*3.3.2. Linear Sweep Voltammetry analysis (LSV)*

LSV analysis is a vital method for evaluating the ORR activity of synthesized nanocomposites combining a rotating-disk electrode (RDE) or rotating ring-disk electrode (RRDE) [83, 86]. Similar to CV, the LSV analysis is also done in an O2-saturated 0.1 M KOH electrolyte solution at different rotation rates of electrode under room temperature. For LSV, the electrolytic bath contains three electrodes: an RDE or RRDE quantitatively coated with the synthesized catalyst, an Ag|AgCl/KCl (saturated) reference electrode, and a Pt wire as an auxiliary electrode. During electrochemical measurement, the working electrode steadily rotates at the required rotation rate, and the current density changes in the potential range corresponding to the CV for one linear sweep are recorded. LSV technique has been extensively used in studying the electrocatalytic ORR kinetics and mechanism.

## *3.3.3. Amperometric technique (I-t)*

Amperometric technique is very crucial for electrocatalytic sensing applications. For ampero‐ metric sensors, current is produced proportional to the concentration of the analyte to be detected.

Figure 11a compares the I−t curves of CuO/GCE and three CuO/GO/GCEs (S1−S3) electrode sensing glucose. Figures 11a and 11b show that the sensors produced an excellent ampero‐ metric current with a short response time. Figures 11c and 11d show the amperometric responses of CuO/GO/GCEs S3 sensor toward the electrocatalytic oxidation of glucose in human serum and the corresponding calibration curve [16]. The sensitivity, lower detection limit, and linear range can thus be calculated from these amperometric data.

## *3.3.4. Electrochemical Impedance Spectroscopy (EIS)*

Electrochemical impedance spectroscopy (EIS) has become a popular and effective technique in recent decades for the determination of double-layer capacitance, characterization of

As shown in Fig. 10a, the commercial Pt/C displays typical CV responses of ORR in N2 and O2-saturated 0.1 M KOH. The black dash line shows CV response in the N2-saturated 0.1 M KOH within a potential window from 0.36 to 1.1 V. It is clearly seen that there is no sign of the typical ORR peak of Pt/C at +0.9 V [19]. However, a distinct performance of ORR (black solid line) is clearly seen in the case of O2-saturated 0.1 M KOH. The clear peak at ~0.9 V of Pt/C indicates that the Pt/C exhibits excellent ORR activity with its standard onset potential (~1.0 V) and peak potential (~0.9 V). Figure 10b compares the electrocatalytic ORR performance of MnCo2O4/N-rmGO, N-rmGO mixture, Co3O4/N-rmGO, and N-rmGO in an N2- and O2 saturated 0.1 M KOH solution, respectively. However, these four electrodes showed different ORR activity in O2 saturated electrolyte solutions. The ORR activity of MnCo2O4/N-rmGO (red solid line) has a more positive peak potential and higher peak current density (0.88 V, 0.5 mA cm−2) than those of the N-rmGO mixture (~0.84 V, 0.38 mA cm−2), Co3O4/N-rmGO (~0.86 V, 0.44 mA cm−2), and N-rmGO (~0.82 V, 0.29 mA cm−2). Therefore, MnCo2O4/N-rmGO material is more promising for ORR application, with a similar performance to that obtained at commer‐

LSV analysis is a vital method for evaluating the ORR activity of synthesized nanocomposites combining a rotating-disk electrode (RDE) or rotating ring-disk electrode (RRDE) [83, 86]. Similar to CV, the LSV analysis is also done in an O2-saturated 0.1 M KOH electrolyte solution at different rotation rates of electrode under room temperature. For LSV, the electrolytic bath contains three electrodes: an RDE or RRDE quantitatively coated with the synthesized catalyst, an Ag|AgCl/KCl (saturated) reference electrode, and a Pt wire as an auxiliary electrode. During electrochemical measurement, the working electrode steadily rotates at the required rotation rate, and the current density changes in the potential range corresponding to the CV for one linear sweep are recorded. LSV technique has been extensively used in studying the

Amperometric technique is very crucial for electrocatalytic sensing applications. For ampero‐ metric sensors, current is produced proportional to the concentration of the analyte to be

Figure 11a compares the I−t curves of CuO/GCE and three CuO/GO/GCEs (S1−S3) electrode sensing glucose. Figures 11a and 11b show that the sensors produced an excellent ampero‐ metric current with a short response time. Figures 11c and 11d show the amperometric responses of CuO/GO/GCEs S3 sensor toward the electrocatalytic oxidation of glucose in human serum and the corresponding calibration curve [16]. The sensitivity, lower detection

Electrochemical impedance spectroscopy (EIS) has become a popular and effective technique in recent decades for the determination of double-layer capacitance, characterization of

limit, and linear range can thus be calculated from these amperometric data.

cially available Pt/C [18].

*3.3.2. Linear Sweep Voltammetry analysis (LSV)*

396 Advanced Catalytic Materials - Photocatalysis and Other Current Trends

electrocatalytic ORR kinetics and mechanism.

*3.3.4. Electrochemical Impedance Spectroscopy (EIS)*

*3.3.3. Amperometric technique (I-t)*

detected.

**Figure 11.** Amperometric responses: (a) CuO (120 °C) and three different RGO-CuO (S1, S2, and S3); (b) the corre‐ sponding calibration curves of (a); (c) S3 to successive additions of human serum contained 50 μM glucose; (d) corre‐ sponding calibration curve of (c). (Reproduced with permission from ref. 16. Copyright ACS 2013)

electrode processes, and identification of complex interfaces. EIS records the response from an electrochemical system by the stimulation of an imposed periodic small amplitude AC signal. EIS measurements are normally done at various AC frequencies, and then, the EIS can be measured by the changes of the ratio between the AC potential and current signal with the corresponding sinusoid frequencies (*ω*). EIS analysis has extensively been performed for ORR to explore the kinetic process of the reaction with some essential information, including the interface and structure of the ORR electrode materials, properties of electric double layer, and diffusion of oxygen. The kinetic electron transfer process for ORR is explained by an EIS plot with a semicircle and a linear portion corresponding to a charge transfer and mass transpor‐ tation procedure at the high-frequency region and the low-frequency region, respectively.
