Quantifying the effects of surface wettability on bubble-mediated water electrolysis

We experimentally investigated hydrogen bubble evolution in water electrolysis, highlighting how surface wettability of cathodic electrodes affects the bubble dynamics and the hydrogen production efficiency. Once an overpotential is applied, hydrogen was immediately produced and nucleated into a large number of gaseous bubbles on the cathodic electrode and in its nearby region. Despite the volume growth of single hydrogen bubbles on different wettable electrodes follows the same 3/2 power law with time, the growth coefficient on a hydrophobic cathodic substrate with θ≈139° is two orders of magnitude higher than that of hydrophilic one with θ≈50°. Moreover, while hydrogen bubbles can detach from hydrophilic electrodes at very small sizes of ∼30 μm, maintaining a high liquid–solid contact, and thus, a high cathodic current, formed hydrogen bubbles on hydrophobic electrodes would continuously grow into large ones, eventually either partially detaching or completely sticking. Based on the kinetics of electrochemical polarization, a linear correlation between the cathodic current and the bubble coverage ratio has been theoretically derived and experimentally verified. Our work provides insight into the bubble-mediated physicochemical processes and relevant findings may find broad applications in diverse gas-evolving reactions.