7872
J. Phys. Chem. B 2005, 109, 7872-7877
Supplement to the Theory of Normal Pulse Voltammetry and Its Application to the Kinetic Study of Methanol Oxidation on a Polycrystalline Platinum Electrode Weilin Xu,† Tianhong Lu,†,‡ Changpeng Liu,† and Wei Xing*,† State Key Laboratory of Electro-analytical Chemistry, Changchun Institute of Applied Chemistry, Graduate School of the Chinese Academy of Sciences, 5625 Renmin Street, Changchun 130022, Jilin, People’s Republic of China, and Department of Chemistry, Nanjing Normal UniVersity, Jiangsu, People’s Republic of China ReceiVed: December 9, 2004; In Final Form: February 28, 2005
The theory of normal pulse voltammetry (NPV) for complex multistep multielectron transfer processes on a plane electrode was advanced and applied to the completely irreversible process of methanol oxidation to formic acid in the potential range from 0.3 to 0.8 V versus Ag/AgCl. The kinetic parameters for this process, such as the standard rate constant (k0) and anodic transfer coefficient (R) for this irreversible heterogeneous electron transfer process at the electrode/solution interface and apparent diffusion coefficient (Dapp) for the homogeneous charge transfer process within liquid film near the electrode surface, were obtained with NPV theory from analyzing the dependence of current-potential curves upon the sampling times. The results showed that this process is truly a very slow, completely irreversible kinetic process, as k0 is in the order of 10-9 cm/s for the rate-determining step. The values of k0 and Dapp decreased with the increase of methanol concentration, while R was independent of the concentration of methanol and its value was 0.35 ( 0.05. Theoretical fitting is very consistent with the experimental data.
1. Introduction The general pulse voltammetric (or polarographic) theory for the simple one-step electrode process on a plane electrode came from polarographic theory.1-10 Pulse polarography differs from polarography in that the potential is applied only for a brief period toward the end of drop life (on a dropping mercury electrode).8 The normal pulse voltammetry (or polarography) is one of the three models of pulse polarography practically employed.9 All the electrode processes are classified into three groups according to their standard rate constants. Reversible waves are characterized by large standard rate constants (>10-3 cm/s), but as the latter becomes progressively smaller, the waves pass through a domain of “quasireversibility” to become “completely irreversible” (
