Carbon fibre cloth-supported iridium oxide/polyaniline bilayer electrode for solid-state potentiometric pH sensing

In this work, a stable solid-state potentiometric pH sensor was developed by integrating an iridium oxide/polyaniline (IrO₂/PANI) bilayer onto conductive carbon fibre cloth (CFC). The resulting IrO₂/PANI/CFC electrode was fabricated through sequential PANI electropolymerization followed by IrO₂ electrodeposition, forming a binder free hybrid interface that combines the proton responsive conductivity of PANI with hydrated/hydroxylated proton active iridium oxide sites. Morphological, elemental, vibrational, and surface chemical analyses confirmed the successful formation of the IrO₂/PANI sensing layer on the CFC substrate. The electrode exhibited a near-Nernstian response over pH 3-11, with a sensitivity of 58.4 ± 0.9 mV pH^-1, good linearity and an estimated pH resolution of approximately 0.01 pH unit. During continuous pH adjustment in Britton-Robinson buffer from pH 4.5 to 11.1, the electrode maintained a comparable sensitivity of 56.8 ± 1.1 mV pH^-1 without removing or washing the sensor. The electrode also showed limited interference from common cations, reversible pH tracking behaviour, acceptable short-term drift and 96.3% sensitivity retention after 45 days of repeated measurement and storage. Real-sample analysis of vinegar, orange juice, and baking powder solution showed good agreement with a commercial glass membrane pH meter. These results demonstrate the potential of IrO₂/PANI/CFC as a low-cost platform for stable potentiometric pH sensing in practical sample environments.