I see in many papers that the Tafel slope of commercial Pt/C for HER is about 30 mV/dec. in 0.5M H2SO4 media, which is quite consistent. However, in 1.0M KOH media, the Tafel slope seems to vary considerable and is between 30 and 65 mV/dev.
For example: 31.8 is reported by Zhang J, et al. Angew. Chem. Int. Ed. 2016, 55, 6702 –6707: http://onlinelibrary.wiley.com/doi/10.1002/ange.201602237/full ) and (51 is reported by Tan Y, et al. Energy Environ. Sci., 2016, 9, 2257-2261 http://pubs.rsc.org/-/content/articlehtml/2016/ee/c6ee01109h ). Could anyone kindly provide any information in this regard? Thanks
Thank you for your question. In my opinion, for ORR, although the Tafel value is mainly determined by the nature of electrocatalyst, this value is also affacted by the concentration of the dissolved oxygen. Due to that the concentration of the dissolved oxygen is sensitive for the experimental operation, the Tafel value is acceptable when it is about 60 mV/dev with some variation. Moreover, as a four-electron transfer reaction, the ORR is also sensitive to the surface of Pt/C electrocatalyst, sometime it is sensitive to many factors. For comparison, HER is an evolution reaction. Therefore, it is lower sensitive to the evolved hydrogen. Moreover, HER is a more simple two-electron reaction, it mechanism is also more simple. Therefore, it is lower sensitive to the surface of Pt/C electrocatalyst.
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