Synergistic charge-regulation of Fe-N4O1 sites coupled with MnO2 clusters via dual-ligand effect for enhanced oxygen reduction reaction

Abstract

It is challenging to rationally construct synergistic charge-regulation of active sites and a lower energy barrier of the determining step for efficient oxygen reduction reaction (ORR). In this work, a novel catalyst (MnO₂)_cluster/Fe,Mn-N-C with Fe-N₄O₁ site coupled by MnO₂ sub-nanometer clusters was successfully synthesized, which is attributed to the dicyanodiamine-glycine (DCD-Gly) dual-ligand effect. Specifically, the higher electrophilic index and the preferential coordination with Fe of N in DCD, and the chelating coordination of Gly with Mn. Experimental and theoretical calculation results indicate that preferential coordination of Fe with N atoms in DCD generates Fe-N₄O₁ sites with axial oxygen coordination, while the coordination of Mn with Gly generates a large number of MnO₂ sub-nanometer clusters. DFT calculations showed that axial oxygen altered the reaction-determining step of ORR at the FeN₄O₁ site. Meanwhile, the MnO₂ sub-nanoclusters further lowered the adsorption energy barriers of the reaction intermediates. This synergistic charge-regulation improved the ORR performance of (MnO₂)_cluster/Fe,Mn-N-C (E_1/2 = 0.90 V). Meanwhile, (MnO₂)_cluster/Fe,Mn-N-C catalyst also exhibits a discharge power density of 201 mW cm⁻² in Zn-air batteries, which was much higher than the commercial Pt/C+RuO₂. The strategy of ligand effect-driven construction provided a new idea for the electronic structure modulation of a monatomic catalyst.