Correlating the Short-Time Current Response of a Hydrogen Evolving Nickel Electrode to Bubble Growth

Gas evolving electrochemical reactions induce bubble formation and growth at surfaces of electrodes. To study one such situation, hydrogen evolution on nickel electrodes, short time chronoamperometric experiments were performed in combination with in-situ microscopy. The entire electrode of 3.14 mm(2) was imaged with confocal microscopy and the current response of the electrode then correlated to the observed bubble growth features. Somehow counterintuitively, first a 2-3% increase in current was observed consistently when a bubble grows close to the electrode on the edge of the electrode holder, made of a polymer. This is argued to be due to the removal of surface attached gas from the electrode. Next, we observe a consecutive regime of decreasing current, in which large bubbles accumulate on the surface. Interestingly, when these surface attached bubbles coalesce, a steep change in current is observed, which is accompanied by a burst of small bubbles nucleating on the surface previously occupied by the large bubble. These phenomena are qualitatively discussed on the basis of existing literature, and implications for improvements for electrodes on which gases are produced, are outlined. (C) The Author(s) 2019. Published by ECS.