On the use of cyclic voltammetry for the screening of oxide catalysts for NO decomposition and reduction

It has been claimed [J. Zhu, D. Xiao, J. Li, X. Yang, Y. Wu, Electrochem. Commun. 7 (2005) 58] that cyclic voltammetry of perovskite-like oxides in a LiClO₄/propylene carbonate electrolyte is a strong tool for selecting those oxides more active for NO decomposition and reduction. This claim is fundamentally wrong, since it is based on: (1) a travesty of Nernst's equation, in which the peak separation in a cyclic voltammogram, a purely kinetic parameter, is substituted for the thermodynamic equilibrium potential (2) a wrong claim that the electron transfer between a transition metal cation in an oxide and a neighbouring oxygen vacancy, a process that occurs within the oxide, without any electron transfer through the electrode-electrolyte interface, is responsible for the voltammetric peaks of lithium insertion/deinsertion observed in cyclic voltammetry (unexplainably, lithium insertion/deinsertion is not mentioned at all in the article) (3) an unproven relationship between the charge of the voltammetric peaks of lithium insertion/deinsertion and the concentration of oxygen vacancies in the oxide (4) an unproven correlation between the reversibility of the lithium insertion/deinsertion process at room temperature and the catalytic process of NO decomposition at 850 °C. Therefore, at present cyclic voltammetry has not been shown to be a useful tool for the screening of catalysts for NO decomposition and reduction.