Emerging Electrochemical Catalysis on {001}-Facet and Defect-Engineered TiO2 for Water Purification

Electrochemical water purification and pollutant monitoring have garnered significant attention due to their unique technical advantages. The pursuit of safe, efficient, and economically viable catalysts remains a critical priority. Titanium dioxide (TiO₂), a prototypical transition-metal oxide with substantial industrial importance, is widely recognized as a benchmark catalyst for photochemical reactions. However, its practical application is limited by restricted light absorption and rapid photocarrier recombination. Recently, TiO₂ has emerged as a promising candidate in electrochemical catalysis, particularly in the fields of energy and environmental science. Its atomic and electronic structures can be precisely engineered through advanced techniques such as nanoscale morphology control, polar-facet engineering, guest-metal doping, and structural-defect modulation. This review examines recent advancements in TiO₂-based electrochemical applications, with a focus on water purification and pollutant monitoring.

In this Account, we present our efforts to harness facet- and defect-engineered TiO₂ as electrochemical catalysts for water purification, addressing critical challenges such as low conductivity and poor reactivity. Initially, we demonstrate that facet-engineered TiO₂, specifically designed to expose the high-energy {001} polar facet, facilitates the dissociation of both pollutant and water molecules. This significantly lowers energy barriers and enhances anodic reactions through both direct and indirect pathways, thereby markedly improving water purification efficiency. Furthermore, the dual photochemical and electrochemical functionalities of a single {001}-tailored TiO₂ electrode enable synergistic UV-light-assisted electrochemical catalysis under low bias conditions, achieving superior energy efficiency and resistance to electrode fouling. Next, we explore the catalytic potential of defect-engineered TiO₂ (TiO_2–x), highlighting the role of titanium (≡Ti³⁺) and oxygen vacancies (O_v) in boosting electrochemical water purification. Surface and subsurface defects, characterized by localized atomic disorder and structural distortions, serve as active sites that drive beneficial structural transformations, enriched electronic distribution, enhanced spin–spin correlations, and polaron hopping mechanisms, all of which contribute to improved cathodic reduction. To stabilize these reactive sites under anodic polarization, we propose a practical visible-light-assisted electrochemical catalysis strategy. This approach leverages mild non-band-gap excitation pathways mediated by defect sub-bands, providing enhanced stability and catalytic efficiency. Finally, we identify the challenges associated with the application of self-engineered TiO₂ in electrochemical water purification and outline directions for future research. Our studies deepen the fundamental understanding of structure–catalysis relationships and exemplify a self-tailoring strategy to advance oxide catalysis without reliance on noble or toxic-metal cocatalysts. By elucidating catalytic mechanisms and adopting innovative synthesis techniques, our insights provide a foundation for designing advanced electrocatalysts. Self-engineered TiO₂ holds the potential to establish a new paradigm in electrochemical catalysis, opening pathways for transformative solutions in environmental remediation.