Electrochemical experiments have sought to map rate determining steps of the water oxidation reaction through the potential dependent, steady state current.  While slopes of these Tafel plots can characterize reactions, they can only be obtained in a limited over-potential range (250 meV) and their detailed interpretation is model dependent for heterogeneous reactions involving multiple charge transfers.  Here, we show how the transient optical spectroscopy of the photo-driven water oxidation reaction directly measures the time-dependent kinetics of interfacial hole transfer at the anode.  At the n-SrTiO3/water interface, the kinetics reveal single exponential time constants spanning 10~ps to 1~ns that can be directly assigned to an over-potential for the water oxidation reaction and that we interpret as the first hole transfer of the catalytic cycle.  For this initial hole transfer, we obtain a coefficient akin to a Tafel slope, a=0.24�0.05, describing the fraction that an applied potential at the surface reduces the activation barrier.  For other catalysts that cannot be excited directly by light, such as Co3O4, a unique photodiode configuration is used to inject holes at ultrafast time scales into the catalyst over-layer and the kinetics of interfacial hole transfer are again measured.  These studies will enable water oxidation catalysts to be differentiated by the early time scale dynamics of interfacial hole transfer.

Investigating electrode kinetics of water splitting with transient spectroscopy of photo-electrochemical cells

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.