Controllable Synthesis Of Different Morphologies Of CuGeO₃ And Their Study On Water Electrolysis Properties

The controllable synthesis and structural optimization of nanomaterials are the basis for improving performance.In recent years,one-dimensional copper germanate?CuGeO₃?nanomaterials have received much attention,due to their potential application in electrochemical sensors,photocatalysis and lithium/sodium-ion batteries,but there are still many defects in the synthesis method and morphology controlling at home and abroad.The inefficient synthesis method,the limitation of copper source materials and the lack of different morphologies have hindered the further application research of CuGeO₃.Cu-based materials exhibit excellent OER performance owing to the wide oxidation state of Cu and are promising candidate electrocatalysts.Based on these,this paper aims to develop the synthesis methods of different morphologies of CuGeO₃,achieve efficient production and controllable synthesis of multiple morphologies,reveal the growth mechanism of different morphologies of CuGeO₃,and study the performance of electrolytic water.The main findings are as follows:Using strong acid copper salts as copper sources,optimizing the one-step hydrothermal method,and introducing NaOH solution to accelerate the dissolution of GeO₂ and adjust the pH value of the entire system,CuGeO₃ nanomaterials in the form of nanorods,hexagonal sheets and nano-blocks were efficiently synthesized in the absence of any surfactants.On this basis,adding ethylenediamine?En?as a structure-directing agent,six different sizes??100 nm,200?300 nm,350?500 nm,400?700 nm,1?2?m and 1?3?m?of uniform CuGeO₃ nanowires were successfully synthesized in 8 hours by controlling the volume of En.The improved one-step hydrothermal method successfully solves the problem that CuGeO₃ nanowires could not be prepared with strong acid copper salts,and CuGeO₃ nanowires of different sizes were synthesized in a short time.The influence of reaction parameters such as pH value,reaction time,and the volume of En on the morphology of CuGeO₃ nanowires were systematically studied.Based on the experimental results,the growth mechanism of CuGeO₃ one-dimensional nanomaterials was also proposed.IIIOn the basis of the improved one-step hydrothermal method,HCl solution was added for acidification,which changed the early nucleation of CuGeO₃ and realized controllable particle self-assembly.Three typical morphologies of CuGeO₃,broom-like micro-nanostructure with the length of 10?30?m,3D hierarchical haemanthus-like micro-nanostructure with the diameter of 5?10?m and plush-flower micro-nanostructure with the diameter of?1?m,were efficiently prepared within 6hours.The obtained 3D hierarchical CuGeO₃ micro-nanostructure is still an orthorhombic single-phase structure with uniform size and stable structure,characterized by X-ray diffraction,X-ray photoelectron spectroscopy,field-emission scanning electron microscope and Raman spectroscopy.The effects of reaction time,reaction temperature and pH value of the previous solution were systematically studied,and the three typical morphologies of CuGeO₃ showed the similar growth trend.Then a three-step growth mechanism was proposed to illustrate the growth mechanism of the3D hierarchical CuGeO₃ micro-nanostructure.The pH value plays a decisive role in the aggregation of early single crystal particles to form a polycrystalline embryo.The larger the pH value,the smaller the polycrystalline embryo clumps,and the lower the chance of recrystallization of similarly oriented nanocrystals to form branches,which determines the final morphological characteristics of the 3D hierarchical CuGeO₃micro-nanostructure.The electrolytic water performance of CuGeO₃ with different morphologies was researched,and characterized by electrochemical linear voltammetry curve,Tafel slope,electrochemical active area,EIS,etc.Experimental data showed that the smaller the size of CuGeO₃ nanowires,the better the performance of OER under alkaline conditions.100?200 nm CuGeO₃ nanorod with the largest specific surface area exposes more active sites,reducing the overpotential of OER by 120 mV;Among the three typical morphologies of CuGeO₃,3D hierarchical haemanthus-like micro-nanostructure exhibited the best OER and HER activity,its overpotential of OER was 562 mV@10mA cm^-2 and the Tafel slope was 108 mV dec^-1,and its overpotential of HER was 513mV@10 mA cm^-2 and the Tafel slope is 150 mV dec^-1.This unique hierarchical structure exposes more electrochemical active area,and 3D structure can maintain structural stability and exhibit better catalytic performance during the catalytic process.Pt-CGO-pH2.7-6h successfully prepared by water-bath thermal method and exhibited excellent acidic HER performance,the overpotential of Pt-CGO-pH2.7-6h was only 45mV at the current density of 10 m A cm^-2,the Tafel slope is 48 mV dec^-1,and it showed good stability.A small load of Pt provides more highly active catalytic sites,and the synergistic effect of Pt and CuGeO₃ increases the electrochemical active area,reduces the charge transfer resistance on the surface of the material,and obtains a better HER catalytic activity.