ساخت آلياژ منيزيم - نيكل نانو ساختار به عنوان ذخيره كننده ي هيدروژن و تاثير حضور نانو ذرات اكسيدي بر خواص آن

چكيده انگليسي :

Investigation on Nano Structure Mg Ni Alloy as Hydrogen Storage Material and the Effect of Nano Oxide Particle on its Properties Akram Shahcheraghy a shahcheraghy@ma iut ac ir April 6 2011 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiProf Ahmad Saatchi Supervisor Email asaatchi@cc iut ac irAssoc Prof Keyvan Raeissi Supervisor Email k raeissi@cc iut ac irAssoc Prof Mohammad Hossein Enayati Advisor Email ena78@cc iut ac irAbstractThe effects of TiO2 additive on the electrochemical hydrogen storage properties of Mg2Ni alloy as anode innickel metal hydride batteries were investigated Mg2Ni alloy was prepared through mechanical alloying The metal powders of Mg and Ni elements mixed in a planetary ball mill for 50 h under an argon protectiveatmosphere Mg to Ni atomic ratio was 2 1 The rotational speed during the ball milling was 500 rpm and theball to powder weight ratio was 20 1 Mg2Ni xTiO2 x 1 5 3 5 and 10 wt composites were alsoproduced by ball milling of produced Mg2Ni and different amounts of TiO2 powders for 2 h by similarprocess described above The crystalline structure and surface configuration of the produced alloys werecharacterized by means of X ray diffractometer XRD transmission electron microscope TEM andscanning electron microscope SEM respectively The produced alloy and composites were demonstrated asthe particles with nanocrystalline amorphous structure The XRD pattern and crystalline size 6 nm have notbeen changed by introducing TiO2 particles TEM images of Mg2Ni particles and 5 wtTiO2 containingcomposite particles after 50 h alloying showed a feature which consists of nanocrystalline grains embeddedin an amorphous matrix can be recognized on light field images of both specimens The average grain size isabout 10 nm which confirms the results obtained by XRD patterns Irregular coarse particles that are usuallyformed during the continuous deformation and cold welding through ball milling process were seen in SEMimages For preparing the working electrode 1 g of alloy powders produced was mixed thoroughly with 5 gNi powder and then compressed under 500 MPa pressure into tablet of 16 mm diameter and 0 6 mmthickness The electrochemical technique used to determine the discharge capacity and cycle stability wasgalvanostat test in 6 M KOH electrolyte at 298 K The first cycle discharge capacities of the samples with 0 1 5 3 5 and 10 wt TiO2 were 62 26 27 80 and 66 mAh g respectively The result showed that the TiO2addition exerts no systematic effect on discharge capacity The lowest amounts of TiO2 1 5 3 wt destroied the discharge capability of the electrode strongly However 5wt TiO2 improved the dischargecapacity greatly On the other hand the highest amount of TiO2 10wt showed no significant improvementas compared to pure Mg2Ni alloy The cycle stability of Mg2Ni has not been affected by TiO2 addition Thepeaks of Mg OH 2 confirm the formation of hydroxide layer on the alloy surface due to charge dischargecycles and the subsequent loss of cycle performance The smooth surface of alloy particles has changed to arough one after the charge discharge cycling indicates the pulverization of this alloy due to the expansion andcontraction of cell volume during charge discharge process The charge discharge kinetics of electrodes wasstudied by using anodic polarization and electrochemical impedance spectroscopy techniques The resultsshowed that the exchange current density which is a measure of electrocatalytic nature of the alloy electrodewas increased by the presence of 5 10 wt TiO2 while adding 1 5 3 wt TiO2 reduced exchange currentdensity The diffusion performance of hydrogen atoms in the electrodes was unchanged in the presence ofTiO2 Result of the anodic polarization confirmed discharge capacity and EIS results The discharge processof Mg2Ni alloy changes from mix controlled at the initial stage of discharge to diffusion controlled at the laststage of discha

شاهچراغي، اكرم

ساخت آلياژ منيزيم - نيكل نانو ساختار به عنوان ذخيره كننده ي هيدروژن و تاثير حضور نانو ذرات اكسيدي بر خواص آن

باتري نيكل-هيدريد فلزي , آلياژ سازي مكانيكي , اكسيد فلزي , خواص الكتروشيميايي