Electrodeposition is an electrochemical method employed to deposit stable and robust gold nanoparticles (AuNPs) on electrode surfaces for creating chemically modified electrodes (CMEs). The use of several electrodeposition techniques with different experimental parameters allow in obtaining various surface morphologies of AuNPs deposited on the electrode surface. By considering the electrodeposition of AuNPs in various background electrolytes could play an important strategy in finding the most suitable formation of the electrodeposited AuNP films on the electrode surface. This is because different electrode roughnesses can have different effects on the electrochemical activities of the modified electrodes. Thus, in this study, the electrodeposition of AuNPs onto the glassy carbon (GC) electrode surfaces in various aqueous neutral and acidic electrolytes was achieved by using the cyclic voltammetry (CV) technique with no adjustable CV parameters. Then, surface morphologies and electrochemical activities of the electrodeposited AuNPs were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), CV, and electrochemical impedance spectroscopy (EIS). The obtained SEM and 3D-AFM images show that AuNPs deposited at the GC electrode prepared in NaNO3 solution form a significantly better, uniform, and homogeneous electrodeposited AuNP film on the GC electrode surface with nanoparticle sizes ranging from ∼36 to 60 nm. Meanwhile, from the electrochemical performances of the AuNP-modified GC electrodes, characterized by using a mixture of ferricyanide and ferrocyanide ions [Fe(CN6)3-/4-], there is no significant difference observed in the case of charge-transfer resistances (R ct) and heterogeneous electron-transfer rate constants (k o), although there are differences in the surface morphologies of the electrodeposited AuNP films. Remarkably, the R ct values of the AuNP-modified GC electrodes are lower than those of the bare GC electrode by 18-fold, as the R ct values were found to be ∼6 Ω (p < 0.001, n = 3). This has resulted in obtaining k o values of AuNP-modified GC electrodes between the magnitude of 10-2 and 10-3 cm s-1, giving a faster electron-transfer rate than that of the bare GC electrode (10-4 cm s-1). This study confirms that using an appropriate supporting background electrolyte plays a critical role in preparing electrodeposited AuNP films. This approach could lead to nanostructures with a more densely, uniformly, and homogeneously electrodeposited AuNP film on the electrode surfaces, albeit utilizing an easy and simple preparation method.
Sulfuric acid is commonly used to electrochemically activate gold electrodes in a variety of electrochemical applications. This work provides the first evaluations of the electrochemical behaviors and a 3D image of an activated screen-printed gold electrode (SPGE, purchased commercially) through electrochemical and imaging analyses. The activated SPGE surface appears rougher than the unactivated SPGE surface when viewed through microtopography images using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Nevertheless, the roughened microscopy structure does not exhibit any substantial changes in roughness factor for the activated SPGE, as indicated by capacitive current analyses. The significant improvement in electrochemical responsiveness of the activated SPGE is mainly attributed to the presence of surface pores created in the microscopic structure as a result of gold oxide layer formation. The presence of surface pores on the activated surface has significantly improved its conductivity by 10-fold. As a result, electron transfer kinetics and mass transports of the activated SPGE are greatly improved. The results presented in this work indicate that the surface of the activated SPGE greatly increased its intrinsic surface pores, and conductivity of the electrode surface and uncovered the electrocatalytic active sites. This significantly improves the activated SPGE's performance in electrochemical applications such as oxygen reduction reaction (ORR). An activated SPGE considerably enhanced limiting current density as well as ∼172 mV versus Ag shifted onset potential to more positive potentials compared to unactivated SPGE.