In situ scanning tunneling microscopy of the adsorption and polymerization of aniline on Au(1 1 1) electrode in nitric acid

• In situ STM reveals the adsorption and polymerization processes of aniline on Au(1 1 1) electrode in nitric acid.
• Two ordered aniline adlattices are identified at different potentials.
• Oxidative polymerization proceeds in the 〈1 1 0〉 directions on the Au(1 1 1) electrode.
• As-formed polyaniline molecules are mostly linear spanning hundreds of nanometer.

In situ scanning tunneling microscopy (STM) is used to study the morphology and molecular structure of polyaniline (PAN) produced electrochemically on Au(1 1 1) 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 〈1 1 0〉 directions of the Au(1 1 1) electrode. A highly ordered (3 × 2√3)rect adlattice is observed between 0.5 and 0.8 V (vs. reversible hydrogen electrode), which restructures into a (3 × 2√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 〈1 1 0〉 directions of the Au(1 1 1) 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.

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