Oxygen vacancy-modified black TiO2 photoanode enabling low photo-assisted charging voltage and high-efficiency zinc–air batteries via photoelectrochemical enhancement

Hydrogenation produces black TiO 2 rich in vacancies/Ti 3+ , which narrows the bandgap and boosts visible-light response. • Unique crystalline core@disordered shell heterostructure accelerates charge transfer and suppresses photocarrier recombination. • Oxygen vacancies act as charge traps to improve conductivity and boost OER kinetics. • The photo-assisted Zn-air battery achieves 1.2 V charging voltage, 92% round-trip efficiency and excellent cycling durability. Converting solar energy into electrochemical energy represents a sustainable strategy; however, the design of photo-assisted zinc–air batteries (ZABs) that can efficiently utilize solar energy faces significant challenges. To address the issues of narrow light absorption range and carrier recombination, this study subjected TiO 2 to hydrogenation treatment to prepare black TiO 2 photoelectrodes (B-T1) with abundant and suitable oxygen vacancies and Ti 3+ defects. The black appearance endows it with a remarkable redshift in the absorption edge and enhanced visible-light absorption, narrowing the bandgap from 3.31 eV to 2.80 eV. Meanwhile, the defects confer upon the black TiO 2 a unique heterostructure featuring a disordered shell surrounding the crystalline core. This structure enhances dipole and interfacial polarization effects and weakens the interaction between the transferred charges and the matrix. The introduction of oxygen vacancies in B-T1 promotes temporary trapping of charge carriers and triggers rapid carrier transfer at the heterojunction interface, hindering the recombination of photogenerated holes. Integrating the B-T1 photoanode into a photo-assisted zinc–air battery reduces the charging voltage from 1.8 V in the dark to 1.2 V under illumination, with an average round-trip efficiency of approximately 92%. Meanwhile, over 60 cycles, no degradation is observed, and the average round-trip efficiency remains around 92%, demonstrating excellent cycling efficiency and stability. This work elucidates the mechanism by which defect engineering induces performance enhancement and provides a new paradigm for designing photoelectrodes with high interfacial charge efficiency and advanced photoelectrochemical hybrid energy storage systems. Black TiO 2 photoelectrodes rich in oxygen vacancies and Ti 3+ defects are fabricated via a facile hydrogenation treatment, which induces a redshift of the light absorption edge. The unique crystalline core@disordered shell heterostructure accelerates interfacial charge transfer, and oxygen vacancies act as charge-trapping sites to optimize carrier transport behavior. Benefiting from these merits, the charging voltage of the zinc–air battery drops from 1.8 V in the dark to 1.2 V under illumination, accompanied by outstanding long-term cycling stability. Download: Download high-res image (324KB) Download: Download full-size image