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Isopolytungstate Adsorption on Platinum: Manifestations of Underpotential Deposition

机译：异钨酸钨在铂上的吸附：低电位​​沉积的表现

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Metatungstate isopolyanion adsorption on smooth polycrystalline Pt and carbon-supported dispersed platinum in sulfuric acid medium is studied by cyclic voltammetry. Manifestations of both reversible and irreversible adsorption are found, with the features typical for heteropolytungstates of the same Keggin structure. When (NH4)6H2W12O40 is added to sulfuric acid solution, H underpotential deposition (UPD) charge starts to redistribute: it decreases at high hydrogen coverage but increases at higher potentials, with appearance of additional reversible redox feature in “double layer region.” The total charge value in diluted metatungstate solutions remains the same as for pure Pt. However, this value decreases with metatungstate concentration. At any fixed (NH4)6H2W12O40 concentration, the total charges in the hydrogen region are practically the same in 0.1 and 0.5 M sulfuric acid. Strongly bonded metatungstate species can be kept at the surface after the transfer to supporting solution. These irreversibly adsorbed species are redox-inactive and demonstrate stronger suppression of H UPD. Excursion to oxygen adsorption region does not result in complete desorption, but redistribution of charge takes place again. Our observations can be assigned (by analogy with Keggin anions adsorption on Au and Ag) to slow adsorbate–metal bonding, with subsequent increase of the number of bonded oxygen atoms. General trends are qualitatively the same for both Pt materials, but dispersed Pt on glassy carbon favors irreversible adsorption. The data confirm that adsorbed metatungstate can undergo reversible reduction at potentials more positive than the equilibrium potential of its first W(V/VI) redox transition (molecular UPD). Comparative electrocatalytic tests are presented for nitrate electroreduction on bare Pt, Pt modified with irreversibly adsorbed metatungstate, and Pt in metatungstate solution. The latter system, containing both forms of tungstate adsorbate, demonstrates high steady-state electrocatalytic activity at potentials below ca. 0.1 V reversible hydrogen electrode (RHE).
机译：通过循环伏安法研究了偏钨酸异聚阴离子在硫酸介质中光滑多晶Pt和碳负载的分散铂上的吸附。发现了可逆和不可逆吸附的表现形式，具有相同Keggin结构的杂多钨酸盐的典型特征。当在硫酸溶液中添加（NH4 ）6 H2 W12 O40 时，H欠电位沉积（UPD）电荷开始重新分布：在高温下会降低氢覆盖，但在更高的电势下会增加，并在“双层区域”中出现其他可逆氧化还原特征。稀释的偏钨酸盐溶液中的总电荷值与纯Pt相同。但是，该值随偏钨酸盐浓度而降低。在任何固定的（NH4 ）6 H2 W12 O40 浓度下，在0.1和0.5 M的硫酸中，氢区域的总电荷几乎相同。转移到支持溶液后，可以将牢固结合的偏钨酸盐物质保留在表面。这些不可逆地吸附的物质是氧化还原惰性的，并显示出对H UPD的更强抑制作用。到氧吸附区的偏移不会导致完全的解吸，但是会再次发生电荷的重新分布。我们的观察结果可以被分配（类似于在金和银上吸附的Keggin阴离子），以减缓被吸附物与金属的键合，并随后增加键合的氧原子数。两种Pt材料的总体趋势在质量上都相同，但是Pt分散在玻璃碳上有助于不可逆的吸附。数据证实，吸附的偏钨酸在比其第一个W（V / VI）氧化还原转变（分子UPD）的平衡电势更正的电势下可以发生可逆还原。提出了比较电催化测试，用于在裸露的Pt，不可逆吸附的偏钨酸修饰的Pt和偏钨酸溶液中的Pt上进行硝酸盐的电还原。包含两种形式的钨酸盐吸附物的后一种系统在低于约200的电势下表现出高稳态电催化活性。 0.1 V可逆氢电极（RHE）。

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