Oxygen Vacancies Trigger Rapid Charge Transport Channels at the Engineered Interface of S-Scheme Heterojunction for Boosting Photocatalytic Performance.

Although oxygen vacancies (Ovs) have been intensively studied in single semiconductor photocatalysts, exploration of intrinsic mechanisms and in-depth understanding of Ovs in S-scheme heterojunction photocatalysts are still limited. Herein, a novel S-scheme photocatalyst made from WO3-Ov/In2S3 with Ovs at the heterointerface is rationally designed. The microscopic environment and local electronic structure of the S-scheme heterointerface are well optimized by Ovs. Femtosecond transient absorption spectroscopy (fs-TAS) reveals that Ovs trigger additional charge movement routes and therefore increase charge separation efficiency. In addition, Ovs have a synergistic effect on the thermodynamic and kinetic parameters of S-scheme photocatalysts. As a result, the optimal photocatalytic performance is significantly improved, surpassing that of single component WO3-Ov and In2S3 (by 35.5 and 3.9 times, respectively), as well as WO3/In2S3 heterojunction. This work provides new insight into regulating the photogenerated carrier dynamics at the heterointerface and also helps design highly efficient S-scheme photocatalysts.

Utilizing Cationic Vacancies and Spontaneous Polarization on Cathode to Enhance Zinc-Ion Storage and Inhibit Dendrite Growth in Zinc-Ion Batteries.

High energy density and intrinsic safety are the central pursuits in developing rechargeable Zinc-ion batteries (ZIBs). The capacity and stability of nickel cobalt oxide (NCO) cathode are unsatisfactory because of its semiconductor character. Herein, we propose a built-in electric field (BEF) approach by synergizing cationic vacancies and ferroelectric spontaneous polarization on cathode side to facilitate electron adsorption and suppress zinc dendrite growth on the anode side. Concretely, NCO with cationic vacancies was constructed to expand lattice spacing for enhanced zinc-ion storage. Heterojunction with BEF leads to the Heterojunction//Zn cell exhibiting a capacity of 170.3 mAh g-1 at 400 mA g-1 and delivering a competitive capacity retention of 83.3 % over 3000 cycles at 2 A g-1 . We conclude the role of spontaneous polarization in suppressing zinc dendrite growth dynamics, which is conducive to developing high-capacity and high-safety batteries via tailoring defective materials with ferroelectric polarization on the cathode.

Oxygen-Deficient α-MnO2 Nanotube/Graphene/N, P Codoped Porous Carbon Composite Cathode To Achieve High-Performing Zinc-Ion Batteries.

A major drawback of α-MnO2-based zinc-ion batteries (ZIBs) is the poor rate performance and short cycle life. Herein, an oxygen-deficient α-MnO2 nanotube (VO-α-MnO2)-integrated graphene (G) and N, P codoped cross-linked porous carbon nanosheet (CNPK) composite (VO-α-MnO2/CNPK/G) has been prepared for advanced ZIBs. The introduction of VO in MnO2 can decrease the value of the Gibbs free energy of Zn2+ adsorption near VO (ca. -0.73 eV) to the thermal neutral value. The thermal neutral value demonstrates that the Zn2+ adsorption/desorption process on VO-α-MnO2 is more reversible than that on α-MnO2. The as-made Zn/VO-α-MnO2 battery is able to deliver a large capacity of 305.0 mAh g-1 and high energy density up to 408.5 Wh kg-1. The good energy storage properties can be attributed to VO. Additionally, the VO-α-MnO2/CNPK/G composite possesses the structure of nanotube arrays, which results from the vertical growth of α-MnO2 nanotubes on CNPK. This unique array structure helps to realize fast ion/electron transfer and stable microstructure. The electrochemical performance of VO-α-MnO2 has been comprehensively improved by compositing with G and CNPK. The VO-α-MnO2/CNPK/G can achieve capacity up to 405.2 mAh g-1, energy density of 542.2 Wh kg-1, and long cycle life (80% capacity retention after 2000 cycles).

Photocatalysis-Assisted Co3O4/g-C3N4 p-n Junction All-Solid-State Supercapacitors: A Bridge between Energy Storage and Photocatalysis.

Supercapacitors with the advantages of high power density and fast discharging rate have full applications in energy storage. However, the low energy density restricts their development. Conventional methods for improving energy density are mainly confined to doping atoms and hybridizing with other active materials. Herein, a Co3O4/g-C3N4 p-n junction with excellent capacity is developed and its application in an all-solid-state flexible device is demonstrated, whose capacity and energy density are considerably enhanced by simulated solar light irradiation. Under photoirradiation, the capacity is increased by 70.6% at the maximum current density of 26.6 mA cm-2 and a power density of 16.0 kW kg-1. The energy density is enhanced from 7.5 to 12.9 Wh kg-1 with photoirradiation. The maximum energy density reaches 16.4 Wh kg-1 at a power density of 6.4 kW kg-1. It is uncovered that the lattice distortion of Co3O4, reduces defects of g-C3N4, and the facilitated photo-generated charge separation by the Co3O4/g-C3N4 p-n junction all make contributions to the promoted electrochemical storage performance. This work may provide a new strategy to enhance the energy density of supercapacitors and expand the application range of photocatalytic materials.

Preparation and Characterization of Fly Ash Coated with Zinc Oxide Nanocomposites.

Calcined fly ash (CFA) was first obtained by calcining fly ash (FA) at 815 °C for two hours. Then, composite powders of CFA coated with zinc oxide nanoparticles (ZnO/CFA, ZCFA) were prepared by heterogeneous nucleation method. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Scanning electronic microscopy (SEM), Whiteness, and Brunauer-Emmett-Teller specific surface area (BET). Effects of pH value, reaction temperature and time, coating amount, solid-to-liquid ratio, the coating agent concentrations, and dropping speed on the whiteness of ZCFA powders were studied. It was shown that after coated with ZnO particles, the whiteness of CFA was increased from 27.0 to 62.6%, and the specific surface area was increased from 5.80 to 14.61 m2/g. Needle ZnO with the average grain size of 46 nm was deposited on the surface of CFA. Si-O-Zn-OH bonds were formed.

Carbon-coated MoO2 nanoclusters anchored on RGO sheets as high-performance electrodes for symmetric supercapacitors.

A carbon-coated molybdenum dioxide-reduced graphene oxide (RGO@MoO2/C) composite was synthesized as a high-performance electrode for supercapacitors via a facile hydrothermal method. In this composite, RGO not only provided high conductivity to benefit effective electron transfer, but also offered nucleation sites to load in situ formed MoO2/C nanoparticles. The MoO2@C nanoparticles interconnected with each other forming nanoclusters and were anchored uniformly on RGO sheets instead of self-agglomerating into large aggregates. This allowed more MoO2 grains to gain easy access to both the conductive network and the electrolyte for efficient electron and ion transfer. Moreover, this effect was achieved after the addition of a rather small amount of GO (5 wt%), which allowed high MoO2/C loading to contribute to the overall capacitance. When the RGO@MoO2/C composite was evaluated as an electrode material for supercapacitors, a synergistic effect was exerted with high specific capacitance (1224.5 F g-1 at 1 A g-1) and large reversibility (92% capacitance retention after 3000 cycles), both of which were of great advantage over individual MoO2/C composite. RGO@MoO2/C was also used to construct a symmetric supercapacitor, which showed enhanced voltage profiles and could light an LED device for dozens of minutes, thus confirming its excellent electrochemical performance.