Solar-Driven Photoelectrochemical Water Oxidation over an n-Type Lead-Titanium Oxyfluoride Anode

Area of Science:

• Materials Science
• Photochemistry
• Electrochemistry

Background:

• Mixed-anion compounds like oxynitrides and oxysulfides are explored for visible-light water oxidation photoanodes.
• However, most suffer from oxidative degradation by photogenerated holes, limiting their stability.
• Developing stable photoanodes is crucial for efficient solar fuel production.

Purpose of the Study:

• To investigate the potential of a novel lead oxyfluoride, Pb₂Ti₂O_5.4F_1.2, as a stable photoanode for visible-light water oxidation.
• To evaluate its photoelectrochemical performance, including photocurrent generation, onset potential, and stability.
• To compare its performance with and without a water oxidation promoter.

Main Methods:

• Synthesis of Pb₂Ti₂O_5.4F_1.2 particles and their deposition on a transparent conductive glass (FTO) support.
• Postdeposition of a TiO₂ overlayer to form the photoanode structure.
• Photoelectrochemical measurements under simulated sunlight (AM1.5G) to assess photocurrent, onset potential, and stability.
• Water oxidation product analysis (O₂) and Faradaic efficiency determination.

Main Results:

• Pb₂Ti₂O_5.4F_1.2 exhibits a band gap of ca. 2.4 eV, enabling visible-light absorption (λ <520 nm).
• The photoanode generated a stable anodic photocurrent with a negative onset potential (-0.6 V vs NHE), independent of pH.
• Exceptional stability was observed even without a water oxidation promoter (e.g., CoO_x).
• Loading CoO_x improved photoresponse by 2-3 times, achieving 93% Faradaic efficiency for O₂ evolution under AM1.5G light with applied potential <1.23 V.
• The photoanode showed no deactivation during 4 hours of operation.

Conclusions:

• Pb₂Ti₂O_5.4F_1.2 is the first reported stable, mixed-anion oxyfluoride photoanode for visible-light water oxidation.
• Its stability and performance, even without a promoter, distinguish it from other mixed-anion photoanodes.
• This material offers a promising pathway for efficient and durable photoelectrochemical water splitting.