Abstract
In the electrolyte process of fluorine production from KF · 2HF melts at 85° C, unusually high polarization arises both at the cell anodes (carbon) and cathodes (mild steel) at moderate current densities. The anomalous polarization behaviour in fluorine evolution at carbon anodes has been extensively studied but much less is known about the origin of hyperpolarization in hydrogen evolution at the cathodes. Here, the results of comparative polarization studies at a Ni-Mo-Cd composite cathode material in a KF · 2HF melt and a corresponding aquo-analogue melt of KOH · 2H2O are reported. Large differences are observed which are attributed to the different wetting characteristics of these two melts at the interface of the Ni-Mo-Cd cathodes that are microporous. Such electrode material also offers a major improvement of cathode polarization over that at mild steel surfaces. Conclusions on wetting effects are based on: (i) a comparative determination of hydrogen-bubble contact angles at the electrode in the two melts and (ii) an evaluation of the double-layer capacitances of the electrode interfaces with the two melts as determined by the fast potential-relaxation method, at short times after current interruption. The apparent double-layer capacitances at a given electrode are very different in the two melts.
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Gao, L., Qian, S.Y. & Conway, B.E. Electrolyte wetting effects in the comparative polarization behaviour of the hydrogen evolution reaction at Ni-Mo-Cd electrodes in KF · 2HF and KOH · 2H2O melts. J Appl Electrochem 25, 6–14 (1995). https://doi.org/10.1007/BF00251258
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DOI: https://doi.org/10.1007/BF00251258