Enhancing H2O2 Generation Using Activated Carbon Electrocatalyst Cathode: Experimental and Computational Insights on Current, Cathode Design, and Reactor Configuration

Granular activated carbon (GAC) serves as a cost-efficient electrocatalyst cathode in electrochemical water treatment. This study investigates the impact of current intensity and cathode mesh size on the electrocatalytic generation of reactive oxygen species (ROS), i.e., hydrogen peroxide <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mrow> <mml:msub><mml:mrow><mml:mi>H</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> <mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> </mml:mrow> </mml:mfenced> </mml:math> and hydroxyl radicals (•OH), for removing p-nitrophenol (PNP) as a representative contaminant. The findings suggest that these parameters exert a factorial effect on PNP removal, which is statistically endorsed via the analysis of variance. The -20 + 40 mesh GAC exhibited superior electrocatalytic performance due to its optimal balance of porosity and active surface area. Additionally, the reactor configuration was also studied. Employing two reactors in series configuration resulted in a 23% increase in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>H</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> <mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> </mml:math> generation and a 32% enhancement in overall PNP removal compared with the single reactor configuration. This enhancement is attributed to (i) the enhanced electroactive area, (ii) the greater retention time of PNP over the electrocatalyst surface, and (iii) the increased dissolved oxygen and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>H</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> <mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> </mml:math> content in the second reactor, promoting the overall <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>H</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> <mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> </mml:math> generation. Numerical simulations were conducted to compute <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>H</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> <mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> </mml:math> concentration profiles, providing a detailed representation of the physical, chemical, and electrochemical processes. The model exhibited a high degree of accuracy compared with the experimental measurements, with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup><mml:mrow><mml:mi>R</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msup> </mml:math> values ranging from ~0.76 to 0.99 and MAE values between ~0.04 and 0.23 mg/L. The simulation results highlight a strong interplay between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>H</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> <mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> </mml:math> generation, its reaction kinetics during PNP removal, and electrode utilization efficiency. These findings emphasize the importance of optimizing the applied current magnitude and reactor operation duration to maximize electrode efficiency and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>H</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> <mml:msub><mml:mrow><mml:mi>O</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> </mml:math> generation and utilization, while minimizing electrochemical bubble blockage. Overall, this study provides fundamental insights to optimize the electroactive area for enhanced ROS generation toward efficient contaminant removal, supporting sustainable groundwater remediation technologies in the face of emerging pollutants.