Charge transport

and metal site stability play a critical role in realizing efficient solar

water splitting in photoelectrochemical devices. Here, we investigate BiVO4-based

composite photoanodes

(labelled as NF@PTA/2PACz/BVO) in which

BiVO4, hole transport layers (HTLs) based on self-assembled

monolayers (SAMs), and carboxyl-functionalized NiFeOOH oxygen evolution

cocatalysts (OECs) structurally similar to the OECs in natural photosystem II, were

assembled sequentially. By designing this particular structure, alignment of

energy levels and stabilization of metal sites can be achieved. And the uncoordinated

(?COOH) carboxylate groups can accelerate the proton transfer. Fundamental

investigations reveal that the NF@PTA/2PACz/BVO

photoanodes

exhibit unique properties including passivated surface traps, excellent carrier

density and lifetime, enlarged photovoltage, and smoother hole transport band structure. Consequently,

the optimum NF@PTA/2PACz/BVO

photoanodes

show the PEC performance of 5.43 mA·cm?2 at

1.23 V vs reversible hydrogen electrode (RHE) with an applied bias

photon-to-current efficiency of 1.45% at 0.75 VRHE. And the C?O?Fe

bond coupling between the coordinating carboxylate and the metals inhibits the leaching

of the metal species and maintains a steady photocurrent density over 8 h of

stability testing. Our work paves the way for the development of more efficient

PEC cells with superior charge separation and breakthroughs in the stability of

metal active sites, thus broadening their potential applications.