Effect of Pyrolysis Conditions on the Performance of Co-Doped MOF-Derived Carbon Catalysts for Oxygen Reduction Reaction

MOF-derived porous carbon is a type of promising catalyst to replace expensive Pt-based catalysts for oxygen reduction reaction (ORR). The catalytic activity for ORR depends closely on pyrolysis conditions. In this work, a Co-doped ZIF-8 material was chosen as a research object. The effect of pyrolysis conditions (temperature, heating rate, two-step heating) on the ORR performance of ZIF-derived carbon catalysts was systematically studied. The Co-ZIF-8 catalyst carbonized at 900 degrees C exhibits better ORR catalytic activity than that carbonized at 800 degrees C and 1000 degrees C. Moreover, a low heating rate can enhance catalytic activity. Two-step pyrolysis is proven to be an effective way to improve the performance of catalysts. Reducing the heating rate in the low-temperature stage is more beneficial to the ORR performance, compared to the heating rate in the high-temperature stage. The results show that the Co-ZIF-8 catalyst exhibits the best performance when the precursor was heated to 350 degrees C at 2 degrees C/min, and then heated to 900 degrees C at 5 degrees C/min. The optimum Co-ZIF-8 catalyst shows a half-wave potential of 0.82 V and a current density of 5.2 mA center dot cm(-2) in 0.1 M KOH solution. It also exhibits high content of defects and good graphitization. TEM mapping shows that Co and N atoms are highly dispersed in the polyhedral carbon skeleton. However, two-step pyrolysis has no significant effect on the stability of the catalyst.