Reagent‐Free Detection of Chemical Oxygen Demand Based on a Complementary Response Multielectrode System

The rapid and reliable determination of chemical oxygen demand (COD) is critical for effective water quality management. This study developed a reagent‐free multielectrode sensing system using complementary electrochemical responses for COD determination. The system integrated Pt, Au, C/CuO x , Co(OH) 2 and Zr(OH) 4 electrodes, each providing distinct surface and catalytic properties for broad‐spectrum detection of carbohydrates, nitrogen‐containing compounds, and alcohols. Linear sweep voltammetry (LSV) with principal component analysis confirmed unique electrochemical fingerprints for each compound class. Feature extraction via LASSO regression and modeling with XGBoost enabled accurate COD prediction in simulated and real water samples, yielding test‐set average percentage relative errors of 5.12% and 6.31%, respectively. Results correlated well with the standard potassium dichromate method (APRE = 7.48%, p > 0.05). This approach offered a rapid, eco‐friendly alternative for COD monitoring and demonstrates potential for dissolved organic matter (DOM) analysis and source tracking.