Different roles of Fe1-xNixOOH co-catalyst on hematite ({\alpha}-Fe2O3) photoanodes with different dopants

TL;DR

This study investigates how Fe1-xNixOOH co-catalysts differently enhance water oxidation on doped hematite photoanodes, revealing that their roles vary based on the underlying dopant and involve both surface and bulk process modifications.

Contribution

It demonstrates that Fe1-xNixOOH co-catalysts have distinct effects on different doped hematite photoanodes, influencing both recombination and hole transfer processes.

Findings

Co-catalyst reduces recombination current in Sn-doped hematite.

In Zn-doped hematite, co-catalyst increases hole current and reduces recombination.

Co-catalyst effects depend on the underlying dopant and involve surface and bulk interactions.

Abstract

Transparent Fe1-xNixOOH overlayers (~2 nm thick) were deposited photoelectrochemically on (001) oriented heteroepitaxial Sn- and Zn-doped hematite (Fe2O3) thin film photoanodes. In both cases, the water photo-oxidation performance was improved by the co-catalyst overlayers. Intensity modulated photocurrent spectroscopy (IMPS) was applied to study the changes in the hole current and recombination current induced by the overlayers. For the Sn-doped hematite photoanode, the improvement in performance after deposition of the Fe1-xNixOOH overlayer was entirely due to reduction in the recombination current, leading to a cathodic shift in the onset potential. For the Zn-doped hematite photoanode, in addition to a reduction in recombination current, an increase in the hole current to the surface was also observed after the overlayer deposition, leading to a cathodic shift in the onset potential as well as an enhancement in the plateau photocurrent. These results demonstrate that Fe1-xNixOOH co-catalysts can play different roles depending on the underlying hematite photoanode. The effect of the co-catalyst is not always limited to changes in the surface properties, but also to an increase in hole current from the bulk to the surface that indicates a possible crosslink between surface and bulk processes.