Experimental study on preparation of oxygen reduction catalyst from coal gasification residual carbon

Abstract

Coal gasification fine slag (GFS) produced from industrial entrained-flow gasification plants typically contains a large amount of residual carbon. Using the GFS coal flotation residue as a carbon source for the oxygen reduction reaction (ORR) catalyst is therefore an effective recycling method that will further promote utilization of the solid waste generated during coal gasification. In this study, ORR catalysts were prepared by the acid treatment, activation, and heteroatom doping of residual GFS carbon. The specific surface area (SSA) of the nitrogen-doped porous carbon catalyst, calculated using the Brunauer–Emmett–Teller method, was 1657 m2/g. In addition, N and/or Fe are in the composition of ORR-active sites which are uniformly distributed on the catalyst surface. Although the catalyst exhibited a rich porous structure and a high degree of graphitization, several graphite lattice defects were also present. In the ORR test, the Fe-N-C catalyst reached a limiting diffusion current density of 4.86 mA/cm2 and a half-wave potential of 0.76 V in a 0.1 M KOH electrolyte, in addition to giving a high electron transfer number of 3.77 and following a predominant four-electron pathway. In the zinc-air battery test, the power density of the Fe-N-C catalyst reached 124.2 mW/cm2, and the battery maintained a charging voltage of 1.99 V after 250 charge/discharge cycles. This ORR catalytic performance obtained for the Fe-N-C catalyst indicates the feasibility of preparing an ORR catalyst from GFS carbon residue, and paves the way for further research in this area.