Electrochemical Quartz Crystal Nanobalance Analyses of Electrocatalysis for Fuel Cells

为了寻找设计高性能燃料电池电催化剂的线索，我们用电化学石英晶体纳米天平（EQCN）分析了Pt-Fe和Pt-Co合金与纯Pt上的电极反应。我们得到了以下结果。1.我们成功地构建了10 MHz-EQCN系统，并证实了其± 0.1Hz（± 0.4ng/cm^2）的最终精度和长时间的高稳定性.在0.1MHClO_4溶液中，铂-铁和铂-钴电极在多次重复电位扫描过程中形成了少量的铂-皮层单层，即，合金组分溶解，随后是薄Pt层的重排。XPS、ICP和EC-STM的结果与EQCN的结果是互补的.用EQCN分析了Pt-Fe和Pt-Co合金电极的CO耐受性。在CO吸附（θ = <co>1）的纯Pt电极上，用正电位扫描， ...更多信息 在0.3 ~ 0.5V（相对于RHE）处观察到一个预氧化峰（P_1），然后在0.7V处观察到一个CO氧化峰（P_2）。每个P_1分别归属于Pt-Fe和Pt-Co合金上弱吸附CO的氧化和纯Pt上吸附羧酸根的氧化。这与我们先前通过原位FTIR的结果是一致的，并且强烈支持了我们提出的纯Pt的Pt皮肤的修改的电子结构。在P_2区，CO被H_2O放电产生的OH氧化，两个电极上由CO或CO相关物种（COOH）氧化形成的空位部分被水合ClO_4阴离子占据.用EQCN分析了Pt、Pt-Fe和Pt-Co电极在O_2饱和的0.1MHClO_4溶液中的氧还原反应。在纯Pt下，恒定量的反应中间体如Pt-O（约. 20%）即使在高过电压下也总是吸附在表面上。相比之下，在Pt-Fe和Pt-Co电极上发现这种中间体的量相当低，可能是由于快速ORR动力学。合金和纯Pt之间的这种差异可以归因于Pt皮的电子结构的改变。少

In order to find a clue for a design of high-performance electrocatalysts for fuel cells, we analyzed electrode reactions on Pt-Fe and Pt-Co alloy in comparison with that on pure Pt by using an electrochemical quartz crystal nanobalance (EQCN). We obtained the following results.1. We succeeded to construct 10MHz-EQCN system with a specially designed electrochemical cell, and confirmed the ultimate accuracy of ±0.1 Hz (±0.4 ng/cm^2) and high stability among long time.2. It was found that the Pt-Fe and Pt-Co electrodes were electrochemically stabilized by a formation of a few monolayers of Pt-skin layer during several repetitive potential sweeps in 0.1 M HClO_4 solution, i.e., a dissolution of alloy components followed by a rearrangement of thin Pt layer. The results obtained by XPS, ICP and EC-STM complement the EQCN results.3. A CO-tolerance at Pt-Fe and Pt-Co alloy electrodes was analyzed by the EQCN. In a positive-going potential scan at CO-adsorbed (θ_<co>=1) electrodes of pure Pt a … More nd Pt-Fe or Pt-Co alloy, a pre-oxidation peak (P_1) was observed at 0.3 to 0.5 V vs. RHE before a major CO oxidation peak (P_2) at 0.7 V. Each P_1 was assigned to an oxidation of weakly-adsorbed CO at Pt-Fe and Pt-Co alloys and adsorbed carboxylate at pure Pt, respectively. This is consistent with our previous results by in-situ FTIR, and strongly supports a modified electronic structure of the Pt-skin from that of pure Pt, which has been proposed by us. At P_2 region, CO is oxidized by OH formed by H_2O discharge and vacant sites on both of the electrodes formed by the oxidation of CO or CO-related species (COOH) are partly occupied by hydrated ClO_4 anions.4. Oxygen reduction reactions (ORR) at Pt, Pt-Fe, and Pt-Co electrodes in O_2-saturated 0.1 M HClO_4 solution were analyzed by the EQCN. At pure Pt, a constant amount of reaction intermediate such as Pt-O (ca. 20 %) always adsorbed on the surface even under high overvoltage. In contrast, the amount of such an intermediate was found to be fairly low at Pt-Fe and Pt-Co electrodes, probably due to a fast ORR kinetics. Such a difference between alloys and pure Pt may be ascribed to modified electronic structure of the Pt-skin. Less