Enhanced hydrogen and methane gas storage of silicon oxycarbide derived carbon

Two polysilsesquioxanes, with an empirical formula (RSiO1.5)(n) R = CH3 (PMS) and CH3-C6H5 (PMPS) were pyrolyzed at 1200 degrees C for 2 h to form SiOC ceramics of variable composition. Etching of polymer-derived SiOC ceramics with chlorine gas at 1200 degrees C produced micro-/mesoporous carbon with a high specific surface area (SSA) reaching up to 2700 m(2)/g, hierarchical pore structure and showing very large pore volumes (up to 1.72 cc/g) without activation. Both, the SiOC precursors and the porous silicon oxycarbide derived carbons (SiOC-CDCs) were characterized in detail. Dissimilarities in the chemical composition and free carbon content of the formed ceramics yielded different microstructures at the nanoscale. This feature affected the final SSA and pore size distribution of the SiOC-CDC materials. The hydrogen and methane storage capacity of the produced SiOC-CDC materials yielded maximum excess gravimetric uptake of 5.5 wt.% H-2 at -196 degrees C and 21.5 wt.% CH4 at 25 degrees C and 60 bar. These values are higher than for other CDCs, nanotubes and activated carbons tested under the same conditions. (C) 2011 Elsevier Inc. All rights reserved.