# Mitigating Electrochemical Effects in Resistive Frost-Detection Sensors
## 4 Discussion
is copper(II) oxide (CuO), while the blue material is copper(II) hydroxide (Cu(OH)\({}_{2}\)). These observations help explain the electrochemical phenomena occurring during the experiment, as detailed below:  
* The cathode acquires a polished, reflective surface:  
As the electrodes were previously exposed to air, a thin layer of Cu\({}_{2}\)O (Copper(I) oxide) is present on both the electrodes. When the sensor is powered, electrons flow into the anode, facilitating a reduction reaction, as described by Equation (11):  
\[\text{Cu}_{2}\text{O}(s)+\text{H}_{2}\text{O}(l)+2e^{-}\to 2\text{Cu}(s)+2 \text{OH}^{-}(aq) \tag{11}\]  
Since copper without an oxide layer has a polished, metallic appearance, this reaction results in a reflective surface. * The presence of copper(II) hydroxide, Cu(OH)\({}_{2}\), and copper(II) oxide, CuO:  
When noble metals are used as electrodes, only OH\({}^{-}\) and H\(+\) ions migrate between the anode and cathode. However, when copper electrodes are used, oxidation at the anode occurs, and Cu\({}^{2+}\) ions form, as shown in Equation (12):  
\[\text{Cu}(s)\rightarrow\text{Cu}^{2+}(aq)+2e^{-} \tag{12}\]  
These copper ions migrate toward the cathode, where they are expected to gain electrons and form copper again. However, upon encountering OH\({}^{-}\) ions, they react to form Cu(OH)\({}_{2}\), as described in Equation (13):  
\[\text{Cu}^{2+}(aq)+2\text{OH}^{-}(aq)\rightarrow\text{Cu}(\text{OH})_{2}(s) \tag{13}\]  
This reaction occurs at both electrodes. Near the anode, Cu\({}^{2+}\) ions form and migrate toward the cathode, while OH\({}^{-}\) ions form at the cathode and migrate toward the anode. Due to the low voltage and current (4.2 V and 0.3 mA, respectively), there is a higher concentration of OH\({}^{-}\) ions near the cathode and Cu\({}^{2+}\) ions near the anode. Cu(OH)\({}_{2}\) can remain stable in pure water without transforming into CuO. However, in the presence of OH\({}^{-}\) ions (as in alkaline solutions), this transformation occurs more rapidly [24]. Under these conditions, copper ions dissolve, forming Cu(OH)\({}_{4}^{2-}\), which eventually leads to the formation of CuO, as described in Equation (14):  
\[\text{Cu(OH)}_{2}(s)+2\text{OH}^{-}(aq)\rightarrow\text{Cu}(\text{OH})_{4}^{2 -}(aq)\rightarrow\text{CuO}(s)+2\text{OH}^{-}(aq)+\text{H}_{2}\text{O}(l) \tag{14}\]  
This explains the presence of copper(II) hydroxide near the cathode and copper(II) oxide near the anode. * Oxygen (O\({}_{2}\)) and hydrogen (H\({}_{2}\)) gas bubbles:  
Gas bubbles formed from oxygen and hydrogen are expected, as explained in the water electrolysis reactions given in chemical Equations (3), (4), (6), and (7). However, the observed oxygen production is visually lower than expected, likely due to the disproportionate consumption of oxygen molecules in the formation of CuO and Cu(OH)\({}_{2}\). These reactions are the key chemical processes observed during the experiment. With this understanding, the behavior of the curve in the continuous voltage sensor readings, shown in Figure 8, can be explained as shown in Table 3:This explanation highlights the dynamics of continuous monitoring and its impact on electrode degradation, as the anode loses copper ions during electrolysis, accelerating the deterioration process. The experiment demonstrates how the control method directly affects sensor reliability and emphasizes the need to account for the effects of electrolysis when using a resistive sensor in a water medium. The pulsed DC excitation control solution addresses this issue by minimizing the duration in which electrolysis occurs between the sensor electrodes.