Next, we investigated the mechanism by which multi-scan DEB coating afforded the modified electrodes their increased sensitivity to Cu(II). We probed this via a few different approaches. First, we imaged the surface morphology using scanning electron microscopy. As seen in Figure , the bare electrode displayed a highly striated surface characteristic of carbon fiber in agreement with those reported by others . The single scan electrodeposition of DEB yielded a film-like smooth layer (Figure ) over the striated features, which were no longer visible. The 3-scan DEB coating yielded more apparent striations compared to the single scan DEB coating but less than the bare. It also yielded small island-like features of varying sizes (Figure Please do not adjust margins Please do not adjust margins 3d). This finding was surprising and points to the formation of an uneven surface for the 3-scan DEB deposition on the CFMs. Next, we evaluated Cu(II) adsorption behaviour on both modified and unmodified electrodes using FSCAV (please see Experimental section). For an unmodified CFM, Cu(II) forms a monolayer on the electrode surface that follows the Langmuir adsorption isotherm (Figure , blue), in agreement with those reported by others . Cu(II) adsorption on DEB-modified CFM (1 scan) was found to follow Langmuir adsorption isotherm (Figure , purple) as well. The adsorption coefficient between DEBmodified electrode and Cu(II) (Kads = (2.21 ± 0.03) x 10 8 ) for 1scan DEB-modified electrode was comparable to that of a bare CFM (Kads = (2.28± 0.01) x 10 8 = 0.0913). Three-scan DEB deposition modified CFM on the other hand, could not be fitted with a Langmuir adsorption model (Figure ). This suggests that this modification yielded a surface with greater heterogeneity, on which Cu(II) coverage could not form a monolayer. This was in agreement with the SEM results, which showed the island-like features for the 3-scan DEB-deposited electrodes. In order to evaluate the impact of DEB modification on the CFM electrical conductivity, EIS was then performed. Theoretically, modifications that increase the conductivity of the surface would yield lower impedance response in EIS across the applied perturbation frequencies . As seen in Figure and, respectively, neither the single-scan electrodeposition of DEB on CFMs nor the multi-scan DEB coated electrodes yield statistically different impedance than that of an unmodified electrode across perturbation frequencies. Such similarity indicates that unmodified electrodes and single scan DEB coating modified CFM are similar in surface electrical conductivity. Additionally, this is further evidence that selfpolymerization was not observed during our electrodeposition experiments of DEB, as self-polymerization would yield a highly conductive polymer and is expected to decrease impedance response across perturbation frequencies. The EIS data were fitted with the equivalent circuit model proposed by Sombers and colleagues 57 comprising of two resistors and two constant phase elements. Table lists the fitted parameters for the 3-scan DEB electrodes and unmodified electrodes. These terms include Q1 (double layer capacitance), R1 (CFM surface and solution resistance combined), Q2 (capacitance arising from the seal of the CFM), and R2 (shunt). The parameters α1 and α2 are modifiers for the constant phase element, which is used to model nonideal capacitor. For instance, an ideal capacitor would have a modifier α equal to 1. One-scan DEB coated electrodes displayed a marginal decrease of 11% in α1. Three-scan DEB deposition decreased α1 by 60% compared to an unmodified electrode. These results suggest that increasing scans of DEB increased the nonideal capacitor nature of the CFM. Nonideal behavior can arise from a few different phenomena, one of which is increased surface roughness . This makes sense for our system as 3-scan DEB had the greatest deviation from ideal capacitor behavior and also has the greatest surface roughness in the form of island-like structures (Figure ). Please do not adjust margins