The efficiency of an electrochemical oxidation/reduction process strongly depends on the ratio of working electrode’s surface area to volume ratio. By making electrodes flexible and employing different configuration such as roll-to-roll membrane, the surface area to volume ratio can be enhanced, therefore improving the overall efficiency of electrochemical oxidation/reduction processes. For the first time, we demonstrate the fabrication of self-supported polypyrrole flexible electrodes, using electropolymerization of pyrrole, for the electrochemical reduction of nitrite in drinking water. To further enhance the electrochemical efficiency and mechanical stability of as-prepared electrodes, different nanoparticles, such as boron-doped diamond, silver, and titanium dioxide are incorporated into the polymer matrix. The homogenous dispersion of nanoparticles in the polymer matrix is demonstrated by SEM and EDX. FTIR shows that nanoparticles do not form any chemical bonds with the as-prepared polypyrrole electrodes and are incorporated in the polymer matrix. Stress-strain curves and bending tests are used to evaluate the mechanical stability of the flexible electrodes and it is observed that the mechanical stability of the electrodes, increases with the incorporation of the nanoparticles. Furthermore, the environmental application of polypyrrole flexible electrodes is determined using the electrochemical reduction of nitrite under potentiostatic conditions. Linear scan voltammetry (LSV) clearly demonstrates the reduction of nitrite based on a higher current response for polypyrrole base electrodes. A nitrite reduction peak, in addition to a higher current response, for nanoparticle embedded polypyrrole electrodes, is observed starting at -0.5V. Over a 6-hour reduction time, the quantitative reduction of nitrite is also evaluated in an electrochemical cell under potentiostatic conditions at various potentials. It is observed that the highest faradaic efficiency of N<sub>2</sub> formation (51%) and faradaic efficiency of nitrite reduction (6.27%) is achieved at a potential of -0.8V. At higher potentials, the nitrite reduction competes with H<sub>2 </sub>evolution, thereby reducing the faradaic efficiency of nitrite reduction. On the sustainable side, polypyrrole is a biocompatible conducting polymer and benefitting from its flexibility, can be used as the next generation of electrodes for electrochemical treatment processes.

Self-supported polypyrrole flexible electrodes for electrochemical reduction of nitrite

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