Pt-Au/CNT@TiO2 as a High-Performance Anode Catalyst for Direct Methanol Fuel Cells

Multi-walled carbon nanotubes (CNT) modified using TiO2 nanoparticles (CNT@TiO2) were prepared. Then, Pt-Au/CNT@TiO2 catalysts were prepared by a deposition-UV-photoreduction method for direct methanol fuel cells. The physico-chemical properties of the catalysts were characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalytic performance was evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. The Pt-Au nanoparticles were found to be uniformly deposited onto the CNT@TiO2 support and had diameters of 2–3 nm. Compared with the Pt-Au/CNT catalyst that was made using a general chemical method, Pt-Au/CNT@TiO2 exhibits higher CO-tolerance for the following reasons. Firstly, the strong interaction between the Pt-Au alloy and TiO2 leads to an increase in electron density on the metallic Pt-Au, which transfers electrons to the ϕ $CO* orbital of CO and weakens C–O binding while the oxidation overpotential is lowered. Secondly, the high-valence Ti ions dissociate water to form OHad (ad: adsorbed) species, which then reacts with the strongly bound COad on the Pt surface to form CO2. ： 以 TiO2 包覆的多壁碳纳米管 (CNT@TiO2) 为载体, Pt 和 Au 为活性物质, 采用沉积紫外光催化还原法制备出高活性的甲醇阳极电催化剂 Pt-Au/CNT@TiO2, 并采用 X 射线衍射、透射电镜和 X 射线光电子能谱对催化剂样品的物化特征进行表征. 催化剂的抗毒性能用循环伏安和交流阻抗测试来表征. 结果表明, 粒径为 2∼3 nm的 Pt-Au 纳米粒子均匀的分散在 CNT@TiO2 载体上. 与普通化学还原方法制备的 Pt-Au/CNT 电催化剂相比, Pt-Au/CNT@TiO2 催化剂表现出更高的抗毒性. 这是因为: (1) Pt-Au 合金和 TiO2 的相互作用使 Pt-Au 合金的电子密度增加, Pt-Au 电子密度的增加会传递部分电子到 CO 的反键轨道上, 从而削弱碳氧键, 最终促使过氧化电位降低; (2) 高价态的钛离子分解水分子从而形成吸附态的 OHad 物种, 此物种与吸附在 Pt 表面的 CO 反应最终生成 CO2.