Correcting for Parasitic Currents in CO Electrooxidation Voltammetry to Enhance Electron Transfer Number Accuracy

Electrooxidation of CO on Pt suffers from parasitic currents that mask intrinsic kinetics. We disentangle these contributions by resolving the plateau region of rotating-disk voltammograms into three parts: (i) diffusion-limited CO oxidation, (ii) double-layer charging, and (iii) formation of Pt surface oxides. Averaging the forward and backward scan cancels the sign-reversing capacitive term, while slowing the scan rate suppresses oxide formation without perturbing the Levich slope. Applied to 5–40 wt% Pt/C, this two-step correction lowers the apparent electron-transfer number from >3 to ≈2.5, approaching the theoretical value of 2. However, reducing Pt loading alone attenuates oxide currents but prevents the system from reaching the true limiting current. The protocol therefore offers a rapid, catalyst-agnostic route to isolate the mass-transport-controlled current, sharpening mechanistic insights and providing more reliable metrics for benchmarking electrocatalysts in CO electrooxidation and related small-molecule reactions.