Oxygen deficient α-FeO photoelectrodes: a balance between enhanced electrical properties and trap-mediated losses.

Intrinsic doping of hematite through the inclusion of oxygen vacancies (V) is being increasingly explored as a simple, low temperature route to preparing active water splitting α-FeO photoelectrodes. Whilst it is widely accepted that the introduction of V leads to improved conductivities, little else is verified regarding the actual mechanism of enhancement. Here we employ transient absorption (TA) spectroscopy to build a comprehensive kinetic model for water oxidation on α-FeO . In contrast to previous suggestions, the primary effect of introducing V is to block very slow (ms) surface hole - bulk electron recombination pathways. In light of our mechanistic research we are also able to identify and address a cause of the high photocurrent onset potential, a common issue with this class of electrodes. Atomic layer deposition (ALD) of AlO is found to be particularly effective with α-FeO , leading to the photocurrent onset potential shifting by 200 mV. Significantly TA measurements on these ALD passivated electrodes also provide important insights into the role of passivating layers, that are relevant to the wider development of α-FeO photoelectrodes.