While charge transport and surface reactivity have thus far been treated as independent phenomena, the interfacial carrier mobility could be highly dependent on reaction intermediates that carry localized charge and can hop from site to site along the surface. Here, we demonstrate the use of surface sensitive transient optical grating spectroscopy to measure this lateral, interfacial carrier diffusivity at surfaces with different reactivity. We find that for n-GaN, for which substantial charge transfer occurs during equilibration with the water oxidation reaction, the interfacial hole diffusivity increases from air by a factor greater than two under 0.1 M HBr and 0.1 M Na2SO4 aqueous electrolytes. (C) 2016 Elsevier B.V. All rights reserved.