A Comparison of Atomistic and Continuum Approaches to the Study of Bonding Dynamics in Electrocatalysis: Microcantilever Stress and in Situ EXAFS Observations of Platinum Bond Expansion Due to

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• 作者：Evan M. Erickson ; Muhammed E. Oruc ; David J. Wetzel ; Michael W. Cason ; Thao T. H. Hoang ; Matthew W. Small ; Diya Li ; Anatoly I. Frenkel ; Andrew A. Gewirth ; Ralph G. Nuzzo
• 刊名：Analytical Chemistry
• 出版年：2014
• 出版时间：August 19, 2014
• 年：2014
• 卷：86
• 期：16
• 页码：8368-8375
• 全文大小：401K
• ISSN：1520-6882

文摘

Microcantilever stress measurements are examined to contrast and compare their attributes with those from in situ X-ray absorption spectroscopy to elucidate bonding dynamics during the oxygen reduction reaction (ORR) on a Pt catalyst. The present work explores multiple atomistic catalyst properties that notably include features of the Pt鈥揚t bonding and changes in bond strains that occur upon exposure to O₂ in the electrochemical environment. The alteration of the Pt electronic and physical structures due to O₂ exposure occurs over a wide potential range (1.2 to 0.4 V vs normal hydrogen electrode), a range spanning potentials where Pt catalyzes the ORR to those where Pt-oxide forms and all ORR activity ceases. We show that Pt鈥揚t surface bond strains due to oxygen interactions with Pt鈥揚t bonds are discernible at macroscopic scales in cantilever-based bending measurements of Pt thin films under O₂ and Ar. Complementary extended X-ray absorption fine structure (EXAFS) measurements of nanoscale Pt clusters supported on carbon provide an estimate of the magnitude and direction of the in-operando bond strains. The data show that under O₂ the M鈥揗 bonds elongate as compared to an N₂ atmosphere across a broad range of potentials and ORR rates, an interfacial bond expansion that falls within a range of 0.23 (卤0.15)% to 0.40 (卤0.20)%. The EXAFS-measured Pt鈥揚t bond strains correspond to a stress thickness and magnitude that is well matched to the predictions of a mechanics mode applied to experimentally determined data obtained via the cantilever bending method. The data provide new quantitative understandings of bonding dynamics that will need to be considered in theoretical treatments of ORR catalysis and substantiate the subpicometer resolution of electrochemically mediated bond strains detected on the macroscale.