Power Ultrasound as Performance Enhancer for Alkaline Water Electrolysis: A Review

The industry is advancing decarbonization in hydrogen production through water splitting technologies like water electrolysis, which involves the hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode. Alkaline water electrolyser (AWE) is particularly suited for industrial applications due to its use of cost-effective and abundant nickel-based electrodes. However, AWE faces significant challenges, including energy losses from gas bubble coverage and poor detachment, known as “bubble resistance”. Recent research highlights the role of power ultrasound in mitigating these issues by leveraging Bjerknes forces. These forces facilitate the ejection of larger bubbles and the coalescence of smaller ones, enhancing gas removal. Additionally, ultrasound improves mass transfer from the electrolyte to electrodes and boosts heat transfer via acoustic streaming and acoustic cavitation, which the latter also enhances electrocatalytic properties for both HER and OER. However, employing ultrasonic fields presents both benefits and challenges for scaling the system.