Solar water splitting in acidic solutions has important technological implications, but has not been demonstrated to date in a dual absorber photoelectrochemical cell. The lack of functionally stable water-oxidation catalysts (WOCs) in acids is a key reason for this slow development. The only WOCs that are stable at low pH are Ir-based systems, which are typically too expensive to be implemented broadly. It is now shown that this deficiency may be corrected by applying an ultra-thin monolayer of a molecular Ir WOC to hematite for solar water splitting in acidic solutions. The turn-on voltage is observed to shift cathodically by 250 mV upon the application of a monolayer of the molecular Ir WOC. When the molecular WOC is replaced by a heterogeneous multilayer derivative, stable solar water splitting for over 5 h is achieved with near-unity Faradaic efficiency.
Keywords: hematite; homogeneous catalysis; iridium; photoelectrochemistry; solar water splitting.
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