Research on electrochemical behaviour of reference electrodes for corrosion test under high hydrostatic pressure for simulating deep-sea

Abstract

• The effects of 0–80 MPa hydrostatic pressure on the performance of three different reference electrodes were studied. • Hydrostatic pressure accelerated the potential fluctuation range and the destruction of the electrode surface. • Hydrostatic pressure promotes the penetration of NaCl solution into the electrode, causing AgCl on the surface to decompose into Ag. • Ag/AgCl reference electrode made by the electrolytic chlorination method is suitable for use in the deep ocean. The reference electrode is one of the most crucial parts of electrochemical testing. However, there is little research on the performance of the deep-sea reference electrode. In this work, three different deep-sea reference electrodes were fabricated, high-purity zinc reference electrode and two kinds of Ag/AgCl reference electrode made by the pressed pellets and the electrolytic chlorination method. The effect of deep-sea hydrostatic pressure varying from 0 MPa to 80 MPa on the electrochemical behaviour in 3.5 wt% NaCl solution was investigated. The potential stability test results showed that the three electrodes’ potentials were relatively stable in the atmospheric environment. At 80 MPa, the potential of the zinc electrode was undulant, the maximum fluctuation range was 0.360 V, and its surface corrosion was severe. As the hydrostatic pressure increased to 80 MPa, the embryo body of the Ag/AgCl electrode prepared by the pressed pellets method became loose and infiltrated amounts of NaCl solution. The potential fluctuation reached 0.036 V. For the Ag/AgCl reference electrode produced by the electrolytic chlorination method, its potential fluctuation under high hydrostatic pressure was not significant, which was 0.003 V. The exchange current density obtained by polarization curve fitting reached 1.281 mA/cm 2 at 80 MPa. The equivalent circuit fitted to the electrochemical impedance spectroscopy indicated that the internal resistance increased slowly with the hydrostatic pressure. The highest value was only 1906 Ω•cm 2 .