DIFFERENT ROLES OF FeNiO_x CO-CATALYST ON HEMATITE PHOTOANODES WITH DIFFERENT DOPANTS

Hematite (a-Fe₂O₃) is an attractive material for solar water splitting based on its favorable properties as a photoanode material in photoelectrochemical (PEC) cells. However, the performance of state-of-the-art hematite photoanodes is still far short of the maximum theoretical efficiency, both in terms of photocurrent and photovoltage. One route for improving photoanode performance is through use of various co-catalysts which reduce the overpotential for water photo-oxidation, thereby leading to a cathodic shift in the applied bias. One of the promising materials for use as a co-catalyst is the earth abundant FeNiO_x.

The presented work will concentrate on transparent FeNiO_x overlayer that was deposited photoelectrochemically on (001) oriented heteroepitaxial Sn- and Zn-doped hematite thin film photoanodes. Intensity modulated photocurrent spectroscopy (IMPS) was applied to study the changes in the hole current and surface recombination current induced by the FeNiO_x overlayers. For the Sn-doped hematite photoanode, the improvement in performance after deposition of the FeNiO_x overlayer was entirely due to reduction in the recombination current. For the Zn-doped hematite photoanode, in addition to a reduction in recombination current, an increase in the hole current was also observed after the FeNiO_x overlayer deposition, leading to a cathodic shift in the onset potential as well as an enhancement in the plateau photocurrent. These results demonstrate that FeNiO_x co-catalysts can play different roles depending on the underlying hematite photoanode.