Nanostructure Preparation Based On Organic Inorganic Acid Alkali Modulation And Electrochemical Performance Study

Morphology of nanomaterials is an embodiment of the functions,which is a hot topic in the fields of chemistry and material science.It is a common sense that controlling pH values by organic-inorganic acid and alkali is feasible to tune morphology,but the formation mechanism of multi-level morphologies is still not clear.In this thesis,the driving force,synergistic effect and growth mechanism of vanadium-based nanomaterials were studied by comparing organic-inorganic acids and alkalis,respectively.We successfully prepared hierarchical structures of nanoflowers,heterojunctions and criss-cross structures,whose electrochemical performance was studied by using them as the electrodes in lithium ion batteries and electrocatalytic oxygen evolution?OER?.The details are as followed:We firstly investigated the regulation effects of different acids on nanostructures of vanadium oxide through adding organic?formic acid and acetic acid?and inorganic acids?sulfuric acid,nitric acid,hydrochloric acid and phosphoric acid?.The results showed that adding formic acid,acetic acid,sulfuric acid,nitric acid induced the formation of nanowire structures.However,vanadium oxide structures evoluted from nanowires,bundles to hierarchical nanoflowers along with increasing amount of hydrochloric acid and phosphate.The results indicated proton as the first driving force leads to the formation of nanoparticles as the assembling units for nanostructures.The coordination effect of phosphate radical is the second driving force for adjusting growth directions,through coordination with exposed vanadium ions at the ledge and kink.As the positive electrode material of lithium ion battery,reductive formic acid increased concentration of V⁴⁺active sites.Hierarchical nanoflowers prepared by phosphoric acid achieves discharge specific capacity of 436.23 m Ah/g at a current density of 0.1 A/g,reaching the theoretical maximum value of vanadium oxide based on insertion/desertion of three lithium ions.The large specific surface area of hierarchical structure and high active site concentration facilitated the diffusion of lithium ion,mitigated volume change and improved catability.Furthermore,we used trienthylamine and ammonia to regulate nanostructures of cobalt-vanadium compounds.The results showed that the cobalt-vanadium compounds had only form amorphological structures by adding triethylamine.However,through the ammonia and calcination temperature,the formation of Macaron and criss-cross cobalt-vanadium compounds were realized.As OER electrocatalyst,compared to other analogues with different crystal phases and morphologies,Macaron Co VO_x@Co VO_yH heterojunction had the best catalytic active sites,with a minimum overpotential of 375m V?100 m A/cm²?and 288 m V?10 m A/cm²?.Macaron Co VO_x@Co VO_yH heterojunction still showed the best cyclic stablity as the anode of lithium ion battery.These results showed that heterojunction structure is beneficial to improve electrochemical performance of nanomaterials.