Smartly Designed Hierarchical MnO2 @Fe3 O4 /CNT Hybrid Films as Binder-free Anodes for Superior Lithium Storage

An amorphous hierarchical MnO2/acetylene black composite with boosted rate performance as an anode for lithium-ion batteries

Amorphization is considered to be an effective way to enhance the electrochemical performances of electrode materials due to the existence of isotropy and numerous defects. Herein, an amorphous hierarchically structured MnO₂/acetylene black (a-MnO₂/AB) composite is successfully fabricated via a redox method and subsequent mechanical ball milling. The a-MnO₂/AB composite is composed of approximately 300 nm flower-like amorphous MnO₂ submicron spheres and acetylene black particles with a diameter of about 50 nm. The a-MnO₂/AB electrode exhibits an initial coulombic efficiency of 73.2%, excellent rate capabilities of 318 mA h g^-1 at 9.6 A g^-1, and high specific capacity retention of 1300 mA h g^-1 after 300 cycles at 1 A g^-1. The amorphous structure can provide more channels for rapid lithium-ion transmission due to the disorder and defects, and the ion-diffusion coefficient (∼5 × 10^-7 cm² s^-1) is higher than those of crystalline materials. Due to the strong interactions (Mn-O-C bonds) between MnO₂ and AB as a result of the ball milling, the composite shows low charge transport resistance and small volume changes during the discharging/charging process. This work provides a facile route for the construction of amorphous hierarchically structured Mn-based oxides as anodes for lithium-ion batteries (LIBs).

Synergistically Coupling Black Phosphorus Quantum Dots with MnO2 Nanosheets for Efficient Electrochemical Nitrogen Reduction Under Ambient Conditions

The electrochemical nitrogen reduction reaction (NRR) is a promising strategy of nitrogen fixation into ammonia under ambient conditions. However, the development of electrochemical NRR is highly bottlenecked by the expensive noble metal catalysts. As a representative 2D nonmetallic material, black phosphorus (BP) has the valence electron structure similar to nitrogen, which can effectively adsorb the inactive nitrogen molecule and activate its triple bond. In addition, the relatively weak hydrogen adsorption can restrict the competitive and vigorous hydrogen evolution reaction. Herein, ultrafine BP quantum dots (QDs) are prepared via liquid-phase exfoliation and then assembled on catalytically active MnO₂ nanosheets through van der Waals interactions. The obtained BP QDs/MnO₂ catalyst demonstrates admirable synergetic effects in electrochemical NRR. The monodisperse BP QDs providing major activity manifest excellent ammonia production steadily with high selectivity, which benefits from the robust confinement of the BP QDs on the wrinkled MnO₂ nanosheets with decent activity. A high ammonia yield rate of 25.3 µg h^-1 mg_cat. ^-1 and faradic efficiency of 6.7% can be achieved at -0.5 V (vs RHE) in 0.1 m Na₂ SO₄ electrolyte, which are dramatically superior to either component. The isotopic labelling and other control tests further exclude the external contamination possibility and attest the genuine activity.

Flexible and high-energy-density Zn/MnO2 batteries enabled by electrochemically exfoliated graphene nanosheets

Electrochemically exfoliated graphene nanosheets were proposed for flexible and high-performance Zn–MnO₂ batteries without polymer binder and metal current collectors.

MXene-supported Co3O4quantum dots for superior lithium storage and oxygen evolution activities

A novel hybrid, composed of Co₃O₄quantum dots supported on Ti₃C₂T_x(MXene) nanosheets, exhibits a strong synergetic effect, and shows superior lithium storage (capacity = 766.5 mA h g⁻¹at 2 A g⁻¹after 400 cycles) and oxygen evolution (overpotential = 340 mV at 10 mA cm⁻²) activities.