Kinetics of the Reduction of Ruthenium Hexaammine at Bismuth Electrodes in Aqueous Solution: Analyzing the Potential Dependence of the Transfer Coefficient

3 years ago

Kinetics of the Reduction of Ruthenium Hexaammine at Bismuth Electrodes in Aqueous Solution: Analyzing the Potential Dependence of the Transfer Coefficient

Ben R. Horrocks, Aondoakaa S. Nomor

The reduction of Ru(NH3)63+ at Bi electrodes in aqueous KCl is much slower than at Pt electrodes. Differential capacitance and ex situ photoemission spectra indicate the presence of a thin oxide layer about 1.5 nm thick on the Bi surface near the formal potential of −0.217 V vs Ag/AgCl/1 M KCl(aq). Despite the presence of this oxide, reproducible impedance spectra near the formal potential were obtained for Ru(NH3)63+ that could be analyzed by using a Randles circuit modified to incorporate a constant phase element. The value of the standard rate constant was 1.47±0.44×10−3 cm s−1. Under the same conditions, impedance spectra for Pt/Ru(NH3)63+ were reversible up to the highest frequencies (105 Hz) employed. The charge-transfer resistance−dc potential curves obtained from the impedance spectra were fitted by a regression model, which contained no a priori assumption about the potential dependence of the transfer coefficient except piecewise linearity. The measured transfer coefficients show clear evidence of diffuse layer effects, but, in addition, an increase in transfer coefficient at the most negative potentials studied was observed and interpreted in terms of the reduction and thinning of the anodic oxide.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/celc.201700604