Water electrolysis is a well-known route to green hydrogen production. However, advances in performance and reductions in cost could still improve its prospects for wide-scale use. So far, much research effort has focused on enhancing the materials that make up electrolysers — for example, catalysts and membranes — and how they are assembled; the impact of external stimuli has been less explored. Now, Amgad Rezk and colleagues at RMIT University and the University of Melbourne show that application of high-frequency sound waves to the hydrogen-evolving electrode can induce a 14-fold improvement in current density for hydrogen production.
The researchers use gold electrodes to demonstrate the effect due to their stable, yet poor activity for the hydrogen evolution reaction. In a pH-neutral electrolyte, they apply a combination of surface and bulk acoustic waves (known as surface-reflected bulk waves) to the electrode. The team suggest that application of the 10 MHz sound waves boosts the activity of the catalyst through multiple mechanisms; they attribute the improvement to enhanced mass transfer and more facile bubble removal from the electrode, but also to changes in the intermolecular bonding of the water molecules. Specifically, they suggest that the sound waves disrupt the tetrahedral hydrogen-bonding water network close to the electrode, allowing the water molecules to be more easily activated, and facilitating the evolution of hydrogen gas. Calculations suggest that the approach yields energy savings of 27%.
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