Vector-Tailored Built-in Electric Field Elevates Ultrafast Charge Transport Dynamics in Solar Hydrogen Production

Abstract Built-in electric fields (BIEF) at semiconductor-cocatalyst interfaces play a critical role in regulating charge transport, yet the influence of BIEF orientation on carrier dynamics remains largely unexplored. Herein, we demonstrate a vector-tailoring strategy to investigate how BIEF direction regulates interfacial charge-transfer behavior. Using g-C3N4 coupled with NiBx (outward-oriented BIEF) and core–shell Ag@NiBx (inward-oriented BIEF) as model systems, we experimentally manipulate the direction of interfacial electric fields through work-function engineering. By combining in situ Kelvin probe force microscopy, light-irradiated X-ray photoelectron/absorption spectroscopy, and femtosecond transient absorption spectroscopy, we directly probe the interfacial potential variation, electronic-state evolution, and ultrafast charge-transfer dynamics. The results reveal that the inward-oriented BIEF promotes more efficient interfacial electron transfer, suppresses charge recombination, and extends the carrier lifetime to 1.4 ns, approximately 2.3-fold higher than that of g-C3N4/NiBx. Consequently, the g-C3N4/Ag@NiBx photocatalyst achieves a hydrogen-evolution rate of 1155 μmol g−1 h−1, representing a 2.9-fold enhancement compared with g-C3N4/NiBx. These findings highlight the importance of BIEF orientation in regulating charge-transfer dynamics and provide an experimentally guided strategy for designing efficient semiconductor-cocatalyst photocatalytic systems.