## 3 Results and Discussion
### Corrosion Behavior of Cu Wafer under Photocatalysis  
Figure 6a displays the Tafel plots of the solutions containing citric acid, CeO\({}_{2}\), and H\({}_{2}\)O\({}_{2}\), using a polished Cu electrode as the working electrode, after different light irradiation times. The corrosion potential (E\({}_{\text{corr}}\)) and corrosion current density (I\({}_{\text{corr}}\)) data calculated from the Tafel plots are summarized in Table 1. The E\({}_{\text{corr}}\) value indicates the ease with which a material dissolves in the electrolyte, reflecting the difficulty of the chemical reaction between the sample and the electrolyte. The I\({}_{\text{corr}}\) value represents the corrosion rate of the material in the electrolyte. Generally, a lower corrosion potential (E\({}_{\text{corr}}\)) signifies a stronger chemical reaction between the solution and the electrode, while a higher corrosion current (I\({}_{\text{corr}}\)) indicates a faster rate of interfacial chemical reactions between the electrode and the electrolyte [32]. As observed from Figure 6a and Table 1, with increasing light irradiation time, the corrosion current gradually decreases, while the corrosion potential shows an increasing trend. This suggests that the citric acid in the solution is being progressively degraded, leading to a reduction in the corrosive capability of the solution. This finding is consistent with the results obtained from UV spectroscopy measurements. Figure 6: (**a**) Tafel curves at different photocatalysis times. (**b**) Nyquist plots at different photocatalysis times, along with the \(R_{S}(R_{1}C_{1})(R_{2}C_{2})\) equivalent circuit model. (**c**) Bode magnitude plots at different photocatalysis times. (**d**) Bode phase plots at different photocatalysis times. The CMP process for Cu can be described as comprising two removal components: a mechanical component involving surface abrasion and a chemical component involving the generation of an oxidized layer and the formation of Cu(II) species, leading to the dissolution of the abraded material [33]. In practical polishing, complexing agents such as citric acid are used to achieve partial polishing by forming Cu(II) complexes that remove the oxidized layer from the Cu surface. The thickness of the oxidized layer on the Cu surface is characterized using EIS. The capacitors (Q\({}_{1}\) and Q\({}_{2}\)) are designed as constant phase elements (CPE). For actual electrochemical reactions, the impedance response of the electrode is rarely ideal, and therefore, it is commonly represented as a CPE element in the equivalent circuit [34]. All impedance data were fitted using the equivalent circuit shown in the upper left corner of Figure 6b \(R_{S}(R_{1}C_{1})(R_{2}C_{2})\). Figure 6b-d show the Nyquist and Bode plots of the Cu electrode in the solution after different irradiation times. The spherical symbols and solid lines represent the original experimental data and the ZVIEW fitting curves, respectively. The experimental results exhibit a double semicircle pattern with frequency increasing in the counterclockwise direction. The magnitude of the impedance values can be expressed as:  
\[|Z|=\sqrt{a^{2}+b^{2}}=\sqrt{a^{2}+\left(\frac{1}{2\pi cf}\right)^{2}} \tag{8}\]  
where \(Z\) is the impedance, \(a\) is the real part of the impedance, \(b\) is the imaginary part of the impedance, \(c\) is the nominal capacitance, and \(f\) is the frequency. \(a\) and \(c\) can be roughly referred to as the resistance and capacitance of the metal surface oxidized layer, respectively [4].