Improvement of the electrocatalytic performance of platinum-free hierarchical Cu/polypyrrole/NiOx anode for methanol oxidation via changing the morphology of polypyrrole sublayer by self-assembled pyrrole monomers and overoxidation

- Cu/Polypyrrole/NiO layer-by-layer electrodes were fabricated electrochemically.
- Morphology of polypyrrole was changed via self-assembled layer of pyrrole monomers.
- The electrodes showed improved electrocatalytic properties for methanol oxidation.
- This improvement was due to the increase of electrodes active surface area.

Platinum-free electrocatalysts have been considered recently due to their low costs and high resistances against poisoning with reaction intermediates. In this work different electrocatalysts based on a matrix of polypyrrole, PPy, were examined for catalysis of methanol oxidation reaction, MOR. The copper substrates were covered by a PPy layer and NiOx nanoparticles were deposited electrochemically on it. The Cu/PPy/NiOx electrodes indicated catalytic performance for MOR. However, it was shown that the modification of the morphology of PPy, influenced its catalytic behavior. The self-assembly of pyrrole monomers on copper, prior to polymerization, led to the formation of tiny PPy nanoparticles between the common cauliflowers shaped PPy masses. The overoxidation was then carried out electrochemically and the PPy matrix encountered changes in morphology with micro/nano cracks. These changes in PPy morphology facilitated the diffusion of methanol electroactive species, which was verified by the cyclic voltammetry and electrochemical impedance spectroscopy results. The enhancement of active surface area and reduction of diffusion resistance for modified electrodes caused significant increment of their electrocatalytic performance. Scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction patterns were used for the characterization of the surface layers.