Work Function Engineering of MXene‐Based Cocatalyst Through Transition‐Metal‐Ion Intercalation for Enhanced Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is a promising technology for solar energy conversion, yet its efficiency is limited by sluggish oxygen evolution reaction (OER) at photoanodes. Although loading oxygen evolution cocatalysts (OECs) can accelerate OER by promoting carrier injection, insufficient carrier separation hinders their performance improvement. Herein, we propose a work function engineering of OECs as an effective approach to enhance carrier separation in PEC systems and demonstrate that transition‐metal‐ion intercalation can regulate the work function of Ti 3 C 2 , an efficient MXene‐based OEC. When transition‐metal‐ion intercalated Ti 3 C 2 is integrated with BiVO 4 , the composite photoanode achieves the highest photocurrent density of 3.43 mA cm −2 at 1.23 V versus RHE and increases the peak ABPE up to 1.47%, both approximately twice the values of BiVO 4 /Ti 3 C 2 . Theoretical calculations and experimental results reveal that transition‐metal‐ion intercalation simultaneously increases the work function of Ti 3 C 2 and accelerates surface reaction kinetics. This leads to a strengthened interfacial built‐in electric field, thereby promoting photogenerated carrier separation and suppressing interfacial recombination. Thus, the PEC water splitting performance is markedly enhanced. This work offers a general and effective route for tailoring the electronic properties of MXenes and establishes work function modulation as a design principle for high‐performance OECs in PEC water splitting.