Preparation Of Pd-Mo₂C-AC Composite Hydrogen Storage Material And Study On Its Hydrogen Storage Properties

Hydrogen is a kind of clean energy with high calorific value and zero carbon emission,and it is considered as a promising alternative to fossil energy to reduce environmental contamination.The key point to implement hydrogen energy lies in the development of cheap and safe hydrogen storage materials that work efficiently at ambient temperature.For this purpose,Mo2C crystals dispersed on the biomass-derived active carbon(AC)was prepared and used as a carrier to load Pd particles to store hydrogen.The preparation method of AC,loading processes and amounts of both Mo and Pd,and the following thermal treatment were optimized in terms of the structure of the formed composites and their hydrogen storage capacities.The main conclusions drawn from the dissertation are shown below.(1)The optimized conditions for converting corn stalk to carbon contains a mass ratio of KOH to feedstock at 3/1 and a decomposition temperature at 800?.Under such conditions,the corn stalk could be totally converted to amorphous AC with 2D layer structures.The specific surface area,pore volume,and the average pore diameter were 2557 m2/g,1.29 ml/g,and 2.0 nm,respectively.At 273 K and a hydrogen pressure of 5 MPa,its hydrogen storage capacity was 0.60 wt%.(2)Pd-Mo2C-AC composites were prepared from biomass-derived active carbon via a stepwise impregnation method.The optimal temperature(3)for the carbonization of Mo species is 700?,and the desired contents of Mo and Pd were 20%and 2%,respectively.The introduction of 20%Mo changed the specific surface area and pore structure of Aslightly but yielding suitable crystals of Mo2C with an average size of 4.7 nm.The appearance of Mo2C promoted the dispersion of Pd significantly due to the strong interaction between Pd and Mo2C,which has been confirmed by the electron transfer from Pt to and Mo2C revealed by XPS data.Such an interaction retarded the sintering of Pd at high temperature and improved the stability of Pd-Mo2C-AC composites.The Pd-Mo2C-AC exhibited excellent repeatability,with the hydrogen storage capacity dropped slightly from 3.03 wt%to 2.89 wt%after ten consecutive H2 storage-release cycles.(4)Co-impregnation of Mo and Pd precursors with the biomass-derived active carbon also led to the highly dispersed Pd-Mo2C-AC composites,which showed the comparable hydrogen storage capacity to their counterpart prepared by the stepwise impregnation method.With the contents of Mo and Pd were controlled at 20%and 2%,respectively,the hydrogen storage capacity of Pd-Mo2C-AC composites prepared by the co-impregnation method was 2.86 wt%and remained still 2.86 wt%even after ten consecutive tests.It suggests the co-impregnation method strongly as a practical method to produce Pd-Mo2C-AC composites.