Iron Catalysts Derived from Hybrid-ligand MOF for Oxygen Reduction Reaction
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In the past decade, platinum-group-metal (PGM) free catalysts for oxygen reduction reaction are attracted extensive attention due to the high cost of PGM catalysts of proton exchange membrane fuel cells (PEMFCs). In particular, PGM free catalysts derived from metal-organic frameworks (MOFs) have been studied extensively due to their rich micropores, high surface areas, and highly ordered structures. Among all kinds of PGM free MOF catalysts, iron catalysts are generally considered as the most promising candidate, because the electrochemical performance of iron catalysts is much better than the other metal catalysts. The primary purpose of this thesis is trying to find a new method of synthesizing single iron atom catalysts for ORR, using binary ligands, to obtain not only highly active but also incredibly stable iron catalysts featured with different structures and morphologies. The precursors of the catalysts are synthesized by mixing ligands and metal salts. Through a one-step thermal activation, the nitrogen coordinated single Fe atom catalyst is obtained. Several kinds of physical characterizations are used to reveal the morphology, structure, pore structure and surface area of catalysts. To compare the performance of mixed-ligand MOF catalysts to single-ligand MOF catalyst, cyclic voltammetry, staircase voltammetry and some other tests were employed. The best catalyst of SDS-5Fe exhibited a half-wave potential of 0.865 V vs. RHE, and the stability test showed over 70% of the performance remained after forty hours’ test. The characterization test showed it had the highest BET SSA of more than 800m2/g. However, the remarkable enhanced ORR performance is still hard to reflect a significant improvement in fuel cell performance. We need to solve severe performance degradation caused by waterflood or other problems.