Size Ranges of Effective Nucleation Cavities on Gas-Evolving Surfaces.

Bubble nucleation has a significant influence on mass transfer and energy conversion in electrochemical gas-evolving reactions. In this work, we establish a theoretical model for bubble nucleation from gas cavities on gas-evolving surfaces. Based on analyses of transient gas diffusion within the concentration boundary layer and supersaturation equation for stable bubble nuclei, we determined the size ranges of effective nucleation cavities on gas-evolving surfaces under different levels of supersaturation conditions. In addition, a criterion for the incipience of bubble nucleation on gas-evolving surfaces is proposed. We investigate the effects of the contact angle, cone angle, concentration boundary layer thickness, ambient pressure, and temperature on the size ranges of effective nucleation cavities, respectively. We demonstrate that a larger contact angle or a smaller cone angle can broaden the size range of effective cavities, thereby promoting bubble nucleation from cavities. We also show that increasing the concentration boundary layer thickness causes larger cavities to become effective nucleation sites, which significantly expands the size range of effective cavities. In contrast, increasing the ambient pressure enables smaller cavities to become effective nucleation sites, resulting in an expansion in the size range of effective cavities. Results of this work will contribute to the manipulation of bubble nucleation densities and the optimal design of gas-evolving electrodes in various electrochemical gas-evolving reactions.