Kobayashi Takeshi, Babu Panakkattu K, Gancs Lajos, Chung Jong Ho, Oldfield Eric, Wieckowski Andrzej
Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, IL 61801, USA.
J Am Chem Soc. 2005 Oct 19;127(41):14164-5. doi: 10.1021/ja0550475.
We report the first direct measurement of CO diffusion on nanoparticle Pt electrocatalysts at the solid/liquid interface, carried out using 13C nuclear magnetic resonance (NMR) with a spin-labeling pulse sequence. Diffusion parameters were measured in the temperature range of 253-293 K for CO adsorbed on commercial Pt-black under saturation coverage. 2H NMR of the same system indicates that the electrolyte remains in the liquid state at temperatures where the CO diffusion experiments were performed. The CO diffusion parameters follow typical Arrhenius behavior with an activation energy of 6.0 +/- 0.4 kcal/mol and a pre-exponential factor of (1.1 +/- 0.6) x 10-8 cm2/s. Exchange between different CO populations, driven by a chemical potential gradient, is suggested to be the main mechanism for CO diffusion. The presence of the electrolyte medium considerably slows down the diffusion of CO as compared to that seen on surfaces of bulk metals under UHV conditions. This work opens up a new approach to the study of surface diffusion of adsorbed molecules on nanoparticle electrode catalysts, including the possibility of correlating diffusion parameters to catalytic activity in real world applications of broad general interest.
我们报告了首次在固/液界面上使用自旋标记脉冲序列的13C核磁共振（NMR）对纳米颗粒铂电催化剂上的CO扩散进行的直接测量。在253 - 293 K的温度范围内，对饱和覆盖下吸附在商用铂黑上的CO的扩散参数进行了测量。同一体系的2H NMR表明，在进行CO扩散实验的温度下，电解质保持液态。CO扩散参数遵循典型的阿伦尼乌斯行为，活化能为6.0±0.4 kcal/mol，指前因子为(1.1±0.6)×10-8 cm2/s。由化学势梯度驱动的不同CO种群之间的交换被认为是CO扩散的主要机制。与超高真空条件下块状金属表面相比，电解质介质的存在大大减缓了CO的扩散。这项工作为研究纳米颗粒电极催化剂上吸附分子的表面扩散开辟了一条新途径，包括在具有广泛普遍意义的实际应用中将扩散参数与催化活性相关联的可能性。
