  Despite widespread interest, a detailed understanding of the dynamics of
proton transfer at interfaces is lacking. Here we use ab initio molecular
dynamics to unravel the connection between interfacial water structure and
proton transfer for the widely studied and experimentally well-characterized
water-ZnO$(10\bar{1}0)$ interface. We find that upon going from a single layer
of adsorbed water to a liquid multilayer changes in the structure are
accompanied by a dramatic increase in the proton transfer rate at the surface.
We show how hydrogen bonding and rather specific hydrogen bond fluctuations at
the interface are responsible for the change in the structure and proton
transfer dynamics. The implications of this for the chemical reactivity and for
the modelling of complex wet oxide interfaces in general are also discussed.
