A Novel Hybrid Point Defect of Oxygen Vacancy and Phosphorus Doping in TiO2 Anode for High-Performance Sodium Ion Capacitor

Pt-supported on N-doped carbon/TiO2 nanomaterials derived from NH2-MIL-125 for efficient photo-thermal RWGS reaction

To mitigate carbon dioxide (CO2) emissions and advance carbon neutrality, the conversion of CO2 into value-added fuels and chemicals via the reverse water-gas shift (RWGS) reaction is recognized as a promising approach. In this study, we designed platinum (Pt)-loaded nitrogen-doped carbon composite dual-phase titanium dioxide (TiO2) nanomaterials to achieve efficient photo-thermal performance in the RWGS reaction. The incorporation of Pt, nitrogen doping, and the selection of an appropriate calcination temperature enhance light responsiveness and reduce the recombination of photo-generated carriers, thereby improving the efficiency of the photo-thermal RWGS reaction. The optimized catalysts exhibited a high CO2 conversion (42.79 %), a carbon monoxide (CO) production rate (81.46 mmol gcat-1 h-1) and over 99.9 % selectivity under conditions of 400 °C and 1.2 W cm-2 light illumination. In addition, electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) analyses revealed that Pt/TiO2@CN-525 was enriched with more oxygen defects, which was facilitate the adsorption and activation of CO2. CO temperature-programmed desorption (CO-TPD) showed that Pt/TiO2@CN-525 possesses a strong desorption capacity for CO. In addition, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) pointed to COOH* as a key intermediate in the reaction process. The photo-thermal co-catalyzed CO2 reduction by CO-TPD as well as in-situ DRIFTS indicated that Pt/TiO2@CN-525 follows the RWGS reaction. This work provides a potential strategy for the synthesis of catalysts for enhancing photo-thermal co-catalyzed RWGS reactions.

S/N Co-Doped Ultrathin TiO2 Nanoplates as an Anode Material for Advanced Sodium-Ion Hybrid Capacitors

Anatase titanium dioxide (TiO2) has emerged as a potential anode material for sodium-ion hybrid capacitors (SICs) in terms of its nontoxicity, high structure stability and cost-effectiveness. However, its inherent poor electrical conductivity and limited reversible capacity greatly hinder its practical application. Here, ultrathin TiO2 nanoplates were synthesized utilizing a hydrothermal technique. The electrochemical kinetics and reversible capacity were significantly improved through sulfur and nitrogen co-doping combined with carbon coating (SN-TiO2/C). Sulfur and nitrogen co-doping generated oxygen vacancies and introduced additional active sites within TiO2, facilitating accelerated Na-ion diffusion and enhancing its reversible capacity. Furthermore, carbon coating provided stable support for electron transfer in SN-TiO2/C during repeated cycling. This synergistic strategy of sulfur and nitrogen co-doping with carbon coating for TiO2 led to a remarkable capacity of 335.3 mAh g-1 at 0.1 A g-1, exceptional rate property of 148.3 mAh g-1 at 15 A g-1 and a robust cycling capacity. Thus, the SN-TiO2/C//AC SIC delivered an impressive energy density of 177.9 W h kg-1. This work proposes an idea for the enhancement of reaction kinetics for energy storage materials through a synergistic strategy.

NH4 + Pre-Intercalation and Mo Doping VS2 to Regulate Nanostructure and Electronic Properties for High Efficiency Sodium Storage

Sodium-ion hybrid capacitors (SIHCs) have attracted much attention due to integrating the high energy density of battery and high out power of supercapacitors. However, rapid Na+ diffusion kinetics in cathode is counterbalanced with sluggish anode, hindering the further advancement and commercialization of SIHCs. Here, aiming at conversion-type metal sulfide anode, taking typical VS2 as an example, a comprehensive regulation of nanostructure and electronic properties through NH4 + pre-intercalation and Mo-doping VS2 (Mo-NVS2) is reported. It is demonstrated that NH4 + pre-intercalation can enlarge the interplanar spacing and Mo-doping can induce interlayer defects and sulfur vacancies that are favorable to construct new ion transport channels, thus resulting in significantly enhanced Na+ diffusion kinetics and pseudocapacitance. Density functional theory calculations further reveal that the introduction of NH4 + and Mo-doping enhances the electronic conductivity, lowers the diffusion energy barrier of Na+, and produces stronger d-p hybridization to promote conversion kinetics of Na+ intercalation intermediates. Consequently, Mo-NVS2 delivers a record-high reversible capacity of 453 mAh g-1 at 3 A g-1 and an ultra-stable cycle life of over 20 000 cycles. The assembled SIHCs achieve impressive energy density/power density of 98 Wh kg-1/11.84 kW kg-1, ultralong cycling life of over 15000 cycles, and very low self-discharge rate (0.84 mV h-1).

Establishing an Ion-Sieving Separator by Depositing Oxygen-Deficient SiOx Layer for Stabilized Zinc Metal Anode

Stable plating/stripping of Zn metal anode remains a great challenge owing to uncontrollable dendrite growth and side reactions. Ion-sieving separators is a unique and promising solution, that possess Zn2+ permeability and promote Zn2+ transport, can effectively alleviate the abovementioned problems. Ion-sieving on glass fiber separator by deposition of oxygen-deficient SiOx layer via active screen plasma technology is achieved. While having chemical composition similar to the glass fiber, the SiOx nanoparticles contain oxygen-rich vacancies that promoted dissociation of the adsorbed water and generation of the hydroxyl groups. The negatively-charged hydroxylated SiOx layer can repel SO4 2- and attract Zn2+, which can alleviate the side reactions. The strong interplay between hydroxyl groups and Zn2+ can boost Zn affinity and yield fast Zn2+ transport. Consequently, the SiOx-deposited GF separator enabled dendrite-free Zn deposition morphology, which displays lower overpotential of 18 mV and longer cycling life over 2000 h for Zn symmetric cell. Such a separator can also be easily scaled up to prepare the high-performance large-area (4 × 6 cm2) pouch Zn-based devices, showing remarkable flexibility and practicality.

Phosphorus-doped TiO2mesoporous nanocrystals for anodes in high-current-rate lithium ion batteries

Limited by the intrinsic low electronic conductivity and inferior electrode kinetics, the use of TiO2as an anode material for lithium ion batteries (LIBs) is hampered. Nanoscale surface-engineering strategies of morphology control and particle size reduction have been devoted to increase the lithium storage performances. It is found that the ultrafine nanocrystal with mesoporous framework plays a crucial role in achieving the excellent electrochemical performances due to the surface area effect. Herein, a promising anode material for LIBs consisting of phosphorus-doped TiO2mesoporous nanocrystals (P-TMC) with ultrafine size of 2-8 nm and high specific surface area (234.164 m2g-1) has been synthesized. It is formed through a hydrothermal process and NaBH4assisted heat treatment for anatase defective TiO2(TiO2-x) formation followed by a simple gas phosphorylation process in a low-cost reactor for P-doping. Due to the merits of the large specific surface area for providing more reaction sites for Li+ions to increase the storage capacity and the presence of oxygen vacancies and P-doping for enhancing material's electronic conductivity and diffusion coefficient of ions, the as-designed P-TMC can display improved electrochemical properties. As a LIB anode, it can deliver a high reversible discharge capacity of 187 mAh g-1at 0.2 C and a good long cycling performance with ∼82.6% capacity retention (101 mAh g-1) after 2500 cycles at 10 C with an average capacity loss of only 0.007% per cycle. Impressively, even the current rate increases to 100 times of the original rate, a satisfactory capacity of 104 mAh g-1can be delivered, displaying good rate capacity. These results suggest the P-TMC a viable choice for application as an anode material in LIB applications. Also, the strategy in this work can be easily extended to the design of other high-performance electrode materials with P-doping for energy storage.

Carbon nanofibers confined polyoxometalate derivatives as flexible self-supporting electrodes for robust sodium storage

Flexible self-supporting film electrodes, which eliminate the need for additional adhesive, conductive agents, or current collectors, offer significant advantages in terms of mechanical properties, specific capacity, and energy density for energy storage applications. In this study, we successfully developed a flexible film electrode by incorporating derivatives of Mo and Fe-based polyoxometalates (POMs-D) into carbon nanofibers (CNFs). The integration of CNFs significantly enhanced the structural stability of POMs-D, while the internally formed electrical field facilitated efficient electron transfer, resulting in good performance in sodium storage. The film electrode demonstrated a high capacitive contribution of 90.0 % for sodium uptake/release at a scan rate of 1.0 mV s-1. It maintained a capacity of approximately 170 mA h g-1 even after 8000 cycles at a current density of 3.0 A g-1. Moreover, the film electrode exhibited a decent capacity with a 40.0-fold increase in current density, along with high power capability and energy density in sodium-ion hybrid supercapacitors, showcasing the versatility. These findings unveil the structure-functionality relationship and offer an advanced approach for developing high-performance film electrode materials, opening new possibilities in the fields of material science and energy storage.

Hierarchically Structured Nb2O5 Microflowers with Enhanced Capacity and Fast-Charging Capability for Flexible Planar Sodium Ion Micro-Supercapacitors

Highlights

Hierarchically structured Nb2O5 microflowers consiste of porous and ultrathin nanosheets. Nb2O5 microflowers exhibit enhanced capacity and rate performance boosting Na ion storage. Planar NIMSCs with charge and kinetics matching show superior areal capacitance and lifespan.

Abstract

Planar Na ion micro-supercapacitors (NIMSCs) that offer both high energy density and power density are deemed to a promising class of miniaturized power sources for wearable and portable microelectronics. Nevertheless, the development of NIMSCs are hugely impeded by the low capacity and sluggish Na ion kinetics in the negative electrode. Herein, we demonstrate a novel carbon-coated Nb2O5 microflower with a hierarchical structure composed of vertically intercrossed and porous nanosheets, boosting Na ion storage performance. The unique structural merits, including uniform carbon coating, ultrathin nanosheets and abundant pores, endow the Nb2O5 microflower with highly reversible Na ion storage capacity of 245 mAh g−1 at 0.25 C and excellent rate capability. Benefiting from high capacity and fast charging of Nb2O5 microflower, the planar NIMSCs consisted of Nb2O5 negative electrode and activated carbon positive electrode deliver high areal energy density of 60.7 μWh cm−2, considerable voltage window of 3.5 V and extraordinary cyclability. Therefore, this work exploits a structural design strategy towards electrode materials for application in NIMSCs, holding great promise for flexible microelectronics.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40820-023-01281-5.

Introducing Hybrid Defects of Silicon Doping and Oxygen Vacancies into MOF-Derived TiO2-X @Carbon Nanotablets Toward High-Performance Sodium-Ion Storage

Titanium dioxide (TiO2 ) is a promising anode material for sodium-ion batteries (SIBs), which suffer from the intrinsic sluggish ion transferability and poor conductivity. To overcome these drawbacks, a facile strategy is developed to synergistically engineer the lattice defects (i.e., heteroatom doping and oxygen vacancy generation) and the fine microstructure (i.e., carbon hybridization and porous structure) of TiO2 -based anode, which efficiently enhances the sodium storage performance. Herein, it is successfully realized that the Si-doping into the MIL-125 metal-organic framework structure, which can be easily converted to SiO2 /TiO2-x @C nanotablets by annealing under inert atmosphere. After NaOH etching SiO2 /TiO2-x @C which contains unbonded SiO2 and chemically bonded SiOTi, thus the lattice Si-doped TiO2-x @C (Si-TiO2-x @C) nanotablets with rich Ti3+ /oxygen vacancies and abundant inner pores are developed. When examined as an anode for SIB, the Si-TiO2-x @C exhibits a high sodium storage capacity (285 mAh g-1 at 0.2 A g-1 ), excellent long-term cycling, and high-rate performances (190 mAh g-1 at 2 A g-1 after 2500 cycles with 95.1% capacity retention). Theoretical calculations indicate that the rich Ti3+ /oxygen vacancies and Si-doping synergistically contribute to a narrowed bandgap and lower sodiation barrier, which thus lead to fast electron/ion transfer coefficients and the predominant pseudocapacitive sodium storage behavior.

Construction of oxygen vacancies and heterostructure in VO2-x/NC with enhanced reversible capacity, accelerated redox kinetics, and stable cycling life for sodium ion storage

Developing anode materials with high reversible capacity, fast redox kinetics, and stable cycling life for Na⁺ storage remains a great challenge. Herein, the VO₂ nanobelts with oxygen vacancies supported on nitrogen-doped carbon nanosheets (VO_2-x/NC) were developed. Benefitting from the enhanced electrical conductivity, the accelerated kinetics, the increased active sites as well as the constructed 2D heterostructure, the VO_2-x/NC delivered extraordinary Na⁺ storage performance in half/full battery. Theoretical calculations (DFT) demonstrated that oxygen vacancies could regulate the adsorption ability for Na⁺, enhance electronic conductivity, as well as achieve rapid and reversible Na⁺ adsorption/desorption. The VO_2-x/NC exhibited high Na⁺ storage capacity of 270 mAh g^-1 at 0.2 A g^-1, and impressive cyclic stability with 258 mAh g^-1 after 1800 cycles at 10 A g^-1. The assembled sodium-ion hybrid capacitors (SIHCs) could achieve maximum energy density/power output of 122 Wh kg^-1/9985 W kg^-1, ultralong cycling life with 88.4% capacity retention after 25,000 cycles at 2 A g^-1, and practical applications (55 LEDs could be actuated for 10 min), promising to be utilized in a practicable Na⁺ storage.

Surface engineered hollow Ni-Co-P@TiO2-x nanopolyhedrons as high performance anode material for sodium storage

With the proposal of carbon peaking and carbon neutrality goals, clean energy storage is attracting more and more attentions. In view of the lack of lithium resource in our earth, sodium-ion batteries are considered as the emerging and promising next-generation energy storage devices. Appropriate high-performance anode materials play a vital role in the development of sodium-ion batteries. Here, a core-shell hollow Ni-Co-P nanopolyhedron interconnected by oxygen defect TiO₂ (Ni-Co-P@TiO_2-x) is reported, which is synthesized by ion etching-hydrolysis and subsequent phosphatization/hydrogenation treatment using ZIF-67 as template and hybrid carbon source. The achieved Ni-Co-P@TiO_2-x material has several distinct advantages including hollow core-shell structure, flexible conductive carbon matrix, stable electroactive coating layer, and efficient pseudocapacitive behavior, resulting in high reversible capacities, remarkable rate capability and excellent cycle stability. The synergetic battery-capacitor characteristic of Ni-Co-P@TiO_2-x material makes it become a promising anode for sodium-ion batteries.

Hexaindium Heptasulfide/Nitrogen and Sulfur Co-Doped Carbon Hollow Microspindles with Ultrahigh-Rate Sodium Storage through Stable Conversion and Alloying Reactions

Group IIIA-VA metal sulfides (GMSs) have attracted increasing attention because of their unique Na-storage mechanisms through combined conversion and alloying reactions, thus delivering large theoretical capacities and low working potentials. However, Na⁺ diffusion within GMSs anodes leads to severe volume change, generally representing a fundamental limitation to rate capability and cycling stability. Here, monodispersed In₆ S₇ /nitrogen and sulfur co-doped carbon hollow microspindles (In₆ S₇ /NSC HMS) are produced by morphology-preserved thermal sulfurization of spindle-like and porous indium-based metal organic frameworks. The resulting In₆ S₇ /NSC HMS anode exhibits theoretical-value-close specific capacity (546.2 mAh g^-1 at 0.1 A g^-1 ), ultrahigh rate capability (267.5 mAh g^-1 at 30.0 A g^-1 ), high initial coulombic efficiency (≈93.5%), and ≈92.6% capacity retention after 4000 cycles. This kinetically favored In₆ S₇ /NSC HMS anode fills up the kinetics gap with a capacitive porous carbon cathode, enabling a sodium-ion capacitor to deliver an ultrahigh energy density of 136.3 Wh kg^-1 and a maximum power density of 47.5 kW kg^-1 . The in situ/ex situ analytical techniques and theoretical calculation both show that the robust and fast Na⁺ charge storage of In₆ S₇ /NSC HMS arises from the multi-electron redox mechanism, buffered volume expansion, negligible morphological change, and surface-controlled solid-state Na⁺ transport.