Adsorption of serine on Pt single-crystal electrodes in sulfuric acid solutions
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Adsorption of the amino acid serine on Pt single-crystal electrodes in sulfuric acid solutions has been studied using cyclic voltammetry and in situ Fourier transform infrared (FTIR) reflection spectroscopy. The results demonstrated that, in the adsorption, serine has suffered an oxidative dissociation that leads to the production of different adsorbates. Through a comparative investigation of serine, ethanolamine, and glycine on a Pt(100) electrode and in situ FTIR studies, adsorbates derived from the adsorption of serine were determined as PtCOOH, PtnCO (PtCOL, Pt2COB), and PtCN species. The cyclic voltammetric results illustrated that the oxidation of the PtCOOH adsorbates occurs in a small current peak (j(p1)) near +0.25 V, while the oxidation of PtnCO and PtCN species gives rise to a large current peak (j(p2)) between +0.39 and +0.52 V, on the three low index planes and nine stepped surfaces lying on the , [01(1) over bar], and [1(1) over bar 0] crystallographic zones. On the basis of the experimental results, a mechanism of adsorption and oxidative dissociation of serine was proposed, which includes the cleavage of the two C-C bonds of the serine molecule, the oxidation of PtH species, and the surface combination of PtCOOH with PtH to form PtnCO adsorbates. It has been revealed that the Pt single-crystal electrodes containing mainly surface sites of (110) and (111) symmetry exhibit a high efficiency for the surface combination of PtCOOH with PtH, while the efficiency the of surface consisting mainly of (100) symmetry elements is relatively low. The surface-structure effects of Pt single-crystal electrodes on the adsorption and oxidative dissociation of serine were clearly demonstrated through the quantitative data measured in cyclic voltammetric studies.