Enhanced oxygen reduction reaction performance of Co@N–C derived from metal-organic frameworks ZIF-67 via a continuous microchannel reactor

Abstract

Traditional methods of preparing metal-organic frameworks (MOFs) compounds have the disadvantages such as poor dispersion, inefficient and discontinuous process. In this work, microchannel reactor is used to prepare MOFs-derived zeolite-imidazole material via flash nanoprecipitation to form ZIF-67 + PEI(FNP), which reduces the MOF synthesis time down to millisecond time interval while keeping the synthesized ZIF-67 + PEI(FNP) highly dispersed. The Co@N–C(FNP)catalyst obtained by flash nanoprecipitation and carbonization has a higher Co content and thus more active sites for oxygen reduction reaction than the Co@N–C(DM) catalyst prepared by direct mixing method. Electrochemical tests show that the Co@N–C(FNP) catalyst prepared by this method has excellent oxygen reduction performance, good methanol resistance and high stability. The onset potential and half-wave potential of Co@N–C(FNP) are 0.92 VRHE and 0.83 VRHE, respectively, which are higher than that of Co@N–C(DM) (Eonset = 0.90 VRHE and E1/2 = 0.83 VRHE). Moreover, the Zn-air battery assembled with Co@N–C(FNP) as the cathode catalyst has high open circuit voltage, high power density and large specific capacity. The performance of these batteries has been comparable to that of Pt/C assembled batteries. Density functional theory (DFT) calculations confirm that the Co (220) crystal plane present in Co@N–C(FNP) have stronger adsorption energy than that of Co (111) crystal plane in Co@N–C(DM), leading to better electrocatalytic performance of the former.