A dual-electrode oxide ion sensor for molten carbonates

Abstract

• A simple sensor for detecting O 2– concentration in molten carbonate was proposed. • The sensor is applicable over both wide temperature and O 2– concentration ranges. • A fast response corresponding to varying O 2– activity can be achieved within a few seconds. • The electrochemical sensor is reliable and reusable with an excellent long-term stability. • The sensor can serve as an indicator for O 2– -involved (electro)chemical reactions. The concentration of oxide ions (O 2– ) determines the physicochemical properties of molten carbonates and modulates (electro)chemical reactions. However, it still lacks an efficient and reliable method to measure O 2– concentration in molten carbonates. Herein, we design a dual-electrode sensor to monitor the O 2– content in real time. For sensing O 2– in the target molten medium, we deliberately selected a Ni/NiO redox couple to serve as an O 2– -responding internal reference membrane electrode (RE in ) assembled in an yttrium-stabilized zirconia tube, which is accessible to achieve a stable and excellent response of O 2– from the bulk melt. To measure the membrane potential of RE in that is associated with the O 2– concentration in the bulk melt, we paired a Ag/Ag 2 SO 4 external reference electrode (RE ex ), which can indicate the potential difference between RE in and RE ex by measuring the open circuit potential (OCP), therefore figuring out the O 2– concentration based on Nernst equation. Taking molten Li 2 CO 3 -Na 2 CO 3 -K 2 CO 3 for example, the homemade dual-electrode sensor is well-responsive with a reliable linear correlation coefficient of R 2 = 0.9992 even the O 2– content is as low as 1.27 × 10 −4 mol kg −1 . The proposed dual-electrode gives clues to the rational design of anion sensor for relatively high-temperature systems.