Cotton-derived biochar fibers modified by doping Al2O3 and MgSO4 for application to hydrogen storage

Biochar fiber and activated biochar fibers from cotton fiber were prepared by carbonization at 400-700°C and activation with 5 wt.% Al2O3 and MgSO4, respectively. The final products were characterized by BET, FTIR, XRD, and SEM-EDS. The hydrogen storage of the final products at 1.5 bar pressure and room temperature was studied. The objective of this research was to study the effects of Al2O3 or MgSO4 on activation and doping of Al or Mg compounds on cotton fibers and hydrogen storage of products at low pressure and room temperature. The results showed that the surface areas, micropore volumes, and average pore sizes developed well with increasing carbonization temperatures from 400°C to 700°C. In addition, the surface functional groups such as OH, C=O, COOH and C-O-C were also more developed with increasing carbonization temperature. Furthermore, the results confirmed that MgO or Al2O3 accumulated on the surface of the composites. The results of hydrogen storage showed that hydrogen uptake capacity due to spillover mechanism increased with increasing of carbonization temperature from 400°C to 700°C during the preparation of biochar fiber and activated biochar fibers. The hydrogen capacity at room temperature and 1.5 bar fell within the range of 0.32-0.44 wt.%, 0.45-0.52 wt.%, and 0.59-0.63 wt.% for biochar fiber, Mg-activated biochar fibers, and Al-activated biochar fibers, respectively. This is because hydrogen molecules bonded on the surface of the products with physisorption. Therefore, hydrogen desorbs even at low temperature. It was concluded that metal biochar fibers made from cotton fiber with doping and activation by Al2O3 and MgSO2 at 400-700°C are candidate adsorbers for hydrogen storage under 1.5 bar and room temperature with fast kinetics (within 30 min), quite high sorption selectivity/capacity (up 0.63 wt.%), and sorption stability/reversibility (at room temperature and 80°C).