Electron transfer rates at Bi and Pt of viologens

The standard heterogeneous rate constants for the reduction of a series of viologen derivatives with a range of inter–ring torsion an- gles were measured at Bi and Pt electrodes. The electrode potentials for the first one–electron reduction of the viologens vary from -684 mV to -1070 mV vs. Ag/0.01M Ag+ ; this enabled a comparison of the behaviour of metallic (Pt) and semi-metallic (Bi) electrodes over a wide range of applied potentials. The differential capacitance (6.5 μF cm−2 ) of Bi/MeCN,TBAPF6 interfaces at the potential of zero charge (pzc = -0.60V) is at least an order of magnitude greater than that calculated on the basis of the bulk Bi carrier density (3 × 1017 cm−3 ) and the differential capacitance (9.5 μF cm−2) of Pt/MeCN interfaces at their pzc (-0.43V) is of the same order. The series of vi- ologen derivatives exhibited simple one-electron redox behaviour and showed similar rate constants at Pt ( 1.8 × 10−4 – 1.6 × 10−3 cm s−1 ) and Bi electrodes (1.1 × 10−4 – 1.9 × 10−3 cm s−1 ) after application of the Frumkin correction. These results demonstrate that the den- sity of states at the Bi surface is much higher than in bulk. Finally, the Frumkin-corrected standard rate constants were observed to be inversely correlated with the inter-ring torsion angle of the viologens.

本数据集测定了一系列具有不同环间扭转角的联吡啶鎓（viologen）衍生物在铋（Bi）与铂（Pt）电极上还原的标准非均相速率常数。该系列联吡啶鎓衍生物的首次单电子还原电极电势相对于Ag/0.01M Ag+参比电极的范围为-684 mV至-1070 mV，这使得我们能够在较宽的施加电势范围内对比金属（Pt）与半金属（Bi）电极的电化学行为。铋/乙腈（MeCN）-四丁基六氟磷酸铵（TBAPF6）界面在零电荷电位（potential of zero charge，pzc = -0.60V）处的微分电容为6.5 μF·cm⁻²，至少比基于体相铋载流子密度（3 × 10¹⁷ cm⁻³）计算得到的数值高一个数量级；而铂/MeCN-TBAPF6界面在其零电荷电位（pzc = -0.43V）处的微分电容为9.5 μF·cm⁻²，二者处于同一数量级。该系列联吡啶鎓衍生物表现出简单的单电子氧化还原行为，经弗鲁姆金（Frumkin）校正后，其在Pt电极上的标准速率常数范围为1.8 × 10⁻⁴ – 1.6 × 10⁻³ cm·s⁻¹，在Bi电极上则为1.1 × 10⁻⁴ – 1.9 × 10⁻³ cm·s⁻¹，两组速率常数水平相近。上述结果表明，铋表面的态密度远高于其体相态密度。最后，经弗鲁姆金校正后的标准速率常数与联吡啶鎓衍生物的环间扭转角呈负相关关系。