Chen Yan Xia, Ye Shen, Heinen Martin, Jusys Zenonas, Osawa Masatoshi, Behm R Jürgen
Department Surface Chemistry and Catalysis, University of Ulm, D-89069 Ulm, Germany.
J Phys Chem B. 2006 May 18;110(19):9534-44. doi: 10.1021/jp057463h.
The potential of in-situ Fourier transform infrared (FTIR) spectroscopy measurements in an attenuated total reflection configuration (ATR-FTIRS) for the evaluation of reaction pathways, elementary reaction steps, and their kinetics is demonstrated for formic acid electrooxidation on a Pt film electrode. Quantitative kinetic information on two elementary steps, formic acid dehydration and CO(ad) oxidation, and on the contributions of the related pathways in the dual path reaction mechanism are derived from IR spectroscopic signals in simultaneous electrochemical and ATR-FTIRS measurements over a wide temperature range (25-80 degrees C). Linearly and multiply bonded CO(ad) and bridge-bonded formate are the only formic acid related stable reaction intermediates detected. With increasing temperature, the steady-state IR signal of CO(ad) increases, while that of formate decreases. Reaction rates for CO(ad) formation via formic acid dehydration and for CO(ad) oxidation as well as the activation energies of these processes were determined at different temperatures, potentials, and surface conditions (with and without preadsorbed CO from formic acid dehydration) from the temporal evolution of the IR intensities of CO(ad) during adsorption/reaction transients, using an IR intensity-CO(ad) coverage calibration. At potentials up to 0.75 V and temperatures from 25 to 80 degrees C, the "indirect" CO pathway contributes less than 5% (at potentials < or =0.6 V significantly below 1%) to the total Faradaic reaction current, making the "direct" pathway by far the dominant one under the present reaction conditions. Much higher activation energies for CO(ad) formation and CO(ad) oxidation compared with the effective activation energy of the total reaction, derived from the Faradaic currents, support this conclusion.
在衰减全反射配置（ATR - FTIRS）下进行原位傅里叶变换红外（FTIR）光谱测量，用于评估铂薄膜电极上甲酸电氧化反应途径、基元反应步骤及其动力学的潜力得到了证明。在较宽温度范围（25 - 80摄氏度）内，通过同时进行电化学和ATR - FTIRS测量，从红外光谱信号中获得了关于两个基元步骤（甲酸脱水和CO(ad)氧化）以及双路径反应机制中相关途径贡献的定量动力学信息。线性和多重键合的CO(ad)以及桥键合的甲酸根是检测到的仅有的与甲酸相关的稳定反应中间体。随着温度升高，CO(ad)的稳态红外信号增加，而甲酸根的稳态红外信号降低。通过甲酸脱水形成CO(ad)的反应速率、CO(ad)氧化反应速率以及这些过程的活化能，是在不同温度、电位和表面条件下（有或没有甲酸脱水预吸附的CO），利用吸附/反应瞬态过程中CO(ad)红外强度的时间演变，并通过红外强度 - CO(ad)覆盖度校准来确定的。在高达0.75 V的电位和25至80摄氏度的温度下，“间接”CO途径对总法拉第反应电流的贡献小于5%（在电位≤0.6 V时显著低于1%），这使得“直接”途径在当前反应条件下成为主导途径。与从法拉第电流得出的总反应有效活化能相比，CO(ad)形成和CO(ad)氧化的活化能要高得多，这支持了这一结论。
