Nanoparticle-based catalysts have been intensively studied not only due to their controllability via size, shape, and composition but also due to economic efficiency with high surface-to-mass ratio. By doping the nanoparticles with non-metallic elements, they are currently receiving a lot of attention because they can control the surface of nanoparticles to improve their electrochemical performance. Here, we conducted an electrochemical study of sulfur-doped Pd nanocubes as an electrochemical catalyst for ethanol oxidation to produce a C₁ product with twelve electrons and C₂ product with four electrons.
Through a variety of instrumental analytic techniques, such as SEM, TEM, HAADF-STEM, EDS, XRD, and XPS, the morphology of S-doped Pd nanocubes according to the degree of sulfurization which is closely related to electrochemical catalytic activity, was investigated in detail. Accordingly, it was found that the S-doped Pd nanocubes became amorphous from the edge of nanocube as the concentration of sulfur increases. The acetic acid and carbon dioxide were mainly produced for ethanol oxidation on Pd nanocube before and after sulfurization. In particular, the selectivity toward carbon dioxide compared to acetic acid increases as the sulfurization proceeds. Therefore, the sulfur can play a role in increase the degree of degradation of ethanol molecules in electrochemistry.
We found a strong correlation between the electrochemical catalytic activity and morphological change of S-doped Pd nanocubes. The S-doped Pd nanocubes with the optimum sulfur concentration of 3 mM lead to a high catalytic activity in the electrochemical reaction compared with pristine Pd nanocubes. The density functional theory calculations were also conducted to elucidate the relation between the surface composition and electrochemical catalytic activity of Pd nanocubes and S-doped Pd nanocubes. Our study suggests that the catalytic activity and selectivity of metal nanoparticles can be finely controlled by doping non-metal species.