On the current-potential curve of a very fast hydrogen evolution process up to high current densities
✍ Scribed by D. Schönfuss; L. Müller
- Publisher
- Elsevier Science
- Year
- 1994
- Tongue
- English
- Weight
- 269 KB
- Volume
- 39
- Category
- Article
- ISSN
- 0013-4686
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✦ Synopsis
The steady-state polarization curve of the hydrogen evolution at highly active Pt-electrodes was determined in 5 M and 0.5 M HjSO 4 up to high current densities. The polarization curve in 5 M HzSO 4 is characterized by four regions, which differ from one another by the slope (b) of the E-log(/) curve. The first three regions at low and medium current densities with b 1 ~ 29mV decade -1 and b z 19mV decade-I and b a --* 0mV decade-1 are due to the reversible hydrogen evolution, if the rate determining step is the transport of hydrogen into the bulk of solution, the electron exchange is reversible and the overvoltage is determined by the Hj-supersaturation at the electrode surface. The slope b~ ~ 29 mV decade -~ is due to the transport of the evolved H 2 into the bulk of solution by diffusion; b 2 ~ 19mV decade -1 is due to the transport by diffusion and by gas bubbles; b 3 -,0mV decade -1 is due to the transport by diffusion and by gas bubbles provided that the Hj-supersaturation at the electrode surface does not further change with growing overvoltage. At high current densities (i > 350 mA cm-2) the slope of the polarization curve is b 4 -~ 120mV decade-~ and the rate determining step is the charge transfer (Volmer) reaction.