZIBs) act as a significant hindrance to their universal utilization as energy storage systems, largely attributed to the scarcity of superior cathode materials. In this study, a novel method that amalgamates oxygen defect engineering and polymer intercalation, guided by theoretical computations, to confront this challenge, is introduced. This approach begins with density functional theory calculations, demonstrating that the shielding effect rendered by polypyrrole (PPy) between NH4 V3 O8 (NVO) layers, along with the cooperative influence of oxygen defects (Od ), optimizes the kinetic transport of Zn2+ . Leveraging these theoretical outcomes, a two-step hydrothermal synthesis procedure is devised to fabricate PPy-intercalated NVO embedded with Od (NVO-Od @PPy). The empirical findings corroborate the theoretical predictions, showcasing that the NVO-Od @PPy//Zn system manifests exceptional cycling stability. Specifically, the NVO-Od @PPy electrode delivers an optimal reversible capacity, yielding 421 mAh g-1 at a current density of 0.1 A g-1 . Remarkably, even at an elevated current density of 10 A g-1 , it sustains a capacity of 175.7 mAh g-1 , while maintaining a capacity retention of 99% over 1000 cycles. This research provides pivotal insights for the engineering of high-performing cathode materials for AZIBs, paving the way for their future advancements.

Synergistic Effects between Lignin, Cellulose and Coal in the Co-Pyrolysis Process of Coal and Cotton Stalk.

In this work, Qiqunahu (QQH) coal, cotton stalk, cellulose and lignin extracted from cotton stalk were selected as raw materials to study the effects of the co-pyrolysis of coal and cotton stalk. Online thermogravimetric mass spectrometry (TG-MS) was used to analyse mass loss and gas release characteristics during co-pyrolysis. The results reveal that the mixture of cotton stalk and coal can significantly enhance the reactivity of the blends and promote the formation of effective gas. The cellulose in the cotton stalk promotes the generation of H2 and CO2 during the co-pyrolysis of coal and cotton stalks. Lignin promotes the production of CH4 and CO2. Cellulose and lignin show an inhibitory effect on the precipitation of small molecular weight hydrocarbon gases during co-pyrolysis. This study provides a better understanding for the co-pyrolysis of biomass and coal.

Iron doping and interface engineering on amorphous/crystalline Fe-NixSy heterostructures toward high-stability and kinetically accelerated water splitting.

It is very important to develop transition metal-based electrocatalysts with excellent activity, high stability and low-cost for overall water splitting. In this work, the Fe-doped NixSy/NF amorphous/crystalline heterostructure nanoarrays (Fe-NixSy/NF) was synthesized by a simple one-step method. The resulting hierarchically structured nanoarrays offer the advantages of large surface area, high structural void fraction and accessible internal surfaces. These advantages not only furnish additional catalytically active sites, but also enhance the stability of the structure and effectively accelerate mass diffusion and charge transport. Experimental and characterization results indicate that Fe doping increases the electrical conductivity of amorphous/crystalline NixSy/NF, and the NiS-Ni3S2 heterojunctions evoke interfacial charge rearrangement and optimize the adsorption free energy of the intermediates, which allows the catalyst to exhibit low overpotential and superior electrocatalytic activity. Especially, the overpotentials of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) of Fe-NixSy/NF at 10 mA cm-2 in an alkaline environment are 102.4 and 230.5 mV, respectively. When applied as a bifunctional catalyst for overall water splitting, it requires only 1.45 V cell voltage to deliver a current density of 10 mA cm-2, which is preferable to the all-noble metal Pt/C || IrO2 electrocatalyst (1.62 mV @ 10 mA cm-2). In addition, Fe-NixSy/NF has excellent stability, and there is no obvious degradation after 96 h continuous operation at a current density of 100 mA cm-2. This work affords insights into the application of doping strategies and crystalline/amorphous synergistic modulation of the electrocatalytic activity of transition metal-based catalysts in energy conversion systems.

Dual-Salt-Induced Hierarchical Porous Structure in a Carbon Sheet for High Performance Supercapacitors.

Porous carbon, one of the characteristic materials for electrochemical energy storage devices, has been paid wide-ranging attention. However, balancing the reconcilable mesopore volume with a large specific surface area (SSA) was still a challenge. Herein, a dual-salt-induced activation strategy was developed to obtain a porous carbon sheet with ultrahigh SSA (3082 m2 g-1), desirable mesopore volume (0.66 cm3 g-1), nanosheet morphology, and high surface O (7.87%) and S (4.0%) content. Hence, as a supercapacitor electrode, the optimal sample possessed a high specific capacitance (351 F g-1 at 1 A g-1) and excellent rate performance (holding capacitance up to 72.2% at 50 A g-1). Furthermore, the assembled zinc-ion hybrid supercapacitor also exhibited superior reversible capacity (142.7 mAh g-1 at 0.2 A g-1) and highly stable cycling (71.2 mAh g-1 at 5 A g-1 after 10,000 cycles with retention of 98.9%). This work was delivered a new possibility for the development of coal resources for the preparation of high performance porous carbon materials.

Dual Electronic Modulations on NiFeV Hydroxide@FeOx Boost Electrochemical Overall Water Splitting.

Nickel-iron based hydroxides have been proven to be excellent oxygen evolution reaction (OER) electrocatalysts, whereas they are inactive toward hydrogen evolution reaction (HER), which severely limits their large-scale applications in electrochemical water splitting. Herein, a heterostructure consisted of NiFeV hydroxide and iron oxide supported on iron foam (NiFeV@FeOx /IF) has been designed as a highly efficient bifunctional (OER and HER) electrocatalyst. The V doping and intimate contact between NiFeV hydroxide and FeOx not only improve the entire electrical conductivity of the catalyst but also afford more high-valence Ni which serves as active sites for OER. Meanwhile, the introduction of V and FeOx reduces the electron density on lattice oxygen, which greatly facilitates desorption of Hads . All of these endow the NiFeV@FeOx /IF with exceptionally low overpotentials of 218 and 105 mV to achieve a current density of 100 mA cm-2 for OER and HER, respectively. More impressively, the electrolyzer requires an ultra-low cell voltage of 1.57 V to achieve 100 mA cm-2 and displays superior electrochemical stability for 180 h, which outperforms commercial RuO2 ||Pt/C and most of the representative catalysts reported to date. This work provides a unique route for developing high-efficiency electrocatalyst for overall water splitting.

"Dual- Engineering" Strategy to Regulate NH4 V4 O10 as Cathodes for High-Performance Aqueous Zinc Ion Batteries.

Aqueous zinc ion batteries (AZIBs) have attracted attention as a promising candidate for secondary battery energy storage due to their safety and environmental benefits. However, the vanadium-based cathode material NH4 V4 O10 has the problem of structural instability. In this paper, it is found by density functional theory calculation that excessive NH4 + located in the interlayer will repel the Zn2+ during the process of Zn2+ insertion. This results in the distortion of the layered structure, further affects the diffusion of Zn2+ and reduces the reaction kinetics. Therefore, part of the NH4 + is removed by heat treatment. In addition, the introduction of Al3+ into the material by hydrothermal method is able to further enhance its zinc storage properties. This dual-engineering strategy shows excellent electrochemical performance (578.2 mAh g-1 at 0.2 A g-1 ). This study provides valuable insights for the development of high performance AZIBs cathode materials.

Nitrogen-Doped Hierarchical Porous Carbon Derived from Coal for High-Performance Supercapacitor.

The surface properties and the hierarchical pore structure of carbon materials are important for their actual application in supercapacitors. It is important to pursue an integrated approach that is both easy and cost-effective but also challenging. Herein, coal-based hierarchical porous carbon with nitrogen doping was prepared by a simple dual template strategy using coal as the carbon precursor. The hierarchical pores were controlled by incorporating different target templates. Thanks to high conductivity, large electrochemically active surface area (483 m2 g-1), hierarchical porousness with appropriate micro-/mesoporous channels, and high surface nitrogen content (5.34%), the resulting porous carbon exhibits a high specific capacitance in a three-electrode system using KOH electrolytes, reaching 302 F g-1 at 1 A g-1 and 230 F g-1 at 50 A g-1 with a retention rate of 76%. At 250 W kg-1, the symmetrical supercapacitor assembled at 6 M KOH shows a high energy density of 8.3 Wh kg-1, and the stability of the cycling is smooth. The energy density of the symmetric supercapacitor assembled under ionic liquids was further increased to 48.3 Wh kg-1 with a power output of 750 W kg-1 when the operating voltage was increased to 3 V. This work expands the application of coal-based carbon materials in capacitive energy storage.

Constructing the quinonyl groups and structural defects in carbon for supercapacitor and capacitive deionization applications.

The structural defects and oxygen-containing functional groups of carbon materials as electrode materials for supercapacitors or capacitive deionization devices are critical to their electrochemical performance. The tuning of surface oxygen-containing functional groups and carbon defects during pyrolysis is key to achieve a high performance in ion storage. Herein, quinonyl-dominant defective porous carbon is prepared by a pyrolysis and cross-linking route using lavender stem and potassium acetate as precursor. Benefiting from the presence of abundant defect and surface quinonyl groups, porous carbon shows an ultra-high specific capacitance of 401 F g-1 (1 A g-1) and a high capacitance retention of 63% at a high current density of 100 A g-1 in a KOH solution. Meanwhile, as a capacitive deionization electrode material, it also exhibited a high adsorption capacity of 25.5 mg g-1 in 500 mg L-1 NaCl solution at 1.2 V. Theoretical density functional theory (DFT) calculation demonstrates that surface quinonyl groups and carbon defects can synergistically facilitate the adsorption of K+ and Na+ during the charge/discharge process. This work provides a new perspective for understanding the role of surface oxygen-containing groups and intrinsic defects of porous carbon materials in electrochemical energy storage and desalination applications.

Tuning the Zn2+ solvation structure in dual-salts hybrid aqueous electrolyte to stabilize the Zn metal anode.

Aqueous Zn-ion battery is expected to become a substitute for Li-ion battery due to its inherent safety, low cost, and environmental friendliness. Dendrite growth and side reaction problems during electroplating lead to its low Coulombic efficiency and unsatisfactory life, which greatly limits its practical application. Here, we propose a dual-salts hybrid electrolyte, which alleviates the above issues by mixing Zn(OTf)2 to ZnSO4 solution. Extensive tests and MD simulations have shown that the dual-salts hybrid electrolyte can regulate the solvation structure of Zn2+, facilitating uniform Zn deposition, and inhibiting side reactions and dendrite growth. Hence, the dual-salts hybrid electrolyte exhibits good reversibility in Zn//Zn batteries, which can provide a lifetime of more than 880 h at 1 mA cm-2 and 1 mAh cm-2. Moreover, the average Coulombic efficiency of Zn//Cu cells in hybrid system can reach 98.2% after 520 h, much better than that of 90.7% in pure ZnSO4 electrolyte and 92.0% in pure Zn(OTf)2 electrolyte. Benefiting from the fast ion exchange rate and high ion conductivity, Zn-ion hybrid capacitor in hybrid electrolyte also displays excellent stability and capacitive performance. This effective strategy for dual-salts hybrid electrolytes provides a promising direction for designing aqueous electrolytes for Zn-ion batteries.

A novel hierarchical book-like structured sodium manganite for high-stable sodium-ion batteries.

As one of the most promising cathodes for rechargeable sodium-ion batteries (SIBs), Layered transition metal oxides with high energy density show poor cycling stability. Judicious design/construction of electrode materials plays a very important role in cycling performance. Herein, a P2-Na0.7MnO2.05 cathode material with hierarchical book-like morphology combining exposed (100) active crystal facets is synthesized by hydrothermal method. Owing to the superiority of the unique hierarchical structure, the electrode delivers a high reversible capacity of 163 mA h g-1 at 0.2C and remarkable high-rate cyclability (88.8% capacity retention after 300 cycles at 10C). Its unique oriented stacking nanosheet constructed hierarchical book-like structure is the origin of the high electrochemical performance, which is able to shorten the diffusion distances of Na+ and electrons, and a certain gap between the nanosheets can also relieve the stress and strain of volume generated during the cycle. In addition, the exposed (100) active crystal facets can provide more channels for the efficient transfer of Na+. Our strategy reported here opens a door to the development of high-stable oxide cathodes for high energy density SIBs.

Hybrid nanoarchitectonics of coal-derived carbon with oxidation-induced morphology-selectivity for high-performance supercapacitor.

Coal-derived porous carbon with a large specific surface area is a common electrode material for supercapacitors. Its deep and branched micropores, dense bulk morphology and amorphous structure have greatly limited its practical applications. Herein, hybrid carbon materials were obtained from coal through oxidation followed by activation. The method allows tuning the morphology, porosity, structure, and the degree of graphitization. The pre-oxidation with KMnO4 can break raw coal into small hydrocarbon fragments, which deposit and grow on the surface of generated MnO during pyrolysis leading to hybrid carbon with mesoporous and graphitic nanostructures. Meanwhile, homogeneous etching of the carbon skeleton by the reaction intermediate of K2CO3 led to the formation of abundant active sites. Hence, the optimized sample exhibited a high capacitance of 333 F g-1 at 1 A g-1, an excellent rate capability with 58% capacitance retention at 100 A g-1 and superior cycle durability in a three-electrode system. Besides, an assembled symmetric two-electrode device displayed a high energy density of 8.9 Wh·kg-1 at 250 W·kg-1. This work proposed a facile and rational synthesis strategy by balancing the tradeoff between active sites and intrinsic conductivity and thus provided a new avenue for the value-added utilization of coal.

Homogeneous activation induced by bacterial cellulose nanofibers to construct interconnected microporous carbons for enhanced capacitive storage.

Porous carbons have been widely applied for capacitive energy storage, yet usually suffer from insufficient rate performance because of the sluggish ion transport kinetics in deep and multi-branched pores. Herein, we fabricated an interconnected microporous capacitive carbon (IMCC) by growing D (+)-glucosamine on bacterial cellulose (BC) nanofibers scaffold, followed by carbonization and activation. The BC nanofibers acted as a sacrificial template during pre-carbonization, facilitating the subsequent KOH permeation and homogeneous activation. By taking advantage of the interconnected microporous structure, the IMCC delivers a high capacitance of 302 F g-1 at 1 A g-1 and an excellent rate capability of 165 F g-1 at 100 A g-1 for aqueous supercapacitor, demonstrating its fast ion transport capability. Impressively, it also shows a superior gravimetric capacity of 177 mAh g-1 at 0.5 A g-1 and remains a high value of 72 mAh g-1 at 20 A g-1 as a cathode material for Zn-ion hybrid capacitor. This facile and cost-effective design strategy exhibits a great potential to construct carbohydrates-derived interconnected microporous carbon materials for high-rate energy storage.