Electrocatalytic glucose oxidation at binary catalyst of nickel and manganese oxides nanoparticles modified glassy carbon electrode: Optimization of the loading level and order of deposition

High Electrocatalytic Performance of CuCoNi@CNTs Modified Glassy Carbon Electrode towards Methanol Oxidation in Alkaline Medium

“…At the NiOx@CNTs/GCE (curve e), the well-defined redox waves of the Ni(II)/Ni(III) transformation in alkaline medium is observed around 0.4 V, which leads to the formation of NiOOH according to [24] (5) 3. Thirdly, the charging current for both CuOx and CoOx, observed in the potential range 0.3 V to 0.55 V in curve b and c, decreased slightly in the same potential range in the case of CuCoNiOx@CNTs/GCE; this is certainly due to the last-mentioned feature in point II.…”

“…This may be due to the increase of the amount of deposit increases the time needed for the surface enrichment with oxides during the passivation step in alkaline medium. Also, by increasing the deposition time, the rate of crystal growth exceeds that of nucleation and results in the formation of bigger deposits rather than the formation of new crystals, which has a negative effect on the deposits' accessible surface area, so the current does not increase directly [24]. On the other hand, with increasing the loading level of the deposit, the peak potential shifts slightly positive, and this could be attributed to the higher potential required for the nucleation of the upper oxides at these high loading levels [24].…”

“…Also, by increasing the deposition time, the rate of crystal growth exceeds that of nucleation and results in the formation of bigger deposits rather than the formation of new crystals, which has a negative effect on the deposits' accessible surface area, so the current does not increase directly [24]. On the other hand, with increasing the loading level of the deposit, the peak potential shifts slightly positive, and this could be attributed to the higher potential required for the nucleation of the upper oxides at these high loading levels [24]. Moreover, the peak of the transformation became sharp (i.e., small potential window of the peak) instead of broad at low loading levels, which confirms a fast kinetics of the transformation process.…”

“…First is dispersing 1 mg of CNTs in a solution of 0.8 mL isopropyl alcohol and 0.2 mL Nafion (5 wt %) and sonicating the solution for 2 h. The second step is casting 5 µL of the carbon dispersion onto the GCE surface and letting it dry for 2 h. Before inserting the electrode into the electrolytic cell, its surface was flushed with the same electrolyte that was used in the measurements in order to confirm the surface wettability [23]. The third step is the potentiostatic deposition of the metallic form of the required deposit on the working electrode (i.e., CNTs/GCE) from an aqueous solution of 0.1 M sodium sulphate (Na 2 SO 4 ) containing 1 mM of the sulphate salt of each metal ion, by applying a constant electrolysis potential of −0.9 V for different time durations [24,25]. The fourth step is the passivation of the metallic deposit in 1 M NaOH by cycling the potential between −0.2 V and 0.55 V for 15 consecutive cycles at a scan rate of 100 mV·s −1 [23,24].…”

“…The third step is the potentiostatic deposition of the metallic form of the required deposit on the working electrode (i.e., CNTs/GCE) from an aqueous solution of 0.1 M sodium sulphate (Na 2 SO 4 ) containing 1 mM of the sulphate salt of each metal ion, by applying a constant electrolysis potential of −0.9 V for different time durations [24,25]. The fourth step is the passivation of the metallic deposit in 1 M NaOH by cycling the potential between −0.2 V and 0.55 V for 15 consecutive cycles at a scan rate of 100 mV·s −1 [23,24]. Figure 1 represents the FE-SEM for CuCoNiOx@CNTs/GCE at (A) 600 s; (B) 900 s; and (C) 1200 s deposition time; as well as the (D) EDX analysis for Sample (C), and Figure 2 shows the XRD pattern of CuCoNiOx@CNTs/GCE.…”