Voltammetric investigations on the relative deactivation of boron-doped diamond, glassy carbon and platinum electrodes during the anodic oxidation of substituted phenols in room temperature ionic liquids

Deactivation behaviour of boron-doped diamond (BDD) had been extensively studied for the first time in three room temperature ionic liquids (RTILs) namely 1-ethyl-3-methyl imidazolium nonaflate (EMIN), triethylmethylammonium methyl sulphate (TEMAMS) and N-hexyl-N,N,N-triethylammonium bis(trifluoromethanesulfonyl)imide (N2226TFSI) along with glassy carbon (GC) and platinum (Pt) electrodes on the anodic oxidation of 2,6-dimethylphenol (2,6-DMP), 2,4-dimethylphenol (2,4-DMP) and 3,4-methylenedioxyphenol (3,4-MDP) using cyclic voltammetry (CV). Voltammetric studies reveal that the anodic potential limit of the electrodes decreases in the order GC > BDD > Pt in these media and EMIN shows the highest anodic limit among the three RTILs. Multisweep CV studies suggest that the three phenols show irreversible and reversible characteristics on the BDD and Pt electrodes respectively. On the other hand, they exhibit reversible redox behaviour in TEMAMS and irreversible nature in EMIN and N2226TFSI media on the GC electrode. The phenolic compounds get oxidised at higher potential on the BDD electrode followed by Pt and GC electrodes and their oxidation potential in the three media increases in the order: TEMAMS < EMIN < N2226TFSI. Anodic polarisation studies in presence of phenols suggests that the Pt and GC do not show any serious electrode fouling; however, the BDD gets deactivated severely, as noted from the Ipa4/Ipa1 values. Passivation of the BDD electrode in the EMIN medium containing the 2,6-DMP was investigated by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The effect of acetonitrile (CH3CN) on the activation of the BDD electrode surface was also studied in detail.

► Deactivation of the BDD in RTILs was compared along with GC and Pt electrodes on the anodic oxidation of substituted phenols using cyclic voltammetry. ► The synthesised RTILs contain nonaflate, TFSI and sulphate based anions. ► GC shows higher anodic potential limit than the BDD and Pt in the RTILs media. ► BDD gets deactivated in all the media on the anodic polarisation of phenols, as confirmed from CV, SEM and AFM whereas Pt and GC do not show any serious fouling. ► Highly polar solvents such as CH3CN activate the fouled BDD surface.