A bridging coordination of urea tailoring metal hydroxides oxygen evolution catalysts promotes stable solar water splitting

Abstract Stability is one of essential factors for evaluating the photoelectrochemical (PEC) water splitting performance on photocorroded semiconductors for practical applications. Cocatalyst decoration can only maintain the stability for several hours, and organic/inorganic hybrid photoelectrodes (e.g. polymer coated photoelectrodes) also has a limited durability. Therefore, it is challenging to develop a facile but effective approach for stabilizing the photoelectrodes. In this work, we induced a handful of cheap urea into the Ni,Fe-based hydroxides as robust and conformal OECs layers, deposited on the BiVO4 photoanodes by an one-step impregnation process. Urea, an assisted nitrogen/carbon source, played an active role on the uniform growth of ultrathin OEC layer, replacing the complex organic cocatalyst. The thickness of urea induced Ni,Fe-based OEC could be modified by tuning the amount of urea, thereby improving the carrier dynamics and protecting photoelectrodes from photocorrosion. The presence of urea facilitates to deposit a homogeneous cocatalyst layer with higher electron transfer than the absence of urea, resulting in a high electrocatalytic OER and PEC performance. The optimized urea-NiFeOOH/BiVO4 photoanode showed a photocurrent density of 4.8 mA cm−2 at 1.23 VRHE with impressive stability over 40 h at a potential of 0.8 VRHE, which is one of the best PEC stabilities using NiFe-based OECs on BiVO4. Benefiting from the strong coordination bond between the metal ions and urea, the C and N elements remained stable in the OEC layer before and after PEC test. This work presents a potential application using cheap, non-precious metal based electrocatalysts to overcome the bottle-necks limiting a long-term stability of PEC water splitting.