A highly stable potentiometric pH sensor based on single-phase perovskite BaIrO₃ nanofibers

In this study, single-phase perovskite BaIrO₃ nanofibers were synthesized by electrospinning and post-calcination with careful control of annealing atmosphere (10 sccm O₂ and 90 sccm He). The synthesized BaIrO₃ nanofibers were applied for potentiometric pH sensing of which performance was compared with that of single Ir-based oxides. Regardless of the reduced noble Ir content, BaIrO₃ nanofibers exhibited excellent sensitivity (super-Nernstian potential response of ca. −67 mV pH⁻¹) and improved reversibility and stability even in very low and high pH regions compared to the nanofibers composed of Ir(0)/IrO₂ and those of pure rutile IrO₂. In fact, BaIrO₃ nanofibers maintained very similar sensitivity for 18 weeks of tested period while Ir/IrO₂ and IrO₂ counterparts showed the significantly decreased sensitivities. In addition, BaIrO₃ nanofibers exhibited superior selectivity to hydrogen ion over alkaline metal ions (e.g., Na⁺ and K⁺). The observed outstanding pH sensing performance of BaIrO₃ was attributed to the sturdy perovskite structure based on strong connectivity between [IrO₆] octahedron units. This study demonstrates the feasibility of perovskite BaIrO₃ as a pH sensing electrode material alternative to or even better than extensively studied Ir oxides.