Long-Term Stable\nReference Electrodes with High-Pressure\nTolerance and Salinity-Independence

The reference electrode’s performance is essential\nfor ensuring\nthe accuracy of electrochemical sensors in marine environments. Yet,\nthe many existing reference electrodes can exhibit sensitivity to\nsalinity variations, potentially leading to inaccuracies in the measurement\nprocess. Herein, we have designed a reliable solid-state reference\nelectrode by introducing SiO<sub><i>x</i></sub>-stabilized\n1-methyl-3-octylimidazolium bis(trifluoromethyl sulfonyl)imide ([C<sub>8</sub>mim<sup>+</sup>] [Ntf<sub>2</sub><sup>–</sup>]) into\na P(VdF-<i>co</i>-HFP) matrix with a SPEEK/[C<sub>8</sub>mim<sup>+</sup>] [Ntf<sub>2</sub><sup>–</sup>] coated Ag/AgCl\nas substrate. The SPEEK/[C<sub>8</sub>mim<sup>+</sup>] [Ntf<sub>2</sub><sup>–</sup>] coating protects the AgCl substrate, and the\nincorporation of SiO<sub><i>x</i></sub> improves the compatibility\nof the IL with the polymer matrix, thereby increasing the electrode’s\nresistance to interference and extending its long-term stability and\nlifespan. The developed reference electrode showed a stable and rapid\nresponse, with potential variations of less than 0.7 mV across various\nsalinity solutions, including practical seawater, lake water, and\ntheir mixture samples. During extended periods of 18 days in deionized\nwater and artificial seawater, the electrode demonstrated negligible\npotential drifts of 0.36 and 0.14 mV/d, respectively. Notably, the\nelectrode could maintain a stable potential even after being stored\nin a preservative solution for 67 days. Furthermore, the electrode\nshowed a stable response to withstand pressures of up to 100 MPa,\ncovering the vast majority of the seafloor. This innovative reference\nelectrode is capable of maintaining a stable reference potential across\nvarious salinities, ionic strength, and full ocean depth, making it\nversatile for use in diverse aquatic environments, underscoring its\nsignificant potential for advancing oceanographic research and enabling\nnew insights into the unexplored depths of oceans.