利用交流阻抗谱揭示Ir(111)电极在酸性溶液中的氢吸附动力学

Unravelling Hydrogen Adsorption Kinetics on Ir(111)Electrode in Acid Solutions by Impedance Spectroscopy

本文利用阻抗谱研究Ir(111)电极在HClO_(4)和H_(2)SO_(4)中溶液中的氢吸附行为.在HClO_(4)溶液中,随着施加电位从0.2 V降到0.1 V(vs RHE),Ir(111)电极上氢吸附速率从1.74×10^(-8)mol·cm^(-2)·s^(-1)增大到3.47×10^(-7)mol·cm^(-2)·s^(-1).与相同条件下Pt(111)电极上的氢吸附速率相比,Ir(111)上的氢吸附速率要小1~2个数量级,这是由于Ir(111)电极与H_(2)O结合能力更强,因此位于水合氢键网络中的氢离子需要克服更高的能垒才能重新定向进而发生欠电位沉积.在H_(2)SO_(4)溶液中,氢吸附电位负移了200 mV,吸附速率也下降了一个数量级,这是由于Ir(111)电极表面强吸附的硫酸根/硫酸氢根物种的阻碍作用.结果表明,在电化学环境下,位于电极表面附近的水分子的取代和重新定向在很大程度上影响了氢吸附过程.

The kinetics for hydrogen(H)adsorption on Ir(111)electrode has been studied in both HClO_(4) and H_(2)SO_(4) solutions by impedance spectroscopy.In HClO_(4),the adsorption rate for H adsorption on Ir(111)increases from 1.74×10^(-8)mol·cm^(-2)·s^(-1) to 3.47×10^(-7)mol·cm^(-2)·s^(-1) with the decrease of the applied potential from 0.2 V to 0.1 V(vs.RHE),which is ca.one to two orders of magnitude slower than that on Pt(111)under otherwise identical condition.This is explained by the stronger binding of water to Ir(111),which needs a higher barrier to reorient during the under potential deposition of H from hydronium within the hydrogen bonded water network.In H_(2)SO_(4),the adsorption potential is ca.200 mV negatively shifted,accompanied by a decrease of adsorption rate by up to one order of magnitude,which is explained by the hindrance of the strongly adsorbed sulfate/bisulfate on Ir(111).Our results demonstrate that under electrochemical environment,H adsorption is strongly affected by the accompanying displacement and reorientation of water molecules that initially stay close to the electrode surface.