Electrocatalytic Activities of Gold Nanoparticles on Glassy Carbon Prepared By Simple Electrochemical Method
Authors: Okada Haruki , Fukuda Yoshitaka , Mukouyama Yoshiharu , Saito Makoto , Nishimura Takashi 
Published: February 2020

Nanoparticles (NPs) of noble metals such as gold and platinum are utilized in a wide range of applications in various fields because of their unique catalytic, electronic, and optical properties. Furthermore, NPs have large surface area to volume ratio, which leads to an increase in catalytic efficiency and also to a cost-reduction. A variety of methods using chemical reactions are currently available for synthesizing NPs in solution phase and also for controlling their shapes and properties. In the field of electrochemistry, platinum NPs (PtNPs) deposited on carbon materials such as graphite, glassy carbon, and carbon blacks have been extensively studied because they are useful as efficient electrocatalysts for fuel cells, water electrolysis, and so on.

Nishimura et al. have developed a simple method for preparing shape-controlled PtNPs on a graphite surface [1]. In the method, the water electrolysis (2H2O → 2H2 + O2) was conducted at a constant current using the graphite electrode and a Pt electrode as the cathode and anode, respectively. The galvanostatic electrolysis was carried out for several hours in a strong acid solution such as HNO3 and H2SO4. During the electrolysis, the Pt anode slightly dissolved to form a small amount of Pt ions whereas the graphite cathode reduced the ions resulting in the formation of PtNPs. The method was cost friendly because PtNPs were obtained without any reducing and stabilizing agents, and also because 72 % of dissolved Pt ions were electrodeposited as PtNPs.

In our previous report [2], we have shown that gold NPs (AuNPs) can be produced by galvanostatic electrolysis using an Au anode and a graphite cathode. This electrolysis was essentially the same as the simple method that has been used to prepare PtNPs [1]. The Au anode, where oxygen evolution occurred, dissolved to form Au ions (Au → Au3+ + 3e-) and the graphite cathode, where hydrogen evolution occurred, reduced them (Au3+ + 3e- → Au).

We recently employed the galvanostatic electrolysis in order to prepare AuNPs on glassy carbon (GC). The experimental setup is shown in Figure 1a. AuNPs were uniformly deposited by conducting the electrolysis for two hours in 0.5 M H2SO4 solution, as can be seen in the SEM image (Figure 1b). Interestingly, the AuNPs showed a good electrocatalytic activity toward the reduction of nitrobenzene (C6H5NO2 + 6H+ + 6 e- → C6H5NH2 + 2H2O) compared with Au-wire electrode (Figures 1c and 1d). This is probably because AuNPs are enclosed by (111) planes, which will be discussed in the presentation.

REFERENCES

[1] T. Nishimura, T. Nakade, T. Morikawa, H. Inoue, Electrochimi. Acta, 129 (2014) 152.

[2] Y. Mukouyama, Y. Fukuda, T. Nishimura, ECS Trans.,
80 (2017) 1425.

[3] Z. Chen, Z. Wang, D. Wu, L. Ma, J. Hazard Mater, 197 (2011) 424.

FIGURE CAPTION

Figure 1. (a) A schematic of the experimental setup for the simple galvanostatic electrolysis. Electrolysis solution: 0.5 M H2SO4. Cathode: GC disc. Anode: Au wire. (b) A SEM image of the GC cathode taken after conducting the electrolysis at 30℃ for two hours. Cathodic and anodic current densities were 10 and 2.5 mA cm-2, respectively. (c and d) Cyclic votammograms (CVs) measured in 0.1 M H2SO4 + 0.016 M nitrobenzene (NB) at a potential scan rate of 0.1 Vs-1. The working electrode used was (c) the AuNPs/GC electrode (total surface area of AuNPs: 0.16 cm2) and (d) an Au-wire electrode (surface area: 2.58 cm2). When the electrode potential (E) < ca. 0.2 V, NB was reduced to form aniline via a two-step reaction (see ref [3]): the formation of phenylhydroxylamine (C6H5NO2 + 4H+ + 4e- → C6H5NHOH + H2O) and its consecutive reduction to aniline (C6H5NHOH + 2H+ + 2e- → C6H5NH2 + H2O).

Figure 1