Abstract
Hydrogen evolution reaction (HER) on Au electrode in perchloric acid and NaOH solutions were studied using an inverted rotating disc electrode (IRDE). IRDE enables investigations of gas evolution reactions in a large potential and current window. In this configuration, the electrode is not obstructed by the product gas bubbles. Potentiodynamic polarization data were acquired at various concentrations of HClO 4 and NaOH, and at a few electrode rotational speeds. At large over-potentials, diffusion-limited currents were observed in HClO 4 solutions. In the case of HER on Au in acidic media, the Volmer-Heyrovsky-Tafel (VHT) mechanism best describes the polarization results. The fractional surface area covered by adsorbed hydrogen and the rate of reaction for individual steps were estimated using the model. At low H + concentrations, HER proceeds mainly by the Volmer-Tafel (VT) pathway while at high H + concentrations, Heyrovsky and Tafel pathways are equally important. In the alkaline media, HER rate was found to be independent of NaOH concentration and electrode rotational speed, and the reaction mechanism could not be identified unambiguously. The results illustrate the importance of analyzing data acquired at several reactant concentrations and at a wide potential range, to identify the reaction mechanism. • Inverted rotating disc electrode to study HER in large potential/current window. • HER in HClO 4 solutions limited by mass transfer of H + ions. • At low acid concentrations, on Au, Volmer-Tafel is the main HER route. • At high acid concentration, on Au, Heyrovsky step also contributes. • HER in alkaline media independent of NaOH concentration and rotational speed.
Published Version
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