Nano-size effect of Au catalyst for electrochemical reduction of oxygen in alkaline electrolyte

Oxygen reduction reaction (ORR) in alkaline electrolyte (0.5 mol/L KOH) was studied on a series of carbon supported Au nanoparticles (NPs) with average sizes ranging from 3 to 14 nm, using the rotating disk electrode methods. Downsizing the Au NPs from 14 to 3 nm resulted in continued enhancement in both the intrinsic and mass-specific activity of Au for ORR but produced no influence on the reaction mechanism or number of transferred electrons per O2-reduction. Careful analyses of the particle shapes of Au NPs with varied sizes by using high-resolution transmission electron microscopy enabled us to estimate the fraction of surface Au atoms at different positions or coordination (energy) state. Correlating the fraction of high energy surface atoms with the Au activity for ORR disclosed the importance of high energy surface atoms in enhancing the intrinsic activity of Au. Fundamental correlation between the Au intrinsic activity for ORR and the experimentally determined surface electronic structure of Au NPs was also established.

摘要使用旋转电极技术考察了一系列碳载金纳米颗粒(颗粒平均尺寸处在3∼14 nm)在碱性电解质(0.5 mol/L KOH)中对氧还原反应的催化行为. 随着金纳米颗粒尺寸由14 nm下降至3 nm, 其对氧还原反应的本征活性和质量比活性均呈现持续走高趋势; 但金颗粒的纳米尺寸对氧还原反应的机理及分子氧还原过程中的电子转移数目并无显著影响. 使用高分辨透射电镜技术表征了金纳米颗粒的形貌, 通过对金颗粒表面不同位置原子的比例进行估算, 发现金颗粒表面高能原子所占比例与金对氧还原反应的本征活性密切相关, 表明高能表面原子决定着金催化剂对氧还原反应的本征活性. 此外, 还将金纳米颗粒对氧还原反应的本征催化活性与其表面电子结构进行了关联.

Graphical AbstractThis work provides a clear demonstration of the structure-sensitive nature of Au for oxgen reduction reaction (ORR) in alkaline electrolyte using a series of nearly monodisperse Au nanoparticles, with their particle sizes varied in the range of 3 to 14 nm using PVP as the only stabilizer.Figure optionsDownload as PowerPoint slide