The onset potential is an important descriptor of the photoelectrochemical water oxidation performance of photoanodes. Herein, we prepared Gd-doped hematite (Gd-Fe 2 O 3 )/iron (III) oxyhydroxide (FeOOH) core-shell photoanodes by in-situ isovalent doping and secondary hydrothermal treatment . This Gd-Fe 2 O 3 /FeOOH photoanode shows a record alkaline water oxidation onset potential (0.59 V vs. reversible hydrogen electrode) in hematite-based photoanodes and a 2.4-fold increase in photocurrent density over pristine hematite . Detailed studies demonstrate that the origin of the ultra-low onset potential is mainly attributed to the synergistic effect of isovalent Gd-doping and FeOOH cocatalyst. Specifically, Gd doping enhances donor density and reduces charge transport resistance, and FeOOH cocatalyst significantly improves water oxidation kinetics. In addition, the strong interfacial coupling of FeOOH and Gd-Fe 2 O 3 promotes electron flow, which also improves the charge separation remarkably. This work gives hope for the achievement of stable and bias-free hematite-based photoanodes.
The phase interface properties of the p-n junction may profoundly affect its photoelectrochemical (PEC) water oxidation performance. Here, we introduced a non-conjugated polymer functional layer (poly(diallyl-dimethylammonium chloride, PDDA) between the interfaces of the p-n junction (Co 3 O 4 /Gd–Fe 2 O 3 ) to tune the interfacial properties . First, the PDDA modulates the band structure so that the composite photoanode (Co 3 O 4 /PDDA/Gd–Fe 2 O 3 ) has an enlarger band bending than the p-n junction. Then, PDDA passivates the surface trap, which synergizes with Co 3 O 4 to provide more active sites for water oxidation. Furthermore, PDDA improves the PEC water oxidation kinetics. Specifically, PDDA extracts holes and adsorbs water oxidation reactants, thus it efficiently transfers photogenerated holes to Co 3 O 4 , promoting the water oxidation reaction in the positive direction. With these positive modulations, PDDA can further enhance the PEC water oxidation performance of the p-n junction. This conceptual work provides insight into the role of the non-conjugated polymer in PEC water splitting .
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