Hydrogen storage properties of highly cross-linked polymers derived from chlorinated polypropylene and polyethylenimine

Highly cross-linked polymer derived from chlorinated polypropylene (CPP) grafted with polyethylenimine (PEI) was synthesized by hydrothermal amination reaction. The influence of different reaction conditions on the structure and properties of highly cross-linked polymer was investigated. The structures of the polymers named CPP-g-PEI were characterized by Fourier transform infrared (FT-IR) spectroscopy, elemental analysis (EA), 13C solid-state NMR (13C NMR), thermogravimetric analysis (TG), scanning electron microscopy (SEM), transmission electron microscope (TEM), powder X-ray diffraction (PXRD) and nitrogen sorption technique. CPP-g-PEI had honeycomb-like pores with an average size of between 5.37 and 13.54 nm and was thermally stable up to 250 °C. CPP-g-PEI was amorphous porous polymer with some spherulites. The N content of CPP-g-PEI increased and the Cl content of CPP-g-PEI decreased after hydrothermal amination reaction. The hydrogen storage properties of different CPP-g-PEI samples were determined by a hydrogen storage analyzer. Among all samples, hydrogen storage capacity of CPP-g-PEI at 100 °C and triethylamine solvent (CPP-g-PEI-2) achieved the highest hydrogen uptake 11.26 wt% at 77 K, 5 MPa. In addition, OH− type CPP-g-PEI (CPP-g-PEIOH−) exhibited a hydrogen uptake of 2.47 wt% at 300 K, 5 MPa. BET specific surface area of the sample was not directly associated with hydrogen storage capacity. Hydrogen adsorption enthalpy of CPP-g-PEI-2 was calculated by the Arrhenius equation to be 38.79 kJ/mol and the adsorption process of CPP-g-PEI was investigated to be reversible physical adsorption.