Urea treated metal organic frameworks-graphene oxide composites derived N-doped Co-based materials as efficient catalyst for enhanced oxygen reduction

Calcining pristine metal organic frameworks in an open system to synthesize N-doped carbon materials always lead to some drawbacks, such as relatively low graphitization degree and great loss of heteroatoms, and these factors greatly influenced the oxygen reduction performance of catalysts. In this work, a closed calcination method with three steps pathway has been developed to calcine the in-situ synthesized Co-MOF-GO/Urea composite to obtain the highly graphitized and high N content materials as enhanced oxygen reduction catalysts. During the pyrolysis process, the urea not only served as the additional N source, but also played the role of etching the pore structure by using the produced ammonia gas from polycondensation reaction. After careful adjustment the mass ratio of urea and graphene oxide, a Co-GO-C/N catalyst with high specific surface area, increased N content and abundant of pore structure has obtained. When being used for electrochemistry oxygen reduction reaction, the optimal Co-GO(50)-C/N(2.5) catalyst exhibits almost comparable oxygen reduction performance with the Pt/C in alkaline media, and the onset and half-wave potentials of which are 92 mV and 97 mV higher than that of pristine Co-MOF derived Co-GO(0)-C/N(0) catalyst. In addition, it also exhibits excellent methanol and ethanol tolerance and outstanding long-term durability.