Photoelectrochemical (PEC) water splitting is an ideal approach for renewable solar fuel production. One of the major problems is that narrow bandgap semiconductors, such as tantalum nitride, though possessing desirable band alignment for water splitting, suffer from poor photostability for water oxidation. For the first time it is shown that the presence of a ferrihydrite layer permits sustainable water oxidation at the tantalum nitride photoanode for at least 6 h with a benchmark photocurrent over 5 mA cm(-2) , whereas the bare photoanode rapidly degrades within minutes. The remarkably enhanced photostability stems from the ferrihydrite, which acts as a hole-storage layer. Furthermore, this work demonstrates that it can be a general strategy for protecting narrow bandgap semiconductors against photocorrosion in solar water splitting.
The oxygen evolution is kinetically the key step in the photocatalytic water splitting. Cocatalysts could lower the activation potential for O 2 evolution. However, the cocatalyst for O 2 evolution has been less investigated, and few effective cocatalysts were reported. This paper reports that the O 2 evolution rate of photocatalytic water splitting under visible light irradiation can be significantly enhanced when the electrocatalyst cobalt− phosphate (denoted as CoPi) was deposited on BiVO 4 . The photocurrent density is also greatly enhanced by loading CoPi on BiVO 4 electrode, and this enhancement in performance shows the similar trend between the photocatalytic activity and photocurrent density. We also found that this tendency is true for BiVO 4 loaded with a series of different electrocatalysts as the cocatalysts. These results demonstrate that an effective electrocatalyst of water oxidation can be also an effective cocatalyst for O 2 evolution from photocatalytic water oxidation. By depositing the CoPi as the oxidation cocatalyst and Pt as the reduction cocatalyst on an yttrium-doped BiVO 4 (Bi 0.5 Y 0.5 VO 4 ), overall water splitting reaction to H 2 and O 2 was realized. Our work also reveals the essential relations between photocatalysis and electrocatalysis in water splitting reaction.
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