✍ Scribed by Piotr K. Wrona; Andrzej Lasia; Martin Lessard; Hugues Ménard
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Ahstrae-Kinetics of the hydrogen evolution reaction (her) were measured at a rhodium electrode in a 1 M solution of KOH at various temperatures between 5 and 75°C. The rn-ts were conducted at a Rh wire electrode activated before every measurement by cycling in the range of potentials between -1.0 and 0.3 V (vs. Hg/HgO/l M KOH) until a stationary behaviour was obtained. Rxperhnents were also carried out on the electrode kept at 25°C for three days at -1.0 V. Jn this case. the current was by about one order of magnitude lower than that observed for the activated electrode. For both ele&odes the her could be described by the Vohner-Heyrovsky muhanism. For activated eRctK&sthecathodic transfer coegicient a changed with temperature from 0.3 to 0.4; at deactivated electrode it was equal to 0.43. The activation resistance decreased with temperature by ahnost two orders of magnitude. The results were analysed according to two models of the impedance on solid ekctmdes. An approximation of both the Tafel plots and the logarithm of the reaction admittance vs. overpotential made the calculation of the rate constant of the slowest step possible, which was three orders of magnitudes greater than that for the. nickel electrode. Total capacities of the double layer at poisoned and activated elec&odes were almost the same and equal to 60-80 pF cm-*. We have concluded that traces of metallic impurities are responsible for poisoning of the electrode.
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