Two-dimensional MnN utilized as high-capacity anode for Li-ion batteries

When developing high performance lithium-ion batteries,high capacity is one of the key indicators.In the last decade,the progress of two-dimensional(2 D) materials has provided new opportunities for boosting the storage capacity.Here,based on first-principles calculation method,we predict that MnN monolayer,a recently proposed 2 D nodal-loop halfmetal containing the metallic element Mn,can be used as a super high-capacity lithium-ion batteries anode.Its theoretical capacity is above 1554 mA-h/g,more than four times that of graphite.Meanwhile,it also satisfies other requirements for a good anode material.Specifically,we demonstrate that MnN is mechanically,dynamically,and thermodynamically stable.The configurations before and after lithium adsorption exhibit good electrical conductivity.The study of Li diffusion on its surface reveals a very low diffusion barrier(~ 0.12 eV),indicating excellent rate performance.The calculated average open-circuit voltage of the corresponding half-cell at full charge is also very low(~0.22 V),which facilitates higher operating voltage.In addition,the lattice changes of the material during lithium intercalation are very small(~ 1.2%-~4.8%),which implies good cycling performance.These results suggest that 2 D MnN can be a very promising anode material for lithium-ion batteries.

Face-to-face heterojunctions within 2D/2D porous NiCo oxyphosphide/g-C_(3)N_(4)towards efficient and stable photocatalytic H_(2)evolution

Constructing 2D/2D face-to-face heterojunctions is believed to be an effective strategy to enhance photocatalytic performance due to the enlarged contact interface and increased surface active sites.Herein,2D porous NiCo oxyphosphide(NiCoOP)was synthesized for the first time and coupled with graphitic carbon nitride(g-C_(3)N_(4))nanosheets to form 2D/2D heterojunctions via an in-situ phosphating method.The optimal 4 wt.%2D/2D NiCoOP/g-C_(3)N_(4)(OPCN)photocatalyst achieves a hydrogen evolution rate of 1.4 mmol·h^(−1)·g^(−1),which is 33 times higher than that of pure g-C_(3)N_(4).The greatly improved photocatalytic performance of the composite photocatalysts could be attributed to the formation of interfacial surface bonding states and sufficient charge transfer channels for accelerating carrier separation and transfer and the porous structure of NiCoOP nanosheets with abundant surface active sites for promoting surface reactions.Amazingly,the 2D/2D OPCN composite photocatalysts also exhibit superior stability during photocatalytic reactions.This study not only designs new noble-metal-free NiCoOP/g-C_(3)N_(4)composite photocatalysts but also provides a new sight in fabricating face-to-face 2D/2D heterojunctions for their application in energy conversion areas.