Engineering spin state modulation through phosphorus-coordinated Fe-NC catalysts for enhanced ORR performance in flexible Al-air batteries

Abstract

The advancement of flexible aluminum-air batteries (AABs) faces a significant obstacle due to the inherently sluggish kinetics of the oxygen reduction reaction (ORR) occurring in the air cathode. To overcome this issue, optimizing the coordination environment of isolated Fe metal centers presents a promising approach for creating high-performance air cathodes. We present a novel phytic acid-assisted approach to incorporate phosphorus (P) into the Fe-NC coordination framework, allowing precise control over doping and coordination structure, which modulates the electronic density and surface polarity, thereby enhancing the graphitic degree, electrochemical activity, and durability of the catalyst. Electrochemical evaluations reveal the Fe-NPC catalyst achieved a higher onset-, half-wave potential (0.99 and 0.88 V vs. RHE), along with a notable lower Tafel slope of 68 mV dec−1. Theoretical studies reveal that P incorporation downshifts the d‐band in the Fe atom, thus weakening the adsorption strength of *OH interaction. Next, micro electro kinetics mapping evaluated through in-situ SECM highlights enhanced surface current of Fe-NPC over other catalysts. Further, the fabricated flexible AABs utilizing Fe-NPC air cathode achieved an OCV of 1.47 V and peak power density of 34.8 mW cm−2. Durability predictions using time-series analysis confirm zero autocorrelation, indicating robust performance of AABs. This study highlights the potential of Fe-NPC as a next-generation catalyst for advanced flexible energy storage applications.