Design Principles for Efficient and Stable Water Splitting Photoelectrocatalysts.

Area of Science:

• Materials Science
• Electrochemistry
• Renewable Energy

Background:

• Photoelectrochemical water splitting offers sustainable hydrogen production for industry and fuel cells.
• Semiconductor stability is a major challenge in photoelectrochemical water splitting systems.
• Metal-insulator-semiconductor (MIS) architectures improve semiconductor stability and can influence charge transfer.

Purpose of the Study:

• To investigate the critical role of the insulator layer and interfaces in MIS systems for photoelectrochemical water splitting.
• To understand how insulator thickness affects charge carrier dynamics and overall system performance.
• To identify and address efficiency loss mechanisms in MIS systems.

Main Methods:

• Fabrication of MIS devices using planar n-type Si protected by HfO2 insulator and Ni or Ir electrocatalysts.
• Precise control of HfO2 insulator thickness using atomic layer deposition (ALD).
• Rigorous electrochemical experiments combined with theory and modeling.

Main Results:

• Tuning insulator thickness controls photogenerated electron and hole flux and recombination, optimizing photovoltage.
• Significant performance losses persist even after optimizing insulator thickness, indicating other limiting factors.
• Identified sources of losses include semiconductor light absorption, interfacial defects, and insulator charge selectivity.

Conclusions:

• Optimizing insulator thickness is crucial but insufficient for maximizing MIS system efficiency.
• Strategies to improve light absorption, reduce interfacial defects, and select better insulators are necessary.
• The developed analytical framework and optimization strategies are broadly applicable to photoelectrochemical devices.