In situ scanning tunneling microscopy of the adsorption and polymerization of aniline on Au(111) electrode in nitric acid

In situ scanning tunneling microscopy (STM) is used to study the morphology and molecular structure of polyaniline (PAN) produced electrochemically on Au(111) electrode in 0.5 M nitric acid containing 30 mM aniline. Aniline molecules are coadsorbed with nitrate anions in zigzagged chains running parallel to the (110) directions of the Au(111) electrode. A highly ordered (3 x 2 root 3)rect adlattice is observed between 0.5 and 0.8 V (vs. reversible hydrogen electrode), which restructures into a (3 x 2 root 21) phase at E > 0.85 V. Guided by the ordered aniline adlayer, the second aniline adlayer is oxidized and polymerizes at 0.92 V, yielding one-dimensional PAN stripes aligned along the (110) directions of the Au(111) substrate. Molecular-resolution STM imaging discerns benzoidal and quinoidal rings in the backbone of PAN. The first two PAN layers grow as a smooth film, but the subsequent layers are deposited in 3D to give a rough morphology. Switching the potential from 0.8 to 0.6 V reconfigures PAN molecules from linear to winding form. (C) 2014 Elsevier B.V. All rights reserved.