Effect of ZIF-8 Crystal Size on the O2 Electro-Reduction Performance of Pyrolyzed Fe–N–C Catalysts

Abstract

Abstract:The effect of ZIF-8 crystal size on the morphology and performance of Fe-N-C catalysts synthesized via the pyrolysis of a ferrous salt, phenanthroline and the metal-organic framework ZIF-8 is investigated in detail. Various ZIF-8 samples with average crystal size ranging from 100 to 1600 nm were prepared. The process parameters allowing a templating effect after argon pyrolysis were investigated. It is shown that the milling speed, used to prepare catalyst precursors, and the heating mode, used for pyrolysis, are critical factors for templating nano-ZIFs into nano-sized Fe-N-C particles with open porosity. Templating could be achieved when combining a reduced milling speed with a ramped heating mode. For templated Fe-N-C materials, the performance and activity improved with decreased ZIF-8 crystal size. With the Fe-N-C catalyst templated from the smallest ZIF-8 crystals, the current densities in H2/O2 polymer electrolyte fuel cell at 0.5 V reached ca. 900 mA cm −2 , compared to only ca. 450 mA cm −2 with our previous approach. This templating process opens the path to a morphological control of Fe-N-C catalysts derived from metal-organic frameworks which, when combined with the versatility of the coordination chemistry of such materials, offers a platform for the rational design of optimized Metal-N-C catalysts.

Metal‐Organic Framework‐Derived Non‐Precious Metal Nanocatalysts for Oxygen Reduction Reaction

“…[89] In order to meet this challenge, Zn-based MOFs are doped with additional transition metals or combined with other MOFs to generate more active sites for ORR. [43,[90][91][92][93] A bimetal-organic framework (bi-MOF) self-adjusted synthesis of support-free porous Co-N-C nanocatalysts were proposed by Sun and co-workers by pyroly sis of Zn/Co bi-MOF (Figure 5). [49] It is worth noting that the composition and morphology of the resultant catalysts can be tailored by changing the Zn/Co ratio in their precursors.…”

Electrocatalysis in Fuel Cells

“…Barkholtz et al optimized the synthesis and post-treatment protocols of ZIF-based Fe-N-C nanocomposites, as well as the membrane electrode assembly (MEA) fabrication process, and achieved an impressive fuel cell performance of 221.9 mA cm −2 at 0.8 V [10]. Armel et al [11] emphasized the importance of the morphology control of Fe-N-C on ORR activity by adjusting the crystal size of ZIF-8, milling speed and heating mode. With the smallest ZIF-8 crystal size (100 nm), the best H2/O2 fuel cell performance of 900 mA cm −2 at 0.5 V was obtained, which was double the value obtained with previous synthesis protocol [11].…”

“…Armel et al [11] emphasized the importance of the morphology control of Fe-N-C on ORR activity by adjusting the crystal size of ZIF-8, milling speed and heating mode. With the smallest ZIF-8 crystal size (100 nm), the best H2/O2 fuel cell performance of 900 mA cm −2 at 0.5 V was obtained, which was double the value obtained with previous synthesis protocol [11]. Zhang and Chen developed a novel method to prepare Fe-N-C catalysts by using a cationic surfactant cetyltrimethylammonium bromide (CTAB) as the template and the negatively charged persulfate ions as the oxidative agent to stimulate the aniline polymerization, resulting in a unique one-dimensional (1D) semi-tubular structure of PANI [12].…”

FeNC catalysts for CO2 electroreduction to CO: effect of nanostructured carbon supports

“…500 nm nanoparticles) are preserved and well dispersed on the support. 10 In contrast, no Fe and N atoms could be detected in rGO, CNT and CNF samples as well as in bare GDL ( Fig. S2 and S3 †).…”