The authors regret that the annotations within Fig. 4(c) are incorrect. ‘Anodic peak current’ should read ‘Cathodic peak current’ and ‘Cathodic peak current’ should read ‘Anodic peak current’. The description about calculated DNa in the sentence running across pp. 329–330 should be exchanged as the same. The full sentence should read: ‘The calculated values of DNa were 3.57 × 10−13 and 5.81 × 10−12 cm2 s−1 according to anodic and cathodic peak current, respectively.’ The authors would like to apologise for any inconvenience caused.