Preparation and evaluation of modified cyanobacteria-derived activated carbon for H2 adsorption

Abstract

A series of porous carbon sorbents obtained by carbonization and activation by KOH/ZnCl₂ of the abundant waste material cyanobacteria was utilized for the adsorption of H₂. During experiments to determine the optimal activation parameters, the activation time had little effect, whereas the KOH/C and ZnCl₂/C mass ratios and activation temperature had a significant impact on adsorption performance. Samples activated by KOH exhibited better adsorption characteristics (such as higher values of S_BET, V_total, V_micro, etc.) than those activated by ZnCl₂. In particular, ACK-2-8, which had an S_BET of 1951 m² g⁻¹, displayed H₂ uptake capacities of nearly 17.3 mg g⁻¹ at −196 °C and 1 bar. In addition, for evaluation of the H₂ adsorption performance, N-doped and P-doped porous carbons were synthesized using HNO₃, NH₃·H₂O and H₃PO₄, respectively, to modify the abovementioned cyanobacteria-derived activated carbon ACK-2-8, and exhibited H₂ adsorption amounts that were 16.8%, 31.8%, and 45.7% higher, respectively, than those of undoped ACK-2-8. Furthermore, it was remarkable that P-doping in conjunction with a moderately high S_BET enhanced the uptake of H₂ by ACK-2-8-2, which had a smaller S_BET than ACK-2-8-3 but the best uptake capacity of up to 25.2 mg g⁻¹, and thereby showed that the relationship between the H₂ adsorption capacity and S_BET of these materials was scarcely linear and was therefore noticeably different from previously reported results for the uptake of H₂ by other carbon sorbents. Hence, it is probable that the considerable H₂ adsorption properties of the material with a moderate S_BET have great potential applications for hydrogen capture or storage.