Monitoring the spontaneous reconstruction of the surface of metal oxides under electrocatalytic reaction conditions is critical to identifying the active sites and establishing structure–activity relationships. Here, we report on a self-terminated surface reconstruction of Ruddlesden–Popper lanthanum nickel oxide (La₂NiO_4+δ) that occurs spontaneously during reaction with alkaline electrolyte species. Using a combination of high-resolution scanning transmission electron microscopy (HR-STEM), surface-sensitive X-ray photoelectron spectroscopy (XPS), and soft X-ray absorption spectroscopy (sXAS), as well as electrochemical techniques, we identify the structure of the reconstructed surface layer as an amorphous (oxy)hydroxide phase that features abundant under-coordinated nickel sites. No further amorphization of the crystalline oxide lattice (beyond the ∼2 nm thick layer formed) was observed during oxygen evolution reaction (OER) cycling experiments. Notably, the formation of the reconstructed surface layer increases the material’s oxygen evolution reaction (OER) activity by a factor of 45 when compared to that of the pristine crystalline surface. In contrast, a related perovskite phase, i.e., LaNiO₃, did not show noticeable surface reconstruction, and also no increase in its OER activity was observed. This work provides detailed insight into a surface reconstruction behavior dictated by the crystal structure of the parent oxide and highlights the importance of surface dynamics under reaction conditions.

中文翻译：

---

探究镍酸镧电催化剂在析氧反应过程中的表面转变

监测电催化反应条件下金属氧化物表面的自发重建对于识别活性位点和建立构效关系至关重要。在这里，我们报告了 Ruddlesden-Popper 氧化镍镧 (La ₂ NiO _4+δ ) 在与碱性电解质反应过程中自发发生的自终止表面重构。结合使用高分辨率扫描透射电子显微镜 (HR-STEM)、表面敏感 X 射线光电子能谱 (XPS) 和软 X 射线吸收光谱 (sXAS) 以及电化学技术，我们鉴定了结构重建的表面层为无定形（羟基）氢氧化物相，具有丰富的欠配位镍位点。在析氧反应（OER）循环实验中，没有观察到晶体氧化物晶格（超出形成的~2 nm厚层）的进一步非晶化。值得注意的是，与原始晶体表面相比，重建表面层的形成使材料的析氧反应 (OER) 活性提高了 45 倍。相反，相关的钙钛矿相，即LaNiO ₃，没有表现出明显的表面重构，并且也没有观察到其OER活性的增加。这项工作提供了对由母体氧化物晶体结构决定的表面重构行为的详细见解，并强调了反应条件下表面动力学的重要性。