Department of Chemistry and Biochemistry , University of Oregon , Eugene , Oregon 97403 , United States.
ACS Appl Mater Interfaces. 2019 Feb 13;11(6):5590-5594. doi: 10.1021/acsami.8b02796. Epub 2018 Apr 30.
Metal (oxy)hydroxides (MO H , M = Fe, Co, Ni, and mixtures thereof) are important materials in electrochemistry. In particular, MO H are the fastest known catalysts for the oxygen evolution reaction (OER) in alkaline media. While key descriptors such as overpotentials and activity have been thoroughly characterized, the nanostructure and its dynamics under electrochemical conditions are not yet fully understood. Here, we report on the structural evolution of NiCoO H nanosheets with varying ratios of Ni to Co, in operando using atomic force microscopy during electrochemical cycling. We found that the addition of Co to NiO H nanosheets results in a higher porosity of the as-synthesized nanosheets, apparently reducing mechanical stress associated with redox cycling and hence enhancing stability under electrochemical conditions. As opposed to nanosheets composed of pure NiO H , which dramatically reorganize under electrochemical conditions to form nanoparticle assemblies, restructuring is not found for NiCoO H with a high Co content. NiFeO H nanosheets show high roughness as-synthesized which increases during electrochemical cycling while the integrity of the nanosheet shape is maintained. These findings enhance the fundamental understanding of MO H materials and provide insight into how nanostructure and composition affect structural dynamics at the nanoscale.
金属（氧）氢氧化物（MO H，M=Fe、Co、Ni 及其混合物）是电化学中的重要材料。特别是，MO H 是碱性介质中氧析出反应（OER）已知的最快催化剂。虽然已经对过电势和活性等关键描述符进行了彻底的表征，但纳米结构及其在电化学条件下的动力学仍未完全理解。在这里，我们报告了不同 Ni/Co 比的 NiCoO H 纳米片在电化学循环过程中使用原子力显微镜进行原位操作时的结构演变。我们发现，将 Co 添加到 NiO H 纳米片中会导致合成的纳米片具有更高的孔隙率，显然会降低与氧化还原循环相关的机械应力，从而提高电化学条件下的稳定性。与由纯 NiO H 组成的纳米片相反，后者在电化学条件下会剧烈重组形成纳米颗粒组装体，而高 Co 含量的 NiCoO H 则不会发生重组。NiFeO H 纳米片在合成时具有高粗糙度，在电化学循环过程中会增加，而纳米片形状的完整性得以保持。这些发现增强了对 MO H 材料的基本理解，并深入了解了结构和组成如何影响纳米尺度的结构动力学。
