Atomic-Scale Insights into Morphological, Structural, and Compositional Evolution of CoOOH during Oxygen Evolution Reaction,ACS Catalysis

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Atomic-Scale Insights into Morphological, Structural, and Compositional Evolution of CoOOH during Oxygen Evolution Reaction
ACS Catalysis ( IF 11.3 ) Pub Date : 2023-01-09 , DOI: 10.1021/acscatal.2c03903
Chenglong Luan ₁ , Manuel Corva ₂ , Ulrich Hagemann ₃ , Hongcai Wang ₁ , Markus Heidelmann ₃ , Kristina Tschulik _{2,

4} , Tong Li ₁

Affiliation

Co-based electrocatalysts are an emerging class of materials for the oxygen evolution reaction (OER). These materials undergo dynamic surface changes, converting to an active Co oxyhydroxide (CoOOH) layer during OER. A better understanding of the structural, morphological, and elemental evolution of CoOOH formed during OER is, therefore, crucial for the optimization of Co-based electrocatalysts. Herein, we propose an innovative multimodal method, which combines X-ray photoelectron spectroscopy, electron backscatter diffraction, high-resolution transmission electron microscopy, and atom probe tomography with electrochemical testing to investigate the temporal evolution of the oxidation state, thickness, morphology, and elemental distribution of the CoOOH layer grown on Co(0001) during OER. We reveal that the oxyhydroxide layer with the highest OER activity is a 5−6 nm thick, strongly hydrated film resembling a β-CoOOH(0001) structure and consisting of stacks of nanocrystals; which explains the X-ray amorphous characteristics of active species formed on Co-based electrocatalysts observed by operando X-ray-based techniques. The large interfacial area at these hydrated β-CoOOH(0001) nanocrystals enables efficient mass transport of reacting hydroxyl ions to catalytically active sites, and thus, high OER rates. As OER proceeds, the well-hydrated β-CoOOH(0001) nanocrystals grow into a monolithic crystalline β-CoOOH(0001) film. This goes along with a decrease in water content and electrochemically accessible catalyst area, resulting in slightly decreased OER currents. Overall, our study unprecedentedly unveils that in situ generated thin β-CoOOH(0001) layer undergoes dynamic morphological and elemental changes along with (de)incorporation of water molecules and hydroxyl groups during OER, which in turn alters OER performance. We demonstrate the strength of our multimodal characterization approach when seeking mechanistic insights into the role of structural and compositional evolution of hydrous oxides in activity during electrocatalytic reactions.

中文翻译：

析氧反应过程中 CoOOH 的形态、结构和成分演变的原子尺度洞察

钴基电催化剂是一类用于析氧反应 (OER) 的新兴材料。这些材料会发生动态表面变化，在 OER 过程中转化为活性羟基氧化钴 (CoOOH) 层。因此，更好地了解 OER 过程中形成的 CoOOH 的结构、形态和元素演化对于优化 Co 基电催化剂至关重要。在此，我们提出了一种创新的多模式方法，将 X 射线光电子能谱、电子背散射衍射、高分辨率透射电子显微镜和原子探针层析成像与电化学测试相结合，以研究氧化态、厚度、形态和和的时间演变。 OER 期间在 Co(0001) 上生长的 CoOOH 层的元素分布。我们发现具有最高 OER 活性的羟基氧化物层是 5-6 nm 厚的强水合膜，类似于 β-CoOOH(0001) 结构，由纳米晶体堆叠组成；这解释了通过原位 X 射线技术观察到的在 Co 基电催化剂上形成的活性物质的 X 射线非晶特征。这些水合 β-CoOOH(0001) 纳米晶体的大界面面积能够将反应性氢氧根离子有效地传质到催化活性位点，从而实现高 OER 速率。随着 OER 的进行，水合良好的 β-CoOOH(0001) 纳米晶体生长成单片结晶 β-CoOOH(0001) 薄膜。这伴随着水含量和电化学可及催化剂面积的减少，导致 OER 电流略有下降。总体，我们的研究前所未有地揭示了原位生成的薄 β-CoOOH(0001) 层在 OER 过程中经历了动态形态和元素变化以及水分子和羟基的（去）结合，这反过来又改变了 OER 性能。在寻求对电催化反应过程中水合氧化物的结构和组成演变在活性中的作用的机械见解时，我们展示了我们的多峰表征方法的优势。

更新日期：2023-01-09

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