Determining the effect of porosities on the hydrogen adsorption capacity of 3D printed PEEK

Abstract

In this investigation, as one of the most common polymer-based materials, polyether-ether-ketone (PEEK) was chosen to study its hydrogen adsorption capacity. The shape and size of porosities control the specific surface area and possible sites of hydrogen adsorption. Therefore, the FDM 3D printing method was utilized to fabricate the PEEK sample with different porosity sizes, and the effect of variation of the process parameters (nozzle temperature and nozzle speed) on the shape and size of porosities and finally, the hydrogen adsorption capacity was evaluated. The effect of the variation of the nozzle temperature on the heat distribution was simulated using COMSOL Multiphysics. The results of the heat temperature distribution exhibited that the shape of the porosities will be differed due to the solidification shrinkage caused by the temperature gradients in the middle areas of the 3D-printed PEEK samples, which was subsequently confirmed by optical microscopy and X-ray Computed Tomography (XCT). Porosities can be classified into three main groups including mesopores, mesopores and macropores. Additionally, 3D printed parts have the porous structure and by designing a porous structure by CAD software, the formation of the macropores and subsequently meso-and micropores is passivated, which can be detected through the XCT results. Consequently, these pores increased the surface area and provide more site for hydrogen adsorption. XCT was carried out, and the results showed the formation of the closed pores, which was decreased by increasing the nozzle temperature due to the presence of the melted filament from 0.64 to 0.19%. The hydrogen adsorption capacity was studied through electrochemical analysis methods including cyclic voltammetry, charge/discharge, and electrochemical impedance spectroscopy. Results showed that the sample was printed with a nozzle temperature of 375 °C and nozzle speed of 30 mm s−1, illustrating the highest electrochemical hydrogen adsorption capacity of 2.66 mAh.g−1, which can be related to the activation of the capillary force and new available sites in the interface of the electrolyte and 3D-printed electrode.