Tuning Iron–Oxygen Covalency in Perovskite Oxides for Efficient Electrochemical Sensing

Transition metal oxides have been extensively explored as novel catalysts for designing electrochemical sensors, but the underlying structure–activity relationship remains poorly understood. Herein, we explore a diverse chemical range of La_1–xSr_xFeO₃ perovskite oxides by evaluating their electrochemical sensing activity toward heavy metals and by determining their electronic structures using density functional theory. We find that tuning perovskite chemistry plays an important role in determining the electrochemical activities and sensitivities, as well as the valence states of Fe. By combining experimental and theoretical analyses, a linear relationship between the Fe–O covalency and the electrochemical activity and sensitivity has been obtained, where LaFeO₃ exhibits the highest activity of 109 mA cm_oxide^–2. Thus, the Fe–O covalency is proposed as a rational activity descriptor for the electrochemical sensing of heavy metals. A novel solid-state gelation method was further developed for the fabrication of perovskite oxide aerogels, based on which a highly efficient electrochemical sensor was constructed with a high sensitivity of 87.06 μM μA^–1 and a low detection limit of 1.7 nM. This work unlocks an effective parameter, that is, Fe–O covalency, for rationally designing Fe-based oxides and deepening the understanding of fundamental parameters to develop highly efficient sensing platforms.