A mechanistic study on the electrocatalysis of the Pu(IV)/Pu(III) redox reaction at a platinum electrode modified with single-walled carbon nanotubes (SWCNTs) and polyaniline (PANI)

The electrochemistry of the Pu(IV)/Pu(III) couple in 1 M sulphuric acid solution was studied on bare and modified platinum electrodes by cyclic voltammetry and electrochemical impedance spectroscopy. The platinum electrode was separately modified with single-walled carbon nanotubes (SWCNT-Pt) and polyaniline (PANI-Pt). The modified electrodes were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray fluorescence (EDXRF). Electrocatalysis of the Pu(IV)/Pu(III) redox reaction was observed on both SWCNT-Pt and PANI-Pt. However, PANI-Pt showed better catalytic action for the electron transfer reaction of the Pu(IV)/Pu(III) couple. The Pu(IV)/Pu(III) couple showed quasi-reversible electron transfer behavior on a bare platinum electrode because of the PtO layer formation by the Pu(IV) solution at the electrode-electrolyte interface. In SWCNT-Pt, the direct interaction between Pu(IV) and platinum was blocked by SWCNTs and it diminished the oxide layer formation at the interface. The lower charge transfer resistance at SWCNT-Pt also promoted the rate of electron transfer reaction of the Pu(IV)/Pu(III) couple. Electrocatalysis of the Pu(IV)/Pu(III) couple on PANI-Pt was attributed to the cumulative effect of the Donnan interaction between the PANI and Pu(IV) anionic complex, specific adsorption of Pu(IV) on the reactive centres, low charge transfer resistance across the electrode-electrolyte interface and a catalytic chemical reaction coupled with the electron transfer reaction. To the best of our knowledge, this paper presents the first evidence of the electrocatalysis of actinides on SWCNT and PANI modified electrodes along with the detailed investigations of their electrocatalysis mechanisms.