Bubble growth and departure modes on wettable/non-wettable porous foams in alkaline water splitting

Bubble growth and departure are ubiquitous phenomena in gas-evolving reactions, which govern the overall energy and mass transport. However, an in-depth understanding of the relationship between bubble dynamics and the electrochemical processes, in particular, the wettability effect on a gas-evolving porous electrode remains elusive. Here, we report the bubble dynamics and overpotential observed during alkaline water splitting on a polytetrafluoroethylene (PTFE) deposited nickel porous electrode. A slight decrease in hydrophilicity induced a drastic transition of bubble dynamics and a significant increase of the transport overpotential. We show that the porous electrode transitioned from a liquid-filled state to a gas-filled state when varying the wettability, which changed the bubble departure sizes and bubble coverage. As a result, there were substantial changes of the transport overpotential. Our work elucidates the fundamental relationship between wettability and water splitting characteristics, which provides a practical scenario for structuring the electrode for gas-evolving reactions.