Fritz-Haber-Institut der Max-Planck-Gesellschaft , Faradayweg 4-6 , 14195 Berlin , Germany.
Rudjer Boskovic Institute , Bijenicka 54 , 10000 Zagreb , Croatia.
J Am Chem Soc. 2019 Apr 24;141(16):6537-6544. doi: 10.1021/jacs.8b12284. Epub 2019 Apr 12.
During the electrochemical reduction of oxygen, platinum catalysts are often (partially) oxidized. While these platinum oxides are thought to play a crucial role in fuel cell degradation, their nature remains unclear. Here, we studied the electrochemical oxidation of Pt nanoparticles using in situ XPS. When the particles were sandwiched between a graphene sheet and a proton exchange membrane that is wetted from the back, a confined electrolyte layer was formed, allowing us to probe the electrocatalyst under wet conditions. We show that the surface oxide formed at the onset of Pt oxidation has a mixed Pt/Pt/Pt composition. The formation of this surface oxide is suppressed when a Br-containing membrane is chosen due to adsorption of Br on Pt. Time-resolved measurements show that oxidation is fast for nanoparticles: even bulk PtO· nHO growth occurs on the subminute time scale. The fast formation of Pt species in both surface and bulk oxide form suggests that Pt-oxides are likely formed (or reduced) even in the transient processes that dominate Pt electrode degradation.
在氧气的电化学还原过程中，铂催化剂通常（部分）会被氧化。虽然这些铂氧化物被认为在燃料电池的降解中起着至关重要的作用，但它们的性质仍不清楚。在这里，我们使用原位 XPS 研究了 Pt 纳米颗粒的电化学氧化。当这些颗粒被夹在石墨烯片和从背面润湿的质子交换膜之间时，形成了一个受限的电解质层，允许我们在湿条件下探测电催化剂。我们表明，在 Pt 氧化开始时形成的表面氧化物具有混合的 Pt/Pt/Pt 组成。当选择含有 Br 的膜时，由于 Br 在 Pt 上的吸附，这种表面氧化物的形成受到抑制。时间分辨测量表明，纳米颗粒的氧化速度很快：甚至在亚分钟的时间尺度上也会发生块状 PtO· nHO 的生长。表面和体相氧化物中 Pt 物种的快速形成表明，即使在主导 Pt 电极降解的瞬态过程中，Pt-氧化物也可能形成（或还原）。
