Volume Dependence of Hydrogen Diffusion for Sorption and Desorption Processes in Cylindrical-Shaped Polymers

Polymers

Kyu Tae Kim¹  Seung Hoon Nahm²  Jae Kap Jung²  Un Bong Baek² 

[1] Electricity and Magnetism Group, Korea Research Institute of Standards and Science, Daejeon 34113, Korea;Hydrogen Energy Materials Research Center, Korea Research Institute of Standards and Science, Daejeon 34113, Korea;

关键词: polymer;    hydrogen diffusion;    hydrogen uptake;    sorption;    desorption;    numerical simulation;   

DOI  :  10.3390/polym14040756

来源: DOAJ

【 摘 要 】

In the actual application of gas transport properties under high pressure, the important factors are sample size dependence and permeation efficiency, related to gas sorption. With a modified volumetric analysis technique, we firstly measured the overall diffusion properties and equilibrium times for reaching the saturation of hydrogen content in both hydrogen sorption and desorption processes. The measured parameters of total uptake (C_∞), total desorbed content (C₀), diffusion coefficient in sorption (D_s), diffusion coefficient in desorption (D_d), sorption equilibrium time (t_s) and desorption equilibrium time (t_d) of hydrogen in two polymers were determined relative to the diameter and thickness of the cylindrical-shaped polymers in the two processes. C_∞ and C₀ did not demonstrate an appreciable volume dependence for all polymers. The identical values of C_∞ and C₀ indicate the reversibility between sorption and desorption, which is interpreted by the occurrence of physisorption by sorbed hydrogen molecules. However, the measured diffusivity of the polymers was found to be increased with increasing thickness above 5 mm. Moreover, the larger D_d values measured in the desorption process compared to D_s may be attributed to an increased amorphous phase and volume swelling caused by increased hydrogen voids and polymer chain scission after decompression. The t_s and t_d were found to be linearly proportional to the square of the thickness above an aspect ratio of 3.7, which was consistent with the numerical simulations based on the solution of Fick’s law. This finding could be used to predict the t_s in a polymer without any measurement, depending on the sample size.

【 授权许可】

Unknown