Bipolar electrodeposition of gradient polypyrrole films as a catalyst matrix for anodic ethanol oxidation

Abstract

Lateral gradient coatings displaying various compositions and microstructures along a single surface are desirable for material screening. Here we report a successful application of bipolar electrochemistry to deposit lateral gradient polypyrrole films on a graphite strip substrate. The gradient film shows varying morphologies and a wettability gradient along the length of the bipolar electrode, with superabsorbent property in the middle portion of the film. The film was use as a catalyst matrix for ethanol oxidation in alkaline electrolyte. Aqueous Ni(NO3)2 solution as the catalyst precursor was absorbed into the film. Area-step cyclic voltammetry was used to evaluate the electrocatalytic activity of various local parts along the gradient film to ethanol oxidation. The local surface with the highest catalytic activity was screened out and the excellent catalytic activity is attributed to the outstanding properties of this zone in both water absorption and electrical conductivity. The nickel oxide catalyst can be highly dispersed in the nanoporous network polymer matrix, due to the uniform penetration of the aqueous precursor solution into the superabsorbent film. XPS and EIS analyses support the catalytic mechanism based on the redox transition between NiOOH and Ni(OH)2. This work indicates that loading aqueous catalyst precursors into superabsorbent conducting polymer films may be a promising method for the preparation of electrocatalysts.