Defect Polarization-Metal Anchoring Coupling Enables Ni2+/Ti3+ Dual Active Sites and TiO6 Octahedral Distortion for Efficient Piezo-PEC Water Splitting of BaTiO3.

Efficient piezo-photoelectrochemical (Piezo-PEC) water splitting is critical for sustainable hydrogen production, yet its performance is largely constrained by sluggish charge separation and inefficient mechanical-to-electrical energy conversion. Here, we introduce a defect polarization-metal anchoring strategy by selectively anchoring Ni at Ba-vacancy-rich regions of BaTiO3 to achieve efficient Piezo-PEC water splitting. Experimental characterizations and density functional theory (DFT) calculations reveal that Ba vacancies reconstruct the local coordination environment of Ti sites, promoting Ti3+ formation and TiO6 octahedral distortion to enhance lattice polarization and the piezoelectric built-in electric field. Ni anchoring further enhances Ti 3d-Ni 3d-O 2p orbital hybridization and Ti─O covalency, forming Ni2+/Ti3+ dual active sites. The enhanced covalency establishes delocalized electron transport pathways to suppress bulk carrier recombination, while the dual active sites accelerate the proton-coupled electron transfer (PCET) via Ti─O─Ni bridges. The reinforced piezoelectric field synergistically couples with the photogenerated field to promote efficient charge separation. Benefiting from these cooperative effects, the Ni/BTO-BaV photoanode delivers a photocurrent density of 2.21 mA cm-2 at 1.23 VRHE under ultrasonic-light coupling, with a piezoelectric coefficient (d33) of 65.13 pm V-1. This work establishes a universal guideline for synergistic modulation of defect polarization and metal sites, guiding the rational design of high-performance photoelectrodes.