Study On The Structure And Property Of V/Cr Phosphides Under High Pressure

Transition metal phosphides attract wide attention with applications for energy conversion and storage,because of their various structures,good electrical conductivity and stability,and other outstanding physical and chemical properties.Pressure can effectively shorten the distance between atoms and provide additional driving force for easier reaction of phase transition,Combining first-principles calculation with high temperature and high pressure experiments,we studied the high-pressure phase structure,electronic properties,mechanical properties and electrocatalytic properties V-P and Cr-P systems in detail.Firstly,USPEX and CALYPSO software were used for structural search,and several high-pressure phases were found,and their space groups were as follows:Pm 3 n-V₃P、P6-V₁₂P₇、P6₃/mmc-V₅P₃、P6₃/mmc-VP、P2₁3-VP、C2/m-VP₂、P2₁3-Cr P、and Pm 3 n-Cr₃P.Secondly,electronic structure analysis shows that I4₁md-VP and C2/m-VP₂are semi-metallic structures at atmospheric pressure,and the other phases are all metals.P atoms gain electrons from vanadium and chromium.When the proportion of P atoms increases,P-P covalent interactions are enhanced,and partial covalent interactions mainly exist between vanadium and chromium atoms and P atoms,while when the proportion of vanadium and chromium atoms increases,metal bonds between metal atoms and ionic interactions between vanadium and chromium atoms and P atoms mainly exist.The increase of pressure increases the bond length in the structure and strengthens electrovalent bond between vanadium and chromium atoms with P atoms.Finally,the simulation of its mechanical properties shows that the increase of vanadium and Chromium metal atoms decreases the brittleness of the system.In the V-P and Cr-P structures with the same space group,the Young’s modulus and bulk elastic modulus of Cr-P structures are obviously larger than those of V-P structures.In the experiment,pure phase P6₃/mmc-VP and C2/m-VP₂were synthesized by high temperature and high pressure method with nano V and red phosphorus as raw materials,which were consistent with the predicted results of theoretical calculation.using nano-vanadium and red phosphorus particles as raw materials,and their electrochemical catalytic performance was tested after grinding and refining From the experimental results,it can be found that VP show the best electrochemical catalytic activity.When the current density is 10 m A/cm²in 1.0 mol/L KOH solution,the HER overpotential of VP and VP₂is192 m V and 209 m V,respectively.When the current density is 30 m A/cm²,the OER overpotential is 328 m V and 341 m V.By analyzing the d-band center of VP and VP₂,we found that the the d-band center of VP is closer to Fermi surface than VP₂,which plays a crictical role in promoting the electrocatalytic poperty of VP.