Hydrophobicity engineering of hierarchically ordered SiO2/Fe-N-C catalyst with optimized triple-phase boundary for boosting oxygen reduction reaction

Abstract

The Fe single-atom catalyst (Fe-N-C) with Fe-Nx active sites is considered a promising alternative to Pt-based catalysts for oxygen reduction reaction (ORR). However, the exposure and utilization efficiency of the Fe-Nx site in Fe-N-C lead to a certain competitive distance with Pt-based catalysts in the ORR process. Herein, a space-confinement strategy triggered by SiO2 templates to optimize the ORR triple-phase boundary of Fe-N-C, is reported. As expected, the optimized SiO2(4)/Fe-N-C exhibits excellent ORR activity with a half-wave potential of 0.886 V in 0.1 M KOH. More importantly, the E1/2 loss of SiO2(4)/Fe-N-C is merely 32 mV after 30,000 cycles. Density functional theory (DFT) calculations confirm SiO2-induced carbon defects critically modulate electronic configurations of FeN4 centers, optimizing adsorption energetics of oxygen intermediates. Remarkably, when utilized as air cathodes for zinc-air batteries (ZABs), the device based on SiO2(4)/Fe-N-C displays record-breaking power density (444.10 mW<middle dot>cm-2) with superior long-term durability over 1013 h, outperforming most reported noble-metal-free electrocatalysts. This work provides a new route to optimize the triple-phase boundary of single-atom catalysts for energy storage applications.