Solar water oxidation reaction promoted by a dopant combination on hematite photoanode

Abstract

Doping is a widely used strategy to enhance hematite photoelectrochemical performance, but a rational consideration on how to combine positive effects of dopants in dual-modified nanostructures is necessary to achieve materials with controlled properties for different technological applications. Here, a polymeric precursor solution method that simultaneously induces bulk doping and interfacial segregation by adding modifiers in different synthesis stages was used in the search of an ideal couple of dopants toward highly efficient hematite photoanodes. Employing optimized concentrations of bulk dopants (Al³⁺, Ga³⁺, Y³⁺, La³⁺) and interfacial modifiers (Nb⁵⁺, Ta⁵⁺), the most synergistic enhancement of photoelectrochemical performance was observed when Y³⁺ and Ta⁵⁺ were combined. The photoanode modified with optimal concentrations of these dopants achieved a total yield of 56.6% of current generated in relation to the maximum value permitted by its absorption properties, remarking a 6-fold increase when compared to pristine hematite (9.9%). Hence, yttrium and tantalum beneficially acted to minimize small polaron domain that prevent electron mobility intragrain, and to increase charge separation efficiency by decreasing the interfacial energies hindering electron hopping trough the grains, respectively. However, the combination of Ga³⁺ and Nb⁵⁺ led to a material with 21.4% of current yield, value comparable to the niobium single-modified photoanode (22.2%), indicating the lack of synergy between these modifiers to address bulk and interfacial issues of hematite. Therefore, this work shows that only chemically compatible combinations of modifiers can deliver efficient hematite-based photoanodes and careful nanostructure engineering must drive the search for an ideal material.