I am facing difficulty in evaluating the cathodic peak current using Randles Sevcik equation, I have already calculated the diffusion coefficient from it but when I am plotting the values versus inverse of the potential, I am getting the negative slope while I should get the positive one. Here I am attaching the literature I have been following to pursue this study. Please clear the doubts.

Thanks

link to article https://pubs.acs.org/doi/suppl/10.1021/acs.inorgchem.0c01215/suppl_file/ic0c01215_si_001.pdf