Surface Effect On Crystal Structure And Ion Storage Of Prussian Blue Analogs Meso-particles

Structure design at a molecular scale is an important strategy for tailoring the properties of coordination crystals.Recently,the physical/chemical properties of the coordination polymers are known to be affected by the mesoscopic structure changes,which has been recognized as a potential strategy for tailoring the properties of coordination crystals.This thesis focused on a kind of ions vessel-Prussian Blue Analogue.The surface effect related to the crystal structure and ions storage of meso-particles was investigated by scanning electron microscopy,transmission electron microscopy,X-ray photoelectron spectroscopy,infrared spectroscopy,powder X-ray diffraction,nitrogen adsorption-desorption,electrochemical workstations and other tests.The results showed that the Fe²⁺on the surface of Prussian Blue Analogue meso-particles can be oxidized to Fe³⁺to form core-shell structure of the unoxidized particles@oxidized layer.With the increase of hydrogen peroxide concentration,the oxidation degree of the particle surface was enhanced.The surface structure after oxidation preferred to change to a cubic phase,but the core of the particle was a trigonal structure.So the stress was generated at the interface,led to change of the crystal structure depending on the size of the particles.When the degree of the surface oxidation exceeded 11%of the total particle,the crystal structure of particles with a size greater than 100 nm was distorted and changed from trigonal to cubic phase;the crystal structure of the particles with a size less than 100 nm remained unchanged.For particles smaller than 100 nm,surface oxidation could increase the specific capacity and the reversible capacity for long cycles,when used as a cathode for sodium-ion batteries.For particles larger than 100 nm,surface oxidation reduced the specific capacity of the particles,but increases the reversible capacity for long cycles.Prussian Blue Analogue meso-particles preferentially dissociated in acid and the rate of decomposition at the surface was greater than the corners.Therefore,the surface of the cubic particles could be selectively removed by hydrochloric acid to form the mesoframes.When used as the positive electrode for alkali metal ion battery,the mesoframes structure increased the contact area between the particles and the electrolyte,shortened the transfer path of the guest alkali metal ions within the particles,and amplified the influence of the surface.The ions storage of the mesoframes was mainly based on that ions cross the liquid-solid interface,while the solid particles was mainly based on the ions transport in the crystal lattice.Different ions storage modes allowed the mesoframes to exhibit superior performance in storage of lithium,sodium,and potassium ions at high rates.Compared to solid particles,aqueous batteries using mesoframes as electrode had larger storage capacity,better rate performance and more stable performance in multiple charge and discharge cycles.