Improving Oxygen Electroreduction Efficiency of Porous Silicon-based Catalysts via Atomic Iron Site-Induced Lattice Expansion.

Developing non-noble metal-based catalysts as alternatives to precious metals for the 4 electron oxygen reduction reaction (ORR) in acidic conditions is crucial in advancing practical proton-exchange membrane fuel cells (PEMFCs) technology. A significant challenge in designing these electrocatalysts is to suppress metal leaching and optimize the adsorption and dissociation free energy of oxygen intermediates during the reaction. Herein, a carbon-encapsulated porous silicon (Si) featuring single iron (Fe) sites was developed as an effective ORR catalyst through a one-step thermal reduction process using silica nanoparticles as precursors. This catalyst exhibited both impressive activity with half-wave potentials (E1/2) of 0.88 V and 0.95 V, alongside robust stability showing minimal decay of 7 and 4 mV after 40,000 potential cycles under acidic and alkaline conditions, respectively. Additionally, as a cathode catalyst in PEMFCs, it reached a peak power density of 0.63 W cm-2 in a 1.0 bar H2-O2 condition, while maintaining notable durability at a constant potential of 0.5 V over a duration of 100 h. Spectroscopic characterizations and theoretical calculations demonstrated that iron atoms were effectively integrated into the crystal lattice of porous Si, resulting in the formation of stable Si─Fe bonds that inhibited the leaching of Fe and the formation of *OOH intermediates, thereby enhancing the ORR performance. This approach facilitates the design of efficient and stable ORR catalysts, which hold significant implications for the advancement of next-generation PEMFCs.