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

Abstract

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 °C exhibits better ORR catalytic activity than that carbonized at 800 °C and 1000 °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 °C at 2 °C/min, and then heated to 900 °C at 5 °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·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.

Co-Incorporated N-Doped Micro–Meso Porous Carbon as an Electrocatalyst for Oxygen Reduction Reaction and Zn–Air Battery

“…This heteroatom content is found to be beneficial as they can perform as active centers due to the synergy between the carbon and the heteroatoms. Also, compared with other preparation methods, MOFs as a precursor can provide better control on heteroatom doping due to the periodicity in the arrangement of atoms in MOFs. − However, pristine MOF-derived carbon possesses limited activity due to the agglomeration of excess adjacent metal particles and the associated reduction in the effective surface area available to initiate electrocatalytic activity. − Recent studies reported that the use of biomass-derived activated carbon as a support material for MOFs and MOF-derived transition-metal-doped carbon can impart enhanced ORR performance due to the uniform dispersion of metal-active sites throughout the carbon support. The catalysts imparted better electrocatalytic activity in an alkaline electrolyte medium.…”