Adaptive semiconductor/electrocatalyst junctions in water-splitting photoanodes.

Area of Science:

• Materials Science
• Electrochemistry
• Photocatalysis

Background:

• Efficient photoelectrochemical water-splitting devices integrate light-absorbing semiconductors (SCs) with electrocatalysts (ECs).
• Understanding the energetics and charge transfer at SC/EC interfaces is crucial for optimizing device performance but remains poorly understood.
• Existing models often assume static interfaces, neglecting dynamic processes that could impact efficiency.

Purpose of the Study:

• To investigate the in situ behavior of semiconductor/electrocatalyst interfaces.
• To elucidate the role of electrocatalyst properties (e.g., ion permeability, redox activity) in determining interface energetics.
• To provide insights for designing next-generation photoelectrochemical water-splitting devices.

Main Methods:

• Fabrication of model electrodes using single-crystal TiO2 coated with various electrocatalysts (Ni(OH)2, NiOOH, IrOx).
• In situ probing of SC/EC interfaces using a dual working electrode setup to independently control and monitor potential and current at both SC and EC.
• Characterization of interface properties, including Schottky barrier height and its dependence on electrocatalyst oxidation state.

Main Results:

• Redox-active, ion-permeable electrocatalysts (Ni(OH)2/NiOOH) form 'adaptive' SC/EC junctions where the Schottky barrier height dynamically changes with electrocatalyst oxidation.
• Ion-impermeable electrocatalysts (IrOx) form 'buried' junctions with constant barrier heights.
• Conversion of NiOx to Ni(OH)2/NiOOH improved apparent photovoltage and fill factor, indicating enhanced charge transfer.

Conclusions:

• The study reveals a new class of 'adaptive' semiconductor junctions formed with redox-active, ion-permeable electrocatalysts.
• Interface energetics are not static but can be modulated by the electrocatalyst's state, offering a new design paradigm for SC/EC devices.
• These findings provide critical insights for optimizing the design and performance of photoelectrochemical water-splitting systems.