Electroreduction of hexavalent chromium using a polypyrrole-modified electrode under potentiostatic and potentiodynamic conditions.

Polypyrrole (ppy)-modified electrode was used for electroreduction of Cr(VI) and showed favorable advantage with extremely higher removal percentage and current efficiency over stainless steel (SS) electrode. In potentiostatic (PS) process and in stagnant solution, ppy electrode achieved a Cr(VI) removal efficiency of 16% and a current efficiency of 23% compared to 0 for SS electrode at a potential of -0.8V. In potentiodynamic (PD) process and in stagnant solutions, ppy electrode exhibited a Cr(VI) removal efficiency of 56% at a potential range from -0.8 to 0.8V whereas SS electrode presented none at the same conditions. Solution stirring promoted mass transportation and dramatically improved Cr(VI) removal efficiency, achieving 92% (ppy electrode) and 18% (SS electrode) in PS process and 100% (ppy electrode) and 36% (SS electrode) in PD process at 100rpm. ppy electrode exhibited an efficient Cr(VI) reduction at a wide potential range from -0.8 to 0.8V than the potential ranges of -0.8 to 0V and 0-0.8V. While ppy stability under PD condition of -0.8 to 0.8V was not as satisfactory as PS condition at -0.8V, but better than PS condition at 0.8V. These results demonstrate that ppy-modified electrode in PD process may be a promising alternative for Cr(VI) electroreduction.