Surface modification and performance effects of oxygen-enriched annealing process on super-hydrophilic TiO2 pH working electrode

The super-hydrophilic TiO₂ pH electrode was modified by oxygen-enriched annealing. • This post-treatment offered tunable production cost suitable for controlled-environment agriculture. • The underlying influence mechanism of modification has been elucidated. • Optimized electrode improved surface hardness and hydrophilicity with stable electrochemical response. • Durability assessment showed lower pH measurement error in unsaturated cultivation substrates. With the escalating demand for rapid and accurate pH detection in controlled-environment agriculture, super-hydrophilic TiO₂ pH electrodes fabricated via chemical etching have emerged as promising candidates for real-time sensing in cultivation substrates, offering tunable production cost and reliable performance. However, their practical deployment is often constrained by limited mechanical durability and unstable interfacial wetting in heterogeneous substrates. In this work, an oxygen-enriched annealing strategy is employed to deliberately tailor the surface structure of TiO₂ electrodes, aiming to enhance interfacial wettability and mechanical robustness rather than solely maximizing intrinsic sensitivity in buffer solutions. This post-treatment significantly modulates the surface morphology, roughness, and composition of the electrodes, elucidating the effects of annealing temperature and duration on their mechanical and wetting properties. The electrode annealed at 350 °C for 30 min (T350-30) developed a uniform interconnected porous microstructure, improving hardness to 208.7 HV0.05 and reducing contact angle to 8.57°. The enlarged specific surface area and abundant amorphous TiO₂ preserved stable pH response, delivering 50.9 mV/pH sensitivity, ≤10 s response time, as well as minimal drift and hysteresis. Durability tests in 66.7% cultivation substrates showed measurement error increased only from 0.07 to 0.14 pH units after 30 insertion–removal cycles, compared with 0.08 to 0.28 pH units for the unannealed electrode. In addition, the annealed electrode exhibited improved stability under sequential exposure to aqueous solutions and ambient air, supporting its stability for practical open-environment. Download: Download high-res image (158KB) Download: Download full-size image