Department of Chemistry, National Taiwan Normal University, 88, Section 4, Ting-chow Road, Taipei 116, Taiwan.
Chemphyschem. 2012 Sep 17;13(13):3194-203. doi: 10.1002/cphc.201200215. Epub 2012 Jun 27.
Sulfur, a pollutant known to poison fuel-cell electrodes, generally comes from S-containing species such as hydrogen sulfide (H(2)S). The S-containing species become adsorbed on a metal electrode and leave atomic S strongly bound to the metal surface. This surface sulfur is completely removed typically by oxidation with O(2) into gaseous SO(2). According to our DFT calculations, the oxidation of sulfur at 0.25 ML surface sulfur coverage on pure Pt(111) and Ni(111) metal surfaces is exothermic. The barriers to the formation of SO(2) are 0.41 and 1.07 eV, respectively. Various metals combined to form bimetallic surfaces are reported to tune the catalytic capabilities toward some reactions. Our results show that it is more difficult to remove surface sulfur from a Ni@Pt(111) surface with reaction barrier 1.86 eV for SO(2) formation than from a Pt@Ni(111) surface (0.13 eV). This result is in good agreement with the statement that bimetallic surfaces could demonstrate more or less activity than to pure metal surfaces by comparing electronic and structural effects. Furthermore, by calculating the reaction free energies we found that the sulfur oxidation reaction on the Pt@Ni(111) surface exhibits the best spontaneity of SO(2) desorption at either room temperature or high temperatures.
硫是一种已知会毒害燃料电池电极的污染物，通常来自含硫物质，如硫化氢 (H(2)S)。含硫物质被吸附在金属电极上，留下与金属表面紧密结合的原子硫。通常，通过与 O(2) 氧化将表面硫完全转化为气态 SO(2) 来去除。根据我们的 DFT 计算，在纯 Pt(111) 和 Ni(111) 金属表面上，当表面硫覆盖度为 0.25 ML 时，硫的氧化是放热的。形成 SO(2) 的势垒分别为 0.41 和 1.07 eV。据报道，各种金属组合形成双金属表面可以调节某些反应的催化能力。我们的结果表明，从 Ni@Pt(111) 表面去除表面硫比从 Pt@Ni(111) 表面（0.13 eV）更困难，因为形成 SO(2) 的反应势垒为 1.86 eV。这一结果与双金属表面通过比较电子和结构效应可能比纯金属表面具有更多或更少的活性的说法一致。此外，通过计算反应自由能，我们发现硫氧化反应在 Pt@Ni(111) 表面上在室温或高温下都表现出 SO(2) 解吸的最佳自发性。
