Precision Engineering of PVC‐Carbon Allotrope Interactions for Advanced Potassium Ion Sensors: Achieving High Sensitivity and Long‐Term Stability

Ions are ubiquitously present in all research fields, having an impact on living organisms. As such, the development of ion sensors is crucial in multiple fields, including diagnosis, agriculture, and water quality analysis. However, the long‐term stability of ion‐selective electrodes is limited by the poor reliability of conventional polymer‐based capacitive interlayers, which are prone to oxidation, water uptake, and high electrochemical noise. To address this challenge, we present the first systematic study of six carbon allotropes, graphene flakes, graphite, single‐ and multi‐walled carbon nanotubes, graphitised mesoporous carbon, and carbon black, as ion‐to‐electron transducers in PVC‐based potassium‐selective electrodes. By correlating morphology, crystallinity, and impedance characteristics with electrochemical outcomes, graphene was identified as the optimal interlayer, achieving ultra‐low noise (27 µV h −1 ) and minimal drift (105 µV h −1 ), while single‐walled carbon nanotubes exhibited record‐low noise (11.6 µV h −1 ) but reduced stability. The origins of these differences were investigated in terms of charge–transfer resistance, capacitance, and interfacial morphology. Density functional theory simulations were performed, demonstrating a strong correlation with these experimental observations. Furthermore, we demonstrated that non‐equilibrium methodologies such as pulse‐amperometry and pulse‐voltammetry significantly enhance sensitivity beyond the Nernstian limit, with values up to 132 mV decade −1 , compared to 84 ± 17 mV decade −1 for graphene flakes under standard potentiometry. Finally, we introduced a cost‐effective and eco‐friendly aerosol‐assisted deposition method to fabricate interlayer/sensing PVC ionophore films with controlled microstructure, composition, and thickness. These results establish a clear structure–property–performance framework for carbon‐based interlayers and highlight graphene flakes as a practical route toward developing stable, miniaturised, and high‐sensitivity potassium ion sensors for biomedical, environmental, and wearable applications.