Electrochemical system of nitrogen-doped TiO2, Fe–N–C, and copper hexacyanoferrate electrodes for photo-assisted energy conversion in acidic wastewater treatment

Abstract

This study explores the electrochemical behavior of nitrogen-doped TiO₂ (TiO_2−yN_y), iron–nitrogen–carbon (Fe–N–C), and copper hexacyanoferrate (CuHCF) electrodes for energy conversion during acidic solution neutralization under visible light. The materials were characterized for particle size, morphology, and structural properties. Time and frequency domain models were applied to determine kinetic parameters and propose reaction mechanisms. Fe–N–C electrodes demonstrated catalytic activity through both direct 4-electron reduction and hydrogen peroxide formation during the oxygen reduction reaction in acidic solution. Nitrogen doping extended the absorption range of TiO₂ to visible light, enabling photoelectrooxidation at low potentials and improving energy conversion efficiency. The CuHCF electrode demonstrated low charge transfer resistance associated with sodium ion insertion/deinsertion, with sufficient ionic mobility to ensure minimal energy loss. This characteristic is essential for the integration of half-reactions in full cells operating in acidic and neutral electrolytes. Under the employed experimental conditions, 62.9 kJ per mole of protons produced or consumed was captured after the first cycle. These findings emphasize the potential of these materials for enhanced, sustainable energy harvesting in acid wastewater treatment.