Effect of mesh size of Ni wire mesh electrodes on alkaline water electrolysis performance: A study based on the observation of bubble departure behavior

Abstract

To enhance the compactness of electrolyzers and mitigate energy losses during high operating current densities, the concept of a zero-gap electrolytic cell design has been proposed, with wire mesh commonly utilized as electrodes owing to its cost effectiveness and easy fabrication. To achieve more efficient hydrogen production, many studies have been done on developing high-performance water electrolysis catalysts based on wire mesh electrode. The structure of wire mesh electrode can influence its gas bubbles release behavior, thereby impacting its water electrolysis performance significantly. However, the relationship between the wire mesh structure, gas bubble behavior on wire mesh, and water electrolysis performance of wire mesh is still unclear. In this study, four types of Ni wire mesh electrodes with varying mesh numbers (20 mesh, 40 mesh, 100 mesh, and 200 mesh) were employed as cathodes in a zero-gap electrolytic cell to investigate the relationship between wire mesh structure, behavior of hydrogen bubble detachment from wire mesh, and hydrogen evolution reaction (HER) performance of wire mesh. At a high current density (i_ECSA = 800 mA/cm²) in 1 M KOH aqueous solution, hydrogen bubbles detach in a higher rate and smaller size from the Ni wire mesh with higher mesh number. In this case, the HER overpotential decreases in the order of 20 mesh >40 mesh >100 mesh >200 mesh, because the higher detachment rate and smaller detachment size of hydrogen bubbles can cause a greater catalytic active sites exposure of Ni wire mesh electrode and lead to a lower HER overpotential. To simulate the operating condition of industrial electrolyzers, a 4 M KOH aqueous solution was also utilized as the electrolyte to explore the aforementioned relationship. Under i_ECSA = 800 mA/cm², the average sizes of hydrogen bubbles detachment from four types of wire mesh electrodes increased to varying degrees comparing with that observed in 1 M KOH aqueous solution. These findings indicate that operating conditions of the electrolysis system may influence the relationship between HER performance of wire mesh and wire mesh structure by altering the behavior of hydrogen bubble on wire mesh. Our study highlighted the importance of evaluating the characteristics of bubble on wire mesh during water electrolysis in order to determine the wire mesh structure with optimum performance.