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 aims to investigate the electrochemical behavior of electrodes composed of Nitrogen-Doped TiO2 (TiO2-yNy), iron-nitrogen-carbon (Fe-N-C), and copper hexacyanoferrate (CuHCF) for energy conversion during the neutralization of acidic solutions under visible electromagnetic radiation. The particle size, morphology, and structural properties of these materials were characterized. Time and frequency domain models/methods were employed to determine kinetic parameters and temporal evolution, as well as to propose reaction mechanisms, providing a comprehensive understanding of the processes involved in each half-reaction. In the analysis of the first-order oxygen reduction reaction (ORR) on Fe-N-C electrodes, both direct 4-electron reduction and hydrogen peroxide formation as an intermediate were observed, demonstrating catalytic activity in acidic and dilute saline solutions comparable to those in more concentrated acid solutions. Nitrogen doping of TiO2, which extends the absorption range of electromagnetic radiation to visible light, enabled photoelectrooxidation reactions of water at low potentials, thereby facilitating significant energy conversion/harvesting. CuHCF electrodes demonstrated efficient sodium ion insertion/deinsertion behavior with low practical irreversibility, which is essential for the integration of the half-reactions in the specific full cell designated for energy conversion across different pH values. Under the experimental conditions used, 62.9 kJ per mol of proton produced (or consumed) was obtained. This study provides valuable insights into materials for photo-assisted energy conversion/harvesting in acid wastewater treatment, emphasizing their potential for more efficient and sustainable solutions.