In-situ catalytic conversion of coal pyrolysis gas to nanoporous carbon rods and superior sodium ion storage performance

Pyrolysis is the primary step for many coal conversion and utilization technologies such as combustion, gasification, activation and cascade utilization. To increase the utilization value of coal pyrolysis gas, this study explores an efficient solution by in-situ conversion of pyrolysis gas into a new type of nanoporous carbon rods, which deliver an excellent performances as a sodium ion battery anode. The conversion was achieved by an MgO-assisted chemical vapor deposition (CVD) process, in which abundant small organic gases (i.e., CH4 and C-2 similar to C-3) and volatile molecules condensable at ambient temperature during bituminous coal pyrolysis could be effectively catalytically deposited onto MgO template and further converted to solid carbon under high temperatures. A series of characterizations of solid, liquid and gaseous products obtained with or without MgO-assisted CVD demonstrated the successful conversion of pyrolysis gas into functional solid carbon while reducing the yield of undesired coal tar. The obtained nanoporous carbon rods (NPCR-850) inherited the rod-like morphology of MgO templates and showed multiple structural merits, including a hierarchical pore configuration with abundant mesopores, good structural stability, and a low oxygen content. When employed as an anode for sodium ion storage, NPCR-850 anodes could maintain a high reversible capacity of 181 mA h g(-1) at 0.2 A g(-1) even after 2000 charge/discharge cycles, corresponding to an outstanding capacity retention of 90%. This study proves the feasibility of the conversion of pyrolysis gas to high-value solid carbon materials and provides a facile pathway to synthesis nanoporous carbon rods for electrochemical Na+ storage.