Zhensheng Hong

Facile synthesis of rutile TiO2 mesocrystals with enhanced sodium storage properties

With the aim of developing high performance anode (negative) materials for sodium ion batteries (NIBs), rutile TiO2 with mesocrystalline structure were designed and used for enhancing the discharge capacity and reaction kinetics. The nanoporous rutile TiO2 mesocrystals constructed by crystallographically oriented nanoparticle subunits with tunable microstructures were successfully prepared via a facile synthesis route. Such rutile TiO2 architecture possesses a large surface area (157 m2 g−1), nanoporous nature and single-crystal-like structure, which could provide a high level of accessibility for the electrolyte and more active sites, and allow the fast electron and ion transport compared with the irregularly oriented nanoparticles. When evaluated as an anode material for sodium-ion storage, this unique architecture exhibited a high reversible capacity over 350 mA h g−1 at 50 mA g−1, superior rate capability with a stable capacity of 151 mA h g−1 at 2 A g−1 and good cycling stability.

Iso-Oriented Anatase TiO2 Mesocages as a High Performance Anode Material for Sodium-Ion Storage

A major obstacle in realizing Na-ion batteries (NIBs) is the absence of suitable anode materials. Herein, we firstly report the anatase TiO2 mesocages constructed by crystallographically oriented nanoparticle subunits as a high performance anode for NIBs. The mesocages with tunable microstructures, high surface area (204u2009m2 g−1) and uniform mesoporous structure were firstly prepared by a general synthesis method under the assist of sodium dodecyl sulfate (SDS). It’s notable that the TiO2 mesocages exhibit a large reversible capacity and good rate capability. A stable capacity of 93u2009mAhg−1 can be retained after 500 cycles at 10u2009C in the range of 0.01–2.5u2009V, indicating high rate performance and good cycling stability. This could be due to the uniform architecture of iso-oriented mesocage structure with few grain boundaries and nanoporous nature, allowing fast electron and ion transport, and providing more active sites as well as freedom for volume change during Na-ion insertion. CV measurements demonstrate that the sodium-ion storage process of anatase mesocages is mainly controlled by pseudocapacitive behavior, which is different from the lithium-ion storage and further facilitates the high rate capability.

Synthesis of Mesoporous Co2+-Doped TiO2 Nanodisks Derived from Metal Organic Frameworks with Improved Sodium Storage Performance

TiO2 is a most promising anode candidate for rechargeable Na-ion batteries (NIBs) because of its appropriate working voltage, low cost, and superior structural stability during chage/discharge process. Nevertheless, it suffers from intrinsically low electrical conductivity. Herein, we report an in situ synthesis of Co2+-doped TiO2 through the thermal treatment of metal organic frameworks precursors of MIL-125(Ti)-Co as a superior anode material for NIBs. The Co2+-doped TiO2 possesses uniform nanodisk morphology, a large surface area and mesoporous structure with narrow pore distribution. The reversible capacity, Coulombic efficiency (CE) and rate capability can be improved by Co2+ doping in mesoporous TiO2 anode. Co2+-doped mesoporous TiO2 nanodisks exhibited a high reversible capacity of 232 mAhg-1 at 0.1 Ag1-, good rate capability and cycling stability with a stable capacity of about 140 mAhg-1 at 0.5 Ag1- after 500 cycles. The enhanced Na-ion storage performance could be due to the increased electrical conductivity revealed by Kelvin probe force microscopy measurements.

A multi-functional gum arabic binder for NiFe2O4 nanotube anodes enabling excellent Li/Na-ion storage performance

Electrode pulverization, low electrochemical reaction kinetics and an unstable SEI layer have prevented the application of transition metal oxides with a conversion-type mechanism. Here, we describe gum arabic (GA) as a green and multi-functional binder for the fabrication of a NiFe2O4 nanotube (NFNT) electrode enabling predominant application in LIBs and NIBs. Firstly, its revealed that the NFNTs–GA electrode possesses better mechanical properties of a higher friction coefficient, better elastic resilience and higher reduced modulus and hardness compared with a NFNTs–PVDF electrode. Secondly, the NFNTs–GA electrode can restrain the side reactions between the electrode and electrolyte, leading to the formation of a remarkably stable and thin SEI layer during discharge and charge processes. Thirdly, it is demonstrated by KPFM that the NFNTs–GA electrode possesses improved surface electrical properties and lower energy for the escape of electrons. Consequently, the NFNTs–GA electrode demonstrates much improved rate capability, cycling stability and columbic efficiency when used as an anode material for LIBs. It displays a stable capacity of 770 mA h g−1 which can be retained after 500 cycles at 0.5 A g−1. More importantly, the NFNTs–GA electrode exhibits a high initial coulombic efficiency of 73% (only 48% for the NFNTs–PVDF electrode) and enhanced electrochemical reaction kinetics with significantly improved oxidation and reduction peaks in the application of NIBs.

In situ generation of electron acceptor to amplify the photoelectrochemical signal from poly(dopamine)-sensitized TiO2 signal crystal for immunoassay

A versatile photoelectrochemical immunoassay protocol was designed for quantitative monitoring of tumor markers by utilizing the poly(dopamine)-sensitized titanium dioxide (TiO2) signal crystal with an ordered mesoporous carbon support. Poly(dopamine) was introduced to alter the optical properties of the TiO2 signal crystal, thereby improving the visible light absorption and photoelectrical responses. More importantly, a new enzyme-like biomimetic catalyst was exploited as the signal amplifier to catalyze the reaction of hydroquinone. The generated product was deposited on the electrode surface and served as an efficient sacrificial electron acceptor, which could receive the photo-generated electrons of the excited semiconductor to assist the cathode photocurrent enhancement. Herein, a competitive-type immunosensor was achieved through the biomimetic catalyst labeled prostate specific antigen competing with the target antigen of different concentrations to react with the specific antibody anchored on the poly(dopamine)-sensitized TiO2 signal crystal. Under optimal conditions, the photocurrent decreased with increasing target concentration in a dynamic working range from 1 × 10-6 ng mL-1 to 50 ng mL-1, which provided a new photoelectrochemical method for tumor markers analysis.

Rational Design and General Synthesis of S-Doped Hard Carbon with Tunable Doping Sites toward Excellent Na-Ion Storage Performance

Heteroatom-doping is a promising strategy to tuning the microstructure of carbon material toward improved electrochemical storage performance. However, it is a big challenge to control the doping sites for heteroatom-doping and the rational design of doping is urgently needed. Herein, S doping sites and the influence of interlayer spacing for two kinds of hard carbon, perfect structure and vacancy defect structure, are explored by the first-principles method. S prefers doping in the interlayer for the former with interlayer distance of 3.997 Å, while S is doped on the carbon layer for the latter with interlayer distance of 3.695 Å. More importantly, one step molten salts method is developed as a universal synthetic strategy to fabricate hard carbon with tunable microstructure. It is demonstrated by the experimental results that S-doping hard carbon with fewer pores exhibits a larger interlayer spacing than that of porous carbon, agreeing well with the theoretical prediction. Furthermore, the S-doping carbon with larger interlayer distance and fewer pores exhibits remarkably large reversible capacity, excellent rate performance, and long-term cycling stability for Na-ion storage. A stable and reversible capacity of ≈200 mAh g-1 is steadily kept even after 4000 cycles at 1 A g-1 .

Engineering of TiO2 Anode toward a Record High Initial Coulombic Efficiency Enabling High-Performance Low-Temperature Na-Ion Hybrid Capacitors

Initial coulombic efficiency (ICE) is an important evaluation index to weigh the applicability of electrode materials, but it is not acknowledged by many researchers. Herein, S-doped TiO2 nanosheets with porous and layered structures are utilized as anodes to fabricate hybrid sodium-ion capacitors in an ether electrolyte with high performance, especially through dramatically improved ICE. For Na-ion half cell tests in a DME electrolyte, S-doped TiO2 nanosheets display record high ICE of 88.6%, excellent rate capability and good cycling performance. We also find that TiO2 material with a large surface area is helpful for reducing the first irreversible capacity in an ether electrolyte, which is different from that observed using a traditional ester-based electrolyte. This could be due to excellent electronic conductivity with charge resistance of ∼1 Ω through the construction of an ultrathin solid electrolyte interphase (SEI) layer. Coupling with an Na3V2(PO4)3 cathode, we verify a successful Na-ion hybrid capacitor, delivering high energy and power density values of 158 W h kg−1 and 1075 W kg−1, respectively, at room temperature. Moreover, it also exhibits satisfactory performance of 82 W h kg−1 at −20 °C and outstanding cycling performance with over 95% retention after 800 cycles even at 1 A g−1 charge and discharge rate.