R. Rodriguez, A. Mendoza, M.I. Rahman, G.M.M. Hossain, C. Carrillo, A.H. Jalal
The University of Texas Rio Grande Valley,
United States
Keywords: chloroform detection, SPEEK, PEMFC sensor, sulfonation
Summary:
Chloroform detection is of critical importance due to its hepatotoxic and carcinogenic nature and its ubiquitous presence in industrial emissions, water supplies, and medical settings. Prolonged exposure to chloroform may cause severe liver and kidney damage, necessitating the development of highly sensitive and scalable sensors for early detection and exposure mitigation. Therefore, this study presents a novel approach for detecting chloroform by developing a sulfonated polyether ether ketone (SPEEK) based proton exchange membrane fuel cell (PEMFC) sensor for potential environmental monitoring, industrial safety, and healthcare diagnostics applications. The SPEEK is derived from its precursor – PEEK, in pallet form, which was first cryogenically treated in liquid nitrogen to facilitate grinding into a fine powder and subsequently sulfonated using concentrated sulfuric acid. The sulfonation process was carefully optimized by varying reaction times at 7 hrs. using titration to achieve membranes with desirable electrochemical properties. SPEEK solution was carefully poured into deionized (DI) water. This transfer was performed in a circular motion to ensure even distribution and the spaghettification of the SPEEK. The resultant white, spongy, and spaghetti-shaped SPEEK was then subjected to multiple washes with DI water until the pH of the SPEEK increased to 5. SPEEK membrane was synthesized using the solution casting method, where a small amount of SPEEK was dissolved in dimethyl sulfoxide (DMSO). After fully dissolved, the solution was carefully dispensed onto flat glass substrates. This solution was then transferred to an oven and dried at 60°C for ~5 hours to ensure complete evaporation of the solvents, resulting in a solid SPEEK membrane. The membrane was cut with a dimension of 1 cm x 1 cm. A hydraulic hot press achieved a sandwich structure of the membrane electrolyte assembly (MEA) with an optimized temperature, pressure, and time at 75 ˚C, 17.5 MPa, and 10 min., respectively. Two pieces of Monel mesh were used as an anode and cathode for the PEMFC applications. In the PEMFC sensor, chloroform is oxidized at the anode, generating proton (H+ ions) that pass through the SPEEK membrane. At the other end, the ambient oxygen is reduced at the cathode. The overall mechanism of the PEMFC sensor follows Nernst’s equation. The sensor’s performance was evaluated using open circuit potential (OCP) measurements and amperometric responses. The PEMFC exhibited OCPs of chloroform and humidity of 1.6 mV and 2.2 mV, respectively, indicating electrochemical stability over time. A stable potential window exists between chloroform and humidity signals over time. When exposed to chloroform vapour in the anode, the sensor produced a peak current output of -34.17 mA over at ~50s, demonstrating its dynamic detection capabilities. These findings underscore the device’s potential for chloroform detection, particularly in environments where chloroform emissions pose significant risks. The scalable and cost-effective SPEEK membranes ensure large-scale applicability, such as improving electrochemical performance and stability for long-term use. This work integrates advanced materials and precise electrochemical characterization to create a transformative sensor for chloroform detection, setting a new benchmark in environmental, industrial, and biomedical monitoring.