Effect of Experimental Operations on the Limiting Current Density of Oxygen Reduction Reaction Evaluated by Rotating-Disk Electrode

The universal linear scan voltammogram measurement on the rotating disk electrode (RDE) has been identified as a simple method to investigate the oxygen reduction activity of electrocatalysts. The steady-state limiting current density I-lim indicates the maximum diffusion current density in the oxygen reduction reaction (ORR) during RDE measurement, which should be a fixed value in theory for a 4e ORR in a particular concentration solution and at a certain rotate speed. However, in experiments, I-lim is always variable and smaller than theoretical value even though with the same the catalyst, electrode, and rotator. So the impact of various experimental operating parameters on I-lim is highly necessary to be investigated. In this paper, factors, such as catalyst loading, O-2 inlet condition, O-2 flow rate, gas tightness, solution concentration, and purity, have been investigated for their effects on the I-lim of ORR on three typical catalysts (20 % commercial Pt/C, Iron/Nitrogen/Carbon-catalyst and N-doped carbon nanotubes). The results indicate that the catalyst loading and O-2 inlet condition are the key factors influencing the I-lim of ORR. While, the O-2 flow rate, gas tightness, solution concentration, and purity have little influence on the I-lim of ORR. The correct I-lim could be obtained under the optimized catalyst loading and the O-2 inlet with an extended sand core tube.