We present experimentally observed molecular adsorbate coverages (e.g., O(H), OOH and HOOH) on real operating dealloyed bimetallic PtMx (M = Ni or Co) catalysts under oxygen reduction reaction (ORR) conditions obtained using X-ray absorption near edge spectroscopy (XANES). The results reveal a complex Sabatier catalysis behavior and indicate the active ORR mechanism changes with Pt–O bond weakening from the O2 dissociative mechanism, to the peroxyl mechanism, and finally to the hydrogen peroxide mechanism. An important rearrangement of the OOH binding site, an intermediate in the ORR, enables facile H addition to OOH and faster O–O bond breaking on 111 faces at optimal Pt–O bonding strength, such as that occurring in dealloyed PtM core-shell nanoparticles. This rearrangement is identified by previous DFT calculations and confirmed from in situ measured OOH adsorption coverages during the ORR. The importance of surface structural effects and 111 ordered faces is confirmed by the higher specific ORR rates on solid core vs porous multi-core nanoparticles.

中文翻译：

---

OOH 结合位点和 Pt 表面结构对 ORR 活性的作用

我们展示了在氧还原反应 (ORR) 条件下，使用 X 射线吸收近边光谱获得的实际操作脱合金双金属 PtMx（M = Ni 或 Co）催化剂上通过实验观察到的分子吸附物覆盖范围（例如，O(H)、OOH 和 HOOH） （XANES）。结果揭示了复杂的 Sabatier 催化行为，并表明随着 Pt-O 键减弱，活性 ORR 机制发生变化，从 O2 解离机制，到过氧化氢机制，最后到过氧化氢机制。OOH 结合位点（ORR 中的中间体）的重要重排使得 H 能够轻松添加到 OOH 中，并在最佳 Pt-O 键合强度下在 111 个面上更快地断裂 O-O 键，例如脱合金 PtM 核-壳纳米粒子中发生的情况。这种重排是通过之前的 DFT 计算确定的，并通过 ORR 期间原位测量的 OOH 吸附覆盖范围进行确认。实心核与多孔多核纳米粒子相比具有更高的特定 ORR 率，证实了表面结构效应和 111 个有序面的重要性。