Kamšek Ana Rebeka, Ruiz-Zepeda Francisco, Bele Marjan, Logar Anja, Dražić Goran, Hodnik Nejc
Department of Materials Chemistry, National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia.
Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, 1000 Ljubljana, Slovenia.
ACS Nano. 2025 Jan 21;19(2):2334-2344. doi: 10.1021/acsnano.4c12528. Epub 2025 Jan 7.
Nanoparticulate electrocatalysts for the oxygen reduction reaction are structurally diverse materials. Scanning transmission electron microscopy (STEM) has long been the go-to tool to obtain high-quality information about their nanoscale structure. More recently, its four-dimensional modality has emerged as a tool for a comprehensive crystal structure analysis using large data sets of diffraction patterns. In this study, we track the alternations of the crystal structure of individual carbon-supported PtCu nanoparticles before and after fuel cell-relevant activation treatment, consisting of a mild acid-washing protocol and potential cycling, essential for forming an active catalyst. To take full advantage of the rich, identical location 4D-STEM capabilities, unsupervised algorithms were used for the complex data analysis, starting with -means clustering followed by non-negative matrix factorization, to find commonly occurring signals within specific nanoparticle data. The study revealed domains with (partially) ordered alloy structures, twin boundaries, and local amorphization. After activation, specific nanoparticle surface sites exhibited a loss of crystallinity which can be correlated to the simultaneous local scarcity of the ordered alloy phase, confirming the enhanced stability of the ordered alloy during potential cycling activation conditions. With the capabilities of our in-house developed identical-location 4D-STEM approach to track changes in individual nanoparticles, combined with advanced data analysis, we determine how activation treatment affects the electrocatalysts' local crystal structure. Such an approach provides considerably richer insights and is much more sensitive to minor changes than traditional STEM imaging. This workflow requires little manual input, has a reasonable computational complexity, and is transferrable to other functional nanomaterials.
用于氧还原反应的纳米颗粒电催化剂是结构多样的材料。扫描透射电子显微镜（STEM）长期以来一直是获取有关其纳米级结构高质量信息的首选工具。最近，其四维模式已成为一种使用大量衍射图案数据集进行全面晶体结构分析的工具。在本研究中，我们追踪了单个碳载PtCu纳米颗粒在与燃料电池相关的活化处理前后的晶体结构变化，该处理包括温和酸洗方案和电位循环，这对于形成活性催化剂至关重要。为了充分利用丰富的、相同位置的4D-STEM功能，使用无监督算法进行复杂数据分析，首先进行k均值聚类，然后进行非负矩阵分解，以在特定纳米颗粒数据中找到常见信号。研究揭示了具有（部分）有序合金结构、孪晶界和局部非晶化的区域。活化后，特定纳米颗粒表面位点表现出结晶度损失，这与有序合金相同时局部稀缺相关，证实了在电位循环活化条件下有序合金的稳定性增强。凭借我们内部开发的相同位置4D-STEM方法追踪单个纳米颗粒变化的能力，结合先进的数据分析，我们确定了活化处理如何影响电催化剂的局部晶体结构。这种方法提供了丰富得多的见解，并且比传统STEM成像对微小变化更敏感。此工作流程几乎不需要人工输入，具有合理的计算复杂度，并且可转移到其他功能纳米材料上。
