Accurate Determination of Catalyst Loading on Glassy Carbon Disk and Its Impact on Thin Film Rotating Disk Electrode for Oxygen Reduction Reaction.

Thin film-rotating disc electrode (TF-RDE) experiment provides a fast research platform for screening of newly developed electrocatalysts for oxygen reduction reaction (ORR) activity; however, precise estimation of their performance parameters is necessary to avoid wastage of resources in the testing of otherwise unpromising electrocatalyst in actual fuel cells. Here we show the importance of the accurate amount of catalyst (e.g., Pt) on glassy carbon (GC) disk of RDE in TF-RDE experiment by characterizing the commercial catalysts for their electrocatalysis performance (electrochemical surface area and ORR activity) values. The Pt loadings used to calculate these performance values were obtained using two schemes, namely, using the literature based (conventional) scheme and an X-ray fluorescence (XRF) based scheme. A parameter called "catalyst-density-of-the-ink" is used to correlate the variations observed in performance values and the amount of Pt on GC disk of RDE obtained using both schemes. The investigation suggests that the actual Pt loading on the GC disk of RDE varies with the ink-conditions, which is considered constant in the conventional scheme and might be one of the reasons of irreproducibility of the data obtained by TF-RDE experiments. The XRF-based scheme, which is simple and direct, can have the potential to replace conventional scheme for accurate catalyst loading estimation, improve experimental reproducibility, and open many other possibilities (e.g., post-mortem analysis of catalyst) in electrocatalysis studies.