Compared with Pt/C catalysts, non-precious metal (NPM) catalysts, with the advantages of low price and high natural abundance, have received extensive attention as the competitive candidate for fuel cell cathode oxygen reduction reaction (ORR) catalyst. Due to the low metal content and active site density of traditional NPM catalysts, higher catalyst loading is commonly required in real fuel cell applications. However, the thicker catalyst layer will lead to the high mass transfer resistance, reducing the performance of NPM catalyst layer, especially in high current density region. This study provide a new idea for high Co-content catalyst design, based on the SiO2 coated zeolite imidazole framework (ZIF) material. By adjusting the Zn/Co ratio in the ZIF precursor and with or without the protection of and by exploring the influence of coated on the change of SiO2, the ZIF microstructure and Co nanoparticle size were carefully optimized. The introduction of SiO2 shell can effectively avoid the agglomeration of metal nanoparticles, during the high-temperature activation process. However, protective effect of SiO2 is also significantly different for ZIF precursors with different Zn/Co ratios. When the Co content in the catalyst precursor is higher (15%), SiO2 shell can significantly reduce the metal nanoparticle size, which provide a new insight for high metal content catalyst design of alkaline fuel cell cathode catalyst.
Keywords non-precious metal, Co-N-C catalyst, SiO2, Oxygen reduction reaction