Preferential nucleation sites regulate hydrogen bubble evolution on mesh electrodes.

Abstract

Gas-bubble evolution substantially affects the efficiency of gas-evolving electrochemical processes, including water electrolysis. Bubble nucleation, growth, coalescence, and detachment influence the electrode potential, while persistent bubble coverage can impede ionic transport and increase ohmic loss. Although these phenomena have been studied extensively on micro- and nanoelectrodes, translating mechanistic insights obtained under simplified conditions to commercially relevant three-dimensional electrodes, such as metal mesh and foams, remains challenging. A major difficulty is the stochastic distribution of bubble nucleation sites, particularly on geometrically complex electrodes. Model electrodes with spatially defined nucleation sites can reduce this uncertainty while retaining key structural features of practical electrodes. Such electrodes may also allow the systematic investigation and control of bubble growth, residence time, and detachment. Here, we report the fabrication of platinum-coated silicon mesh cathodes containing hydrophobic pits that serve as preferential bubble nucleation sites. This platform combines the spatial control of an idealized model electrode with the architecture of a practical mesh electrode. Hydrogen-gas bubble behaviour was compared among four configurations: (i) silicon meshes coated with Pt on both faces and containing hydrophobic pits on one face; (ii) silicon meshes coated with Pt on one face and hydrophobic pits confined to one face; (iii) silicon meshes coated with Pt on both faces but without hydrophobic pits; and (iv) conventional nickel meshes. The effects of pit position and density on the bubble growth rate and bubble coverage fraction were quantified, and spatial variations in the growth rate were analysed across several current-density regimes. Preferential nucleation sites markedly altered bubble evolution. On electrode faces without hydrophobic pits, large bubbles remained attached at the mesh apertures, whereas patterned faces exhibited localized nucleation and less persistent bubble coverage at low current densities. These signatures are consistent with more frequent bubble detachment at smaller departure sizes. Thus, controlled nucleation can regulate bubble growth and release within a three-dimensional mesh geometry. The silicon mesh platform therefore helps bridge the gap between mechanistic studies on idealized microelectrodes and the design of practical gas-evolving electrodes for efficient water electrolysis.

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