High-Precision Performance of a Full-Ocean-Depth pH Sensor: Calibration and Assessment under Simulated Hadal Pressure...

Area of Science:

• Oceanography
• Electrochemistry
• Materials Science

Background:

• Hadal zone pH monitoring is vital for deep-sea carbon dynamics.
• Extreme pressures and biochemical conditions challenge current sensors.
• Existing sensors lack robustness and proper calibration for full-ocean-depth use.

Purpose of the Study:

• To develop a robust solid-state electrochemical pH sensor system for hadal zone applications.
• To establish a high-pressure calibration protocol for deep-sea pH sensors.
• To evaluate sensor performance under simulated hadal pressure conditions.

Main Methods:

• Developed a sensor with a sulfonated poly(ether ether ketone)/ionic liquid composite IrO_x working electrode and a pressure-tolerant silica-stabilized ionic liquid reference electrode.
• Established a standardized high-pressure calibration protocol using Tris-artificial seawater buffers.
• Evaluated sensor performance across the full-ocean-depth pressure range (0.1-120 MPa).

Main Results:

• The sensor demonstrated near-Nernstian sensitivity with minimal potential deviations (<1.6 mV or <0.03 pH units) across the pressure range.
• Achieved high reversibility, repeatability, and long-term stability with minimal drift (0.01 pH units over 65 h at 120 MPa).
• Successfully captured pressure-driven acidification in simulated hadal seawater during a 7-day experiment.

Conclusions:

• The developed sensor system is robust and suitable for real-time in situ pH monitoring in the hadal zone.
• Provides a reliable method for calibration and pH assessment under simulated full-ocean-depth pressures.
• Advances the capability to study deep-sea carbon dynamics.