Seidel Y E, Schneider A, Jusys Z, Wickman B, Kasemo B, Behm R J
Institute of Surface Chemistry and Catalysis, Ulm University, Ulm D-89069, Germany.
Faraday Discuss. 2008;140:167-84; discussion 185-207. doi: 10.1039/b806437g.
The role of mesoscopic mass transport and re-adsorption effects in electrocatalytic reactions was investigated using the oxygen reduction reaction (ORR) as an example. The electrochemical measurements were performed on structurally well-defined nanostructured model electrodes under controlled transport conditions in a thin-layer flow cell. The electrodes consist of arrays of Pt ultra-microelectrodes (nanodisks) of defined size (diameter approximately 100 nm) separated on a planar glassy carbon (GC) substrate, which were fabricated employing hole-mask colloidal lithography (HCL). The measurements reveal a distinct variation in the ORR selectivity with Pt nanodisk density and with increasing electrolyte flow, showing a pronounced increase of the H2O2 yield, by up to 65%, when increasing the flow rate from 1 to 30 microL s(-1). These results are compared with previous findings and discussed in terms of a reaction model proposed recently (A. Schneider et al., Phys. Chem. Chem. Phys., 2008, 10, 1931), which includes (i) direct reduction to H2O on the Pt surface and (ii) additional H2O2 formation and desorption on both Pt and carbon surfaces and subsequent partial re-adsorption and further reduction of the H2O2 molecules on the Pt surface. The potential of model studies on structurally defined catalyst surfaces and under well-defined mass transport conditions in combination with simulations for the description of electrocatalytic reactions is discussed.
以氧还原反应（ORR）为例，研究了介观质量传输和再吸附效应在电催化反应中的作用。在薄层流动池中，在可控传输条件下，对结构明确的纳米结构模型电极进行了电化学测量。电极由在平面玻璃碳（GC）基底上隔开的特定尺寸（直径约100 nm）的铂超微电极（纳米盘）阵列组成，这些电极采用孔掩膜胶体光刻（HCL）制备。测量结果表明，ORR选择性随铂纳米盘密度和电解质流量增加而有明显变化，当流速从1 μL s⁻¹增加到30 μL s⁻¹时，H₂O₂产率显著增加，最高可达65%。将这些结果与先前的发现进行了比较，并根据最近提出的反应模型（A. Schneider等人，《物理化学化学物理》，2008年，10卷，1931页）进行了讨论，该模型包括：（i）在铂表面直接还原为H₂O；（ii）在铂和碳表面上额外形成和脱附H₂O₂，随后H₂O₂分子在铂表面进行部分再吸附和进一步还原。讨论了在结构明确的催化剂表面和明确的质量传输条件下进行模型研究，并结合模拟来描述电催化反应的潜力。
