Self-repairing nanoporous MCNT/Ag/AgCl composite electrode as a low-cost and long-term stable marine potentiometric sensor

Maintenance-free, cost-effective, and long-lasting potentiometric sensors are highly anticipated for marine detection. Solid-state silver/silver chloride (Ag/AgCl) is considered the most suitable non-polarizable electrode for that purpose. However, the conventional fabrication of thin-film or porous Ag/AgCl electrodes has limitations in the case of simultaneous cost-effectiveness and stability endurance. In the present study, the multi-walled carbon nanotube (MCNT)/Ag/AgCl composite electrode with a 70 mg/cm2 Ag load was prepared, having nanoporous MCNT/Ag conductive skeleton, and a three-dimensionally spreading Ag/AgCl thin layer. The prepared MCNT/Ag/AgCl composite electrode showed an excellent electrode performance, including low resistance, high exchange current density, and stable potential with long-term stability and low cost. The process kinetics and self-repairing mechanism between Ag and AgCl with the help of MCNT were elucidated. The usage of MCNT/Ag/AgCl composite electrode as a solid-state reference electrode and ocean electric field sensor was successfully evaluated, which provides a promising marine potentiometric sensor application for this nanoporous metal composite electrode via a novel preparation method.