A Novel Ni/ZnO/Cu Composite Electrode with High Sensitivity for Detection of Chemical Oxygen Demand

The water monitoring parameter of chemical oxygen demand (COD) is a universal way to assess organic pollution in aqueous systems. Though the ways for the detection of COD have been developed for decades, it is still a challenge to achieve highly sensitive and portable COD detectors. In this work, a new electrode composite of Ni/ZnO/Cu (CE-1) was prepared for the electrochemical tests of COD. The electrode was structural characterized by using scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray Diffractometer (XRD), which showed that self-supported Cu microflowers were successfully electrodeposited on the ZnO micro-prims that were firstly loaded on the Ni foils. The electrochemical behaviors were investigated with the comparison of CE-1 and the electrode that Cu nanoparticles were directly deposited on the Ni foil (CE-2). It shows that CE-1 possesses much superior electrochemical properties than CE-2, which indicates that the introduction of ZnO micro-rod the electrode can significantly enhance the electrocatalysis property. CE-1 exhibited a linear COD detection range of 2.3603 to 577.8 mg/L as well as an excellent correlation with the classic dichromate method (R 2  = 0.99933). Moreover, low detection limit of 0.6036 mg/L (the signal blank/slope=3) and high sensitivity of 2.403 × 10 −2 mA / (mg • L −1 ) can be simultaneously achieved by using CE-1, which is hard to attain for its counterparts reported in literature. CE-1 also shows good concordance with the classic method for real water sample detections. Consequently, the environmentally friendly CE-1 is supposed as a promising candidate for COD detection electrode.