Nucleophilic hydrolysis enables HF-etched MXene kilofarad specific capacitance and excellent rate performance.

Here, an unusual MXene with a high ratio of oxygen functional groups was prepared by hydrothermal treatment of HF-etched MXene in aqueous KOH solution. The prepared MXene (H-220) exhibits ultrahigh specific capacitance (1030 F g-1 in a potential window of 0.85 V), and excellent rate and cycling performance simultaneously in a sulfuric acid electrolyte, and can act as an anode material of proton batteries.

Crystalline MnCO3@Amorphous MnOx Composite as Cathode Material for High-Performance Aqueous Zinc-Ion Batteries.

Rechargeable aqueous zinc-ion batteries (RAZIBs) have received extensive attention because of their advantages of low cost, high safety, and nontoxicity. However, problems such as dissolution of the active cathode material, dendrites/passivation of the zinc anode, and slow reaction kinetics hindered their further applications. In this work, a crystalline/amorphous composite-type material composed of crystalline MnCO3 and amorphous MnOx was prepared and used as the cathode material for RAZIBs. The MnCO3@amorphous MnOx (MnCO3@A-MnOx) composite possesses the merits of both the pure crystalline phase of MnCO3 and the amorphous phase of MnOx, which can deliver better electrochemical performance than the corresponding single component in repeated cycles. In addition, crystalline MnCO3 undergoes a complex phase transition to the active MnO2 during the first charge process, providing the composite with a stable structure and additional electrochemical capacity. The electrochemical measurement results indicate that the MnCO3@A-MnOx electrode can display high reversible discharge capacity at 0.1 A g-1, excellent rate performance at 5.0 A g-1, and long cycling stability over 2000 cycles, showing great potential as a cathode material for high-performance RAZIBs.

Critical Role of Aromatic C(sp2)-H in Boosting Lithium-Ion Storage.

Exploring high-sloping-capacity carbons is of great significance in the development of high-power lithium-ion batteries/capacitors (LIBs/LICs). Herein, an ion-catalyzed self-template method is utilized to synthesize the hydrogen-rich carbon nanoribbon (HCNR), achieving high specific and rate capacity (1144.2/471.8 mAh g-1 at 0.1/2.5 A g-1). The Li+ storage mechanism of the HCNR is elucidated by in situ spectroscopic techniques. Intriguingly, the protonated aromatic sp2-hybridized carbon (C(sp2)-H) can provide additional active sites for Li+ uptake via reversible rehybridization to sp3-C, which is the origin of the high sloping capacity. The presence of this sloping feature suggests a highly capacitance-dominated storage process, characterized by rapid kinetics that facilitates superior rate performance. For practical usage, the HCNR-based LIC device can deliver high energy/power densities of 198.3 Wh kg-1/17.9 kW kg-1. This work offers mechanistic insights on the crucial role of aromatic C(sp2)-H in boosting Li+ storage and opens up new avenues to develop such sloping-type carbons for high-performance rechargeable batteries/capacitors.

FeNbO4 nanochains with a five-electron transfer reaction toward high capacity and fast Li storage.

High capacity and outstanding rate performance of the FeNbO4 nanochain anode with both intercalation and conversion reactions for lithium-ion batteries are demonstrated. The unique one-dimensional structure and intercalation pseudocapacitive behavior of FeNbO4 accelerate the reaction kinetics. In situ X-ray diffractometer measurement confirms a five-electron transfer mechanism for Li storage.

Ion-catalyzed synthesis of N/O co-doped carbon nanorods with hierarchical pores for high-rate Na-ion storage.

Appropriate heteroatom doping and pore structure optimization are cost-effective technologies to improve the electronic conductivity and ion diffusion kinetics of hard carbons (HCs). Here, we report an ion-catalyzed synthesis of N/O co-doped carbon nanorods (NOCNRs) with abundant hierarchical pores, achieving high-capacity and high-rate Na-ion storage (336 mA h g-1 at 0.1 A g-1 and 196 mA h g-1 at 20.0 A g-1).

Synthesis of Si/C Composites by Silicon Waste Recycling and Carbon Coating for High-Capacity Lithium-Ion Storage.

It is of great significance to recycle the silicon (Si) kerf slurry waste from the photovoltaic (PV) industry. Si holds great promise as the anode material for Li-ion batteries (LIBs) due to its high theoretical capacity. However, the large volume expansion of Si during the electrochemical processes always leads to electrode collapse and a rapid decline in electrochemical performance. Herein, an effective carbon coating strategy is utilized to construct a precise Si@CPPy composite using cutting-waste silicon and polypyrrole (PPy). By optimizing the mass ratio of Si and carbon, the Si@CPPy composite can exhibit a high specific capacity and superior rate capability (1436 mAh g-1 at 0.1 A g-1 and 607 mAh g-1 at 1.0 A g-1). Moreover, the Si@CPPy composite also shows better cycling stability than the pristine prescreen silicon (PS-Si), as the carbon coating can effectively alleviate the volume expansion of Si during the lithiation/delithiation process. This work showcases a high-value utilization of PV silicon scraps, which helps to reduce resource waste and develop green energy storage.

Enhancing High-Capacity and High-Rate Sodium-Ion Storage through Synergistic N,S Dual Doping of Hard Carbon.

Hard carbon, as the most promising commercial anode materials of sodium-ion batteries (SIBs), has suffered from the coupling limitations on initial Coulombic efficiency (ICE), capacity, and rate capability. Herein, to break such coupling limitations, sulfur-rich nitrogen-doped carbon nanomaterials (S-NC) were synthesized by a synergistic modification strategy, including structure/morphology regulation and dual heteroatom doping. The small specific surface area of S-NC is beneficial for inhibiting excessive growth of solid electrolyte interphase (SEI) film and irreversible interfacial reaction. The covalent S can serve as active electrochemical sites by Faradaic reactions and provide extra capacity. Benefit by N, S co-doping, S-NC shows large interlayer spacing, high defects, good electronic conductivity, strong ion adsorption performance, and fast Na+ ion transport, which combined with a more significant pore volume result in speedier reaction kinetics. Hence, S-NC possesses a high reversible specific capacity of 464.7 mAh g-1 at 0.1 A g-1 with a high ICE of 50.7%, excellent rate capability (209.8 mAh g-1 at 10.0 A g-1 ), and superb long-cycle capability delivering a capacity of 229.0 mAh g-1 (85% retention) after 1800 cycles at 5.0 A g-1 .

In Situ Construction of Zn2Mo3O8/ZnO Hierarchical Nanosheets on Graphene as Advanced Anode Materials for Lithium-Ion Batteries.

Transition-metal oxides as anodes for lithium-ion batteries (LIBs) have attracted enormous interest because of their high theoretical capacity, low cost, and high reserve abundance. Unfortunately, they commonly suffer from poor electronic and ionic conductivity and relatively large volume expansion during discharge/charge processes, thereby triggering inferior cyclic performance and rate capability. Herein, a molybdenum-zinc bimetal oxide-based composite structure (Zn2Mo3O8/ZnO/rGO) with rectangular Zn2Mo3O8/ZnO nanosheets uniformly dispersed on reduced graphene oxide (rGO) has been prepared by using a simple and controllable cyanometallic framework template method. The Zn2Mo3O8/ZnO rectangular nanosheets with desirable porous features are composed of nanocrystalline subunits, facilitating the exposure of abundant active sites and providing sufficient contact with the electrolyte. Benefiting from the composition and structural merits as well as the induced synergistic effects, the Zn2Mo3O8/ZnO/rGO composite as LIB anodes delivers superior electrochemical properties, including high reversible capacity (960 mA h g-1 after 100 cycles at 200 mA g-1), outstanding rate performance (417 mA h g-1 at 10,000 mA g-1), and admirable long-term cyclic stability (862 mA h g-1 after 400 cycles at 1000 mA g-1). The mechanism of lithium storage and the formation of SEI film are systematically elucidated. This work provides an effective strategy for synthesizing promising Mo-cluster compound-based anodes for high-performance LIBs.

Nb and Ni Nanoparticles Anchored on N-Doped Carbon Nanofiber Membrane as Self-Supporting Anode for High-Rate Lithium-Ion Batteries.

A flexible N-doped carbon nanofiber membrane loaded with Nb and Ni nanoparticles (Nb/Ni@NC) was prepared using electrospinning technology and a subsequent thermal annealing method and used as a self-supporting anode material for lithium-ion batteries. The Nb/Ni@NC nanofiber membrane had excellent flexibility and could be folded and bent at will without fragmentation and wrinkling; the nanofibers also had a uniform and controllable morphology with a diameter of 300-400 nm. The electrochemical results showed that the flexible Nb/Ni@NC electrode could deliver a high discharge capacity of 378.7 mAh g-1 after 200 cycles at 0.2 A g-1 and an initial coulombic efficiency of 67.7%, which was higher than that of the pure flexible NC anode in contrast. Moreover, a reversible discharge capacity of 203.6 mAh g-1 after 480 cycles at 1.0 A g-1 was achieved by the flexible Nb/Ni@NC electrode with a capacity decay for each cycle of only 0.075%, which showed an excellent rate capability and cycling stability.

Storage of Lithium-Ion by Phase Engineered MoO3 Homojunctions.

With high theoretical specific capacity, the low-cost MoO3 is known to be a promising anode for lithium-ion batteries. However, low electronic conductivity and sluggish reaction kinetics have limited its ability for lithium ion storage. To improve this, the phase engineering approach is used to fabricate orthorhombic/monoclinic MoO3 (α/h-MoO3) homojunctions. The α/h-MoO3 is found to have excessive hetero-phase interface. This not only creates more active sites in the MoO3 for Li+ storage, it regulates local coordination environment and electronic structure, thus inducing a built-in electric field for boosting electron/ion transport. In using α/h-MoO3, higher capacity (1094 mAh g-1 at 0.1 A g-1) and rate performance (406 mAh g-1 at 5.0 A g-1) are obtained than when using only the single phase h-MoO3 or α-MoO3. This work provides an option to use α/h-MoO3 hetero-phase homojunction in LIBs.

Regulating Oxygen Configuration in Hierarchically Porous Carbon Nanosheets for High-Rate and Durable Na+ Storage.

Surface oxygen functionalities (particularly C-O configuration) in carbon materials have negative influence on their electrical conductivity and Na+ storage performance. Herein, we propose a concept from surface chemistry to regulate the oxygen configuration in hierarchically porous carbon nanosheets (HPCNS). It is demonstrated that the C-O/C=O ratio in HPCNS reduces from 1.49 to 0.43 and its graphitization degree increases by increasing the carbonization temperature under a reduction atmosphere. Remarkably, such high graphitization degree and low C-O content of the HPCNS-800 are favorable for promoting its electron/ion transfer kinetics, thus endowing it with high-rate (323.6 mAh g-1 at 0.05 A g-1 and 138.5 mAh g-1 at 20.0 A g-1 ) and durable (96 % capacity retention over 5700 cycles at 10.0 A g-1 ) Na+ storage performance. This work permits the optimization of heteroatom configurations in carbon for superior Na+ storage.

Ferroelectric benzimidazole additive-induced interfacial water confinement for stable 2.2 V supercapacitor electrolytes exposed to air.

Deep eutectic solvents (DESs) are known as low-cost and environmentally friendly electrolytes for supercapacitors. However, because DESs are particularly vulnerable to moisture adsorption in the air, the voltage window (<1.2 V) is significantly lower than expected. Herein, we report a new ferroelectric benzimidazole (BI) additive that, by restricting water electrochemical activity at the DES/carbon electrode interface, allows air-exposed DESs to reach a high voltage of 2.2 V. The optimized DES with 0.5 wt% BI addition not only increases the voltage but also the capacitance and energy density while maintaining excellent cycling stability. This study addresses the voltage drop of DESs in air, providing insights into the design of additives that inhibit interfacial water splitting.

Kinetic Analysis of Bio-oil Derived Hierarchically Porous Carbon for Superior Li+/Na+ Storage.

Herein, an efficient biomass utilization is proposed to prepare bio-oil-derived carbon (BODPC) with hierarchical pores and certain H/O/N functionalities for superior Li+/Na+ storage. Kinetic analyses reveal that BODPC has similar behavior in the electrochemical Li+ and Na+ storage processes, in terms of physical adsorption (Stage I), chemical redox reactions with surface functionalities (Stage II), and insertion into the graphitic interlayer (Stage III). Promisingly, BODPC exhibits a high reversible specific capacity (1881.7 mAh g-1 for Li+ and 461.0 mAh g-1 for Na+ at 0.1 A g-1), superior rate capability (674.1 mAh g-1 for Li+ and 125.7 mAh g-1 for Na+ at 5.0 A g-1), and long-term cyclability. More notably, the BODPC with highly capacitive-dominant behavior would hold great promise for the applications of high-power, durable, and safe rechargeable batteries/capacitors.

Sawdust-Derived Activated Carbon with Hierarchical Pores for High-Performance Symmetric Supercapacitors.

The recyclable utilization of waste biomass is increasingly important for the development of a sustainable society. Here, the sawdust-derived activated carbon (SD-AC) has been prepared via a convenient H3PO4-based activation method and further trialed as an electrode for use as a high-performance symmetric supercapacitor. The as-prepared SD-AC possesses a hierarchically porous structure with micropores (0.55 nm) and mesopores (2.58 nm), accounting for its high specific surface area of 621 m2 g-1, with a pore volume of 0.35 cm3 g-1. Such a hierarchically porous structure can offer a favorable pathway for fast ion penetration and transportation, enhancing its electrochemical performance. As a result, the SD-AC electrode exhibits a maximum specific capacitance of up to 244.1 F g-1 at 1.0 A g-1, a high rate capability (129.06 F g-1 at 20 A g-1), and an excellent cycling performance, with 87% retention over 10,000 cycles at 10 A g-1. Of particular note is that the SD-AC-based symmetric supercapacitor achieves a maximum energy density of 19.9 Wh kg-1 at the power density of 650 W kg-1, with a long-term cycle lifespan. This work showcases the recyclable utilization of waste biomass for the preparation of high-value activated carbon for efficient energy storage.

Heterogeneous cobalt polysulfide leaf-like array/carbon nanofiber composites derived from zeolite imidazole framework for advanced asymmetric supercapacitors.

Developing new electrode materials is one of the keys to improving the energy density of supercapacitors. In this article, a novel cobalt polysulfide/carbon nanofibers (C,N-CoxSy/CNF) film derived from zeolitic imidazolate framework is first prepared by a facile strategy. The composite material with two-dimensional leaf-shaped nanoarray neatly grown on the surface of carbon nanofibers is composed of CoS, CoS2, Co9S8, N-doped carbon nanosheets, and carbon nanofibers. It is found that the composite can not only increase the contact area with the electrolyte but also provide abundant redox-active sites and a Faraday capacitance for the entire electrode. The C,N-CoxSy/CNF composite exhibits excellent electrochemical properties, including a high capacity of up to 1080F g -1 at 1 A g -1 and a good rate capability (80.4 % from 1 A g -1 to 10 A g -1). A C,N-CoxSy/CNF//AC asymmetric supercapacitor device is assembled using C,N-CoxSy/CNF as the positive electrode and activated carbon as the negative electrode, showing high energy density (37.29 Wh kg -1@813.6 W kg -1) and good cycle stability (90.5% of initial specific capacitance at 10 g-1 after 5000 cycles). This C,N-CoxSy/CNF composite material may also be used as a potential electrode for future lithium-ion batteries, zinc-ion batteries, lithium-sulfur batteries, etc.

Operando mechanistic and dynamic studies of N/P co-doped hard carbon nanofibers for efficient sodium storage.

In situ Raman and electrochemical results reveal that Na+ adsorbs on the surface/defective sites of N/P-HCNF and inserts randomly into its turbostratic nanodomains in the dilute state without a staged formation, which can facilitate fast Na+ diffusion kinetics for efficient sodium storage.

Facile Synthesis of Uniform Mesoporous Nb2O5 Micro-Flowers for Enhancing Photodegradation of Methyl Orange.

The removal of organic pollutants using green environmental photocatalytic degradation techniques urgently need high-performance catalysts. In this work, a facile one-step hydrothermal technique has been successfully applied to synthesize a Nb2O5 photocatalyst with uniform micro-flower structure for the degradation of methyl orange (MO) under UV irradiation. These nanocatalysts are characterized by transmission and scanning electron microscopies (TEM and SEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, and UV-Vis diffuse reflectance spectroscopy (DRS). It is found that the prepared Nb2O5 micro-flowers presents a good crystal phases and consist of 3D hierarchical nanosheets with 400-500 nm in diameter. The surface area is as large as 48.6 m2 g-1. Importantly, the Nb2O5 micro-flowers exhibit superior catalytic activity up to 99.9% for the photodegradation of MO within 20 mins, which is about 60-fold and 4-fold larger than that of without catalysts (W/O) and commercial TiO2 (P25) sample, respectively. This excellent performance may be attributed to 3D porous structure with abundant catalytic active sites.

Oxygen vacancies boosted the electrochemical kinetics of Nb2O5-x for superior lithium storage.

The introduction of oxygen vacancies (OVs) into Nb2O5 can not only provide more active sites for lithium storage but also change the electronic structure of Nb2O5 to boost electron/ion transport kinetics. Consequently, the defective Nb2O5-x exhibits high lithium storage capacity, superior rate capability, and cycling stability.

Porous α-Fe2O3 nanoparticles encapsulated within reduced graphene oxide as superior anode for lithium-ion battery.

A facile route for the controllable synthesis of porous α-Fe2O3 supported by three-dimensional reduced graphene oxide (rGO) is presented. The synergistic effect between α-Fe2O3 and rGO can increase the electrolyte infiltration and improve lithium ion diffusion as well. Moreover, the combination of rGO nanosheets can increase the available surface area to provide more active sites and prevent α-Fe2O3 nanoparticles from agglomeration during the cycling process to ensure its long-term cycle performance. Consequently, the α-Fe2O3/rGO nanocomposites exhibit higher reversible specific capacity (1418.2 mAh g-1 at 0.1 A g-1), better rate capability (kept 804.5 mAh g-1 at 5.0 A g-1) and cycling stability than the α-Fe2O3 nanoparticles. Owing to the superior electrochemical performance, the α-Fe2O3/rGO nanocomposites might have a great potential as anode for lithium-ion batteries.

Sonochemical assisted fabrication of 3D hierarchical porous carbon for high-performance symmetric supercapacitor.

A scalable fabrication of 3D hierarchical porous carbon structure (3D-HPC) has been achieved via a simple sonochemical route at different pyrolysis temperatures. It is worth noting that all the 3D-HPC samples possess oxygen-functional groups after activation by KOH and self-doped by nitrogen, which are beneficial to improving their surface wettability as well as increasing the electro-active surface area between the electrode and the surrounding electrolyte, consequently enhancing their electrochemical performance. Remarkably, the resulting carbon sample pyrolyzed at 850 °C (AC-850) possesses a maximum doping level of 2.75 at% and a high surface area of 1376.19 m2 g-1, which exhibits high electrochemical performance with high capacitance up to 269.19 F g-1 at a current density of 2 A g-1. Moreover remarkably, the AC-850-based symmetric supercapacitor delivers a high energy density of 21.4 Wh kg-1 at a power density of 531.2 W kg-1 with excellent rate performance and superior cycling stability (94.7% retention over 5000 cycles). The present approach is very suitable for large scale production of high-quality porous carbon materials at low cost, which can be used in different aspects, such as energy storage, gas storage, environmental remediation, and so on.