Electrochemical Chloride Activation by Iridium-Doped Tin Oxide for Oxidative Treatment of Urine Wastewater

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The escalating presence of nitrogen pollutants in urine wastewater poses a significant environmental challenge. Among the array of methods available to tackle this issue, electrochemical oxidation processes that produce reactive chlorine species (RCS) from readily available chloride ions appear as a promising solution. Despite the investigation of various anode materials, current options continue to face challenges such as low selectivity in generating reactive chlorine species (RCS), instability, and significant energy consumption. This study investigated iridium-doped tin oxide (Ir-SnO2) as an efficient, stable, and energy-saving anode for RCS-mediated treatment of urine wastewater. The Ir-SnO2 anode surpassed counterparts like IrO2 SnO2 and Sb-SnO2, showcasing its superior electrochemical performance marked by high current density, minimal charge transfer resistance, and a significant active surface area. Additionally, it attained outstanding current efficiency of 91.7% and energy efficiency of 7.79 mmol Wh-1 for generating reactive chlorine species (RCS) at 30 mA cm–2 in a diluted 0.1 M chloride solution. Density functional theory (DFT) calculations corroborated experimental findings, indicating that the introduction of Ir to SnO2 boosts chlorine adsorption by altering the electronic structure, thereby reducing overpotential and enhancing electrocatalytic activity for chlorine evolution reactions. Ir-SnO2 also showcased impressive effectiveness in removing ammonia nitrogen, total nitrogen, and chemical oxygen demand, achieving efficiencies of 100%, 97.8%, and 89.1%, respectively. These outcomes rivaled those attained by IrO2 (dimensional stable anode, DSA), surpassing the performance of the boron-doped diamond (BDD) anode. Additionally, Ir-SnO2 demonstrated the lowest energy consumption compared to benchmark DSA and BDD anodes when treating urine wastewater. In stability evaluations, the Ir-SnO2 electrode maintained a stable anodic cell potential for 100 hours of continuous electrolysis in a 0.1 M NaCl electrolyte and remained operational over five cycles without any signs of deactivation.