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    Effect of Supporting Background Electrolytes on the Nanostructure Morphologies and Electrochemical Behaviors of Electrodeposited Gold Nanoparticles on Glassy Carbon Electrode Surfaces
    (Amer Chemical Soc, 2021) Zakaria, Nor Dyana; Omar, Muhamad Huzaifah; Kamal, Najahtul Najihah Ahmad; Razak, Khairunisak Abdul; Soenmez, Turgut; Balakrishnan, Venugopal; Hamzah, Hairul Hisham
    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 similar to 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 similar to 6 Omega (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.
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    Mechanistic pathways and kinetic studies of oxygen reduction reaction (ORR) at Covalent Triazine Frameworks (CTFs)
    (Pergamon-Elsevier Science Ltd, 2024) Soenmez, Turgut; Uecker, Jan; Hamzah, Hairul Hisham; Palkovits, Regina
    Herein, four different metal-free nitrogen containing Covalent Triazine Frameworks (CTFs) based on their applied monomers (DCP, DCBP, mDCB and pDCB) are synthesized via a classical ionothermal synthesis route (ZnCl2, 400/600 degrees C). These materials are fully characterized and their electrochemical activities for ORR are tested and compared to each other including Carbon Super P and Pt black as standards in 0.1 M KOH. While DCP provides similar catalytic activity to Carbon Super P showing mostly a 2e- process (n=2.95) with high H2O2 formation of 52.6 %, the other three CTFs (DCBP, mDCB and pDCB) possess higher ORR activities, surprisingly even much higher limiting current densities than Pt black, proving that O2 is mainly reduced via direct 4epathway since n values are in the range of 3.52 to 3.62 and the detected H2O2 values are in the range of 19-23.9 %. Among the studied CTFs, mDCB reaches a limiting current density of -5.61 mA cm-2 (1.21 mA cm-2 larger than that for Pt black, -4.40 mA cm-2) with 0.11 V larger onset potential compared to Pt black. The significant electrochemical performances of the CTF materials in ORR via a 4e- process are correlated to the high specific surface areas (up to 2500 m2 g-1), large pore volumes (up to 2.05 cm3 g-1) and the largest total N-graphitic/ quaternary contents as well as micro-mesoporous structure properties.