Ion-selective-membrane-free high-pressure potentiometric ammonium ion sensing

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Sensing

Background:

• Current solid-contact ion-selective electrodes (SC-ISEs) for ammonium (NH4+) rely on organic ion-selective membranes (ISMs).
• These ISMs present challenges including the water-layer effect and poor mechanical stability.
• There is a need for robust and stable NH4+ sensors, especially for high-pressure applications.

Purpose of the Study:

• To develop an ion-selective membrane-free (ISM-free) sensor for potentiometric NH4+ detection.
• To investigate the use of a bifunctional copper hexacyanoferrate (CuHCF) material as both transducer and recognition element.
• To achieve stable and selective NH4+ sensing under high-pressure conditions.

Main Methods:

• Fabrication of an ISM-free potentiometric NH4+ sensor utilizing a copper hexacyanoferrate (CuHCF) framework.
• Integration of a silver/silver tetraphenylborate solid-contact reference electrode for an all-solid-state system.
• Evaluation of sensor performance, including Nernstian response, selectivity, and stability under 1 MPa pressure.

Main Results:

• The developed sensor demonstrated Nernstian response sensitivity for NH4+ detection.
• The sensor exhibited comparable selectivity to existing methods under 1 MPa pressure.
• Crucially, the ISM-free design eliminated the water-layer effect and ensured long-term stability.

Conclusions:

• A novel concept for ISM-free, high-pressure potentiometric NH4+ sensing has been successfully demonstrated.
• Copper hexacyanoferrate (CuHCF) proves effective as a bifunctional material for NH4+ transduction and recognition.
• This approach offers a promising alternative to conventional SC-ISEs, addressing key limitations in stability and interfacial effects.