Hydrogen-induced optical properties of FC/Pd/Mg films:Roles of grain size and grain boundary

摘要

Nanomodification is an effective method to solve the thermodynamic and kinetics limitation of Magnesium(Mg)-based materials,which shows promising application prospects in hydrogen energy field.However,the role of the grain size of pure Mg on the hydrogen-induced performance of the hydrogen sensitive thin film under cyclic hydrogen loading/unloading process at room temperature has rarely been studied systematically.To study the relationship between the structure of Mg layer and the hydrogen-induced optical performance of fluorocarbon(FC)/Pd/Mg films,a series of Mg with different internal structures were prepared by changing the velocity of sputtered atoms under different sputtering powers.The FC/Pd/Mg(40 W)film with fine nanostructure showed faster hydrogenation/dehydrogenation kinetics as well as a larger optical conversion range,which can be attributed to the large population of grain boundaries with high grain boundary energy and more hydrogen diffusion path.As sputtering power gradually increased from 40 W to 300 W,the grain inside films grew larger.The FC/Pd/Mg(300 W)film had more columnar-like regions inside and less grain boundaries with lower energy contributing to slower hydrogen absorption/desorption kinetics and lower optical conversion range.