Underpotential deposition of silver on polycrystalline platinum studied by cyclic voltammetry and rotating ring-disc techniques
Underpotential deposition of silver on polycrystalline platinum studied by cyclic voltammetry and rotating ring-disc techniques
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DOI：
10.1039/a703872k
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发表时间：
1997-11-21
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影响因子：
--
通讯作者：
Avaca, LA
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文献类型：
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作者：
Mascaro, LH;Santos, MC;Avaca, LA
结合循环伏安法和旋转环盘法研究了银（UPD Ag）在多晶铂表面的欠电位沉积。提出了一种新的伏安法，用于UPD银脱附测量中阳极电荷密度的正确计算。它包括通过测量伏安实验中与PtO还原相关的电荷来评估表面氧化的贡献。这种方法允许人们获得对总阳极电荷密度的个别贡献。用旋转环盘系统进行的采集实验充分证实了该方法的有效性。通过这种方法，在0.5 M H2SO4-5.0 x 10(-6) M AgNO3溶液中，在多晶Pt上沉积了完整的银单层，实验最大覆盖率为90%。剩下的表面被残留的氢原子覆盖。这一现象对于纯UPD银或包含大块银的沉积都很明显。因此，除了ad- ads原子与底物之间的失配外，UPD Ag通过涉及单电子转移的直接机制发生，并导致完整的Ag-ads单层。在超过两层的沉积中观察到吸附氢的再现。这与银的三维成核后的表面重排有关，银的三维成核产生了h吸附的自由位点。在这项工作中没有发现银插入Pt相的证据。
The underpotential deposition of Ag (UPD Ag) on polycrystalline Pt surfaces has been studied combining cyclic voltammetry and rotating ring-disc measurements. A new voltammetric methodology is proposed for the proper calculation of the anodic charge density in UPD Ag desorption measurements. It involves an evaluation of the surface oxidation contribution by measurement of the charge related to PtO reduction in the following scan of the voltammetric experiment. This methodology allows one to obtain the individual contributions to the total anodic charge density. Collecting experiments carried out with the rotating ring-disc system fully confirmed the validity of the procedure. In this way, a complete monolayer of Ag deposited on polycrystalline Pt from a 0.5 M H2SO4-5.0 x 10(-6) M AgNO3 solution showed an experimental maximum coverage of 90%. The remaining surface was covered by residual H atoms. This phenomenon was evident for either pure UPD Ag or for depositions involving also bulk Ag. Therefore, apart from the misfit between ad-atoms and substrate, UPD Ag occurs by a straightforward mechanism involving one-electron transfer and resulting in a complete monolayer of Ag-ads. The reappearance of adsorbed hydrogen was observed for depositions beyond two monolayers. This was associated with a surface rearrangement followed by three-dimensional nucleation of Ag that generates free-sites for H-adsorption. No evidence of Ag insertion in the Pt phase was detected in this work.