Fabrication of an All-Solid-State Carbonate Ion-Selective Electrode with Carbon Film as Transducer and Its Preliminary Application in Deep-Sea Hydrothermal Field Exploration

Real-time measurements of carbonate ion concentrations in the ocean are critical to advancing marine environmental monitoring and research into deep-sea hydrothermal activity. Herein, we report the first example of deep-sea hydrothermal field exploration using a carbonate ion-selective electrode (ISE). The novel carbonate ISE was composed of a Ni wire as substrate, carbon film as transducers and carbonate-selective membrane layers. This paper describes the preparation process of the electrode and characterises its performance via scanning electron microscopy (SEM) and electrochemical analysis. The detection limit of the electrode for CO32− is 2.821 × 10−6 mol/L, the linear response range is 1.0 × 10−5–1.0 × 10−1 mol/L and the Nernst slope was −30.4 mV/decade. In April 2021, the carbonate ISE was mounted on multi-parameter sensors with pH and Eh (redox) electrodes for the search of hydrothermal activity at the Southwest Indian Ridge. The simultaneous potential anomalies appeared at this carbonate electrode with the pH and Eh electrodes when passing through the hydrothermal field. The study of the hydrothermal field was supported by the in situ camera video and the sulphide samples. Additionally, the carbonate electrode provides enhanced information of water chemistry for the study of the hydrothermal field.