Electrochemically Driven Acidification Using 3D PANI Mesh Arrays: A Reagent-Free Approach for Sustainable pH Control

Abstract

We present a reagent-free electrochemical setup consisting of a newly developed 3D polyaniline (PANI)-coated stainless steel (PANI-SS) mesh array, which enables efficient pH control in both bulk and small-volume aqueous samples. Specifically, a customized electrochemical cell with a total volume of 40 mL hosts multiple PANI-SS meshes connected in parallel as the working electrode, together with a screen-printed carbon counter electrode and an Ag/AgCl reference electrode. The 3D mesh architecture substantially enhances the electroactive surface area, enabling rapid and scalable proton delivery that can be tuned by varying the number of meshes. A single PANI-SS mesh releases ∼3 μmol of protons upon applying 0.4 V for 200 s, lowering the pH of 40 mL of an NaCl solution from 5.5 to 4.3. Increasing the number of meshes to four further decreases the final pH to 3.4. The system also performs effectively in complex environmental samples such as brackish water, reducing the pH from 7.3 to ca. 3.8. Likewise, it successfully acidifies sediment-seawater suspensions (5% sediment) to the target pH range of 4–5, which is required for certain bioremediation processes. The PANI meshes can be sustainably regenerated through operation in acidic mining leachates, enabling reversible reuse and supporting a circular process. These findings demonstrate the potential of 3D PANI-based systems for efficient, scalable, and environmentally friendly acidification without the use of external chemical reagents.