Abstract
In order to diminish the overpotential required for the electrochemical reduction of 
, a metal complex‐fixed polyaniline (PAn)/prussian blue (PB)‐modified electrode has been developed, and the roles of the two laminated films as well as a fixed metal complex are disclosed here. The onset potential for the reduction of 
to lactic acid, a major product, is close to the thermodynamic value (
vs. SCE). The metal complex operating as the catalyst is a large aromatic anion, which is bound to the conducting polymer through π‐interaction and not undoped during the cathodic polarization. The existence of R‐OH, 
, 
, and 
groups in the coated film was confirmed by Fourier transform infrared reflection spectroscopy, supporting the involvement of the observed products (lactic acid, formic acid, methanol, ethanol, etc.). A cause for the generation of 
species such as lactic acid may be bifunctional activation of 
in which the electrophilic carbon atom links to the amino group of PAn and the basic oxygen atom coordinates to the central metal of the complex.