Chemically Welded, Capillary‐Printed Ion‐Selective Membranes for Durable Solid‐State Chloride Sensors in Dynamic Marine Environments

ABSTRACT

Salinity is a critical environmental parameter governing ocean circulation, biogeochemical processes, and ecosystem health, yet existing conductivity‐based sensors remain costly and sensitive to variations in ionic composition. Here, we present a low‐cost, scalable potentiometric chloride (Cl ⁻ )‐sensing platform for salinity monitoring in dynamic marine environments. The system integrates a chemically welded ion‐selective membrane (ISM) fabricated via capillary‐bridge printing using controlled meniscus deposition and a miniaturized Ag/AgCl reference electrode. This printing process is modeled as a function of contact angle, tip speed, and viscosity, enabling precise control of membrane thickness and interfacial bonding. The meniscus‐driven deposition is coupled with polymer–substrate interpenetration, ensuring strong adhesion and structural uniformity. The resulting ISM suppresses the formation of an interfacial water layer and exhibits enhanced resistance to delamination under prolonged aqueous exposure. The Cl ⁻ ‐selective electrodes exhibit a stable response at environmentally relevant concentrations, with low variability and reduced drift, while the custom reference electrode achieves stable performance with minimal concentration dependence. Ocean deployment demonstrates robust performance under strong salinity gradients and tidal dynamics. Differences between Cl ⁻ ‐derived and conductivity‐derived salinity measurements are analyzed in relation to ionic composition, demonstrating the complementary roles of selective and non‐selective sensing.